CN112097835A - Resonant SAW temperature-humidity sensor and preparation method thereof - Google Patents
Resonant SAW temperature-humidity sensor and preparation method thereof Download PDFInfo
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- CN112097835A CN112097835A CN202011000715.9A CN202011000715A CN112097835A CN 112097835 A CN112097835 A CN 112097835A CN 202011000715 A CN202011000715 A CN 202011000715A CN 112097835 A CN112097835 A CN 112097835A
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Abstract
The invention discloses a resonance type SAW-based temperature-humidity sensor, which comprises a monocrystalline silicon substrate, silicon oxide, aluminum nitride, metal Al, a polyimide dielectric layer and a sealing cavity.
Description
Technical Field
The invention relates to a resonant SAW temperature-humidity sensor and a preparation method thereof, belonging to the technical field of micro-electromechanical systems.
Background
In the production process and scientific experiments, various parameters are monitored and controlled, and the temperature and the humidity are used as basic parameters of the system, so that a field irrelevant to the humidity is difficult to find. With the development of scientific technology, more and more production processes and scientific experiments are carried out under extreme environments such as high temperature, high pressure, strong electromagnetic interference and the like, so that the original temperature sensor made of a thermocouple or a semiconductor material has limitation, and the temperature-humidity integrated sensor based on the resonance SAW can be wireless and passive, i.e. the sensor does not need any energy supply and can realize absolute passivity. Through measurement, the SAW sensor still keeps excellent performance in extreme severe environments such as high temperature, high pressure, strong electromagnetic interference and the like. The SAW sensor based on the MEMS processing technology has the characteristics of small volume, low price, compatibility with an integrated circuit process and good product consistency.
The invention provides a resonant SAW temperature-humidity integrated sensor, which adopts an epitaxial monocrystalline silicon cavity sealing process during preparation, so that a sealed cavity is generated in a monocrystalline silicon substrate, the variable size of the sealed cavity is detected through an SAW resonator, the pressure of the environment is detected, and the electric wave is returned through an MEMS processing technology integrated microstrip antenna, so that the sensor has the characteristics of wireless and passive performance and can work in extremely severe environments such as high temperature, high pressure, sealed space and the like.
The invention firstly provides a method for preparing the SAW integrated sensor by adopting an epitaxial monocrystalline silicon cavity sealing process, can prepare the SAW temperature-humidity integrated sensor, has smaller process difficulty compared with the conventional SAW device preparation process, and is compatible with a CMOS IC process. The SAW micro sensor prepared by the method has the advantages of simple structure, high mechanical strength, batch production, low cost and the like.
Disclosure of Invention
The invention provides a resonant SAW temperature-humidity integrated sensor and a preparation method thereof, the device is compatible with an integrated circuit process, the structure reliability is high, the signal processing and transmission can be integrated, the sensitivity is higher, and the influence of the environment is small.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a temperature-humidity sensor based on resonant SAW comprises a monocrystalline silicon substrate, silicon oxide, aluminum nitride, metal Al, a polyimide dielectric layer and a sealed cavity; a plurality of sealed cavities are formed below the outer surface of the monocrystalline silicon substrate, and silicon oxide uniformly grows on the outer surface of the monocrystalline silicon substrate; aluminum nitride grows at two ends of the silicon oxide respectively; and metal Al is sputtered on the aluminum nitride at two ends, and a polyimide dielectric layer is coated on the metal Al at one end.
Preferably, the metal Al includes microstrip antennas, interdigital electrodes IDTs and reflective gratings.
Preferably, the polyimide dielectric layer covers the interdigital electrodes IDTs at one end.
Preferably, the monocrystalline silicon substrate is N-type monocrystalline silicon.
A method for preparing a temperature-humidity sensor based on resonant SAW comprises the following steps:
s1, etching shallow grooves with certain depth on the surfaces of two ends of a monocrystalline silicon substrate by an anisotropic reactive ion etching process;
s2, carrying out isotropic vertical corrosion on the monocrystalline silicon substrate to form a cavity with a certain depth;
s3, growing a monocrystalline silicon substrate through an epitaxial process, and forming a sealed cavity in the monocrystalline silicon substrate;
s4, smoothing the surface of the monocrystalline silicon substrate through a chemical mechanical polishing process;
s5, uniformly depositing silicon oxide on the surface of the monocrystalline silicon substrate by using a low-pressure chemical vapor deposition method;
s6, growing aluminum nitride on two sides of the silicon oxide respectively, and photoetching and corroding to form a piezoelectric layer structure of the SAW device according to the design layout;
s7, manufacturing a photomask according to design data, selecting proper photoresist to coat the surface of the substrate, copying the device pattern onto the photoresist, etching and sputtering metal Al according to the copied pattern, and photoetching and corroding to form a reflecting grating of the SAW, interdigital electrodes IDTs and a microstrip antenna;
s8, coating polyimide on the interdigital electrodes IDTs at one end.
Preferably, the height of the cavity of the sealed cavity is 5 μm.
Preferably, the aluminum nitride and polyimide are each 2 μm thick.
Has the advantages that:
1) the humidity detection is established on the basis of a sealed cavity structure, and the sealed cavity structure is formed by an epitaxial monocrystalline silicon substrate growth process.
2) The invention realizes wireless and passive sensor by monolithic integration preparation of the resonance SAW temperature-humidity sensor and the microstrip antenna.
3) The invention is compatible with the integrated circuit process, can realize the monolithic integration of the sensor and the processing circuit, and can reduce the cost, improve the sensitivity, reduce the parasitic, and the like.
4) The invention can realize the measurement of two physical parameters on the same monocrystalline silicon substrate, thereby reducing the production cost and improving the applicability of the device.
5) The invention adopts the resonance type SAW resonator, and can easily identify two different resonators in the sensor through the time coding technology without aliasing.
Drawings
Fig. 1 is a schematic view of an overall structure of a resonance type SAW temperature-humidity sensor and a method for manufacturing the same according to the present invention;
FIG. 2 is a schematic diagram of a partial structure of a resonant SAW temperature-humidity sensor and a method for fabricating the same according to the present invention;
FIG. 3 is a schematic diagram of a partial structure of a resonant SAW temperature-humidity sensor and a method for fabricating the same according to the present invention;
FIG. 4 is a schematic diagram of a partial structure of a resonant SAW temperature-humidity sensor and a method for fabricating the same according to the present invention;
FIG. 5 is a schematic diagram of a partial structure of a resonant SAW temperature-humidity sensor and a method for fabricating the same according to the present invention;
FIG. 6 is a schematic diagram of a partial structure of a resonant SAW temperature-humidity sensor and a method for fabricating the same according to the present invention;
FIG. 7 is a schematic diagram of a partial structure of a resonant SAW temperature-humidity sensor and a method for fabricating the same according to the present invention;
FIG. 8 is a schematic diagram of a partial structure of a resonant SAW temperature-humidity sensor and a method for fabricating the same according to the present invention;
fig. 9 is a partial structural view of a resonance type SAW temperature-humidity sensor and a method for manufacturing the same according to the present invention;
in the figure: the antenna comprises a monocrystalline silicon substrate 1, silicon oxide 2, aluminum nitride 3, metal Al4, a polyimide dielectric layer 5, a sealed cavity 6, a microstrip antenna 7, interdigital electrodes IDTs8 and a reflecting grid 9.
Detailed Description
The invention is described below with reference to the accompanying drawings, which are intended to cover several modifications and embodiments of the invention.
As shown in fig. 1, a resonance type SAW based temperature-humidity sensor includes a monocrystalline silicon substrate 1, silicon oxide 2, aluminum nitride 3, metal Al4, a polyimide dielectric layer 5 and a sealed cavity 6; a plurality of sealed cavities 6 are arranged below the outer surface of the monocrystalline silicon substrate 1, and silicon oxide 2 is uniformly grown on the outer surface of the monocrystalline silicon substrate 1; aluminum nitride 3 grows at two ends of the silicon oxide 2 respectively; metal Al4 is sputtered on the aluminum nitride 3 at two ends, and a polyimide dielectric layer 5 is coated on the metal Al4 at one end.
Preferably, the metal Al4 includes a microstrip antenna 7, interdigital electrodes IDTs8 and a reflective grating 9.
Preferably, the polyimide dielectric layer 5 covers the interdigital electrodes IDTs8 at one end.
Preferably, the monocrystalline silicon substrate 1 is N-type monocrystalline silicon.
As shown in fig. 2 to 9, a method for manufacturing a resonance type SAW based temperature-humidity sensor includes the following specific steps:
s1, etching shallow grooves with certain depth on the surfaces of two ends of a monocrystalline silicon substrate 1 by an anisotropic reactive ion etching process;
s2, carrying out isotropic vertical corrosion on the monocrystalline silicon substrate 1 to form a cavity with a certain depth;
s3, growing a monocrystalline silicon substrate 1 through an epitaxial process, and forming a sealed cavity 6 in the monocrystalline silicon substrate 1;
s4, smoothing the surface of the monocrystalline silicon substrate 1 by a chemical mechanical polishing process;
s5, uniformly depositing silicon oxide 2 on the surface of the monocrystalline silicon substrate 1 by using a low-pressure chemical vapor deposition method;
s6, growing aluminum nitride 3 on two sides of the silicon oxide 2 respectively, and photoetching and corroding to form a piezoelectric layer structure of the SAW device according to the design layout;
s7, manufacturing a photomask according to design data, selecting proper photoresist to coat the surface of the substrate, copying the device pattern on the photoresist, etching and sputtering metal Al4 according to the copied pattern, and photoetching and corroding to form a reflecting grating 9 of the SAW, interdigital electrodes IDTs8 and a microstrip antenna 7;
and S8, coating polyimide 5 above the interdigital electrodes IDTs8 at one end.
Preferably, the cavity height of the sealed cavity 6 is 5 μm.
Preferably, the aluminum nitride 3 and polyimide 5 are each 2 μm thick.
The SAW resonator comprises interdigital electrodes IDTs8 and a reflecting grid 9, and the relation between the resonant frequency and the temperature of the resonator is shown as a formula:
wherein T isrefIs a reference temperature, f0Is the resonant frequency, v, at the reference temperature0Is the velocity of the SAW at the reference temperature, TCD is the delay temperature coefficient, and λ is the wavelength of the SAW.
The thickness of the polyimide 5 is 2 mu m, the dielectric layer is not conductive through a probe test, the insulating property is good, the initial decomposition temperature of the polyimide 5 is generally about 500 ℃, the thermal decomposition temperature of the polyimide 5 synthesized by pyromellitic dianhydride and p-phenylenediamine reaches 600 ℃, and the polyimide 5 can resist extremely low temperature and cannot be brittle in liquid helium at the temperature of-269 ℃; the polyimide 5 is very sensitive to external moisture, and after water absorption, the thickness and the quality can be changed, so that the surface acoustic wave transmitted by the interdigital electrodes IDTs8 is changed, and the external humidity is measured; the polyimide 5 is coated on the surface of the metal Al4, and when the concentration of water vapor in the environment changes, the amount of water molecules absorbed by the polyimide 5 changes, so that the quality changes, and the pressure is applied to the aluminum oxide 3.
The resonant frequency of the SAW resonator of the present invention is related to the pressure applied to the resonator as follows:
wherein v is0SAW acoustic velocity at standard atmospheric pressure, r1、r2、r3Is the elastic constant associated with alumina 3 silica,1、2、2is the strain component of the surface distribution of the alumina 3 caused by the applied pressure. The pressure is obtained by measuring the frequency and converted into a humidity measurement.
The thickness degree of the interdigital electrodes IDTs8 determines the range of the resonance frequency of the SAW resonator, if the SAW resonator works in an environment below 500MHz, the thinnest of the interdigital electrodes IDTs8 is not less than 1.5 μm, the performance of the interdigital electrodes IDTs8 is good or bad, and the performance is greatly dependent on the shape of the finger strips and the smoothness degree of the edges, and the rough edges can cause the diffuse reflection of waves to increase the loss and reduce the Q value.
In the invention, the SAW resonator can make the maximum response to the frequency which is the same as the resonant frequency in the signals received by the microstrip antenna 7, the temperature sensor is close to the humidity sensor to ensure that the temperature sensor is placed under the same temperature state, the temperature sensor is placed on the sealed cavity 6 to improve the sensitivity of the sensor, and the deformation piezoelectric effect of the sealed cavity 6 is more obvious.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and decorations can be made without departing from the invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (7)
1. A temperature-humidity sensor based on resonant SAW is characterized by comprising a monocrystalline silicon substrate (1), silicon oxide (2), aluminum nitride (3), metal Al (4), a polyimide dielectric layer (5) and a sealed cavity (6); a plurality of sealed cavities (6) are arranged below the outer surface of the monocrystalline silicon substrate (1), and silicon oxide (2) is uniformly grown on the outer surface of the monocrystalline silicon substrate (1); aluminum nitride (3) grows at two ends of the silicon oxide (2) respectively; metal Al (4) is sputtered on the aluminum nitride (3) at two ends, and a polyimide dielectric layer (5) is coated on the metal Al (4) at one end.
2. A resonant SAW-based temperature-humidity sensor according to claim 1, wherein the metallic Al (4) comprises microstrip antennas (7), interdigital electrodes IDTs (8) and reflective gratings (9).
3. A resonant SAW-based temperature-humidity sensor according to claim 1, wherein the polyimide dielectric layer (5) is overlaid on top of the interdigital electrodes IDTs (8) at one end.
4. A resonant SAW-based temperature-humidity sensor according to claim 1, wherein the monocrystalline silicon substrate (1) is N-type monocrystalline silicon.
5. A method for manufacturing a resonance type SAW based temperature-humidity sensor, wherein the resonance type SAW based temperature-humidity sensor as claimed in claims 1-4 is prepared by the following steps:
s1, etching shallow grooves with certain depth on the surfaces of two ends of a monocrystalline silicon substrate (1) through an anisotropic reactive ion etching process;
s2, carrying out isotropic vertical corrosion on the monocrystalline silicon substrate (1) to form a cavity with a certain depth;
s3, growing a monocrystalline silicon substrate (1) through an epitaxial process, and forming a sealed cavity (6) in the monocrystalline silicon substrate (1);
s4, smoothing the surface of the monocrystalline silicon substrate (1) through a chemical mechanical polishing process;
s5, uniformly depositing silicon oxide (2) on the surface of the monocrystalline silicon substrate (1) by using a low-pressure chemical vapor deposition method;
s6, growing aluminum nitride (3) on two sides of the silicon oxide (2) respectively, and photoetching and corroding to form a piezoelectric layer structure of the SAW device according to the design layout;
s7, manufacturing a photomask according to design data, selecting proper photoresist to coat the surface of the substrate, copying the device pattern on the photoresist, etching and sputtering metal Al (4) according to the copied pattern, photoetching and corroding to form a reflecting grating (9) of the SAW, interdigital electrodes IDTs (8) and a microstrip antenna (7);
s8, coating polyimide (5) above the interdigital electrodes IDTs (8) at one end.
6. A method of manufacturing a resonant SAW based temperature-humidity sensor according to claim 5, wherein said sealed cavity (6) has a cavity height of 5 μm.
7. A method for manufacturing a resonance type SAW based temperature-humidity sensor according to claim 5, wherein said aluminum nitride (3) and polyimide (5) are both 2 μm thick.
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Citations (5)
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|---|---|---|---|---|
| CN101532975A (en) * | 2008-03-12 | 2009-09-16 | 中国科学院电子学研究所 | Constant temperature measurement-type micro humidity sensor and producing method thereof |
| CN102944325A (en) * | 2012-11-29 | 2013-02-27 | 东南大学 | Passive wireless temperature and humidity integrated sensor |
| CN106159078A (en) * | 2015-03-19 | 2016-11-23 | 中科鼎源（北京）科技有限公司 | The structure of a kind of SAW temperature sensor and manufacture method |
| CN110006490A (en) * | 2019-04-19 | 2019-07-12 | 河海大学常州校区 | A kind of temperature, pressure integrated sensor and preparation method thereof |
| CN111486904A (en) * | 2020-06-09 | 2020-08-04 | 杭州能工科技有限公司 | Resonant type surface acoustic wave wireless passive temperature/humidity sensor |
-
2020
- 2020-09-22 CN CN202011000715.9A patent/CN112097835A/en active Pending
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101532975A (en) * | 2008-03-12 | 2009-09-16 | 中国科学院电子学研究所 | Constant temperature measurement-type micro humidity sensor and producing method thereof |
| CN102944325A (en) * | 2012-11-29 | 2013-02-27 | 东南大学 | Passive wireless temperature and humidity integrated sensor |
| CN106159078A (en) * | 2015-03-19 | 2016-11-23 | 中科鼎源（北京）科技有限公司 | The structure of a kind of SAW temperature sensor and manufacture method |
| CN110006490A (en) * | 2019-04-19 | 2019-07-12 | 河海大学常州校区 | A kind of temperature, pressure integrated sensor and preparation method thereof |
| CN111486904A (en) * | 2020-06-09 | 2020-08-04 | 杭州能工科技有限公司 | Resonant type surface acoustic wave wireless passive temperature/humidity sensor |
Non-Patent Citations (2)
| Title |
|---|
| ABDURRASHID SHUAIBU HASSAN: "MEMS Based Humidity Sensor with Integration of Temperature Sensor", 《MATERIALS TODAY: PROCEEDINGS》 * |
| 齐本胜: "SAW温度传感器测温***中的天线设计", 《电子技术应用》 * |
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Application publication date: 20201218 |