WO2019150631A1 - Gas sensor - Google Patents

Gas sensor Download PDF

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Publication number
WO2019150631A1
WO2019150631A1 PCT/JP2018/031820 JP2018031820W WO2019150631A1 WO 2019150631 A1 WO2019150631 A1 WO 2019150631A1 JP 2018031820 W JP2018031820 W JP 2018031820W WO 2019150631 A1 WO2019150631 A1 WO 2019150631A1
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Prior art keywords
gas sensor
metal oxide
oxide film
gas
film
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PCT/JP2018/031820
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French (fr)
Japanese (ja)
Inventor
晃平 吉川
笹子　佳孝
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日立金属株式会社
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Publication of WO2019150631A1 publication Critical patent/WO2019150631A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/22—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance

Definitions

  • the present invention relates to a gas sensor, for example, a technique effective when applied to a gas sensor in which current-voltage characteristics change according to gas concentration.
  • Patent Document 1 uses a metal oxide layer formed on a semiconductor substrate as a gas detection layer, and detects a change in current resulting from a change in resistance of the gas detection layer during gas flow.
  • a field effect transistor type gas sensor for detecting gas concentration is described.
  • Nitrogen oxide (NOx) is a gas that adversely affects the human body that is generated by the combustion of biomass, fossil fuel, etc., and depending on the type, is a gas that has a high global warming potential, and its emissions can be reduced. It has been demanded.
  • a work function type gas sensor represented by a field effect type gas sensor.
  • a work function type gas sensor is a gas sensor whose threshold voltage changes according to the gas concentration of the gas to be detected. Similar to the field effect type gas sensor, there are a capacitive type gas sensor and a diode type gas sensor as the gas sensor whose current-voltage characteristics change according to the gas concentration.
  • the field effect type gas sensor, the capacitive type gas sensor, and the diode type gas sensor are collectively referred to as a work function type gas sensor.
  • the ion conductivity needs to change due to the reaction between the gas to be detected and the metal oxide. Therefore, in a gas sensor using a single metal oxide film, the metal oxide constituting the metal oxide film is reactive with the gas to be detected, and the change in ion conductivity obtained from this reaction. Is required to be sufficiently high. For this reason, in a gas sensor using a single metal oxide film, there are few choices of metal oxides that satisfy the requirements. Therefore, in a gas sensor that uses a metal oxide film as a gas detection film, it is difficult to improve the gas concentration detection performance.
  • An object of the present invention is to improve the performance of a gas sensor.
  • the gas sensor in one embodiment is a gas sensor that detects the concentration of the gas to be detected.
  • the gas sensor includes an insulating film formed on the semiconductor substrate, a first metal oxide film formed on the insulating film, and a second metal oxide film formed on the first metal oxide film. And a metal film in contact with the second metal oxide film. A part of the second metal oxide film is exposed.
  • the performance of the gas sensor can be improved.
  • (A) is sectional drawing which shows the typical structure of the gas sensor in embodiment
  • (b) is a perspective view which shows the typical structure of the gas sensor in embodiment. It is a figure which shows typically the circuit structure for detecting the gas concentration of to-be-detected gas (nitrogen oxide gas) electrically using the gas sensor in embodiment. It is a graph explaining the method to calculate the gas concentration of to-be-detected gas (nitrogen oxide gas) using the circuit structure shown in FIG. It is a graph which shows the relationship between a voltage change value and the gas concentration of to-be-detected gas. It is a figure which shows the typical structure of the ion pump part in embodiment.
  • FIG. (A) is sectional drawing which shows the typical structure of the gas sensor in the modification 1
  • (b) is a perspective view which shows the typical structure of the gas sensor in the modification 1.
  • FIG. (A) is sectional drawing which shows the typical structure of the gas sensor in the modification 2
  • (b) is a perspective view which shows the typical structure of the gas sensor in the modification 2.
  • (A) is sectional drawing which shows the typical structure of the gas sensor in the modification 3
  • (b) is a perspective view which shows the typical structure of the gas sensor in the modification 3.
  • the constituent elements are not necessarily indispensable unless otherwise specified and apparently essential in principle. Needless to say.
  • FIG. 1 is a diagram illustrating a schematic configuration of a gas sensor 100 according to the present embodiment.
  • FIG. 1A is a cross-sectional view illustrating a schematic configuration of the gas sensor 100 in the present embodiment
  • FIG. 1B is a perspective view illustrating a schematic configuration of the gas sensor 100 in the present embodiment.
  • the gas sensor shown in FIGS. 1A and 1B is, for example, a field effect gas sensor that detects the gas concentration of nitrogen oxide gas (NOx) that is the gas to be detected 20.
  • NOx nitrogen oxide gas
  • the gas sensor in the present embodiment includes a semiconductor substrate 10 mainly composed of silicon (silicon) or silicon carbide (silicon carbide), for example.
  • a gate insulating film 13 made of, for example, a silicon oxide film is formed on the semiconductor substrate 10.
  • the gas sensor in the present embodiment has a semiconductor substrate 10 based on silicon (Si) or silicon carbide (SiC), and a gate insulating film 13 made of a silicon oxide film is formed on the semiconductor substrate 10. Is formed.
  • a gate electrode is formed on the gate insulating film 13. Specifically, a metal oxide film 14 is formed on the gate insulating film 13, and a metal oxide film 15 is formed on the metal oxide film 14. Further, a metal film 16 is formed on the metal oxide film 15. As described above, in the gas sensor 100 according to the present embodiment, the gate electrode is formed on the metal oxide film 14, the metal oxide film 15 formed on the metal oxide film 14, and the metal oxide film 15. Metal film 16. At this time, as shown in FIGS. 1A and 1B, a nitrogen oxide gas, which is a gas to be detected, flows above the gate electrode. A part of the metal oxide film 15 that constitutes a part of the gate electrode is exposed, and the nitrogen oxide gas is in contact with a part of the surface of the metal oxide film 15. .
  • the gas sensor 100 according to the present embodiment has a channel formation region formed in the semiconductor substrate 10 immediately below the gate insulating film 13, and a source region 11 and a drain region 12 sandwiching the channel formation region. As described above, the gas sensor 100 according to the present embodiment is schematically configured.
  • the metal oxide film 14 in the present embodiment has ionic conductivity.
  • the metal oxide film 15 has a catalytic function for changing the adsorption species of the detection gas adsorbed on the surface of the metal oxide film 15. Specifically, for example, when a gas containing nitrogen oxide gas (NOx) comes into contact with the metal oxide film 15, the metal oxide film 15 is denatured by nitrogen monoxide (NO) and more easily absorbed. It has a function of changing to an adsorption species such as nitrogen (NO 2 ).
  • the metal oxide film 14 has a property that the ion conductivity changes due to the adsorbed species adsorbed on the surface of the metal oxide film 15.
  • a detection gas 20 containing a nitrogen oxide gas flows above the gas sensor 100 in the present embodiment.
  • a part of the surface of the metal oxide film 15 is exposed.
  • nitrogen oxide gas contacts the exposed surface of the metal oxide film 15.
  • the metal oxide film 15 has a catalytic function of changing the adsorption species of the nitrogen oxide gas adsorbed on the surface of the metal oxide film 15.
  • the metal oxide film 15 has a function of supplying oxygen to the nitrogen oxide gas adsorbed on the surface of the metal oxide film 15. Therefore, when the nitric oxide (NO) contained in the nitrogen oxide gas comes into contact with the metal oxide film 15 by the catalytic function of the metal oxide film 15, the metal oxide film against the nitric oxide (NO). 15 is supplied with oxygen. As a result, nitric oxide (NO) changes to nitrogen dioxide (NO 2 ) and the like that are easier to adsorb. Then, nitrogen dioxide (NO 2 ) or the like moves from the metal oxide film 15 to the lower metal oxide film 14, and oxygen ions (O 2 ) from the nitrogen dioxide (NO 2 ) or the like to the metal oxide film 14.
  • the gas sensor 100 can detect the gas concentration of the nitrogen oxide gas based on the change in the threshold voltage.
  • the gate insulating film 13 in this embodiment shown in FIGS. 1A and 1B is made of, for example, an oxide containing silicon (Si) typified by silicon oxide.
  • Si oxide containing silicon
  • FIGS. 1A and 1B By using an oxide containing silicon for the gate insulating film 13 in this embodiment, leakage current from the gate electrode can be suppressed. As a result, noise caused by the leakage current can be reduced, so that the detection accuracy of the gas sensor 100 in the present embodiment can be improved.
  • the metal oxide film 14 having ion conductivity is made of an oxide containing zirconium (Zr), for example. Further, the metal oxide film 14 having ion conductivity may be configured to include the first metal and the second metal. At this time, the first metal is zirconium (Zr).
  • the second metal is calcium (Ca), magnesium (Mg), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm).
  • the addition amount of elements other than zirconium (Zr) is desirably 1% or more and 15% or less in terms of molar ratio.
  • the metal oxide film 14 can be made of an oxide containing zirconium.
  • the crystal structure of the metal oxide constituting the metal oxide film 14 is monoclinic or tetragonal. Or cubic.
  • the crystal structure of a metal oxide containing only zirconium is monoclinic, while the crystal structure of a metal oxide containing zirconium (first metal) and the second metal is tetragonal or cubic.
  • the tetragonal or cubic crystal structure is more likely to cause oxygen deficiency and the ionic conductivity is more likely to change than the monoclinic crystal structure.
  • it is desirable that the metal oxide film 14 is made of a metal oxide containing zirconium (first metal) and the above-described second metal from the viewpoint of increasing the ionic conductivity.
  • the metal oxide film 15 is made of an oxide containing nickel (Ni), for example.
  • Ni nickel
  • a catalytic function for changing the adsorption species of the gas to be detected adsorbed on the surface of the metal oxide film 15 can be realized with respect to the metal oxide film 15, and the metal oxide film 15 and the metal film 16 are in close contact with each other. Can be improved.
  • the metal oxide film 15 includes rhodium (Rh), palladium (Pd), platinum (Pt), ruthenium (Ru), copper (Cu), iron (Fe), cobalt (Co), manganese. It may also contain at least one element selected from (Mn), cerium (Ce), and zirconium (Zr). At this time, elements other than nickel are not necessarily contained in the metal oxide film 15 in the form of an oxide.
  • the metal oxide film 15 is desirably at least partially porous.
  • the adhesive strength with the upper metal film 16 may be insufficient.
  • the particle size of the metal oxide constituting the metal oxide film 15 is desirably 10 nm or more and 10 ⁇ m or less.
  • the metal film 16 in the present embodiment is composed of a film containing at least one element selected from platinum (Pt), gold (Au), palladium (Pd), and rhodium (Rh).
  • the metal film 16 thus configured is not necessarily exposed to the atmosphere of the gas to be detected.
  • the metal film 16 is made of a noble metal typified by platinum
  • the noble metal typified by platinum has a catalytic function of changing the adsorption species of nitric oxide (NO). Therefore, for example, at the contact portion between the metal oxide film 15 and the metal film 16 indicated by “A” in FIG. 1B, a synergistic effect of the catalytic function of the metal oxide film 15 and the catalytic function of the metal film 16 is obtained. It is considered that a change from nitric oxide (NO) to nitrogen dioxide (NO 2 ) is likely to occur. From this, in the gas sensor 100 of the present embodiment, the contact portion (indicated by “A” in FIG. 1B) between the metal oxide film 15 and the metal film 16 is exposed. desirable.
  • the gas sensor 100 in the present embodiment is a field effect gas sensor. That is, the gas sensor 100 can basically be composed of an n-channel field effect transistor or a p-channel field effect transistor.
  • the source region 11 and the drain region 12 are composed of an n-type semiconductor region.
  • the semiconductor substrate is made of silicon
  • an n-type semiconductor is introduced by introducing an n-type impurity (donor) typified by phosphorus (P) or arsenic (As) into the semiconductor substrate by ion implantation.
  • P phosphorus
  • As arsenic
  • the source region 11 and the drain region 12 are composed of a p-type semiconductor region.
  • a p-type impurity (acceptor) represented by boron (B) is introduced into the semiconductor substrate by an ion implantation method, thereby forming a source region composed of the p-type semiconductor region. 11 and the drain region 12 can be formed.
  • the semiconductor substrate 10 in the present embodiment can be composed of, for example, silicon (Si) or silicon carbide (SiC).
  • Si silicon
  • SiC silicon carbide
  • the gas sensor 100 in the present embodiment is configured as described above.
  • the gas concentration of the gas to be detected nitrogen oxide gas
  • a circuit configuration for this purpose will be described.
  • FIG. 2 is a diagram schematically showing a circuit configuration for electrically detecting the gas concentration of the gas to be detected (nitrogen oxide gas) using the gas sensor 100 according to the present embodiment.
  • a source terminal 101, a drain terminal 102, and a gate terminal 103 are electrically connected to the gas sensor 100.
  • the source region 11 of the gas sensor 100 shown in FIG. 1A and FIG. 1B is electrically connected to the source terminal 101 shown in FIG. 2, and FIG. 1A and FIG.
  • the drain region 12 of the gas sensor 100 shown in b) is electrically connected to the drain terminal 102 shown in FIG.
  • the gate electrode (metal film 16) of the gas sensor 100 shown in FIGS. 1A and 1B is electrically connected to the gate terminal 103 shown in FIG.
  • the gate voltage is applied to the metal film 16 functioning as the gate electrode by the gate voltage application device 104 electrically connected to the metal film 16.
  • the source terminal 101 that is electrically connected to the source region 11 of the gas sensor 100 is grounded to the ground potential.
  • the drain terminal 102 electrically connected to the drain region 12 of the gas sensor 100 is electrically connected to the current measuring device 105 and the drain voltage applying device 106.
  • the gate voltage applied from the gate voltage application device 104 to the gate terminal 103 is controlled while the drain voltage is applied from the drain voltage application device 106 to the drain terminal 102.
  • the threshold voltage of the gas sensor 100 changes according to the gas concentration of the gas to be detected (nitrogen oxide gas) that the gas sensor 100 contacts
  • the gas to be detected nitrogen oxide gas
  • the gas concentration is measured.
  • the calculation method of the gas concentration of to-be-detected gas (nitrogen oxide gas) is demonstrated.
  • FIG. 3 is a graph illustrating a method for calculating the gas concentration of the gas to be detected (nitrogen oxide gas) using the circuit configuration shown in FIG.
  • a field effect transistor when a gate voltage lower than a threshold voltage is applied to a gate electrode, a channel (inversion layer) is not formed between the source region 11 and the drain region 12, and almost no current flows.
  • a channel (inversion layer) when a certain or higher gate voltage is applied to the gate electrode, a channel (inversion layer) is formed between the source region 11 and the drain region 12, and the source region 11 and the drain region 12 During this time, a current flows.
  • a certain current value is defined as a threshold current
  • a gate voltage for obtaining this threshold current is defined as a threshold voltage.
  • the vertical axis indicates the drain current
  • the horizontal axis indicates the gate voltage.
  • the threshold current I1 is shown.
  • the ion conductivity of the metal oxide film 14 changes depending on the gas concentration of the gas to be detected (nitrogen oxide gas), and accordingly, the gas sensor (field effect transistor) 100 operates.
  • the threshold voltage also changes. Therefore, first, a threshold voltage (V1) in a reference gas having a known gas concentration is measured (curve 30). Next, the threshold voltage (V2) when the gas to be detected flows is measured (curve 40). At this time, for example, as shown in FIG. 3, if there is a potential difference between the threshold voltage (V1) and the threshold voltage (V2), the gas concentration of the detected gas is determined from the gas concentration of the reference gas. You can see that it is changing.
  • FIG. 4 is a graph showing the relationship between the voltage change value (V2-V1) and the gas concentration of the gas to be detected. If the correlation shown in FIG. 4 is grasped in advance and acquired as back data, for example, from the threshold voltage of the gas sensor 100 obtained when a gas to be detected whose gas concentration is unknown is flowed, The gas concentration of the unknown gas to be detected can be calculated.
  • the first feature point in the present embodiment is that a metal oxide film 14 and a metal oxide film 15 having different functions are included in the gas sensor 100. It is the point which comprises the laminated film. Thereby, according to the gas sensor 100 in this Embodiment, the performance improvement of the gas sensor 100 can be aimed at.
  • the gas concentration of the gas to be detected is detected by utilizing the fact that the threshold voltage changes according to the gas concentration of the gas to be detected.
  • a metal oxide film is used as a gas detection film.
  • the metal oxide film that is a constituent element of the gas sensor is required to change its ionic conductivity by reacting the gas to be detected and the metal oxide. Therefore, for example, in a gas sensor using a single metal oxide film, the metal oxide constituting the metal oxide film is reactive with the gas to be detected, and the ionic conductivity obtained from this reaction. Is required to be sufficiently high.
  • a gas sensor that uses a single metal oxide film there are fewer options for metal oxides that satisfy the requirements. For this reason, in a gas sensor using a single metal oxide film, there is little room for selecting a single metal oxide film that satisfies the requirements, and it is difficult to improve the gas concentration detection performance. That is, a gas sensor that uses a single metal oxide film is required to have a catalytic function that changes the ion conductivity of the gas to be detected and that changes the adsorption species of the gas to be detected adsorbed on the surface. In particular, in order to improve the gas concentration detection sensitivity of the gas sensor, a large change in ion conductivity is required.
  • the gas to be detected is a nitrogen oxide gas
  • the object to be adsorbed on the surface is required. It is also important to have a catalytic function that changes the adsorption species of the detection gas. Because nitrogen monoxide (NO) contained in the nitrogen oxide gas has a property that it is difficult to adsorb on the metal oxide film, the gas concentration is detected on the assumption that it is adsorbed on the metal oxide film. This is because in the gas sensor, the detection accuracy of the gas concentration cannot be improved with nitric oxide (NO).
  • NO nitrogen monoxide
  • nitrogen monoxide which is difficult to adsorb on the metal oxide film
  • nitrogen dioxide which is easy to adsorb on the metal oxide film. Therefore, it is necessary to change the adsorbed species.
  • a highly sensitive gas sensor is not used for the first time by using a metal oxide film that has a catalytic function to change the species of gas to be detected adsorbed on the surface. It can be realized.
  • the metal oxide film 14 and the metal oxide film 15 having different functions constitute a laminated film.
  • the metal oxide film 14 having ion conductivity and the metal oxide film 15 having a catalytic function for changing the adsorption species of the detection gas adsorbed on the surface constitute a laminated film.
  • the type of the film can be selected only from the viewpoint of having a property that the change in ion conductivity is large.
  • the type of film can be selected only from the viewpoint of having a catalytic function that changes the adsorption species of the gas to be detected adsorbed on the surface.
  • the metal oxide film 14 and the metal oxide film 15 having different functions constitute a laminated film
  • the metal oxide film 14 The room for selection of each material of the metal oxide film 15 widens.
  • the gas sensor 100 according to the present embodiment can easily improve the gas concentration detection sensitivity of the gas to be detected. That is, according to the first feature point in the present embodiment, both the viewpoint of having a large change in ion conductivity and the viewpoint of having a catalytic function for changing the adsorption species of the detection gas adsorbed on the surface are achieved. Compared to the case of selecting a material, there is far more room for selecting a material.
  • the room for selecting the material constituting the metal oxide film is widened, so that the performance of the gas sensor 100 can be easily improved. Furthermore, the room for selecting a material constituting the metal oxide film is expanded, so that a room for preferentially selecting a material having the same performance and a low manufacturing cost is expanded. In other words, according to the first feature point in the present embodiment, it is possible to easily improve the performance of the gas sensor 100 and to obtain an excellent effect in that the manufacturing cost can be reduced.
  • the second feature point in the present embodiment is that, for example, a part of the surface of the metal oxide film 15 is exposed as shown in FIGS. 1 (a) and 1 (b).
  • a part of the surface of the metal oxide film 15 comes into contact with the atmosphere of the gas to be detected (nitrogen oxide gas), and thus the detection to be adsorbed on the surface is performed.
  • the function of the metal oxide film 15 having a catalytic function for changing the gas adsorption species can be sufficiently exhibited.
  • oxygen is supplied to nitrogen monoxide (NO) contained in the gas to be detected (nitrogen oxide gas) to change into nitrogen dioxide (NO 2 ).
  • NO 2 nitrogen dioxide
  • the second feature of the present embodiment as a result of surface nitrogen dioxide of the metal oxide film 15 (NO 2) is adsorbed in accordance with the gas concentration, improve the detection accuracy of the gas concentration in the gas sensor 100 can do.
  • the surface of the metal oxide film 15 is the metal oxide film 14.
  • the function of the metal oxide film 15 having a catalytic function for changing the adsorption species of the gas to be detected adsorbed on the surface cannot be sufficiently exhibited.
  • the gas sensor 100 employs a configuration in which the metal oxide film 14 is formed on the gate insulating film 13 and the metal oxide film 15 is formed on the metal oxide film 14. Yes.
  • the structure which a part of surface of the metal oxide film 15 exposes from the metal film 16 becomes possible. Therefore, according to the gas sensor 100 of the present embodiment, the second feature point described above is embodied, and the function of the metal oxide film 15 having a catalytic function for changing the adsorption species of the gas to be detected adsorbed on the surface is sufficient. It will be possible to demonstrate.
  • the adsorption amount of the adsorbed species (nitrogen dioxide) according to the gas concentration of the gas to be detected (nitrogen oxide gas) can be ensured, and the detection accuracy of the gas concentration is improved. can do.
  • the metal oxide film 15 it is desirable to increase the surface area of the metal oxide film 15 from the viewpoint of securing the adsorption amount of the adsorbed species (nitrogen dioxide) according to the gas concentration of the gas to be detected (nitrogen oxide gas). Specifically, it is desirable that at least a part of the metal oxide film 15 is porous while adopting the second feature point in the present embodiment. However, when the metal oxide film 15 is made of a porous material, the adhesive strength with the upper metal film 16 may be insufficient. For this reason, the particle size of the metal oxide constituting the metal oxide film 15 is desirably 10 nm or more and 10 ⁇ m or less.
  • the gas sensor 100 in this Embodiment while the adsorption amount of the adsorption species adsorbed on the surface of the metal oxide film 15 can be increased, the adhesive strength between the metal oxide film 15 and the metal film 16 is increased. Can be secured.
  • the third feature point in the present embodiment is that a gas sensor module including the gas sensor 100 is provided with an ion pump unit that removes a gas component different from the gas to be detected. Thereby, the detection accuracy of the gas concentration of the gas to be detected can be improved by the gas sensor module in the present embodiment.
  • oxygen gas or the like has a function of changing the ionic conductivity of the metal oxide film 14 having ionic conductivity. Therefore, when oxygen gas is mixed in the atmosphere together with the gas to be detected (nitrogen oxide gas), it is as if a value higher than the actual gas concentration of the gas to be detected (nitrogen oxide gas) is calculated. Arise. That is, when oxygen gas is mixed in the atmosphere together with the gas to be detected (nitrogen oxide gas), the noise component for the gas sensor 100 increases and the performance of the gas sensor 100 is degraded. Therefore, in the present embodiment, for example, a gas sensor module including an ion pump unit that removes oxygen gas from the atmosphere in which the gas sensor 100 is disposed is configured together with the gas sensor 100.
  • interference gas typified by oxygen gas which is a noise source
  • the gas sensor module of the present embodiment the detection accuracy of the gas concentration of the gas to be detected (nitrogen oxide gas) is improved. can do.
  • FIG. 5 is a diagram showing a schematic configuration of the ion pump unit 50 in the present embodiment.
  • an ion pump unit 50 in the present embodiment includes an ion pump electrode 50A, an ion conductive film 50B, and an ion pump electrode 50C. That is, the ion conductive film 50B is disposed on the ion pump electrode 50A, and the ion pump electrode 50C is disposed on the ion conductive film 50B.
  • the ion pump electrode 50A is formed in contact with the lower surface of the ion conductive film 50B, while the ion pump electrode 50C is formed in contact with the upper surface of the ion conductive film 50B.
  • Each of the ion pump electrode 50A and the ion pump electrode 50C is made of, for example, platinum (Pt), rhodium (Rh), palladium (Pd), or the like.
  • the ion conductive film 50B is made of, for example, zirconia (ZrO 2 ) to which yttria (Y 2 O 3 ) or the like is added.
  • the ion pump unit 50 can flow an ion current by applying a voltage between the ion pump electrode 50A and the ion pump electrode 50C.
  • the ion conductive film 50B is made of zirconia (ZrO 2 ) added with yttria (Y 2 O 3 ) or the like, the ion conductive film 50B becomes an oxygen ion conductor.
  • oxygen molecules (O 2 ) are decomposed into oxygen ions (O 2 ⁇ ) on the lower surface of the ion pump electrode 50A, and oxygen ions (O 2 ⁇ ) Moves to the ion pump electrode 50C through the ion conductive film 50B.
  • the oxygen ions (O 2 ⁇ ) that have reached the ion pump electrode 50C are neutralized by passing electrons to the ion pump electrode 50C, and are released as oxygen molecules from the upper surface of the ion pump electrode 50C.
  • the ion pump unit 50 provided in the gas sensor module causes the gas to be detected (nitrogen oxide gas) and the interference gas (oxygen gas) that becomes noise to be detected.
  • Interfering gas oxygen gas
  • variation of the ion conductivity of the metal oxide film 14 contained in the gas sensor 100 resulting from interference gas can be suppressed. Therefore, according to the gas sensor module having the third feature point in the present embodiment, it is possible to improve the detection accuracy of the gas concentration of the gas to be detected (nitrogen oxide gas) without being adversely affected by the interference gas.
  • FIG. 6 is a diagram illustrating a schematic configuration of the gas sensor 100 according to the first modification of the embodiment.
  • FIG. 6A is a cross-sectional view illustrating a schematic configuration of the gas sensor 100 according to the first modification
  • FIG. 6B is a perspective view illustrating a schematic configuration of the gas sensor 100 according to the first modification.
  • FIG. 6A and 6B the gas sensor 100 according to the first modification has the same configuration as the gas sensor 100 according to the embodiment except that the metal film 16 has a comb-teeth shape. ing. That is, in the gas sensor 100 according to the first modification, as shown in FIGS.
  • the metal film 16A, the metal film 16B, and the metal film 16C are disposed on the metal oxide film 15, Comb-shaped electrodes are formed by the metal film 16A, the metal film 16B, and the metal film 16C.
  • the comb-shaped electrode it is easy to apply a voltage to the lower metal oxide film 15 and to distribute the gas to be detected.
  • the response speed and the response sensitivity can be improved.
  • FIG. 7 is a diagram illustrating a schematic configuration of the gas sensor 100 according to the second modification of the embodiment.
  • FIG. 7A is a cross-sectional view illustrating a schematic configuration of the gas sensor 100 according to the second modification
  • FIG. 7B is a perspective view illustrating a schematic configuration of the gas sensor 100 according to the second modification.
  • the gas sensor 100 according to the second modification is the same as the gas sensor 100 according to the embodiment except that the metal film 16 is provided inside the metal oxide film 15. It has the same configuration as In other words, the metal film 16 is not exposed to the atmosphere containing the gas to be detected (nitrogen oxide gas).
  • the response sensitivity of the gas sensor 100 is increased as a result of an increase in the area of the metal oxide film 15 in contact with the atmosphere containing the gas to be detected (nitrogen oxide gas). Can be improved.
  • FIG. 8 is a diagram illustrating a schematic configuration of the gas sensor 100 according to Modification 3 of the embodiment.
  • FIG. 8A is a cross-sectional view illustrating a schematic configuration of the gas sensor 100 according to the third modification
  • FIG. 8B is a perspective view illustrating a schematic configuration of the gas sensor 100 according to the third modification.
  • FIG. 8A and 8B in the gas sensor 100 according to the third modification, the metal oxide film 15, the metal oxide film 14, the gate insulating film 13, and the semiconductor substrate 10 are exposed to the atmosphere.
  • the gas sensor 100 according to the embodiment is configured to roll over.
  • the area of contact of the metal oxide film 15 with the atmosphere containing the gas to be detected increases, and as a result, the response sensitivity of the gas sensor 100 is increased. Can be improved.
  • the field effect gas sensor in which the threshold voltage changes according to the gas concentration has been described as an example.
  • the technical idea in the embodiment is not limited thereto, for example, according to the gas concentration.
  • the present invention can also be applied to a capacitive gas sensor in which a change in current-voltage characteristics caused by a change in capacitance occurs.
  • the capacitive gas sensor is sandwiched between an upper electrode made of a metal oxide film 14, a metal oxide film 15 and a metal film 16, a lower electrode made of a semiconductor substrate 10, an upper electrode and the lower electrode, And it can comprise so that it may have the capacity
  • the nitrogen oxide gas has been described as the gas to be detected.
  • the technical idea in the embodiment is not limited to this, and the detection target of the gas sensor that basically uses the oxidation-reduction reaction is not limited thereto.
  • the present invention can be widely applied to the detection of the gas concentration of the gas.
  • the present invention is applicable to sulfur oxide gas (SOx) and ammonia gas (NH 3 ) as the gas to be detected.
  • the embodiment includes the following forms.
  • a gas sensor for detecting the concentration of a gas to be detected An insulating film formed on the semiconductor substrate; A first metal oxide film formed on the insulating film; A second metal oxide film formed on the first metal oxide film; A metal film in contact with the second metal oxide film; Have The gas sensor, wherein a part of the second metal oxide film is exposed.
  • the insulating film is a gate insulating film;
  • the gate electrode formed on the gate insulating film is The first metal oxide film;
  • Consisting of The gas sensor further includes: A channel formation region formed in the semiconductor substrate immediately below the gate insulating film; A source region and a drain region sandwiching the channel formation region; Having a gas sensor.
  • the gas sensor constitutes a capacitive element,
  • the gas sensor An upper electrode comprising the first metal oxide film, the second metal oxide film, and the metal film;
  • the gas sensor according to appendix 1 An ion pump for removing a gas component different from the gas to be detected; With The ion pump part is An ion conducting membrane; A first ion pump electrode formed in contact with the lower surface of the ion conductive film; A second ion pump electrode formed in contact with the upper surface of the ion conductive film; A gas sensor module.

Abstract

The present invention improves performance of a gas sensor. A gas sensor (100) detects concentration of a gas (20) to be detected. The gas sensor (100) has: a gate insulating film (13) formed on a semiconductor substrate (10); a metal oxide film (14) formed on the gate insulating film (13); a metal oxide film (15) formed on the metal oxide film (14); and a metal film (16) in contact with the metal oxide film (15). A part of the metal oxide film (15) is exposed.

Description

ガスセンサGas sensor
　本発明は、ガスセンサに関し、例えば、ガス濃度に応じて電流－電圧特性に変化が生じるガスセンサに適用して有効な技術に関する。 The present invention relates to a gas sensor, for example, a technique effective when applied to a gas sensor in which current-voltage characteristics change according to gas concentration.
　特開２０１５－１０２５３８号公報（特許文献１）には、半導体基板上に形成された金属酸化物層をガス検知層として利用し、ガス流通時のガス検知層の抵抗変化に由来する電流変化からガス濃度を検出する電界効果トランジスタ型ガスセンサが記載されている。 Japanese Patent Laying-Open No. 2015-102538 (Patent Document 1) uses a metal oxide layer formed on a semiconductor substrate as a gas detection layer, and detects a change in current resulting from a change in resistance of the gas detection layer during gas flow. A field effect transistor type gas sensor for detecting gas concentration is described.
特開２０１５－１０２５３８号公報JP2015-102538A
　窒素酸化物（ＮＯｘ）は、バイオマスや化石燃料などの燃焼にともなって発生する人体に悪影響を及ぼすガスであるとともに、種類によっては高い地球温暖化係数を有するガスであり、その排出量の削減が求められている。 Nitrogen oxide (NOx) is a gas that adversely affects the human body that is generated by the combustion of biomass, fossil fuel, etc., and depending on the type, is a gas that has a high global warming potential, and its emissions can be reduced. It has been demanded.
　窒素酸化物の排出量は燃焼条件などによっても変化することから、ガソリンエンジン車やディーゼルエンジン車などの内燃機関を有する自動車においては、エンジンでの燃焼制御による窒素酸化物の排出量を削減することが試みられている。このようなエンジンでの燃焼制御においては、排気ガスに含まれる窒素酸化物のガス濃度を迅速に測定して、その結果を制御系へとフィードバックする必要がある。 Nitrogen oxide emissions vary depending on combustion conditions, etc., so in automobiles with internal combustion engines such as gasoline engine vehicles and diesel engine vehicles, reduce nitrogen oxide emissions through engine combustion control. Has been tried. In combustion control in such an engine, it is necessary to quickly measure the gas concentration of nitrogen oxide contained in the exhaust gas and feed back the result to the control system.
　このようなニーズに対応する新規なガスセンサとしては、電界効果型ガスセンサに代表される仕事関数型ガスセンサが挙げられる。仕事関数型ガスセンサは、被検出ガスのガス濃度に応じてしきい値電圧が変化するガスセンサである。電界効果型ガスセンサと同様に、ガス濃度に応じて電流－電圧特性が変化するガスセンサには、容量型ガスセンサやダイオード型ガスセンサがある。本明細書では、電界効果型ガスセンサと容量型ガスセンサとダイオード型ガスセンサとを総称して仕事関数型ガスセンサと呼ぶ。 As a new gas sensor corresponding to such needs, there is a work function type gas sensor represented by a field effect type gas sensor. A work function type gas sensor is a gas sensor whose threshold voltage changes according to the gas concentration of the gas to be detected. Similar to the field effect type gas sensor, there are a capacitive type gas sensor and a diode type gas sensor as the gas sensor whose current-voltage characteristics change according to the gas concentration. In this specification, the field effect type gas sensor, the capacitive type gas sensor, and the diode type gas sensor are collectively referred to as a work function type gas sensor.
　金属酸化物膜をガス検出膜として利用するガスセンサにおいては、被検出ガスと金属酸化物が反応することにより、イオン伝導性が変化する必要がある。したがって、単一の金属酸化物膜を使用するガスセンサにおいては、この金属酸化物膜を構成する金属酸化物が被検出ガスとの反応性があり、かつ、この反応から得られるイオン伝導性の変化が十分に高いことが要求される。このため、単一の金属酸化物膜を使用するガスセンサにおいては、要求を満たす金属酸化物の選択肢が少ない。したがって、金属酸化物膜をガス検出膜として利用するガスセンサにおいて、ガス濃度の検出性能を向上することが難しくなる。 In a gas sensor that uses a metal oxide film as a gas detection film, the ion conductivity needs to change due to the reaction between the gas to be detected and the metal oxide. Therefore, in a gas sensor using a single metal oxide film, the metal oxide constituting the metal oxide film is reactive with the gas to be detected, and the change in ion conductivity obtained from this reaction. Is required to be sufficiently high. For this reason, in a gas sensor using a single metal oxide film, there are few choices of metal oxides that satisfy the requirements. Therefore, in a gas sensor that uses a metal oxide film as a gas detection film, it is difficult to improve the gas concentration detection performance.
　本発明の目的は、ガスセンサの性能を向上することにある。 An object of the present invention is to improve the performance of a gas sensor.
　その他の課題と新規な特徴は、本明細書の記述および添付図面から明らかになるであろう。 Other issues and novel features will become clear from the description of the present specification and the accompanying drawings.
　一実施の形態におけるガスセンサは、被検出ガスの濃度を検出するガスセンサである。このとき、ガスセンサは、半導体基板上に形成された絶縁膜と、絶縁膜上に形成された第１金属酸化物膜と、第１金属酸化物膜上に形成された第２金属酸化物膜と、第２金属酸化物膜と接する金属膜とを有する。そして、第２金属酸化物膜の一部は、露出している。 The gas sensor in one embodiment is a gas sensor that detects the concentration of the gas to be detected. At this time, the gas sensor includes an insulating film formed on the semiconductor substrate, a first metal oxide film formed on the insulating film, and a second metal oxide film formed on the first metal oxide film. And a metal film in contact with the second metal oxide film. A part of the second metal oxide film is exposed.
　一実施の形態によれば、ガスセンサの性能向上を図ることができる。 According to one embodiment, the performance of the gas sensor can be improved.
（ａ）は、実施の形態におけるガスセンサの模式的な構成を示す断面図であり、（ｂ）は、実施の形態におけるガスセンサの模式的な構成を示す斜視図である。(A) is sectional drawing which shows the typical structure of the gas sensor in embodiment, (b) is a perspective view which shows the typical structure of the gas sensor in embodiment. 実施の形態におけるガスセンサを使用して、電気的に被検出ガス（窒素酸化物ガス）のガス濃度を検出するための回路構成を模式的に示す図である。It is a figure which shows typically the circuit structure for detecting the gas concentration of to-be-detected gas (nitrogen oxide gas) electrically using the gas sensor in embodiment. 図２に示す回路構成を使用して、被検出ガス（窒素酸化物ガス）のガス濃度を算出する方法を説明するグラフである。It is a graph explaining the method to calculate the gas concentration of to-be-detected gas (nitrogen oxide gas) using the circuit structure shown in FIG. 電圧変化値と被検出ガスのガス濃度との関係を示すグラフである。It is a graph which shows the relationship between a voltage change value and the gas concentration of to-be-detected gas. 実施の形態におけるイオンポンプ部の模式的な構成を示す図である。It is a figure which shows the typical structure of the ion pump part in embodiment. （ａ）は、変形例１におけるガスセンサの模式的な構成を示す断面図であり、（ｂ）は、変形例１におけるガスセンサの模式的な構成を示す斜視図である。(A) is sectional drawing which shows the typical structure of the gas sensor in the modification 1, (b) is a perspective view which shows the typical structure of the gas sensor in the modification 1. FIG. （ａ）は、変形例２におけるガスセンサの模式的な構成を示す断面図であり、（ｂ）は、変形例２におけるガスセンサの模式的な構成を示す斜視図である。(A) is sectional drawing which shows the typical structure of the gas sensor in the modification 2, (b) is a perspective view which shows the typical structure of the gas sensor in the modification 2. （ａ）は、変形例３におけるガスセンサの模式的な構成を示す断面図であり、（ｂ）は、変形例３におけるガスセンサの模式的な構成を示す斜視図である。(A) is sectional drawing which shows the typical structure of the gas sensor in the modification 3, (b) is a perspective view which shows the typical structure of the gas sensor in the modification 3.
　以下の実施の形態においては便宜上その必要があるときは、複数のセクションまたは実施の形態に分割して説明するが、特に明示した場合を除き、それらはお互いに無関係なものではなく、一方は他方の一部または全部の変形例、詳細、補足説明等の関係にある。 In the following embodiments, when it is necessary for the sake of convenience, the description will be divided into a plurality of sections or embodiments. However, unless otherwise specified, they are not irrelevant to each other. There are some or all of the modifications, details, supplementary explanations, and the like.
　また、以下の実施の形態において、要素の数等（個数、数値、量、範囲等を含む）に言及する場合、特に明示した場合および原理的に明らかに特定の数に限定される場合等を除き、その特定の数に限定されるものではなく、特定の数以上でも以下でもよい。 Further, in the following embodiments, when referring to the number of elements (including the number, numerical value, quantity, range, etc.), especially when clearly indicated and when clearly limited to a specific number in principle, etc. Except, it is not limited to the specific number, and may be more or less than the specific number.
　さらに、以下の実施の形態において、その構成要素（要素ステップ等も含む）は、特に明示した場合および原理的に明らかに必須であると考えられる場合等を除き、必ずしも必須のものではないことは言うまでもない。 Further, in the following embodiments, the constituent elements (including element steps and the like) are not necessarily indispensable unless otherwise specified and apparently essential in principle. Needless to say.
　同様に、以下の実施の形態において、構成要素等の形状、位置関係等に言及するときは、特に明示した場合および原理的に明らかにそうではないと考えられる場合等を除き、実質的にその形状等に近似または類似するもの等を含むものとする。このことは、上記数値および範囲についても同様である。 Similarly, in the following embodiments, when referring to the shape, positional relationship, etc., of components, etc., unless otherwise specified, and in principle, it is considered that this is not clearly the case, it is substantially the same. Including those that are approximate or similar to the shape. The same applies to the above numerical values and ranges.
　また、実施の形態を説明するための全図において、同一の部材には原則として同一の符号を付し、その繰り返しの説明は省略する。なお、図面をわかりやすくするために平面図であってもハッチングを付す場合がある。 In all the drawings for explaining the embodiments, the same members are, in principle, given the same reference numerals, and the repeated explanation thereof is omitted. In order to make the drawings easy to understand, even a plan view may be hatched.
　＜ガスセンサの構成＞
　図１は、本実施の形態におけるガスセンサ１００の模式的な構成を示す図である。特に、図１（ａ）は、本実施の形態におけるガスセンサ１００の模式的な構成を示す断面図であり、図１（ｂ）は、本実施の形態におけるガスセンサ１００の模式的な構成を示す斜視図である。図１（ａ）および図１（ｂ）に示すガスセンサは、例えば、被検出ガス２０である窒素酸化物ガス（ＮＯｘ）のガス濃度を検出する電界効果型ガスセンサである。 <Configuration of gas sensor>
FIG. 1 is a diagram illustrating a schematic configuration of a gas sensor 100 according to the present embodiment. In particular, FIG. 1A is a cross-sectional view illustrating a schematic configuration of the gas sensor 100 in the present embodiment, and FIG. 1B is a perspective view illustrating a schematic configuration of the gas sensor 100 in the present embodiment. FIG. The gas sensor shown in FIGS. 1A and 1B is, for example, a field effect gas sensor that detects the gas concentration of nitrogen oxide gas (NOx) that is the gas to be detected 20.
　図１（ａ）および図１（ｂ）に示すように、本実施の形態におけるガスセンサは、例えば、シリコン（珪素）やシリコンカーバイド（炭化珪素）を主成分とする半導体基板１０を有し、この半導体基板１０上には、例えば、酸化シリコン膜からなるゲート絶縁膜１３が形成されている。言い換えれば、本実施の形態におけるガスセンサは、シリコン（Ｓｉ）やシリコンカーバイド（ＳｉＣ）を母体とする半導体基板１０を有し、この半導体基板１０上には、酸化シリコン膜からなるゲート絶縁膜１３が形成されている。 As shown in FIG. 1A and FIG. 1B, the gas sensor in the present embodiment includes a semiconductor substrate 10 mainly composed of silicon (silicon) or silicon carbide (silicon carbide), for example. On the semiconductor substrate 10, a gate insulating film 13 made of, for example, a silicon oxide film is formed. In other words, the gas sensor in the present embodiment has a semiconductor substrate 10 based on silicon (Si) or silicon carbide (SiC), and a gate insulating film 13 made of a silicon oxide film is formed on the semiconductor substrate 10. Is formed.
　そして、ゲート絶縁膜１３上には、ゲート電極が形成されている。具体的に、ゲート絶縁膜１３上には、金属酸化物膜１４が形成されており、この金属酸化物膜１４上には、金属酸化物膜１５が形成されている。さらに、金属酸化物膜１５上には、金属膜１６が形成されている。このように、本実施の形態におけるガスセンサ１００では、ゲート電極は、金属酸化物膜１４と、金属酸化物膜１４上に形成された金属酸化物膜１５と、金属酸化物膜１５上に形成された金属膜１６とを含む。このとき、図１（ａ）および図１（ｂ）に示すように、ゲート電極の上方に被検出ガスである窒素酸化物ガスが流れるようになっている。そして、ゲート電極の一部を構成する金属酸化物膜１５の一部は、露出しており、金属酸化物膜１５の表面の一部に、窒素酸化物ガスが接触するように構成されている。 A gate electrode is formed on the gate insulating film 13. Specifically, a metal oxide film 14 is formed on the gate insulating film 13, and a metal oxide film 15 is formed on the metal oxide film 14. Further, a metal film 16 is formed on the metal oxide film 15. As described above, in the gas sensor 100 according to the present embodiment, the gate electrode is formed on the metal oxide film 14, the metal oxide film 15 formed on the metal oxide film 14, and the metal oxide film 15. Metal film 16. At this time, as shown in FIGS. 1A and 1B, a nitrogen oxide gas, which is a gas to be detected, flows above the gate electrode. A part of the metal oxide film 15 that constitutes a part of the gate electrode is exposed, and the nitrogen oxide gas is in contact with a part of the surface of the metal oxide film 15. .
　さらに、本実施の形態におけるガスセンサ１００は、ゲート絶縁膜１３の直下の半導体基板１０に形成されたチャネル形成領域と、このチャネル形成領域を挟むソース領域１１とドレイン領域１２とを有している。以上のようにして、本実施の形態におけるガスセンサ１００が模式的に構成されていることになる。 Furthermore, the gas sensor 100 according to the present embodiment has a channel formation region formed in the semiconductor substrate 10 immediately below the gate insulating film 13, and a source region 11 and a drain region 12 sandwiching the channel formation region. As described above, the gas sensor 100 according to the present embodiment is schematically configured.
　＜金属酸化物膜の性質＞
　次に、金属酸化物膜１４と金属酸化物膜１５の性質について説明する。本実施の形態における金属酸化物膜１４は、イオン伝導性を有する。一方、金属酸化物膜１５は、金属酸化物膜１５の表面に吸着する被検出ガスの吸着種を変化させる触媒機能を有する。具体的に、金属酸化物膜１５は、例えば、窒素酸化物ガス（ＮＯｘ）を含むガスが金属酸化物膜１５に接触すると、一酸化窒素（ＮＯ）が変性して、より吸着が容易な二酸化窒素（ＮＯ２）などの吸着種に変化させる機能を有している。そして、金属酸化物膜１４は、金属酸化物膜１５の表面に吸着した吸着種に起因して、イオン伝導性が変化する性質を有する。 <Property of metal oxide film>
Next, the properties of the metal oxide film 14 and the metal oxide film 15 will be described. The metal oxide film 14 in the present embodiment has ionic conductivity. On the other hand, the metal oxide film 15 has a catalytic function for changing the adsorption species of the detection gas adsorbed on the surface of the metal oxide film 15. Specifically, for example, when a gas containing nitrogen oxide gas (NOx) comes into contact with the metal oxide film 15, the metal oxide film 15 is denatured by nitrogen monoxide (NO) and more easily absorbed. It has a function of changing to an adsorption species such as nitrogen (NO 2 ). The metal oxide film 14 has a property that the ion conductivity changes due to the adsorbed species adsorbed on the surface of the metal oxide film 15.
　＜ガスセンサにおける概念的なガス濃度の検出メカニズム＞
　続いて、本実施の形態におけるガスセンサによって、窒素酸化物ガスのガス濃度を検出することができる概念的な検出メカニズムについて説明する。まず、図１（ａ）および図１（ｂ）に示すように、本実施の形態におけるガスセンサ１００の上方には、窒素酸化物ガスを含む被検出ガス２０が流れている。このとき、本実施の形態１におけるガスセンサ１００では、金属酸化物膜１５の表面の一部が露出している。このため、露出している金属酸化物膜１５の表面には、窒素酸化物ガスが接触する。このとき、金属酸化物膜１５は、金属酸化物膜１５の表面に吸着する窒素酸化物ガスの吸着種を変化させる触媒機能を有する。言い換えれば、金属酸化物膜１５は、金属酸化物膜１５の表面に吸着した窒素酸化物ガスに対して酸素を供給する機能を有する。したがって、この金属酸化物膜１５の触媒機能によって、窒素酸化物ガスに含まれる一酸化窒素（ＮＯ）が金属酸化物膜１５に接触すると、一酸化窒素（ＮＯ）に対して、金属酸化物膜１５から酸素が供給される。この結果、一酸化窒素（ＮＯ）は、より吸着が容易な二酸化窒素（ＮＯ２）などに変化する。そして、二酸化窒素（ＮＯ２）などが金属酸化物膜１５から下層の金属酸化物膜１４に移動して、金属酸化物膜１４に対して、二酸化窒素（ＮＯ２）などから、酸素イオン（Ｏ２－）が供給される結果、金属酸化物膜１４のイオン伝導性が変化する。これにより、ソース領域１１とドレイン領域１２に挟まれたチャネル形成領域に加わる電界強度が変化して、ソース領域１１とドレイン領域１２との間を流れる電流およびその電流を流すためのしきい値電圧（ゲート電圧）が変化する。このことから、本実施の形態におけるガスセンサ１００においては、このしきい値電圧の変化に基づいて、窒素酸化物ガスのガス濃度を検出することができる。 <Conceptual detection mechanism of gas concentration in gas sensor>
Next, a conceptual detection mechanism that can detect the gas concentration of the nitrogen oxide gas by the gas sensor in the present embodiment will be described. First, as shown in FIG. 1A and FIG. 1B, a detection gas 20 containing a nitrogen oxide gas flows above the gas sensor 100 in the present embodiment. At this time, in the gas sensor 100 according to the first embodiment, a part of the surface of the metal oxide film 15 is exposed. For this reason, nitrogen oxide gas contacts the exposed surface of the metal oxide film 15. At this time, the metal oxide film 15 has a catalytic function of changing the adsorption species of the nitrogen oxide gas adsorbed on the surface of the metal oxide film 15. In other words, the metal oxide film 15 has a function of supplying oxygen to the nitrogen oxide gas adsorbed on the surface of the metal oxide film 15. Therefore, when the nitric oxide (NO) contained in the nitrogen oxide gas comes into contact with the metal oxide film 15 by the catalytic function of the metal oxide film 15, the metal oxide film against the nitric oxide (NO). 15 is supplied with oxygen. As a result, nitric oxide (NO) changes to nitrogen dioxide (NO 2 ) and the like that are easier to adsorb. Then, nitrogen dioxide (NO 2 ) or the like moves from the metal oxide film 15 to the lower metal oxide film 14, and oxygen ions (O 2 ) from the nitrogen dioxide (NO 2 ) or the like to the metal oxide film 14. As a result of the supply of 2- ), the ionic conductivity of the metal oxide film 14 changes. As a result, the electric field strength applied to the channel formation region sandwiched between the source region 11 and the drain region 12 changes, and the current flowing between the source region 11 and the drain region 12 and the threshold voltage for flowing the current. (Gate voltage) changes. From this, the gas sensor 100 according to the present embodiment can detect the gas concentration of the nitrogen oxide gas based on the change in the threshold voltage.
　＜ゲート絶縁膜の構成材料＞
　次に、本実施の形態におけるゲート絶縁膜１３を構成する材料について説明する。図１（ａ）および図１（ｂ）に示す本実施の形態におけるゲート絶縁膜１３は、例えば、酸化シリコンに代表されるシリコン（Ｓｉ）を含む酸化物から構成される。本実施の形態におけるゲート絶縁膜１３にシリコンを含む酸化物を使用することにより、ゲート電極からのリーク電流を抑制することができる。この結果、リーク電流に起因するノイズを低減できることから、本実施の形態におけるガスセンサ１００の検出精度を向上できる。 <Constituent material of gate insulating film>
Next, the material constituting the gate insulating film 13 in this embodiment will be described. The gate insulating film 13 in this embodiment shown in FIGS. 1A and 1B is made of, for example, an oxide containing silicon (Si) typified by silicon oxide. By using an oxide containing silicon for the gate insulating film 13 in this embodiment, leakage current from the gate electrode can be suppressed. As a result, noise caused by the leakage current can be reduced, so that the detection accuracy of the gas sensor 100 in the present embodiment can be improved.
　＜金属酸化物膜の構成材料＞
　続いて、本実施の形態における金属酸化物膜１４を構成する材料について説明する。イオン伝導性を有する金属酸化物膜１４は、例えば、ジルコニウム（Ｚｒ）を含む酸化物から構成される。また、イオン伝導性を有する金属酸化物膜１４は、第１金属と第２金属とを含むように構成することもできる。このとき、第１金属は、ジルコニウム（Ｚｒ）である。一方、第２金属は、カルシウム（Ｃａ）、マグネシウム（Ｍｇ）、イットリウム（Ｙ）、ランタン（Ｌａ）、セリウム（Ｃｅ）、プラセオジウム（Ｐｒ）、ネオジウム（Ｎｄ）、プロメチウム（Ｐｍ）、サマリウム（Ｓｍ）、ユーロピウム（Ｅｕ）、ガドリニウム（Ｇｄ）、テルビウム（Ｔｂ）、ジスプロシウム（Ｄｙ）、ホルミウム（Ｈｏ）、エルビウム（Ｅｒ）、ツリウム（Ｔｍ）、イッテルビウム（Ｙｂ）、ルテチウム（Ｌｕ）、ハフニウム（Ｈｆ）から選ばれる少なくとも１種類の金属である。ここで、ジルコニウム（Ｚｒ）以外の元素の添加量は、モル比で１％以上１５％以下であることが望ましい。 <Constituent material of metal oxide film>
Subsequently, a material constituting the metal oxide film 14 in the present embodiment will be described. The metal oxide film 14 having ion conductivity is made of an oxide containing zirconium (Zr), for example. Further, the metal oxide film 14 having ion conductivity may be configured to include the first metal and the second metal. At this time, the first metal is zirconium (Zr). On the other hand, the second metal is calcium (Ca), magnesium (Mg), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm). ), Europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), hafnium (Hf) At least one kind of metal selected from. Here, the addition amount of elements other than zirconium (Zr) is desirably 1% or more and 15% or less in terms of molar ratio.
　上述したように、金属酸化物膜１４は、ジルコニウムを含む酸化物から構成することができるが、この場合、金属酸化物膜１４を構成する金属酸化物の結晶構造は、単斜晶や正方晶や立方晶となる。特に、ジルコニウムだけを含む金属酸化物の結晶構造は、単斜晶となる一方、ジルコニウム（第１金属）と上述した第２金属とを含む金属酸化物の結晶構造は、正方晶や立方晶となる。このとき、正方晶や立方晶の結晶構造は、単斜晶の結晶構造と比較して、酸素欠損を生じやすく、イオン伝導性が変化しやすくなる。このため、イオン伝導性の変化を大きくする観点から、金属酸化物膜１４を、ジルコニウム（第１金属）と上述した第２金属とを含む金属酸化物から構成することが望ましい。 As described above, the metal oxide film 14 can be made of an oxide containing zirconium. In this case, the crystal structure of the metal oxide constituting the metal oxide film 14 is monoclinic or tetragonal. Or cubic. In particular, the crystal structure of a metal oxide containing only zirconium is monoclinic, while the crystal structure of a metal oxide containing zirconium (first metal) and the second metal is tetragonal or cubic. Become. At this time, the tetragonal or cubic crystal structure is more likely to cause oxygen deficiency and the ionic conductivity is more likely to change than the monoclinic crystal structure. For this reason, it is desirable that the metal oxide film 14 is made of a metal oxide containing zirconium (first metal) and the above-described second metal from the viewpoint of increasing the ionic conductivity.
　続いて、本実施の形態における金属酸化物膜１５を構成する材料について説明する。金属酸化物膜１５は、例えば、ニッケル（Ｎｉ）を含む酸化物から構成される。この場合、金属酸化物膜１５に対して、金属酸化物膜１５の表面に吸着する被検出ガスの吸着種を変化させる触媒機能を実現できるとともに、金属酸化物膜１５と金属膜１６との密着性を向上することができる。さらに、金属酸化物膜１５は、ニッケルの他に、ロジウム（Ｒｈ）、パラジウム（Ｐｄ）、白金（Ｐｔ）、ルテニウム（Ｒｕ）、銅（Ｃｕ）、鉄（Ｆｅ）、コバルト（Ｃｏ）、マンガン（Ｍｎ）、セリウム（Ｃｅ）、ジルコニウム（Ｚｒ）から選ばれる少なくとも１種類の元素を含むこともできる。このとき、ニッケル以外の元素は、必ずしも酸化物の形態で金属酸化物膜１５に含まれていなくてもよい。 Subsequently, materials constituting the metal oxide film 15 in the present embodiment will be described. The metal oxide film 15 is made of an oxide containing nickel (Ni), for example. In this case, a catalytic function for changing the adsorption species of the gas to be detected adsorbed on the surface of the metal oxide film 15 can be realized with respect to the metal oxide film 15, and the metal oxide film 15 and the metal film 16 are in close contact with each other. Can be improved. In addition to nickel, the metal oxide film 15 includes rhodium (Rh), palladium (Pd), platinum (Pt), ruthenium (Ru), copper (Cu), iron (Fe), cobalt (Co), manganese. It may also contain at least one element selected from (Mn), cerium (Ce), and zirconium (Zr). At this time, elements other than nickel are not necessarily contained in the metal oxide film 15 in the form of an oxide.
　さらに、金属酸化物膜１５の表面に吸着させる吸着種の吸着量を多くする観点から、金属酸化物膜１５の表面積を大きくすることが望ましい。具体的に、金属酸化物膜１５は、少なくとも一部が多孔質であることが望ましい。ただし、金属酸化物膜１５を多孔質から構成する場合、上層の金属膜１６との接着強度が不充分となる可能性がある。このため、金属酸化物膜１５を構成する金属酸化物の粒径は、１０ｎｍ以上１０μｍ以下であることが望ましい。これにより、本実施の形態におけるガスセンサ１００によれば、金属酸化物膜１５の表面に吸着させる吸着種の吸着量を多くすることができるとともに、金属酸化物膜１５と金属膜１６との接着強度を確保することができる。 Furthermore, it is desirable to increase the surface area of the metal oxide film 15 from the viewpoint of increasing the amount of adsorbed species adsorbed on the surface of the metal oxide film 15. Specifically, the metal oxide film 15 is desirably at least partially porous. However, when the metal oxide film 15 is made of a porous material, the adhesive strength with the upper metal film 16 may be insufficient. For this reason, the particle size of the metal oxide constituting the metal oxide film 15 is desirably 10 nm or more and 10 μm or less. Thereby, according to the gas sensor 100 in this Embodiment, while the adsorption amount of the adsorption species adsorbed on the surface of the metal oxide film 15 can be increased, the adhesive strength between the metal oxide film 15 and the metal film 16 is increased. Can be secured.
　＜金属膜の構成材料＞
　次に、本実施の形態における金属膜１６を構成する材料について説明する。本実施の形態における金属膜１６は、白金（Ｐｔ）、金（Ａｕ）、パラジウム（Ｐｄ）、ロジウム（Ｒｈ）から選ばれる少なくとも１種類の元素を含む膜から構成される。 <Components of metal film>
Next, the material which comprises the metal film 16 in this Embodiment is demonstrated. The metal film 16 in the present embodiment is composed of a film containing at least one element selected from platinum (Pt), gold (Au), palladium (Pd), and rhodium (Rh).
　このように構成される金属膜１６は、必ずしも、被検出ガスの雰囲気に露出させる必要はない。ただし、金属膜１６を白金に代表される貴金属から構成する場合、白金に代表される貴金属は、一酸化窒素（ＮＯ）の吸着種を変化させる触媒機能を有している。したがって、例えば、図１（ｂ）の「Ａ」で示す金属酸化物膜１５と金属膜１６との接触部位では、金属酸化物膜１５の触媒機能と金属膜１６の触媒機能との相乗効果によって、一酸化窒素（ＮＯ）から二酸化窒素（ＮＯ２）への変化が生じやすくなると考えられる。このことから、本実施の形態のガスセンサ１００において、金属酸化物膜１５と金属膜１６との接触部分（図１（ｂ）の「Ａ」で示されている）は、露出していることが望ましい。 The metal film 16 thus configured is not necessarily exposed to the atmosphere of the gas to be detected. However, in the case where the metal film 16 is made of a noble metal typified by platinum, the noble metal typified by platinum has a catalytic function of changing the adsorption species of nitric oxide (NO). Therefore, for example, at the contact portion between the metal oxide film 15 and the metal film 16 indicated by “A” in FIG. 1B, a synergistic effect of the catalytic function of the metal oxide film 15 and the catalytic function of the metal film 16 is obtained. It is considered that a change from nitric oxide (NO) to nitrogen dioxide (NO 2 ) is likely to occur. From this, in the gas sensor 100 of the present embodiment, the contact portion (indicated by “A” in FIG. 1B) between the metal oxide film 15 and the metal film 16 is exposed. desirable.
　＜ソース領域およびドレイン領域の構成材料＞
　本実施の形態におけるガスセンサ１００は、電界効果型ガスセンサである。つまり、ガスセンサ１００は、基本的に、ｎチャネル型電界効果トランジスタやｐチャネル型電界効果トランジスタから構成することができる。 <Constituent materials of source region and drain region>
The gas sensor 100 in the present embodiment is a field effect gas sensor. That is, the gas sensor 100 can basically be composed of an n-channel field effect transistor or a p-channel field effect transistor.
　例えば、ガスセンサ１００をｎチャネル型電界効果トランジスタから構成する場合、ソース領域１１およびドレイン領域１２は、ｎ型半導体領域から構成される。具体的に、半導体基板がシリコンから構成される場合、イオン注入法によって、リン（Ｐ）や砒素（Ａｓ）に代表されるｎ型不純物（ドナー）を半導体基板に導入することにより、ｎ型半導体領域からなるソース領域１１およびドレイン領域１２を形成することができる。 For example, when the gas sensor 100 is composed of an n-channel field effect transistor, the source region 11 and the drain region 12 are composed of an n-type semiconductor region. Specifically, when the semiconductor substrate is made of silicon, an n-type semiconductor is introduced by introducing an n-type impurity (donor) typified by phosphorus (P) or arsenic (As) into the semiconductor substrate by ion implantation. A source region 11 and a drain region 12 composed of regions can be formed.
　一方、ガスセンサ１００をｐチャネル型電界効果トランジスタから構成する場合、ソース領域１１およびドレイン領域１２は、ｐ型半導体領域から構成される。具体的に、半導体基板がシリコンから構成される場合、イオン注入法によって、ボロン（Ｂ）に代表されるｐ型不純物（アクセプタ）を半導体基板に導入することにより、ｐ型半導体領域からなるソース領域１１およびドレイン領域１２を形成することができる。 On the other hand, when the gas sensor 100 is composed of a p-channel field effect transistor, the source region 11 and the drain region 12 are composed of a p-type semiconductor region. Specifically, in the case where the semiconductor substrate is made of silicon, a p-type impurity (acceptor) represented by boron (B) is introduced into the semiconductor substrate by an ion implantation method, thereby forming a source region composed of the p-type semiconductor region. 11 and the drain region 12 can be formed.
　＜半導体基板の構成材料＞
　続いて、本実施の形態における半導体基板１０を構成する材料について説明する。本実施の形態における半導体基板１０は、例えば、シリコン（Ｓｉ）やシリコンカーバイド（ＳｉＣ）から構成することができる。特に、本実施の形態におけるガスセンサ１００を自動車のエンジンから排気される排気ガスなどの高温ガス内で使用する場合、熱電子に起因するノイズを低減する観点から、バンドギャップの大きなシリコンカーバイド（ＳｉＣ）を使用することが望ましい。 <Constituent materials for semiconductor substrates>
Subsequently, materials constituting the semiconductor substrate 10 in the present embodiment will be described. The semiconductor substrate 10 in the present embodiment can be composed of, for example, silicon (Si) or silicon carbide (SiC). In particular, when the gas sensor 100 according to the present embodiment is used in a high-temperature gas such as exhaust gas exhausted from an automobile engine, silicon carbide (SiC) having a large band gap is used from the viewpoint of reducing noise caused by thermal electrons. It is desirable to use
　＜ガスセンサの電気回路構成＞
　本実施の形態におけるガスセンサ１００は、上記のように構成されており、以下に、本実施の形態におけるガスセンサ１００を使用して、電気的に被検出ガス（窒素酸化物ガス）のガス濃度を検出するための回路構成について説明する。 <Electric circuit configuration of gas sensor>
The gas sensor 100 in the present embodiment is configured as described above. Hereinafter, the gas concentration of the gas to be detected (nitrogen oxide gas) is electrically detected using the gas sensor 100 in the present embodiment. A circuit configuration for this purpose will be described.
　図２は、本実施の形態におけるガスセンサ１００を使用して、電気的に被検出ガス（窒素酸化物ガス）のガス濃度を検出するための回路構成を模式的に示す図である。図２において、ガスセンサ１００には、ソース端子１０１とドレイン端子１０２とゲート端子１０３とが電気的に接続される。具体的に、図１（ａ）および図１（ｂ）に示すガスセンサ１００のソース領域１１は、図２に示すソース端子１０１と電気的に接続され、かつ、図１（ａ）および図１（ｂ）に示すガスセンサ１００のドレイン領域１２は、図２に示すドレイン端子１０２と電気的に接続される。また、図１（ａ）および図１（ｂ）に示すガスセンサ１００のゲート電極（金属膜１６）は、図２に示すゲート端子１０３と電気的に接続される。このような接続構成において、ゲート電極として機能する金属膜１６へのゲート電圧の印加は、金属膜１６と電気的に接続されたゲート電圧印加装置１０４で行なわれる。また、ガスセンサ１００のソース領域１１と電気的に接続されたソース端子１０１は、グランド電位に接地されている。一方、ガスセンサ１００のドレイン領域１２と電気的に接続されたドレイン端子１０２は、電流測定機器１０５とドレイン電圧印加装置１０６と電気的に接続されている。以上のような回路構成において、ドレイン電圧印加装置１０６からドレイン端子１０２にドレイン電圧を印加した状態で、ゲート電圧印加装置１０４からゲート端子１０３に印加するゲート電圧を制御する。この場合、ガスセンサ１００が接触する被検出ガス（窒素酸化物ガス）のガス濃度に応じて、ガスセンサ１００のしきい値電圧が変化することを利用して、被検出ガス（窒素酸化物ガス）のガス濃度が計測される。以下では、被検出ガス（窒素酸化物ガス）のガス濃度の算出方法について説明する。 FIG. 2 is a diagram schematically showing a circuit configuration for electrically detecting the gas concentration of the gas to be detected (nitrogen oxide gas) using the gas sensor 100 according to the present embodiment. In FIG. 2, a source terminal 101, a drain terminal 102, and a gate terminal 103 are electrically connected to the gas sensor 100. Specifically, the source region 11 of the gas sensor 100 shown in FIG. 1A and FIG. 1B is electrically connected to the source terminal 101 shown in FIG. 2, and FIG. 1A and FIG. The drain region 12 of the gas sensor 100 shown in b) is electrically connected to the drain terminal 102 shown in FIG. Further, the gate electrode (metal film 16) of the gas sensor 100 shown in FIGS. 1A and 1B is electrically connected to the gate terminal 103 shown in FIG. In such a connection configuration, the gate voltage is applied to the metal film 16 functioning as the gate electrode by the gate voltage application device 104 electrically connected to the metal film 16. The source terminal 101 that is electrically connected to the source region 11 of the gas sensor 100 is grounded to the ground potential. On the other hand, the drain terminal 102 electrically connected to the drain region 12 of the gas sensor 100 is electrically connected to the current measuring device 105 and the drain voltage applying device 106. In the circuit configuration as described above, the gate voltage applied from the gate voltage application device 104 to the gate terminal 103 is controlled while the drain voltage is applied from the drain voltage application device 106 to the drain terminal 102. In this case, using the fact that the threshold voltage of the gas sensor 100 changes according to the gas concentration of the gas to be detected (nitrogen oxide gas) that the gas sensor 100 contacts, the gas to be detected (nitrogen oxide gas) The gas concentration is measured. Below, the calculation method of the gas concentration of to-be-detected gas (nitrogen oxide gas) is demonstrated.
　＜ガス濃度の算出方法＞
　図３は、図２に示す回路構成を使用して、被検出ガス（窒素酸化物ガス）のガス濃度を算出する方法を説明するグラフである。まず、電界効果トランジスタでは、ゲート電極にしきい値電圧よりも小さいゲート電圧を印加する場合、ソース領域１１とドレイン領域１２との間にチャネル（反転層）が形成されずに、電流がほとんど流れない。ところが、電界効果トランジスタでは、ゲート電極にある一定以上のゲート電圧を印加すると、ソース領域１１とドレイン領域１２との間にチャネル（反転層）が形成され、急激にソース領域１１とドレイン領域１２との間に電流が流れるようになる。そこで、本実施の形態では、ある電流値をしきい値電流とし、このしきい値電流を得るためのゲート電圧をしきい値電圧と定義する。具体的に、図３において、縦軸は、ドレイン電流を示しており、横軸は、ゲート電圧を示している。そして、縦軸には、しきい値電流Ｉ１が示されている。 <Calculation method of gas concentration>
FIG. 3 is a graph illustrating a method for calculating the gas concentration of the gas to be detected (nitrogen oxide gas) using the circuit configuration shown in FIG. First, in a field effect transistor, when a gate voltage lower than a threshold voltage is applied to a gate electrode, a channel (inversion layer) is not formed between the source region 11 and the drain region 12, and almost no current flows. . However, in a field effect transistor, when a certain or higher gate voltage is applied to the gate electrode, a channel (inversion layer) is formed between the source region 11 and the drain region 12, and the source region 11 and the drain region 12 During this time, a current flows. Therefore, in this embodiment, a certain current value is defined as a threshold current, and a gate voltage for obtaining this threshold current is defined as a threshold voltage. Specifically, in FIG. 3, the vertical axis indicates the drain current, and the horizontal axis indicates the gate voltage. On the vertical axis, the threshold current I1 is shown.
　本実施の形態におけるガスセンサ１００では、被検出ガス（窒素酸化物ガス）のガス濃度によって、金属酸化物膜１４のイオン伝導性が変化し、これに伴って、ガスセンサ（電界効果トランジスタ）１００のしきい値電圧も変化する。そこで、まず、既知のガス濃度を有するリファレンスガスにおけるしきい値電圧（Ｖ１）を測定しておく（曲線３０）。次に、被検出ガスを流した場合におけるしきい値電圧（Ｖ２）を測定する（曲線４０）。このとき、例えば、図３に示すように、しきい値電圧（Ｖ１）としきい値電圧（Ｖ２）との間に電位差が生じていると、被検出ガスのガス濃度がリファレンスガスのガス濃度から変化していることがわかる。 In the gas sensor 100 according to the present embodiment, the ion conductivity of the metal oxide film 14 changes depending on the gas concentration of the gas to be detected (nitrogen oxide gas), and accordingly, the gas sensor (field effect transistor) 100 operates. The threshold voltage also changes. Therefore, first, a threshold voltage (V1) in a reference gas having a known gas concentration is measured (curve 30). Next, the threshold voltage (V2) when the gas to be detected flows is measured (curve 40). At this time, for example, as shown in FIG. 3, if there is a potential difference between the threshold voltage (V1) and the threshold voltage (V2), the gas concentration of the detected gas is determined from the gas concentration of the reference gas. You can see that it is changing.
　ここで、例えば、既知の被検出ガスのガス濃度とガスセンサ１００のしきい値電圧との相関関係を調べると、例えば、図４に示すグラフが得られる。図４は、電圧変化値（Ｖ２－Ｖ１）と被検出ガスのガス濃度との関係を示すグラフである。このような図４に示す相関関係を予め把握してバックデータとして取得しておけば、例えば、ガス濃度が未知の被検出ガスを流した場合に得られたガスセンサ１００のしきい値電圧から、未知の被検出ガスのガス濃度を算出することができる。 Here, for example, when the correlation between the gas concentration of the known gas to be detected and the threshold voltage of the gas sensor 100 is examined, for example, a graph shown in FIG. 4 is obtained. FIG. 4 is a graph showing the relationship between the voltage change value (V2-V1) and the gas concentration of the gas to be detected. If the correlation shown in FIG. 4 is grasped in advance and acquired as back data, for example, from the threshold voltage of the gas sensor 100 obtained when a gas to be detected whose gas concentration is unknown is flowed, The gas concentration of the unknown gas to be detected can be calculated.
　＜実施の形態における特徴＞
　次に、本実施の形態における特徴点について説明する。本実施の形態における第１特徴点は、例えば、図１（ａ）および図１（ｂ）に示すように、ガスセンサ１００において、互いに機能の異なる金属酸化物膜１４と金属酸化物膜１５とが積層膜を構成している点にある。これにより、本実施の形態におけるガスセンサ１００によれば、ガスセンサ１００の性能向上を図ることができる。 <Features in Embodiment>
Next, feature points in the present embodiment will be described. For example, as shown in FIG. 1A and FIG. 1B, the first feature point in the present embodiment is that a metal oxide film 14 and a metal oxide film 15 having different functions are included in the gas sensor 100. It is the point which comprises the laminated film. Thereby, according to the gas sensor 100 in this Embodiment, the performance improvement of the gas sensor 100 can be aimed at.
　例えば、電界効果型ガスセンサにおいては、被検出ガスのガス濃度に応じてしきい値電圧が変化することを利用して、被検出ガスのガス濃度を検出する。このような電界効果型ガスセンサにおいては、金属酸化物膜をガス検出膜として利用する。そして、このガスセンサの構成要素となる金属酸化物膜には、被検出ガスと金属酸化物が反応することにより、イオン伝導性が変化することが要求される。したがって、例えば、単一の金属酸化物膜を使用するガスセンサにおいては、この金属酸化物膜を構成する金属酸化物が被検出ガスとの反応性があり、かつ、この反応から得られるイオン伝導性の変化が十分に高いことが要求される。このため、単一の金属酸化物膜を使用するガスセンサにおいては、要求を満たす金属酸化物の選択肢が少なくなる。このことから、単一の金属酸化物膜を使用するガスセンサにおいては、要求を満たす単一の金属酸化物膜を選択する余地が少なく、ガス濃度の検出性能を向上することが難しくなる。つまり、単一の金属酸化物膜を使用するガスセンサにおいては、イオン伝導性の変化が大きく、かつ、表面に吸着する被検出ガスの吸着種を変化させる触媒機能を有することが要求される。特に、ガスセンサにおけるガス濃度の検出感度を向上するためには、イオン伝導性の変化が大きいことが要求されるが、さらに、被検出ガスが窒素酸化物ガスの場合には、表面に吸着する被検出ガスの吸着種を変化させる触媒機能を有することも重要となってくる。なぜなら、窒素酸化物ガスに含まれる一酸化窒素（ＮＯ）は、金属酸化物膜に吸着しにくい性質を有していることから、金属酸化物膜に吸着することを前提としてガス濃度を検出するガスセンサでは、一酸化窒素（ＮＯ）では、ガス濃度の検出精度を向上することができないからである。すなわち、窒素酸化物ガスのガス濃度の検出感度を向上するためには、金属酸化物膜に吸着しにくい一酸化窒素（ＮＯ）を金属酸化物膜に吸着しやすい二酸化窒素（ＮＯ２）のように吸着種を変化させる必要があるのである。つまり、窒素酸化物ガスのガス濃度を検出するガスセンサにおいては、表面に吸着する被検出ガスの吸着種を変化させる触媒機能を有する金属酸化物膜を使用することによって、初めて、高感度なガスセンサを実現できるのである。 For example, in a field effect type gas sensor, the gas concentration of the gas to be detected is detected by utilizing the fact that the threshold voltage changes according to the gas concentration of the gas to be detected. In such a field effect gas sensor, a metal oxide film is used as a gas detection film. The metal oxide film that is a constituent element of the gas sensor is required to change its ionic conductivity by reacting the gas to be detected and the metal oxide. Therefore, for example, in a gas sensor using a single metal oxide film, the metal oxide constituting the metal oxide film is reactive with the gas to be detected, and the ionic conductivity obtained from this reaction. Is required to be sufficiently high. For this reason, in a gas sensor that uses a single metal oxide film, there are fewer options for metal oxides that satisfy the requirements. For this reason, in a gas sensor using a single metal oxide film, there is little room for selecting a single metal oxide film that satisfies the requirements, and it is difficult to improve the gas concentration detection performance. That is, a gas sensor that uses a single metal oxide film is required to have a catalytic function that changes the ion conductivity of the gas to be detected and that changes the adsorption species of the gas to be detected adsorbed on the surface. In particular, in order to improve the gas concentration detection sensitivity of the gas sensor, a large change in ion conductivity is required. Furthermore, when the gas to be detected is a nitrogen oxide gas, the object to be adsorbed on the surface is required. It is also important to have a catalytic function that changes the adsorption species of the detection gas. Because nitrogen monoxide (NO) contained in the nitrogen oxide gas has a property that it is difficult to adsorb on the metal oxide film, the gas concentration is detected on the assumption that it is adsorbed on the metal oxide film. This is because in the gas sensor, the detection accuracy of the gas concentration cannot be improved with nitric oxide (NO). That is, in order to improve the detection sensitivity of the nitrogen oxide gas concentration, nitrogen monoxide (NO), which is difficult to adsorb on the metal oxide film, is converted to nitrogen dioxide (NO 2 ), which is easy to adsorb on the metal oxide film. Therefore, it is necessary to change the adsorbed species. In other words, in a gas sensor that detects the gas concentration of nitrogen oxide gas, a highly sensitive gas sensor is not used for the first time by using a metal oxide film that has a catalytic function to change the species of gas to be detected adsorbed on the surface. It can be realized.
　この点に関し、本実施の形態では、ガスセンサ１００において、互いに機能の異なる金属酸化物膜１４と金属酸化物膜１５とが積層膜を構成している。具体的に、本実施の形態では、イオン伝導性を有する金属酸化物膜１４と、表面に吸着する被検出ガスの吸着種を変化させる触媒機能を有する金属酸化物膜１５とが積層膜を構成している。この場合、金属酸化物膜１４に対しては、イオン伝導性の変化が大きい性質を有する観点からだけで膜の種類を選択することができる。同様に、金属酸化物膜１５に対しては、表面に吸着する被検出ガスの吸着種を変化させる触媒機能を有する観点からだけで膜の種類を選択することができる。したがって、ガスセンサ１００において、互いに機能の異なる金属酸化物膜１４と金属酸化物膜１５とが積層膜を構成しているという本実施の形態における第１特徴点によれば、金属酸化物膜１４と金属酸化物膜１５のそれぞれの材料の選択の余地が広がる。このことは、本実施の形態におけるガスセンサ１００によれば、被検出ガスのガス濃度の検出感度を容易に向上させることができることを意味する。つまり、本実施の形態における第１特徴点によれば、イオン伝導性の変化が大きい性質を有する観点と、表面に吸着する被検出ガスの吸着種を変化させる触媒機能を有する観点とを両立する材料を選択する場合に比べて、遥かに材料の選択の余地が広がる。この結果、本実施の形態における第１特徴点によれば、金属酸化物膜を構成する材料の選択の余地が広がることによって、容易にガスセンサ１００の性能向上を図ることができる。さらには、金属酸化物膜を構成する材料の選択の余地が広がることによって、性能が同等であり、かつ、製造コストの低い材料を優先的に選択できる余地が広がる。つまり、本実施の形態における第１特徴点によれば、容易にガスセンサ１００の性能向上を図ることができるとともに、製造コストの削減も可能となる点で優れた効果を得ることができる。 In this regard, in the present embodiment, in the gas sensor 100, the metal oxide film 14 and the metal oxide film 15 having different functions constitute a laminated film. Specifically, in the present embodiment, the metal oxide film 14 having ion conductivity and the metal oxide film 15 having a catalytic function for changing the adsorption species of the detection gas adsorbed on the surface constitute a laminated film. doing. In this case, for the metal oxide film 14, the type of the film can be selected only from the viewpoint of having a property that the change in ion conductivity is large. Similarly, for the metal oxide film 15, the type of film can be selected only from the viewpoint of having a catalytic function that changes the adsorption species of the gas to be detected adsorbed on the surface. Therefore, in the gas sensor 100, according to the first feature point in the present embodiment that the metal oxide film 14 and the metal oxide film 15 having different functions constitute a laminated film, the metal oxide film 14 The room for selection of each material of the metal oxide film 15 widens. This means that the gas sensor 100 according to the present embodiment can easily improve the gas concentration detection sensitivity of the gas to be detected. That is, according to the first feature point in the present embodiment, both the viewpoint of having a large change in ion conductivity and the viewpoint of having a catalytic function for changing the adsorption species of the detection gas adsorbed on the surface are achieved. Compared to the case of selecting a material, there is far more room for selecting a material. As a result, according to the first feature point in the present embodiment, the room for selecting the material constituting the metal oxide film is widened, so that the performance of the gas sensor 100 can be easily improved. Furthermore, the room for selecting a material constituting the metal oxide film is expanded, so that a room for preferentially selecting a material having the same performance and a low manufacturing cost is expanded. In other words, according to the first feature point in the present embodiment, it is possible to easily improve the performance of the gas sensor 100 and to obtain an excellent effect in that the manufacturing cost can be reduced.
　続いて、本実施の形態における第２特徴点は、例えば、図１（ａ）および図１（ｂ）に示すように、金属酸化物膜１５の表面の一部を露出する点にある。これにより、本実施の形態におけるガスセンサ１００によれば、金属酸化物膜１５の表面の一部が、被検出ガス（窒素酸化物ガス）の雰囲気に接することになるため、表面に吸着する被検出ガスの吸着種を変化させる触媒機能を有する金属酸化物膜１５の機能を充分に発揮することができる。この結果、金属酸化物膜１５の表面においては、被検出ガス（窒素酸化物ガス）に含まれる一酸化窒素（ＮＯ）に対して、酸素を供給して、二酸化窒素（ＮＯ２）に変化させることができる。これにより、本実施の形態における第２特徴点によれば、金属酸化物膜１５の表面に二酸化窒素（ＮＯ２）がガス濃度に応じて吸着する結果、ガスセンサ１００におけるガス濃度の検出精度を向上することができる。 Subsequently, the second feature point in the present embodiment is that, for example, a part of the surface of the metal oxide film 15 is exposed as shown in FIGS. 1 (a) and 1 (b). Thereby, according to the gas sensor 100 in the present embodiment, a part of the surface of the metal oxide film 15 comes into contact with the atmosphere of the gas to be detected (nitrogen oxide gas), and thus the detection to be adsorbed on the surface is performed. The function of the metal oxide film 15 having a catalytic function for changing the gas adsorption species can be sufficiently exhibited. As a result, on the surface of the metal oxide film 15, oxygen is supplied to nitrogen monoxide (NO) contained in the gas to be detected (nitrogen oxide gas) to change into nitrogen dioxide (NO 2 ). be able to. Thus, according to the second feature of the present embodiment, as a result of surface nitrogen dioxide of the metal oxide film 15 (NO 2) is adsorbed in accordance with the gas concentration, improve the detection accuracy of the gas concentration in the gas sensor 100 can do.
　例えば、ゲート絶縁膜１３上に金属酸化物膜１５を形成し、かつ、金属酸化物膜１５上に金属酸化物膜１４を形成する構成では、金属酸化物膜１５の表面が金属酸化物膜１４で覆われることになり、表面に吸着する被検出ガスの吸着種を変化させる触媒機能を有する金属酸化物膜１５の機能を充分に発揮することができなくなる。 For example, in a configuration in which the metal oxide film 15 is formed on the gate insulating film 13 and the metal oxide film 14 is formed on the metal oxide film 15, the surface of the metal oxide film 15 is the metal oxide film 14. Thus, the function of the metal oxide film 15 having a catalytic function for changing the adsorption species of the gas to be detected adsorbed on the surface cannot be sufficiently exhibited.
　これに対し、本実施の形態におけるガスセンサ１００では、ゲート絶縁膜１３上に金属酸化物膜１４を形成し、かつ、金属酸化物膜１４上に金属酸化物膜１５を形成する構成が採用されている。これにより、本実施の形態におけるガスセンサ１００では、金属酸化物膜１５の表面の一部が金属膜１６から露出する構成が可能となる。したがって、本実施の形態におけるガスセンサ１００によれば、上述した第２特徴点が具現化され、表面に吸着する被検出ガスの吸着種を変化させる触媒機能を有する金属酸化物膜１５の機能を充分に発揮することができることになる。このため、本実施の形態におけるガスセンサ１００によれば、被検出ガス（窒素酸化物ガス）のガス濃度に応じた吸着種（二酸化窒素）の吸着量を確保できる結果、ガス濃度の検出精度を向上することができる。 In contrast, the gas sensor 100 according to the present embodiment employs a configuration in which the metal oxide film 14 is formed on the gate insulating film 13 and the metal oxide film 15 is formed on the metal oxide film 14. Yes. Thereby, in the gas sensor 100 in this Embodiment, the structure which a part of surface of the metal oxide film 15 exposes from the metal film 16 becomes possible. Therefore, according to the gas sensor 100 of the present embodiment, the second feature point described above is embodied, and the function of the metal oxide film 15 having a catalytic function for changing the adsorption species of the gas to be detected adsorbed on the surface is sufficient. It will be possible to demonstrate. For this reason, according to the gas sensor 100 in the present embodiment, the adsorption amount of the adsorbed species (nitrogen dioxide) according to the gas concentration of the gas to be detected (nitrogen oxide gas) can be ensured, and the detection accuracy of the gas concentration is improved. can do.
　特に、被検出ガス（窒素酸化物ガス）のガス濃度に応じた吸着種（二酸化窒素）の吸着量を確保する観点からは、金属酸化物膜１５の表面積を大きくすることが望ましい。具体的に、本実施の形態における第２特徴点を採用しながら、さらに、金属酸化物膜１５は、少なくとも一部が多孔質であることが望ましい。ただし、金属酸化物膜１５を多孔質から構成する場合、上層の金属膜１６との接着強度が不充分となる可能性がある。このため、金属酸化物膜１５を構成する金属酸化物の粒径は、１０ｎｍ以上１０μｍ以下であることが望ましい。これにより、本実施の形態におけるガスセンサ１００によれば、金属酸化物膜１５の表面に吸着させる吸着種の吸着量を多くすることができるとともに、金属酸化物膜１５と金属膜１６との接着強度を確保することができる。 In particular, it is desirable to increase the surface area of the metal oxide film 15 from the viewpoint of securing the adsorption amount of the adsorbed species (nitrogen dioxide) according to the gas concentration of the gas to be detected (nitrogen oxide gas). Specifically, it is desirable that at least a part of the metal oxide film 15 is porous while adopting the second feature point in the present embodiment. However, when the metal oxide film 15 is made of a porous material, the adhesive strength with the upper metal film 16 may be insufficient. For this reason, the particle size of the metal oxide constituting the metal oxide film 15 is desirably 10 nm or more and 10 μm or less. Thereby, according to the gas sensor 100 in this Embodiment, while the adsorption amount of the adsorption species adsorbed on the surface of the metal oxide film 15 can be increased, the adhesive strength between the metal oxide film 15 and the metal film 16 is increased. Can be secured.
　次に、本実施の形態における第３特徴点は、ガスセンサ１００を備えるガスセンサモジュールに、被検出ガスとは異なるガス成分を除去するイオンポンプ部を設ける点にある。これにより、本実施の形態におけるガスセンサモジュールによって、被検出ガスのガス濃度の検出精度を向上することができる。 Next, the third feature point in the present embodiment is that a gas sensor module including the gas sensor 100 is provided with an ion pump unit that removes a gas component different from the gas to be detected. Thereby, the detection accuracy of the gas concentration of the gas to be detected can be improved by the gas sensor module in the present embodiment.
　例えば、酸素ガスなどは、イオン伝導性を有する金属酸化物膜１４のイオン伝導性を変化させる働きを有する。したがって、被検出ガス（窒素酸化物ガス）とともに、酸素ガスが雰囲気に混入していると、あたかも、被検出ガス（窒素酸化物ガス）の実際のガス濃度よりも高い値を算出するということが生じる。つまり、被検出ガス（窒素酸化物ガス）とともに、酸素ガスが雰囲気に混入していると、ガスセンサ１００に対するノイズ成分が大きくなり、ガスセンサ１００の性能低下を招くことになる。そこで、本実施の形態では、例えば、ガスセンサ１００とともに、ガスセンサ１００が配置される雰囲気から酸素ガスを除去するイオンポンプ部を含むガスセンサモジュールを構成している。これにより、雰囲気からノイズ源となる酸素ガスに代表される妨害ガスを除去できるため、本実施の形態におけるガスセンサモジュールによれば、被検出ガス（窒素酸化物ガス）のガス濃度の検出精度を向上することができる。 For example, oxygen gas or the like has a function of changing the ionic conductivity of the metal oxide film 14 having ionic conductivity. Therefore, when oxygen gas is mixed in the atmosphere together with the gas to be detected (nitrogen oxide gas), it is as if a value higher than the actual gas concentration of the gas to be detected (nitrogen oxide gas) is calculated. Arise. That is, when oxygen gas is mixed in the atmosphere together with the gas to be detected (nitrogen oxide gas), the noise component for the gas sensor 100 increases and the performance of the gas sensor 100 is degraded. Therefore, in the present embodiment, for example, a gas sensor module including an ion pump unit that removes oxygen gas from the atmosphere in which the gas sensor 100 is disposed is configured together with the gas sensor 100. As a result, interference gas typified by oxygen gas, which is a noise source, can be removed from the atmosphere. Therefore, according to the gas sensor module of the present embodiment, the detection accuracy of the gas concentration of the gas to be detected (nitrogen oxide gas) is improved. can do.
　図５は、本実施の形態におけるイオンポンプ部５０の模式的な構成を示す図である。図５において、本実施の形態におけるイオンポンプ部５０は、イオンポンプ電極５０Ａとイオン伝導膜５０Ｂと、イオンポンプ電極５０Ｃとを有する。すなわち、イオンポンプ電極５０Ａ上にイオン伝導膜５０Ｂが配置され、かつ、イオン伝導膜５０Ｂ上にイオンポンプ電極５０Ｃが配置されている。言い換えれば、イオンポンプ電極５０Ａは、イオン伝導膜５０Ｂの下面に接して形成されている一方、イオンポンプ電極５０Ｃは、イオン伝導膜５０Ｂの上面に接して形成されている。イオンポンプ電極５０Ａとイオンポンプ電極５０Ｃのそれぞれは、例えば、白金（Ｐｔ）、ロジウム（Ｒｈ）、パラジウム（Ｐｄ）などから構成される。また、イオン伝導膜５０Ｂは、例えば、イットリア（Ｙ２Ｏ３）などを添加したジルコニア（ＺｒＯ２）から構成される。 FIG. 5 is a diagram showing a schematic configuration of the ion pump unit 50 in the present embodiment. In FIG. 5, an ion pump unit 50 in the present embodiment includes an ion pump electrode 50A, an ion conductive film 50B, and an ion pump electrode 50C. That is, the ion conductive film 50B is disposed on the ion pump electrode 50A, and the ion pump electrode 50C is disposed on the ion conductive film 50B. In other words, the ion pump electrode 50A is formed in contact with the lower surface of the ion conductive film 50B, while the ion pump electrode 50C is formed in contact with the upper surface of the ion conductive film 50B. Each of the ion pump electrode 50A and the ion pump electrode 50C is made of, for example, platinum (Pt), rhodium (Rh), palladium (Pd), or the like. The ion conductive film 50B is made of, for example, zirconia (ZrO 2 ) to which yttria (Y 2 O 3 ) or the like is added.
　イオンポンプ部５０は、イオンポンプ電極５０Ａとイオンポンプ電極５０Ｃとの間に電圧を印加することにより、イオン電流を流すことができる。例えば、イオン伝導膜５０Ｂを、イットリア（Ｙ２Ｏ３）などを添加したジルコニア（ＺｒＯ２）から構成する場合、イオン伝導膜５０Ｂは、酸素イオン伝導体となる。イオンポンプ電極５０Ａにイオンポンプ電極５０Ｃを基準にした負電圧を印加すると、イオンポンプ電極５０Ａの下面で酸素分子（Ｏ２）が酸素イオン（Ｏ２－）に分解され、酸素イオン（Ｏ２－）がイオン伝導膜５０Ｂを介して、イオンポンプ電極５０Ｃに移動する。そして、イオンポンプ電極５０Ｃに到達した酸素イオン（Ｏ２－）は、電子をイオンポンプ電極５０Ｃに渡して中性となり、酸素分子となってイオンポンプ電極５０Ｃの上面から放出される。 The ion pump unit 50 can flow an ion current by applying a voltage between the ion pump electrode 50A and the ion pump electrode 50C. For example, when the ion conductive film 50B is made of zirconia (ZrO 2 ) added with yttria (Y 2 O 3 ) or the like, the ion conductive film 50B becomes an oxygen ion conductor. When a negative voltage based on the ion pump electrode 50C is applied to the ion pump electrode 50A, oxygen molecules (O 2 ) are decomposed into oxygen ions (O 2− ) on the lower surface of the ion pump electrode 50A, and oxygen ions (O 2− ) Moves to the ion pump electrode 50C through the ion conductive film 50B. The oxygen ions (O 2− ) that have reached the ion pump electrode 50C are neutralized by passing electrons to the ion pump electrode 50C, and are released as oxygen molecules from the upper surface of the ion pump electrode 50C.
　このようにして、本実施の形態における第３特徴点によれば、ガスセンサモジュールに設けられたイオンポンプ部５０によって、被検出ガス（窒素酸化物ガス）とノイズとなる妨害ガス（酸素ガス）とを含むガス雰囲気から、妨害ガス（酸素ガス）を除去することができる。これにより、妨害ガスに起因する、ガスセンサ１００に含まれる金属酸化物膜１４のイオン伝導性の変動を抑制することができる。したがって、本実施の形態における第３特徴点を備えるガスセンサモジュールによれば、妨害ガスの悪影響を受けることなく、被検出ガス（窒素酸化物ガス）のガス濃度の検出精度を向上することができる。 In this way, according to the third feature point in the present embodiment, the ion pump unit 50 provided in the gas sensor module causes the gas to be detected (nitrogen oxide gas) and the interference gas (oxygen gas) that becomes noise to be detected. Interfering gas (oxygen gas) can be removed from the gas atmosphere containing gas. Thereby, the fluctuation | variation of the ion conductivity of the metal oxide film 14 contained in the gas sensor 100 resulting from interference gas can be suppressed. Therefore, according to the gas sensor module having the third feature point in the present embodiment, it is possible to improve the detection accuracy of the gas concentration of the gas to be detected (nitrogen oxide gas) without being adversely affected by the interference gas.
　＜変形例１＞
　図６は、実施の形態の変形例１におけるガスセンサ１００の模式的な構成を示す図である。特に、図６（ａ）は、本変形例１におけるガスセンサ１００の模式的な構成を示す断面図であり、図６（ｂ）は、本変形例１におけるガスセンサ１００の模式的な構成を示す斜視図である。図６（ａ）および図６（ｂ）に示すように、本変形例１におけるガスセンサ１００は、金属膜１６を櫛歯形状にしたこと以外は、実施の形態におけるガスセンサ１００と同様の構成をしている。すなわち、本変形例１におけるガスセンサ１００では、図６（ａ）および図６（ｂ）に示すように、金属酸化物膜１５上に金属膜１６Ａと金属膜１６Ｂと金属膜１６Ｃとが配置され、金属膜１６Ａと金属膜１６Ｂと金属膜１６Ｃとによって、櫛歯形状の電極が形成されている。このように、櫛歯形状の電極を使用することにより、下層の金属酸化物膜１５への電圧印加および被検出ガスの流通が容易となる。この結果、本変形例１におけるガスセンサ１００によれば、応答速度および応答感度の向上を図ることができる。 <Modification 1>
FIG. 6 is a diagram illustrating a schematic configuration of the gas sensor 100 according to the first modification of the embodiment. In particular, FIG. 6A is a cross-sectional view illustrating a schematic configuration of the gas sensor 100 according to the first modification, and FIG. 6B is a perspective view illustrating a schematic configuration of the gas sensor 100 according to the first modification. FIG. As shown in FIGS. 6A and 6B, the gas sensor 100 according to the first modification has the same configuration as the gas sensor 100 according to the embodiment except that the metal film 16 has a comb-teeth shape. ing. That is, in the gas sensor 100 according to the first modification, as shown in FIGS. 6A and 6B, the metal film 16A, the metal film 16B, and the metal film 16C are disposed on the metal oxide film 15, Comb-shaped electrodes are formed by the metal film 16A, the metal film 16B, and the metal film 16C. As described above, by using the comb-shaped electrode, it is easy to apply a voltage to the lower metal oxide film 15 and to distribute the gas to be detected. As a result, according to the gas sensor 100 in the first modification, the response speed and the response sensitivity can be improved.
　＜変形例２＞
　図７は、実施の形態の変形例２におけるガスセンサ１００の模式的な構成を示す図である。特に、図７（ａ）は、本変形例２におけるガスセンサ１００の模式的な構成を示す断面図であり、図７（ｂ）は、本変形例２におけるガスセンサ１００の模式的な構成を示す斜視図である。図７（ａ）および図７（ｂ）に示すように、本変形例２におけるガスセンサ１００は、金属膜１６が金属酸化物膜１５の内部に設けられている以外は、実施の形態におけるガスセンサ１００と同様の構成をしている。言い換えれば、金属膜１６は、被検出ガス（窒素酸化物ガス）を含む雰囲気に対して未露出となっている。このように構成されている本変形例２におけるガスセンサ１００によれば、被検出ガス（窒素酸化物ガス）を含む雰囲気と接触する金属酸化物膜１５の面積が大きくなる結果、ガスセンサ１００の応答感度の向上を図ることができる。 <Modification 2>
FIG. 7 is a diagram illustrating a schematic configuration of the gas sensor 100 according to the second modification of the embodiment. In particular, FIG. 7A is a cross-sectional view illustrating a schematic configuration of the gas sensor 100 according to the second modification, and FIG. 7B is a perspective view illustrating a schematic configuration of the gas sensor 100 according to the second modification. FIG. As shown in FIGS. 7A and 7B, the gas sensor 100 according to the second modification is the same as the gas sensor 100 according to the embodiment except that the metal film 16 is provided inside the metal oxide film 15. It has the same configuration as In other words, the metal film 16 is not exposed to the atmosphere containing the gas to be detected (nitrogen oxide gas). According to the gas sensor 100 in the second modification configured as described above, the response sensitivity of the gas sensor 100 is increased as a result of an increase in the area of the metal oxide film 15 in contact with the atmosphere containing the gas to be detected (nitrogen oxide gas). Can be improved.
　＜変形例３＞
　図８は、実施の形態の変形例３におけるガスセンサ１００の模式的な構成を示す図である。特に、図８（ａ）は、本変形例３におけるガスセンサ１００の模式的な構成を示す断面図であり、図８（ｂ）は、本変形例３におけるガスセンサ１００の模式的な構成を示す斜視図である。図８（ａ）および図８（ｂ）に示すように、本変形例３におけるガスセンサ１００では、金属酸化物膜１５と金属酸化物膜１４とゲート絶縁膜１３と半導体基板１０とが雰囲気に曝されるように、実施の形態におけるガスセンサ１００を横転させた構成をしている。このように構成されている本変形例３におけるガスセンサ１００によれば、被検出ガス（窒素酸化物ガス）を含む雰囲気に金属酸化物膜１５が接触する面積が大きくなる結果、ガスセンサ１００の応答感度の向上を図ることができる。 <Modification 3>
FIG. 8 is a diagram illustrating a schematic configuration of the gas sensor 100 according to Modification 3 of the embodiment. In particular, FIG. 8A is a cross-sectional view illustrating a schematic configuration of the gas sensor 100 according to the third modification, and FIG. 8B is a perspective view illustrating a schematic configuration of the gas sensor 100 according to the third modification. FIG. As shown in FIGS. 8A and 8B, in the gas sensor 100 according to the third modification, the metal oxide film 15, the metal oxide film 14, the gate insulating film 13, and the semiconductor substrate 10 are exposed to the atmosphere. As described above, the gas sensor 100 according to the embodiment is configured to roll over. According to the gas sensor 100 of the third modification configured as described above, the area of contact of the metal oxide film 15 with the atmosphere containing the gas to be detected (nitrogen oxide gas) increases, and as a result, the response sensitivity of the gas sensor 100 is increased. Can be improved.
　＜変形例４＞
　実施の形態では、ガス濃度に応じてしきい値電圧が変化する電界効果型ガスセンサを例に挙げて説明したが、実施の形態における技術的思想は、これに限らず、例えば、ガス濃度に応じて、静電容量が変化に起因する電流－電圧特性の変化が生じる静電容量型ガスセンサにも適用することができる。例えば、静電容量型ガスセンサは、金属酸化物膜１４と金属酸化物膜１５と金属膜１６とからなる上部電極と、半導体基板１０からなる下部電極と、上部電極と前記下部電極に挟まれ、かつ、絶縁膜からなる容量絶縁膜とを有するように構成することができる。 <Modification 4>
In the embodiment, the field effect gas sensor in which the threshold voltage changes according to the gas concentration has been described as an example. However, the technical idea in the embodiment is not limited thereto, for example, according to the gas concentration. Thus, the present invention can also be applied to a capacitive gas sensor in which a change in current-voltage characteristics caused by a change in capacitance occurs. For example, the capacitive gas sensor is sandwiched between an upper electrode made of a metal oxide film 14, a metal oxide film 15 and a metal film 16, a lower electrode made of a semiconductor substrate 10, an upper electrode and the lower electrode, And it can comprise so that it may have the capacity | capacitance insulating film which consists of insulating films.
　＜変形例５＞
　実施の形態では、被検出ガスとして、窒素酸化物ガスを取り挙げて説明したが、実施の形態における技術的思想は、これに限らず、基本的に酸化還元反応を利用するガスセンサの検出対象となるガスのガス濃度の検出に幅広く適用することができる。例えば、被検出ガスとして、硫黄酸化物ガス（ＳＯｘ）やアンモニアガス（ＮＨ３）にも適用できる。 <Modification 5>
In the embodiment, the nitrogen oxide gas has been described as the gas to be detected. However, the technical idea in the embodiment is not limited to this, and the detection target of the gas sensor that basically uses the oxidation-reduction reaction is not limited thereto. The present invention can be widely applied to the detection of the gas concentration of the gas. For example, the present invention is applicable to sulfur oxide gas (SOx) and ammonia gas (NH 3 ) as the gas to be detected.
　以上、本発明者によってなされた発明をその実施の形態に基づき具体的に説明したが、本発明は前記実施の形態に限定されるものではなく、その要旨を逸脱しない範囲で種々変更可能であることは言うまでもない。 As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.
　前記実施の形態は、以下の形態を含む。 The embodiment includes the following forms.
　（付記１）
　被検出ガスの濃度を検出するガスセンサであって、
　半導体基板上に形成された絶縁膜と、
　前記絶縁膜上に形成された第１金属酸化物膜と、
　前記第１金属酸化物膜上に形成された第２金属酸化物膜と、
　前記第２金属酸化物膜と接する金属膜と、
　を有し、
　前記第２金属酸化物膜の一部は、露出している、ガスセンサ。 (Appendix 1)
A gas sensor for detecting the concentration of a gas to be detected,
An insulating film formed on the semiconductor substrate;
A first metal oxide film formed on the insulating film;
A second metal oxide film formed on the first metal oxide film;
A metal film in contact with the second metal oxide film;
Have
The gas sensor, wherein a part of the second metal oxide film is exposed.
　（付記２）
　付記１に記載のガスセンサにおいて、
　前記絶縁膜は、ゲート絶縁膜であり、
　前記ゲート絶縁膜上に形成されたゲート電極は、
　前記第１金属酸化物膜と、
　前記第２金属酸化物膜と、
　前記金属膜と、
　から構成され、
　前記ガスセンサは、さらに、
　前記ゲート絶縁膜の直下の前記半導体基板内に形成されたチャネル形成領域と、
　前記チャネル形成領域を挟むソース領域およびドレイン領域と、
　を有する、ガスセンサ。 (Appendix 2)
In the gas sensor according to appendix 1,
The insulating film is a gate insulating film;
The gate electrode formed on the gate insulating film is
The first metal oxide film;
The second metal oxide film;
The metal film;
Consisting of
The gas sensor further includes:
A channel formation region formed in the semiconductor substrate immediately below the gate insulating film;
A source region and a drain region sandwiching the channel formation region;
Having a gas sensor.
　（付記３）
　付記１に記載のガスセンサにおいて、
　前記ガスセンサは、容量素子を構成し、
　前記ガスセンサは、
　前記第１金属酸化物膜と前記第２金属酸化物膜と前記金属膜とからなる上部電極と、
　前記半導体基板からなる下部電極と、
　前記上部電極と前記下部電極に挟まれ、かつ、前記絶縁膜からなる容量絶縁膜と、
　を有する、ガスセンサ。 (Appendix 3)
In the gas sensor according to appendix 1,
The gas sensor constitutes a capacitive element,
The gas sensor
An upper electrode comprising the first metal oxide film, the second metal oxide film, and the metal film;
A lower electrode made of the semiconductor substrate;
A capacitive insulating film sandwiched between the upper electrode and the lower electrode and made of the insulating film;
Having a gas sensor.
　（付記４）
　付記１に記載のガスセンサにおいて、
　前記被検出ガスは、窒素酸化物である、ガスセンサ。 (Appendix 4)
In the gas sensor according to appendix 1,
The gas sensor, wherein the gas to be detected is nitrogen oxide.
　（付記５）
　付記１に記載のガスセンサと、
　被検出ガスとは異なるガス成分を除去するイオンポンプ部と、
　を備え、
　前記イオンポンプ部は、
　イオン伝導膜と、
　前記イオン伝導膜の下面に接するように形成された第１イオンポンプ電極と、
　前記イオン伝導膜の上面に接するように形成された第２イオンポンプ電極と、
　を有する、ガスセンサモジュール。 (Appendix 5)
The gas sensor according to appendix 1,
An ion pump for removing a gas component different from the gas to be detected;
With
The ion pump part is
An ion conducting membrane;
A first ion pump electrode formed in contact with the lower surface of the ion conductive film;
A second ion pump electrode formed in contact with the upper surface of the ion conductive film;
A gas sensor module.
　１０　半導体基板
　１１　ソース領域
　１２　ドレイン領域
　１３　ゲート絶縁膜
　１４　金属酸化物膜
　１５　金属酸化物膜
　１６　金属膜
　２０　被検出ガス
　１００　ガスセンサ DESCRIPTION OF SYMBOLS 10 Semiconductor substrate 11 Source region 12 Drain region 13 Gate insulating film 14 Metal oxide film 15 Metal oxide film 16 Metal film 20 Detected gas 100 Gas sensor

Claims (15)

  1. 　被検出ガスの濃度を検出するガスセンサであって、
    　半導体基板上に形成された絶縁膜と、
    　前記絶縁膜上に形成された第１金属酸化物膜と、
    　前記第１金属酸化物膜上に形成された第２金属酸化物膜と、
    　前記第２金属酸化物膜と接する金属膜と、
    　を有し、
    　前記第２金属酸化物膜の一部は、露出している、ガスセンサ。     A gas sensor for detecting the concentration of a gas to be detected,
    An insulating film formed on the semiconductor substrate;
    A first metal oxide film formed on the insulating film;
    A second metal oxide film formed on the first metal oxide film;
    A metal film in contact with the second metal oxide film;
    Have
    The gas sensor, wherein a part of the second metal oxide film is exposed.
  2. 　請求項１に記載のガスセンサにおいて、
    　前記第１金属酸化物膜は、イオン伝導性を有し、
    　前記第２金属酸化物膜は、前記第２金属酸化物膜の表面に吸着する前記被検出ガスの吸着種を変化させる触媒機能を有する、ガスセンサ。     The gas sensor according to claim 1,
    The first metal oxide film has ion conductivity,
    The gas sensor, wherein the second metal oxide film has a catalytic function of changing an adsorbed species of the detection gas adsorbed on the surface of the second metal oxide film.
  3. 　請求項２に記載のガスセンサにおいて、
    　前記第１金属酸化物膜は、前記第２金属酸化物膜の表面に吸着した前記吸着種に起因して、イオン伝導性が変化する、ガスセンサ。     The gas sensor according to claim 2,
    The first metal oxide film is a gas sensor in which ion conductivity changes due to the adsorbed species adsorbed on the surface of the second metal oxide film.
  4. 　請求項１に記載のガスセンサにおいて、
    　前記金属膜は、前記金属膜の表面に吸着する前記被検出ガスの吸着種を変化させる触媒機能を有する、ガスセンサ。     The gas sensor according to claim 1,
    The said metal film is a gas sensor which has a catalyst function which changes the adsorption | suction species of the said to-be-detected gas adsorbed on the surface of the said metal film.
  5. 　請求項１に記載のガスセンサにおいて、
    　前記第１金属酸化物膜は、ジルコニウムを含む酸化物からなる膜である、ガスセンサ。     The gas sensor according to claim 1,
    The gas sensor, wherein the first metal oxide film is a film made of an oxide containing zirconium.
  6. 　請求項１に記載のガスセンサにおいて、
    　前記第１金属酸化物膜は、第１金属と第２金属とを含み、
    　前記第１金属は、ジルコニウムであり、
    　前記第２金属は、カルシウム、マグネシウム、イットリウム、ランタン、セリウム、プラセオジウム、ネオジウム、プロメチウム、サマリウム、ユーロピウム、ガドリニウム、テルビウム、ジスプロシウム、ホルミウム、エルビウム、ツリウム、イッテルビウム、ルテチウム、ハフニウムから選ばれる少なくとも１種類の金属である、ガスセンサ。     The gas sensor according to claim 1,
    The first metal oxide film includes a first metal and a second metal,
    The first metal is zirconium;
    The second metal is at least one selected from calcium, magnesium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and hafnium. A gas sensor that is a metal.
  7. 　請求項６に記載のガスセンサにおいて、
    　前記第１金属酸化物膜を構成する金属酸化物の結晶構造は、正方晶または立方晶である、ガスセンサ。     The gas sensor according to claim 6, wherein
    The gas sensor according to claim 1, wherein a crystal structure of the metal oxide constituting the first metal oxide film is a tetragonal crystal or a cubic crystal.
  8. 　請求項１に記載のガスセンサにおいて、
    　前記第２金属酸化物膜は、ニッケルを含む酸化物からなる膜である、ガスセンサ。     The gas sensor according to claim 1,
    The gas sensor, wherein the second metal oxide film is a film made of an oxide containing nickel.
  9. 　請求項８に記載のガスセンサにおいて、
    　前記第２金属酸化物膜は、ロジウム、パラジウム、白金、ルテニウム、銅、鉄、コバルト、マンガン、セリウム、ジルコニウムから選ばれる少なくとも１種類の元素を含む膜である、ガスセンサ。     The gas sensor according to claim 8, wherein
    The gas sensor, wherein the second metal oxide film is a film containing at least one element selected from rhodium, palladium, platinum, ruthenium, copper, iron, cobalt, manganese, cerium, and zirconium.
  10. 　請求項１に記載のガスセンサにおいて、
    　前記第２金属酸化物膜は、少なくとも一部が多孔質である、ガスセンサ。     The gas sensor according to claim 1,
    The gas sensor, wherein at least a part of the second metal oxide film is porous.
  11. 　請求項１に記載のガスセンサにおいて、
    　前記金属膜は、白金、金、パラジウム、ロジウムから選ばれる少なくとも１種類の元素を含む膜である、ガスセンサ。     The gas sensor according to claim 1,
    The gas sensor is a gas sensor, wherein the metal film is a film containing at least one element selected from platinum, gold, palladium, and rhodium.
  12. 　請求項１に記載のガスセンサにおいて、
    　前記第２金属酸化物膜と前記金属膜との接触部分は、露出している、ガスセンサ。     The gas sensor according to claim 1,
    A gas sensor in which a contact portion between the second metal oxide film and the metal film is exposed.
  13. 　請求項１に記載のガスセンサにおいて、
    　前記金属膜は、未露出である、ガスセンサ。     The gas sensor according to claim 1,
    The gas sensor is an unexposed gas sensor.
  14. 　請求項１に記載のガスセンサにおいて、
    　前記絶縁膜は、酸化シリコン膜である、ガスセンサ。     The gas sensor according to claim 1,
    The gas sensor, wherein the insulating film is a silicon oxide film.
  15. 　請求項１に記載のガスセンサにおいて、
    　前記半導体基板は、炭化珪素を主成分として含む、ガスセンサ。     The gas sensor according to claim 1,
    The gas sensor, wherein the semiconductor substrate contains silicon carbide as a main component.
PCT/JP2018/031820 2018-01-31 2018-08-28 Gas sensor WO2019150631A1 (en)

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JPS63128246A (en) * 1986-11-19 1988-05-31 Seitai Kinou Riyou Kagakuhin Shinseizou Gijutsu Kenkyu Kumiai Field effect transistor type gaseous oxygen sensor
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