JP4371772B2 - Thin film gas sensor - Google Patents

Thin film gas sensor Download PDF

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JP4371772B2
JP4371772B2 JP2003368182A JP2003368182A JP4371772B2 JP 4371772 B2 JP4371772 B2 JP 4371772B2 JP 2003368182 A JP2003368182 A JP 2003368182A JP 2003368182 A JP2003368182 A JP 2003368182A JP 4371772 B2 JP4371772 B2 JP 4371772B2
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sensing
thin film
outer periphery
gas
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JP2005134165A (en
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卓弥 鈴木
光男 小林
健二 国原
誠 吉田
誠 岡村
総一 田畑
勝己 檜垣
久男 大西
猛 橋本
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Osaka Gas Co Ltd
Fuji Electric FA Components and Systems Co Ltd
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Fuji Electric FA Components and Systems Co Ltd
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Description

本発明は、電池駆動を念頭においた低消費電力型の薄膜ガスセンサに関する。   The present invention relates to a low power consumption thin film gas sensor with battery driving in mind.

一般的にガスセンサは、ガス漏れ警報器などの用途に用いられ、ある特定ガス、例えば、CO、CH4、C3H8、CH3OH等に選択的に感応するデバイスであり、その性格上、高感度、高選択性、高応答性、高信頼性、低消費電力が必要不可欠である。ところで、家庭用として普及しているガス漏れ警報器には、都市ガス用やプロパンガス用の可燃性ガス検知を目的としたものと燃焼機器の不完全燃焼ガス検知を目的としたもの、または、両方の機能を合わせ持ったものなどがあるが、いずれもコストや設置性の問題から普及率はそれほど高くない。そういった事から普及率の向上をはかるべく、設置性の改善、具体的には、電池駆動としコードレス化する事が望まれている。
電池駆動を実現するためには低消費電力化が最も重要であるが、接触燃焼式や半導体式のガスセンサでは、２００℃〜５００℃の高温に加熱し検知する必要がある。そこで、微細加工プロセスにより、ダイヤフラム構造などの高断熱・低熱容量の構造とした薄膜ガスセンサの実現が待たれている。 Generally, gas sensors are used for applications such as gas leak alarms, and are devices that are selectively sensitive to certain specific gases, such as CO, CH 4 , C 3 H 8 , CH 3 OH, etc. High sensitivity, high selectivity, high responsiveness, high reliability, and low power consumption are indispensable. By the way, the gas leak alarms that are widely used for home use include those for the purpose of detecting flammable gases for city gas and propane gas, and those for the purpose of detecting incomplete combustion gases in combustion equipment, or There are things that have both functions, but the penetration rate is not so high due to cost and installation problems. For this reason, in order to improve the diffusion rate, it is desired to improve the installation property, specifically, to be battery-driven and cordless.
Low power consumption is the most important for realizing battery drive, but in a catalytic combustion type or semiconductor type gas sensor, it is necessary to detect by heating to a high temperature of 200 ° C. to 500 ° C. Therefore, the realization of a thin film gas sensor having a high heat insulation and low heat capacity structure such as a diaphragm structure by a microfabrication process is awaited.

薄膜ガスセンサとしては、電池駆動を可能とするガス感知感度を高めるとともにノイズの小さいＳ／Ｎ比を高めるため、ガス感知層を２層構造として、第２層（後述する感知第１層に相当）の両端に電極層を接合した薄膜ガスセンサが報告されている（特許文献１参照）。
しかしながら、このような薄膜ガスセンサでは、感知層と触媒を添加した半導体薄膜層とが同面積かつ同位置に形成されているため、感知層の側面からガスが進入してしまいガス選択性が不十分であるという問題点があった。 As a thin film gas sensor, the gas sensing layer has a two-layer structure in order to increase the gas sensing sensitivity that enables battery driving and to increase the S / N ratio with low noise, and the second layer (corresponding to the sensing first layer described later). A thin film gas sensor in which electrode layers are bonded to both ends has been reported (see Patent Document 1).
However, in such a thin film gas sensor, since the sensing layer and the semiconductor thin film layer to which the catalyst is added are formed in the same area and at the same position, gas enters from the side surface of the sensing layer and gas selectivity is insufficient. There was a problem that.

特開２０００−２９２３９９号公報JP 2000-292399 A

一般に、感知層に半導体薄膜を用いた場合、感知層単体では複数の還元性ガス種に感応してしまい、ある特定のガスだけに選択的に感応することは困難である。そこで、感知層の上にPdまたはPt等の貴金属触媒からなる選択燃焼層を設け、検知ガスより酸化活性の強いガスを燃焼させることが有効である。
さらに、感知層と選択燃焼層の間には、触媒を添加した半導体薄膜層をある一定の条件で形成することで、選択性が向上する。 In general, when a semiconductor thin film is used for the sensing layer, the sensing layer alone is sensitive to a plurality of reducing gas species, and it is difficult to selectively sense only a specific gas. Therefore, it is effective to provide a selective combustion layer made of a noble metal catalyst such as Pd or Pt on the sensing layer and burn a gas having a stronger oxidation activity than the detection gas.
Further, the selectivity is improved by forming a semiconductor thin film layer to which a catalyst is added between the sensing layer and the selective combustion layer under a certain condition.

本発明者らは、上記問題点に鑑み、従来技術の課題を解決するため研究を進め、ダイヤフラム構造で高断熱・低熱容量を有し、かつ、優れたガス選択性を有する薄膜ガスセンサを開発すべく、鋭意検討した。
その結果、本発明者らは、ガス感知層を形成する２層構造において感知第１層と感知第２層の設置状態を特定するとともに、さらに必要により選択燃焼層を特定の配置で設けることによって、かかる問題点が一気に解決されることを見出した。本発明は、かかる見地より完成されたものである。 In view of the above problems, the present inventors have advanced research to solve the problems of the prior art, and develop a thin film gas sensor having a diaphragm structure, high heat insulation and low heat capacity, and excellent gas selectivity. As a result, we studied diligently.
As a result, the present inventors specify the installation state of the first sensing layer and the second sensing layer in the two-layer structure forming the gas sensing layer, and further, if necessary, provide the selective combustion layer in a specific arrangement. I found out that this problem could be solved at once. The present invention has been completed from such a viewpoint.

本発明では、感知第１層として、SnO2層あるいはドナーとなる＋５価ないし＋６価の元素を添加したSnO2層を設け、さらにその上に感知第２層として触媒となる元素を添加したSnO2層を積層した２層構造のガス感知層について、このガス感知層を成す感知第２層の外周部が、感知第１層の外周部よりも全て外側であるように形成する。
すなわち、本発明は、薄膜状の支持膜の外周部または両端部をSi基板により支持し、外周部または両端部が厚く中央部が薄く形成されたダイヤフラム様の支持基板上に、薄膜のヒータを形成し、この薄膜のヒータ層を電気絶縁膜で覆い、その上に感知第１層としてSnO2層またはドナーとなる＋５価ないし＋６価の元素を添加したSnO2層を設け、さらにその上に感知第２層として触媒となる元素を添加したSnO2層を積層した２層構造のガス感知層を形成し、このガス感知層に接して所定間隔を置いて１対の金属からなる感知電極層を設けてなる薄膜ガスセンサであって、該ガス感知層をなす感知第２層の外周部が、該感知第１層の外周部よりも全て外側に設置されていることを特徴とする薄膜ガスセンサを提供するものである。感知第２層の外周部が全ての位置で感知第１層の外周部よりも外側にあるため、薄膜上に形成される感知第１層の垂直方向の側面部は、全て感知第２層によって覆われることとなる。かかる構成によって、感知第２層を経ない、感知第１層の側面からのガス流入を防止し、外部からのガス全てが、感知第２層、感知第１層、という順序で感知第１層に到達するようになる。 In the present invention, a SnO 2 layer or a SnO 2 layer added with a +5 to +6 valent element serving as a donor is provided as the sensing first layer, and a catalyst serving as a sensing O2 layer is further provided thereon. The gas sensing layer having a two-layer structure in which two layers are stacked is formed such that the outer periphery of the sensing second layer constituting the gas sensing layer is entirely outside the outer periphery of the sensing first layer.
That is, the present invention supports a thin film heater on a diaphragm-like support substrate in which the outer peripheral portion or both end portions of a thin film-like support film are supported by a Si substrate, and the outer peripheral portion or both end portions are thick and the central portion is thin. The thin heater layer is covered with an electrical insulating film, and a SnO 2 layer or a SnO 2 layer to which a +5 to +6 valent element as a donor is added is provided as a first sensing layer, and further on the SnO 2 layer. As a second sensing layer, a gas sensing layer having a two-layer structure in which an SnO 2 layer added with an element serving as a catalyst is laminated is formed, and a sensing electrode layer made of a pair of metals in contact with the gas sensing layer at a predetermined interval. A thin film gas sensor comprising: a sensing second layer forming a gas sensing layer, wherein the outer peripheral portion of the sensing second layer is entirely disposed outside the outer peripheral portion of the sensing first layer. It is to provide. Since the outer periphery of the sensing second layer is outside the outer periphery of the sensing first layer at all positions, the vertical side surfaces of the sensing first layer formed on the thin film are all formed by the sensing second layer. It will be covered. With this configuration, gas inflow from the side surface of the sensing first layer without passing through the sensing second layer is prevented, and all the gas from the outside is detected in the order of the sensing second layer and the sensing first layer. To come to reach.

ここで、前記ガス感知層の感知第２層の外周部と感知第１層の外周部との距離の最小値は、該感知第２層の膜厚と等しいか、あるいはそれ以上であることが好ましい。詳述すれば、感知第１層および感知第２層の薄膜平面上の形状は四角形や円形以外にも、他の多角形や楕円形状など各種の形状を採ることができる。そして、感知第１層の平面上の形状と感知第２層の平面上の形状とは、同じであっても異なっていても良い。よって、感知第２層の外周部と感知第１層の外周部との平面上での距離は、各感知層の形状や大きさによって変動することがある。このような場合、変動する距離の最小値が少なくとも感知第２層の膜厚と等しいかそれ以上であることが好ましい。
また、前記ガス感知層の感知第２層の触媒としては、Ru、Rh、Pd 、Os、IrおよびPtからなる群より選ばれる少なくとも１つの元素を含む態様が挙げられる。 Here, the minimum value of the distance between the outer periphery of the sensing second layer and the outer periphery of the sensing first layer of the gas sensing layer may be equal to or greater than the thickness of the sensing second layer. preferable. More specifically, the shape of the sensing first layer and the sensing second layer on the thin film plane can take various shapes such as a polygonal shape and an elliptical shape in addition to a square shape and a circular shape. The shape of the sensing first layer on the plane and the shape of the sensing second layer on the plane may be the same or different. Therefore, the distance on the plane between the outer periphery of the sensing second layer and the outer periphery of the sensing first layer may vary depending on the shape and size of each sensing layer. In such a case, it is preferable that the minimum value of the fluctuating distance is at least equal to or greater than the film thickness of the sensing second layer.
Further, examples of the catalyst of the sensing second layer of the gas sensing layer include an embodiment containing at least one element selected from the group consisting of Ru, Rh, Pd, Os, Ir, and Pt.

本発明では更に、前記ガス感知層の感知第２層の上に、Al2O3、Cr2O3、Fe2O3、Ni2O3、ZnO、SiO2などの多孔質金属酸化物とPdまたはPt等の貴金属触媒とからなる選択燃焼層を、その外周部が感知第２層の外周部よりも全て外側であるように形成する態様が好適である。選択燃焼層の外周部が全ての位置で感知第２層の外周部よりも外側にあるため、薄膜上に形成される感知第２層の垂直方向の側面部は、全て選択燃焼層によって覆われることとなる。かかる構成によって、選択燃焼層を経ない、ガス感知層への側面からのガス流入を防止し、外部からのガス全てが、選択燃焼層、感知第２層、感知第１層、という順序で感知第１層に到達するようになる。 In the present invention, a porous metal oxide such as Al 2 O 3 , Cr 2 O 3 , Fe 2 O 3 , Ni 2 O 3 , ZnO, and SiO 2 is further formed on the second sensing layer of the gas sensing layer. A mode in which the selective combustion layer composed of a noble metal catalyst such as Pd or Pt is formed such that the outer peripheral portion thereof is entirely outside the outer peripheral portion of the sensing second layer is preferable. Since the outer peripheral portion of the selective combustion layer is outside the outer peripheral portion of the sensing second layer at all positions, all the vertical side portions of the sensing second layer formed on the thin film are covered with the selective combustion layer. It will be. Such a configuration prevents gas from flowing into the gas sensing layer from the side without passing through the selective combustion layer, and all external gases are sensed in the order of the selective combustion layer, the sensing second layer, and the sensing first layer. The first layer is reached.

この選択燃焼層については、その外周部と前記感知第２層の外周部との距離の最小値が、選択燃焼層の膜厚と等しいか、あるいはそれ以上であることが好ましい。詳述すれば、上記感知第１層および感知第２層の場合と同様に、選択燃焼層の薄膜平面上の形状は円形や四角形以外にも、楕円形状や他の多角形など各種の形状を採ることができる。そして、ガス感知層の平面上の形状と選択燃焼層の平面上の形状とは、同じであっても異なっていても良い。よって、感知第２層の外周部と選択燃焼層の外周部との平面上での距離は、それぞれの形状や大きさによって変動することがある。このような場合、変動する距離の最小値が少なくとも選択燃焼層の膜厚と等しいかそれ以上であることが好ましい。
また、前記感知第２層の触媒としては、Ru、Rh、Pd 、Os、IrおよびPtからなる群より選ばれる少なくとも１つの元素を含む態様が挙げられる。 For the selective combustion layer, it is preferable that the minimum value of the distance between the outer peripheral portion and the outer peripheral portion of the sensing second layer is equal to or greater than the film thickness of the selective combustion layer. Specifically, as in the case of the first sensing layer and the second sensing layer, the shape of the selective combustion layer on the thin film plane may be various shapes such as an elliptical shape and other polygonal shapes in addition to a circular shape and a rectangular shape. Can be taken. The shape of the gas sensing layer on the plane and the shape of the selective combustion layer on the plane may be the same or different. Accordingly, the distance on the plane between the outer periphery of the sensing second layer and the outer periphery of the selective combustion layer may vary depending on the shape and size of each. In such a case, it is preferable that the minimum value of the fluctuating distance is at least equal to or greater than the film thickness of the selective combustion layer.
The sensing second layer catalyst includes an embodiment containing at least one element selected from the group consisting of Ru, Rh, Pd, Os, Ir and Pt.

以上説明したように、感知第１層として、SnO2層あるいはドナーとなる＋５価ないし＋６価の元素を添加したSnO2層を設け、さらにその上に感知第２層として触媒となる元素を添加したSnO2層を積層した２層構造のガス感知層について、ガス感知層を成す感知第２層の外周部が、感知第１層の外周部よりも全て外側であるように形成することで、感度および選択性に優れた薄膜ガスセンサを得ることが出来る。 As described above, the sensing first layer is the SnO 2 layer or the SnO 2 layer added with the +5 to +6 valent elements as the donor, and further the sensing element as the sensing second layer is added thereon. For the gas sensing layer having a two-layer structure in which the SnO 2 layers are laminated, the outer periphery of the sensing second layer forming the gas sensing layer is formed so as to be entirely outside the outer periphery of the sensing first layer. A thin film gas sensor excellent in sensitivity and selectivity can be obtained.

本発明のガスセンサは、電池駆動を念頭においた低消費電力型の薄膜ガスセンサであり、具体的には、高感度、高選択性、高応答性、高信頼性、低消費電力などの特性を有する薄膜ガスセンサである。以下、本発明を実施する最良の形態によって詳細に説明するが、本発明はこれらの実施の形態によって何ら限定されるものではない。
図１に、後述の実施例で詳細に説明する薄膜ガスセンサの断面構造を示す。
本実施の形態では一例として、平面の形状が四角形の感知第１層１および感知第２層２からなる２層構成のガス感知層を形成する。そのガス感知層の上には、平面の形状が円形の選択燃焼層３を形成する。選択燃焼層３、感知第１層１、感知第２層２の平面形状は、図２に示す通りである。 The gas sensor of the present invention is a low power consumption thin film gas sensor with battery driving in mind, and specifically has characteristics such as high sensitivity, high selectivity, high response, high reliability, and low power consumption. It is a thin film gas sensor. Hereinafter, although the present invention will be described in detail according to the best mode for carrying out the present invention, the present invention is not limited to these embodiments.
FIG. 1 shows a cross-sectional structure of a thin film gas sensor which will be described in detail in an embodiment described later.
In the present embodiment, as an example, a gas sensing layer having a two-layer structure including a sensing first layer 1 and a sensing second layer 2 having a quadrangular planar shape is formed. A selective combustion layer 3 having a circular planar shape is formed on the gas sensing layer. The planar shapes of the selective combustion layer 3, the sensing first layer 1, and the sensing second layer 2 are as shown in FIG.

図２（ｂ）に示した従来型のセンサ（比較例１）では、感知第１層１と感知第２層２が同面積かつ同位置に形成されており、具体的には、四角形の一辺である幅ｃは共通の長さを有する。これに対して、図２（ａ）に示した本発明のセンサ（実施例１）では、感知第２層２が感知第１層１よりも大きく、具体的には、四角形の一辺の長さである幅ｂが幅ａよりも大きい。   In the conventional sensor shown in FIG. 2B (Comparative Example 1), the first sensing layer 1 and the second sensing layer 2 are formed in the same area and at the same position. The width c is a common length. On the other hand, in the sensor (Example 1) of the present invention shown in FIG. 2A, the sensing second layer 2 is larger than the sensing first layer 1, and specifically, the length of one side of the square. The width b is greater than the width a.

本発明の実施の形態では、幅ａについては感知層電極４の電極間隔によって任意に定められるものであり特に限定されるものではないが、感知第１層１が四角形の場合、例えばａは２０〜２０００μｍ、好ましくは５０〜５００μｍの範囲である。感知第１層１の膜厚についても特に限定されるものではなく、例えば０．２〜１０μｍの範囲で任意に定めることができる。また、感知第２層２も同様に四角形の場合、幅ｂは、幅ａに感知第２層２の膜厚ｌの２倍の長さを加えたのと同等かそれ以上であることが必要である。具体的には、ｂ≧ａ＋２ｌ の関係になる。感知第２層２の膜厚ｌについても特に限定されるものではなく任意に定められるが、例えば０．０１〜２．０μｍの範囲である。   In the embodiment of the present invention, the width a is arbitrarily determined according to the electrode interval of the sensing layer electrode 4 and is not particularly limited. However, when the sensing first layer 1 is a square, for example, a is 20 It is -2000 micrometers, Preferably it is the range of 50-500 micrometers. The thickness of the sensing first layer 1 is not particularly limited, and can be arbitrarily determined within a range of 0.2 to 10 μm, for example. Similarly, when the second sensing layer 2 is also square, the width b needs to be equal to or greater than the width a plus twice the thickness l of the sensing second layer 2. It is. Specifically, the relationship is b ≧ a + 2l. The film thickness l of the sensing second layer 2 is not particularly limited and is arbitrarily determined, but is, for example, in the range of 0.01 to 2.0 μm.

また、選択燃焼層３は、感知第２層２の外周部よりも全ての位置で外側であるように形成されており、図２では、円形状の選択燃焼層３の直径ｄは幅ｂよりも大きく、さらに全体を覆う必要から四角形の感知第２層２の対角線の長さよりも直径ｄは大きい。
本実施の形態では、幅ｂについては感知第１層１との関係によって定められるものであり特に限定されるものではないが、感知第２層２が四角形の場合、例えばｂは５０〜２０００μｍ、好ましくは１００〜１０００μｍの範囲である。また、選択燃焼層３が円形の場合、直径ｄは、一辺幅ｂの四角形の対角線の長さに選択燃焼層３の膜厚ｍの２倍の長さを加えたのと同等かそれ以上であることが必要である。選択燃焼層３の膜厚ｍは任意に定められるものであり特に限定されるものではないが、例えば１．０〜５０μｍの範囲である。
以下、本実施の形態の薄膜ガスセンサおよびその製造方法について、図面を参照しながら実施例により更に詳細に説明するが、本発明はこの実施例によって何ら制限されるものでない。 Further, the selective combustion layer 3 is formed so as to be outside at all positions from the outer peripheral portion of the sensing second layer 2. In FIG. 2, the diameter d of the circular selective combustion layer 3 is larger than the width b. The diameter d is larger than the diagonal length of the quadrangular sensing second layer 2 because it is necessary to cover the whole.
In the present embodiment, the width b is determined by the relationship with the sensing first layer 1 and is not particularly limited. However, when the sensing second layer 2 is a square, for example, b is 50 to 2000 μm, Preferably it is the range of 100-1000 micrometers. Further, when the selective combustion layer 3 is circular, the diameter d is equal to or more than the length of the diagonal line of the square with a side width b plus twice the thickness m of the selective combustion layer 3. It is necessary to be. The film thickness m of the selective combustion layer 3 is arbitrarily determined and is not particularly limited, but is, for example, in the range of 1.0 to 50 μm.
Hereinafter, the thin film gas sensor according to the present embodiment and the manufacturing method thereof will be described in more detail with reference to the drawings. However, the present invention is not limited to the examples.

図１における薄膜ガスセンサにおいては、先ず、両面に熱酸化膜が付いたSi基板上にダイアフラム構造２０の支持膜及び熱絶縁膜１１として、Si3N4層９とSiO2層８を順次プラズマＣＶＤ法にて形成する。次に、Pt-Wヒータ層６、SiO2絶縁層７の順にスパッタ法で形成し、その上に接合層５、感知層電極４を形成する。成膜はＲＦマグネトロンスパッタリング装置を用い、通常のスパッタリング方法によって行う。成膜条件は、接合層５（PtあるいはAu）および感知層電極４（TaあるいはTi）ともに同じであり、Arガス圧力1Pa、基板温度300℃、ＲＦパワー2W／cm2、膜厚は、接合層／感知膜電極＝50ｎｍ／200ｎｍである。 In the thin film gas sensor shown in FIG. 1, first, a Si 3 N 4 layer 9 and a SiO 2 layer 8 are sequentially formed by plasma CVD as a support film of a diaphragm structure 20 and a thermal insulating film 11 on a Si substrate having thermal oxide films on both sides. Form by the method. Next, the Pt—W heater layer 6 and the SiO 2 insulating layer 7 are formed by sputtering in this order, and the bonding layer 5 and the sensing layer electrode 4 are formed thereon. Film formation is performed by an ordinary sputtering method using an RF magnetron sputtering apparatus. The film formation conditions are the same for both the bonding layer 5 (Pt or Au) and the sensing layer electrode 4 (Ta or Ti). The Ar gas pressure is 1 Pa, the substrate temperature is 300 ° C., the RF power is 2 W / cm 2 , and the film thickness is Layer / Sensing membrane electrode = 50 nm / 200 nm.

次いで、本発明に係る２層構成のガス感知層を形成する。成膜はＲＦマグネトロンスパッタリング装置を用い、反応性スパッタリング方法によって行う。ターゲットは、感知第１層１にはSbを0.5wt%を有するSnO2を用い、感知第２層２にはPt15wt%を有するSnO2を用いる。成膜条件は、Ar+O2ガス圧力2Pa、基板温度150〜300℃、ＲＦパワー2W／cm2、膜厚は、感知第１層は500ｎｍ、感知第２層は50ｎｍである。
続いて、選択燃焼層３を形成する。Pd 7.0wt%添加したγ−アルミナ（平均粒径2〜3μｍ）にアルミナゾルを5〜20ｗｔ％添加しペーストとし、感知膜であるSnO2の直上にスクリーン印刷し、その後500℃で一時間焼成する。焼成後の選択燃焼層３の膜厚は30〜35μｍである。ここで、選択燃焼層３、感知第１層１、感知第２層２の平面形状は、図２に示す通りである。 Next, a two-layer gas sensing layer according to the present invention is formed. Film formation is performed by a reactive sputtering method using an RF magnetron sputtering apparatus. The target uses SnO 2 having 0.5 wt% Sb for the sensing first layer 1 and SnO 2 having Pt 15 wt% for the sensing second layer 2. The film formation conditions are Ar + O 2 gas pressure 2 Pa, substrate temperature 150 to 300 ° C., RF power 2 W / cm 2 , and the film thickness is 500 nm for the first sensing layer and 50 nm for the second sensing layer.
Subsequently, the selective combustion layer 3 is formed. Add 5 to 20 wt% alumina sol to γ-alumina added with 7.0 wt% Pd (average particle size 2 to 3 μm) to make a paste, screen print directly on SnO 2 as the sensing film, and then fire at 500 ° C for 1 hour . The film thickness of the selective combustion layer 3 after firing is 30 to 35 μm. Here, the planar shapes of the selective combustion layer 3, the sensing first layer 1, and the sensing second layer 2 are as shown in FIG.

図２（ｂ）に示した比較例１では、感知第１層１と感知第２層２が同面積かつ同位置に形成されており、具体的には、四角形の一辺である幅ｃが９０μｍで共通の長さを有する。これに対して、図２（ａ）に示した実施例１では、感知第２層２の幅ｂが感知第１層１の幅ａよりも大きく、具体的には、四角形の一辺の長さである幅ｂが１００μｍであり、幅ａの９０μｍよりも大きい。これにより、図１に示す垂直方向の形状部分を含めて、感知第１層１の外周部全体は感知第２層２により覆われており、感知層の側面からガスが進入を防止してガス選択性が向上する。
また、選択燃焼層３は、図２では、円形状の選択燃焼層３の直径ｄは２２０μｍであり幅ｂの１００μｍよりも大きく、さらに四角形（略正方形）の感知第２層２の対角線の長さ約１４０〜１５０μｍよりも直径ｄは大きい。
最後に、基板裏面よりエッチングによりＳｉを除去し、ダイアフラム構造とする。 In the comparative example 1 shown in FIG. 2B, the first sensing layer 1 and the second sensing layer 2 are formed in the same area and at the same position. Specifically, the width c which is one side of the quadrangle is 90 μm. Have a common length. On the other hand, in the first embodiment shown in FIG. 2A, the width b of the sensing second layer 2 is larger than the width a of the sensing first layer 1, specifically, the length of one side of the quadrangle. The width b is 100 μm and is larger than the width a of 90 μm. As a result, the entire outer peripheral portion of the sensing first layer 1 including the vertical shape portion shown in FIG. 1 is covered with the sensing second layer 2, and gas is prevented from entering from the side surface of the sensing layer. Selectivity is improved.
In addition, in FIG. 2, the selective combustion layer 3 has a circular selective combustion layer 3 having a diameter d of 220 μm, which is larger than 100 μm of the width b, and the length of the diagonal line of the square (substantially square) sensing second layer 2. The diameter d is larger than about 140 to 150 μm.
Finally, Si is removed from the back surface of the substrate by etching to form a diaphragm structure.

次に、上記製造方法によりＣＯセンサとして作製された薄膜ガスセンサの特性を示す。
下記表１に、図２（ａ）に示す実施例１のＣＯセンサ、および、図２（ｂ）に示す比較例１のＣＯセンサ、それぞれの特性を示す。ＣＯ濃度勾配は、ＣＯガス濃度に対するセンサ抵抗値の変化割合を示し、この値が大きいほどガス濃度に対するセンサ出力の分解能が高くなる。ここでは、ＣＯ100ppm中とＣＯ500ppm中のセンサ抵抗値の比を示す。また選択性は、妨害ガスとなる水素およびメタンに対するＣＯとの感度比であり、水素1000ppm中とＣＯ100ppm中、メタン4000ppm中とＣＯ100ppm中、それぞれでのセンサ抵抗値の比を示す。この値が大きいほど、妨害ガスの影響が少なく優れたセンサ特性といえる。
下記表1の結果から、実施例の方が比較例よりもＣＯ濃度勾配およびガス選択性の両方について高い性能を有することがわかる。 Next, characteristics of the thin film gas sensor manufactured as a CO sensor by the above manufacturing method will be shown.
Table 1 below shows the characteristics of the CO sensor of Example 1 shown in FIG. 2A and the CO sensor of Comparative Example 1 shown in FIG. The CO concentration gradient indicates the rate of change of the sensor resistance value with respect to the CO gas concentration. The larger this value, the higher the resolution of the sensor output with respect to the gas concentration. Here, the ratio of the sensor resistance value in CO 100 ppm and CO 500 ppm is shown. Selectivity is a sensitivity ratio of hydrogen and methane as interference gas to CO with respect to methane, and indicates a ratio of sensor resistance values in 1000 ppm of hydrogen and 100 ppm of CO, 4000 ppm of methane and 100 ppm of CO. It can be said that the larger this value, the less the influence of interfering gas and the better the sensor characteristics.
From the results in Table 1 below, it can be seen that the example has higher performance for both CO concentration gradient and gas selectivity than the comparative example.

Figure 0004371772
Figure 0004371772

以上、本発明の実施の形態について説明したが、本発明は、本発明の技術的思想に基づいて種々の変形及び変更が可能である。   While the embodiments of the present invention have been described above, the present invention can be variously modified and changed based on the technical idea of the present invention.

本発明によれば、ダイヤフラム構造で高断熱・低熱容量を有し、かつ、優れたガス選択性を有する薄膜ガスセンサを提供可能であり、例えば可燃性ガス検知や不完全燃焼ガス検知などガス漏れ警報器の分野で特に有効に用いることが期待でき、産業上の意義は極めて大きい。   According to the present invention, it is possible to provide a thin film gas sensor having a diaphragm structure, high heat insulation and low heat capacity, and excellent gas selectivity. It can be expected to be used particularly effectively in the field of ceramics, and its industrial significance is extremely great.

本実施の形態における薄膜ガスセンサの積層構造を示す縦断面図である。It is a longitudinal cross-sectional view which shows the laminated structure of the thin film gas sensor in this Embodiment. 本実施の形態における薄膜ガスセンサのガス感知層の平面形状を上から見た概略図である。It is the schematic which looked at the plane shape of the gas sensing layer of the thin film gas sensor in this Embodiment from the top.

符号の説明Explanation of symbols

１ 感知第１層
２ 感知第２層
３ 選択燃焼層
４ 感知層電極
５ 接合層
６ ヒータ層（Ｐｔ−Ｗ）
７ 絶縁層（スパッタSiO2）
８ ＣＶＤ−SiO2
９ ＣＶＤ−Si3N4
１０ 熱酸化SiO2
１１ 支持膜、熱絶縁膜
１２ 基板
２０ ダイヤフラム構造 DESCRIPTION OF SYMBOLS 1 Sensing 1st layer 2 Sensing 2nd layer 3 Selective combustion layer 4 Sensing layer electrode 5 Joining layer 6 Heater layer (Pt-W)
7 Insulating layer (Sputtered SiO 2 )
8 CVD-SiO 2
9 CVD-Si 3 N 4
10 Thermal oxidation SiO 2
11 Support film, thermal insulation film 12 Substrate 20 Diaphragm structure

Claims (5)

薄膜状の支持膜の外周部または両端部をSi基板により支持し、外周部または両端部が厚く中央部が薄く形成されたダイヤフラム様の支持基板上に、薄膜のヒータを形成し、この薄膜のヒータ層を電気絶縁膜で覆い、その上に感知第１層としてSnO2層またはドナーとなる＋５価ないし＋６価の元素を添加したSnO2層を設け、さらにその上に感知第２層として触媒となる元素を添加したSnO2層を積層した２層構造のガス感知層を形成し、このガス感知層に接して所定間隔を置いて１対の金属からなる感知電極層を設けてなる薄膜ガスセンサであって、該ガス感知層をなす感知第２層の外周部が、該感知第１層の外周部よりも全て外側に設置され、
前記感知第２層の上に、多孔質金属酸化物および貴金属触媒からなる選択燃焼層を、その 外周部が該感知第２層の外周部よりも全て外側であるように形成したことを特徴とする薄膜ガスセンサ。A thin film heater is formed on a diaphragm-like support substrate in which the outer periphery or both ends of the thin support film are supported by a Si substrate, and the outer periphery or both ends are thick and the center is thin. The heater layer is covered with an electrical insulating film, and a SnO 2 layer or a SnO 2 layer added with +5 to +6 elements as donors is provided thereon as a sensing first layer, and a catalyst as a sensing second layer thereon. A thin film gas sensor comprising a gas sensing layer having a two-layer structure in which SnO 2 layers to which an element to be added is laminated are laminated, and a sensing electrode layer made of a pair of metals in contact with the gas sensing layer at a predetermined interval And the outer periphery of the sensing second layer forming the gas sensing layer is all disposed outside the outer periphery of the sensing first layer ,
A selective combustion layer comprising a porous metal oxide and a noble metal catalyst is formed on the sensing second layer so that the outer peripheral portion thereof is entirely outside the outer peripheral portion of the sensing second layer. Thin film gas sensor. 前記ガス感知層の感知第２層の外周部と感知第１層の外周部との距離の最小値が、該感知第２層の膜厚と等しいか、あるいはそれ以上であることを特徴とする、請求項１に記載の薄膜ガスセンサ。  The minimum value of the distance between the outer periphery of the second sensing layer and the outer periphery of the first sensing layer is equal to or greater than the thickness of the second sensing layer. The thin film gas sensor according to claim 1. 前記感知第２層の触媒として、Ru、Rh、Pd 、Os、IrおよびPtからなる群より選ばれる少なくとも１つの元素を含むことを特徴とする、請求項１に記載の薄膜ガスセンサ。  The thin film gas sensor according to claim 1, wherein the sensing second layer catalyst includes at least one element selected from the group consisting of Ru, Rh, Pd, Os, Ir, and Pt. 前記選択燃焼層の外周部と前記感知第２層の外周部との距離の最小値が、選択燃焼層の膜厚と等しいか、あるいはそれ以上であり、かつ、該感知第２層の外周部と前記感知第１層の外周部との距離の最小値が、該感知第２層の膜厚と等しいか、あるいはそれ以上であることを特徴とする、請求項１に記載の薄膜ガスセンサ。The minimum value of the distance between the outer periphery of the selective combustion layer and the outer periphery of the sensing second layer is equal to or greater than the film thickness of the selective combustion layer, and the outer periphery of the sensing second layer 2. The thin film gas sensor according to claim 1 , wherein the minimum value of the distance between the first layer and the outer periphery of the sensing first layer is equal to or greater than the thickness of the sensing second layer. 前記感知第２層の触媒として、Ru、Rh、Pd 、Os、IrおよびPtからなる群より選ばれる少なくとも１つの元素を含むことを特徴とする、請求項１に記載の薄膜ガスセンサ。The thin film gas sensor according to claim 1 , wherein the sensing second layer catalyst includes at least one element selected from the group consisting of Ru, Rh, Pd, Os, Ir, and Pt.
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