JP2010060481A - Thin film gas sensor and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin film gas sensor for reducing penetration of silica sol (silica colloid) in a pore and a gap and improving mechanical strength of a gas selection combustion layer and improving detection performance of a gas sensitive layer even in the porous gas sensitive layer (SnO<SB>2</SB>layer) covered with the gas selection combustion layer containing silica sol as a binder, and to provide a method of manufacturing such a thin film gas sensor. <P>SOLUTION: In the thin film gas sensor and the method of manufacturing the same, a liquid 60 having a high boiling point is filled into a plurality of gaps 532 and a plurality of pores 533 in the gas sensitive film 53 and the gas selection combustion film 54 is formed so that the gas sensitive film 53 is covered, the gas sensitive film 53 and the gas selection combustion film 54 are baked, the liquid 60 having a high boiling point of the gaps 532 and the pores 533 is evaporated, the gaps 532 and the pores 533 are formed in the gas sensitive film 53, and the gas sensitive layer 53 and the gas selection combustion layer 54 are formed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a low power consumption thin film gas sensor with battery driving in mind, and a method of manufacturing the thin film gas sensor.

Generally, a gas sensor is used for applications such as a gas leak alarm. The gas sensor is a device that is selectively sensitive to a specific gas such as carbon monoxide (CO), methane gas (CH ₄ ), propane gas (C ₃ H ₈ ), ethanol vapor (C ₂ H ₅ OH), and the like. In terms of its character, high sensitivity, high selectivity, high response, high reliability, and low power consumption are indispensable.

  By the way, gas leak alarms that are widely used for household use are intended for detecting flammable gases for city gas and propane gas, for detecting incomplete combustion gases in combustion equipment, or both. However, the penetration rate of gas leak alarms is so high due to problems of cost and installation (gas detection is necessary but power cannot be supplied). Absent. Therefore, in order to improve the diffusion rate of the gas leak alarm device, it is desired to improve the installation property, specifically, to be cordless as a battery-driven gas leak alarm device.

Low power consumption of the gas sensor is the most important for realizing the battery drive of the gas leak alarm. However, in order to operate a catalytic combustion type or semiconductor type gas sensor, the gas sensing film of the gas sensor needs to be heated to a high temperature of 200 ° C. to 500 ° C., and this heating is a factor that consumes electric power. A gas sensor using a gas sensing film prepared by sintering powder such as SnO ₂ uses a method such as screen printing to reduce the thickness of the gas sensing film as much as possible to reduce the heat capacity of the gas sensing film. However, thinning has a limit, and the gas sensing film is not thin enough. For this reason, when the gas sensor is driven by a battery, the heat capacity of the gas sensing film is too large, and a large amount of power is required to heat the gas sensing film to a high temperature, resulting in an increase in battery consumption. For this reason, it has been difficult to put into practical use a gas sensor that drives the gas sensing film with a battery.

  Thus, a thin film gas sensor with low power consumption that is practically acceptable has been developed and put into practical use as a diaphragm structure with high heat insulation and low heat capacity by a microfabrication process. Next, such a thin film gas sensor will be described. FIG. 6 is a longitudinal sectional view schematically showing a conventional thin film gas sensor.

This conventional thin film gas sensor includes a silicon substrate (hereinafter referred to as Si substrate) 1, a heat insulating support layer 2, a heater layer 3, an electric insulating layer 4, and a gas detection layer 5. Specifically, the heat insulating support layer 2 has a three-layer structure of a thermally oxidized SiO ₂ layer 21, a CVD-Si ₃ N ₄ layer 22, and a CVD-SiO ₂ layer 23. The gas detection layer 5 includes a bonding layer 51, a sensing electrode layer 52, a gas sensitive layer 53, and a gas selective combustion layer 54 in detail. This gas sensitive layer 53 is a tin dioxide layer doped with antimony (Sb) (hereinafter referred to as SnO ₂ layer), and the gas selective combustion layer 54 is an alumina sintered material carrying palladium (Pd) or platinum (Pt) as a catalyst. (Hereinafter referred to as catalyst-supported Al ₂ O ₃ sintered material). The heater layer 3 and the gas detection layer 5 (specifically, the gas sensitive layer 53 via the sensing electrode layer 52) are connected to a driving / processing unit (not shown).

  This conventional thin-film gas sensor is a sensor that utilizes a phenomenon in which the electrical resistance value (sensor resistance value) of the gas-sensitive layer 53 that is an oxide semiconductor changes by contact with various gas components. A metal oxide semiconductor heated to about 200 to 500 ° C. has a characteristic that its conductivity changes depending on the gas concentration. A metal oxide semiconductor adsorbs oxygen in air to increase resistance, but in a combustible gas, adsorbs combustible gas to reduce resistance.

The details are as follows.
When in the air, the gas sensitive layer 53 that is an n-type metal oxide semiconductor such as a SnO ₂ layer activates and adsorbs oxygen or the like on the surface of the gas sensitive layer 53. Since oxygen has a strong electron accepting property and adsorbs negative charges, a space charge layer is formed on the surface of the gas sensitive layer 53. Therefore, the gas sensitive layer 53 is reduced in electrical conductivity and increased in resistance.
The gas sensitive layer 53 which is an n-type metal oxide semiconductor such as a SnO ₂ layer is heated to about 200 to 500 ° C. in the gas sensitive layer 53 in an electron donating reducing gas such as a combustible gas. Thus, when a combustion reaction of the flammable gas occurs, the adsorbed oxygen on the surface of the gas sensitive layer 53 is consumed, and the electrons captured by the adsorbed oxygen are returned to the gas sensitive layer 53, whereby the inside of the gas sensitive layer 53 The electron density increases. Therefore, the gas sensitive layer 53 is increased in electrical conductivity and reduced in resistance.

The gas sensitive layer 53 can detect various gases, but it is difficult to selectively detect a specific gas.
Therefore, the gas detection layer 5 has a structure in which the entire surface of the gas sensitive layer 53 which is a SnO ₂ layer is covered with a gas selective combustion layer 54 made of a catalyst-supported Al ₂ O ₃ sintered material.
The gas selective combustion layer 54 has a function of improving the sensitivity of only a specific gas in the gas detection layer 5 in order to burn a gas having a stronger oxidation activity than the detection gas. Further, the size and thickness of the gas detection layer 5 and the ratio with the diaphragm diameter of the Si substrate 1 are also devised. Thereby, a certain specific gas selectivity is further improved, and the reduction of power consumption is attained.

Such a thin film gas sensor is a sensor in which the driving method of the heater layer 3 is devised in order to realize low power consumption for detecting combustible gases such as CH ₄ and C ₃ H ₈ . In this driving method, the driving time is shortened as an intermittent operation with a duty ratio (ratio of time during which the heater is turned on) of about 1/300 to 1/100. Therefore, in a high humidity or high-concentration alcohol environment, moisture or alcohol adsorbed on the gas sensitive layer 53 and the gas selective combustion layer 54 during the off time sufficiently longer than the on time cannot be desorbed by heating in a short time. May interfere with gas detection.

  Now, in the case of a diaphragm structure in which thin films are laminated, distortion of about several μm occurs, so that the gas selective combustion layer 54 also needs a mechanical strength of a certain level or more. In order to ensure the mechanical strength of the gas selective combustion layer 54, it is common to add a binder such as silica sol or alumina sol.

  When the binder is silica sol, the adhesiveness with the electrical insulating layer 4 as the base is excellent, and the gas selective combustion layer 54 does not peel from the electrical insulating layer 4 even when driven for a long time, but a large amount of moisture and alcohol are adsorbed on the silica sol As a result, the gas selective combustion function is impaired, and the silica sol coats the gas sensitive layer 53, whereby the initial characteristics, particularly the gas sensing characteristics are impaired.

  When the binder is alumina sol, excellent initial characteristics can be obtained without any deterioration in the function of the gas selective combustion 54 due to adsorption of moisture and alcohol, and no deterioration in gas sensing characteristics due to the coating of the gas sensitive layer 53, but the gas sensitive layer 53. There is a problem that the adhesive strength between the electric insulating layer 4 and the gas selective combustion layer 54 in the periphery of the gas is low, and the gas selective combustion layer 54 is peeled off from the electric insulating layer 4 by driving for a long time. Further, in the case of the alumina sol, when the gas selective combustion layer 54 is formed, there is a problem that the variation in characteristics becomes large due to the poor controllability of the shape and the large variation.

  In the case of forming the gas selective combustion layer 54, the constituent material of the gas selective combustion layer 54 is formed into a paste and then formed by screen printing or dispenser application. In this case, it is better to use a high boiling point organic solvent as the solvent. Is less evaporated, the viscosity of the paste is stable, the shape of the gas selective combustion layer 54 is good, and the variation is kept small. In general, when the binder is silica sol, both the one using an organic solvent as the solvent and the one using water are stable, but when the binder is an alumina sol, only the one using water is present. What was there cannot exist stably. Therefore, in the case of silica sol, variation in shape can be suppressed by using an organic solvent system, but in the case of alumina sol, variation in shape becomes large because it is aqueous.

The inventors of the present application have filed a patent application for the present invention as an invention that solves the above problems. This patent application has been published as Japanese Patent Application Laid-Open No. 2005-017242 (Patent Document 1). In the invention disclosed in the application, after forming a thin layer of silica sol having a high adhesion strength with the porous gas sensing film (SnO ₂ ) and the SiO ₂ insulating film in the lower layer, the upper layer is thick with good gas sensing characteristics. A two-layer structure selection layer in which an alumina sol selection layer is formed is employed.
With the two-layer structure selection layer, the selection layer does not peel off from the underlying layer, and a thin film gas sensor with good gas sensing characteristics is obtained.

Japanese Patent Laying-Open No. 2005-017242 (paragraph numbers [0012] to [0016], FIG. 1)

In the two-layer structure selective layer, it has been found that the silica sol selective layer has problems such as a reduction in R _air (resistance in _air ) in a high temperature and high humidity (60 ° C./80% RH) test. Such a phenomenon is not observed in the alumina sol selective layer, which is considered to be caused by a large amount of moisture adsorbed on the silica sol of the silica sol selective layer.

Therefore, the cause of the large amount of moisture adsorption to the silica sol in the gas selective combustion layer 54 using the silica sol as a binder was investigated using means such as microscopic analysis. This result will be described with reference to the drawings. 7 and 8 are explanatory views for explaining a large amount of moisture adsorption on the silica sol. As shown in FIG. 7, the gas sensitive layer 53 formed on the electrical insulating layer 4 (sputtered SiO ₂ layer) and the sensing electrode layer 52 is an aggregate of columnar crystals 531 of SnO ₂ having a diameter of 10 nm to 100 nm and is columnar. A gap 532 of 5 nm to 50 nm exists between the crystals 531. Furthermore, innumerable pores 533 of several nm exist on the surface and inside of the columnar crystal 531 of SnO ₂ . The pores are classified into micropores (<2 nm), mesopores (2 nm to 50 nm), and macropores (> 50 nm) based on the size (pore diameter).

In the case of the gas selective combustion layer 54 using silica sol as a binder, as shown in FIG. 8, at the time of performing heat treatment (firing of the gas selective combustion layer 54), gaps 532 and pores of the gas sensitive layer 53 of porous SnO ₂ It was found that SiO ₂ fine particles having a size of several nanometers were deposited from the gas selective combustion layer 54 in 533. The bonding strength between the gas sensitive layer 53 and the gas selective combustion layer 54 is determined by the bonding strength of the surfaces, and the SiO ₂ fine particles that have entered the gaps 532 and the pores 533 of the gas sensitive layer 53 hardly contribute to the bonding strength. . Further, since the SiO ₂ fine particles are reduced, the mechanical strength of the gas selective combustion layer 54 is slightly reduced. Then, the outermost surface of SiO ₂ fine particles / SnO _{2 that} is well-suited to moisture is formed and interacts with moisture in the air to promote generation of OH groups and condensation of moisture, thereby causing R _air (resistance in the _air ) of the gas sensitive layer 53. ).

The above does not happen with alumina sol. This difference is due to the fact that the silica colloid size of silica sol is as small as several nanometers, so that it easily penetrates into SnO ₂ pores of several tens of nanometers and is highly dispersed on the surface of SnO ₂ pores. It is estimated that the alumina hydrate in the inside has a large colloidal size of 100 to 200 nm and cannot penetrate into the SnO ₂ pores (<50 nm) (it can only be a fired product with a particle size of> several hundred nm). ing. Therefore, alumina sol does not diffuse at least into the pores of the porous gas sensing film (SnO ₂ film), and therefore no portion that promotes the generation of OH groups and condensation of moisture is generated on the surface of SnO ₂ pores.

In view of the advantages and disadvantages of these silica sols and alumina sols, it is desirable to select both silica sol as the binder and solve both the problems specific to silica sol to achieve both improved adhesion and improved mechanical strength. In other words, the gas selective combustion layer using silica sol as the binder would like to make a thin film gas sensor with improved sensitivity characteristics by preventing the penetration of silica sol (silica colloid) into the pores of the porous gas sensing membrane (SnO ₂ membrane). There was a request. Note that the two-layer structure selection layer of Patent Document 1 requires a screen printing process twice, which is slightly disadvantageous in terms of cost. There has been a demand for a thin film gas sensor that is favorable in terms of cost.

Therefore, the present invention has been made to solve the above-mentioned problems, and the object of the present invention is to provide a porous gas-sensitive layer (SnO ₂ layer) covered with a gas selective combustion layer containing silica sol as a binder. A thin film gas sensor that reduces the penetration of silica sol (silica colloid, SiO ₂ fine particles) in the gap to improve the mechanical strength of the gas selective combustion layer and the detection performance of the gas sensitive layer, and such The object is to provide a method of manufacturing a thin film gas sensor.

In the thin film gas sensor of the present invention, a gas sensitive film is formed by a gas selective combustion film in which a gas sensitive film before firing is filled with a filling of components scattered by heating, and silica sol (silica colloid, SiO ₂ fine particles) is added as a binder. It is formed to cover and prevent the penetration of silica sol (silica colloid, SiO ₂ fine particles) into the pores and gaps of the gas sensitive membrane, and both the gas sensitive membrane and the gas selective combustion membrane are baked to evaporate the filler. Thus, a gas-sensitive layer in which pores and gaps are formed.

According to the invention of claim 1,
A Si substrate having a through hole;
A diaphragm-like heat insulating support layer stretched over the opening of the through hole;
A heater layer provided on the thermally insulating support layer;
An electrically insulating layer provided to cover the heat insulating support layer and the heater layer;
A pair of sensing electrode layers provided on the electrically insulating layer;
A gas sensitive layer provided on the electrically insulating layer so as to pass a pair of sensing electrode layers;
A gas selective combustion layer covering the gas sensitive layer;
With
The gas sensitive layer is a thin film gas sensor characterized in that a plurality of micropores, a plurality of mesopores and a plurality of macropores communicate with the outside.

According to this configuration, the gas sensitive layer of the thin film gas sensor has a plurality of micropores, a plurality of mesopores, and a plurality of macropores, and prevents the silica sol (silica colloid, SiO ₂ fine particles) from penetrating from the outside. Because it is a layer that communicates reliably, it greatly increases the contact area and adsorbs a lot of oxygen in the air (at low temperatures) to ensure high resistance, and in the flammable gas (at high temperatures) Adsorbs to ensure low resistance. In this way, the conductivity is surely changed depending on the gas concentration.

According to invention of Claim 2,
The gas sensitive layer is an aggregate of columnar crystals having a cross-sectional diameter of 10 nm to 100 nm, having a plurality of gaps of 5 nm to 50 nm between the columnar crystals, and having a plurality of pores on the surface and inside of the columnar crystals. The thin film gas sensor according to claim 1, wherein the thin film gas sensor is a layer including micropores, mesopores, and macropores in the plurality of gaps and the plurality of pores.

  An aggregate of columnar crystals having a plurality of gaps between the columnar crystals, and having a plurality of pores on and inside the columnar crystals, and micropores and mesopores in the plurality of gaps and the plurality of pores. In addition, the gas sensitive layer having the macropores enhances detection performance by reliably performing oxygen adsorption and contact with the detection target gas.

According to invention of Claim 3,
The thin film gas sensor according to claim 1, wherein the gas sensitive layer is a layer formed of SnO ₂ (tin dioxide).

It has been found that SnO ₂ is particularly preferred as the gas sensitive layer.

According to invention of Claim 4,
The gas selective combustion layer is a layer made of an Al ₂ O ₃ (alumina) sintered material supporting Pd (palladium) or Pt (platinum) as a catalyst. The thin film gas sensor described in one item was used.

The gas selective combustion layer, which is an Al ₂ O ₃ sintered material carrying Pd (palladium) or Pt (platinum) as a catalyst and covers the gas sensitive layer, improves the selectivity of the detection target gas in the gas sensitive layer.

According to the invention of claim 5,
It is a manufacturing method of the thin film gas sensor according to any one of claims 1 to 4,
Forming the gas sensitive layer and the gas selective combustion layer on a substrate;
A gas sensitive film forming step of forming a gas sensitive film on the electrical insulating layer;
A filling step of filling a plurality of gaps and a plurality of pores of the gas sensitive membrane with a high boiling point liquid;
A gas selective combustion film forming step of forming a gas selective combustion film so as to cover the gas sensitive film;
The gas sensitive membrane and the gas selective combustion membrane are heated above the boiling point of the high boiling point liquid to evaporate the high boiling point liquid in the gaps and pores to form gaps and pores in the gas sensitive membrane, and the gas sensitive membrane and gas A firing step of firing the selective combustion film to form a gas sensitive layer and a gas selective combustion layer;
It was set as the manufacturing method of the thin film gas sensor characterized by having.

A gas selective combustion film was formed after filling a plurality of gaps and a plurality of pores of the gas sensitive film with a high boiling point liquid, and the high boiling point liquid was removed when the gas selective combustion film was fired.
In such a manufacturing method, since silica sol (silica colloid, SiO ₂ fine particles) does not precipitate in the gas sensitive layer, many silica sols (silica colloid, SiO ₂ fine particles) are used for adhesion, and the gas sensitive layer, the gas selective combustion layer, And the adhesive strength between the electrical insulating layer and the gas selective combustion layer are increased. Further, gaps and pores without silica sol (silica colloid, SiO ₂ fine particles) are formed in the gas sensitive layer, that is, the outermost surface of SiO ₂ fine particles / SnO ₂ that is well-suited to moisture is not formed. The generation of OH groups and the condensation of moisture are promoted by interaction, so that the occurrence of a situation of R _air (resistance in the air) of the gas sensitive layer is less likely to occur.

According to the invention of claim 6,
The filling step is a step of immersing the substrate in the high boiling point liquid after exposing the substrate formed up to the gas sensitive film in an atmosphere having a saturated vapor pressure or higher of the high boiling point liquid for a predetermined time. The manufacturing method of the thin film gas sensor according to Item 5.

The filling process is performed in two stages, and is exposed to an atmosphere at a saturated vapor pressure or higher for a high boiling point liquid for a certain period of time, so that the high boiling point liquid reaches the pores in particular, and is then immersed in the high boiling point liquid. Thus, the high boiling point liquid is surely permeated into the pores and gaps.
In particular, filling of pores having a small diameter such as micropores and mesopores of a porous gas-sensitive membrane is preferably performed using a gas-state filling material and utilizing capillary condensation into the pores. This is achieved by exposing the porous gas-sensitive membrane to a space filled with the saturated vapor pressure of the filling material. For macropores, liquid impregnation is used.

According to the invention of claim 7,
The gas selective combustion film forming step is a step of forming a gas selective combustion film having a predetermined shape by screen printing or the like on a gas sensitive film using a printing paste formed by mixing an organic solvent mainly composed of catalyst powder and silica sol binder. The method of manufacturing a thin film gas sensor according to claim 5 or 6, wherein the method is a thin film gas sensor.

  Specifically, the gas selective combustion film forming step is clarified as a step of forming (screen printing) a gas selective combustion layer using a printing paste.

According to the invention described in claim 8,
The filling process is a high boiling liquid is a method of manufacturing a thin film gas sensor according to any one of claims 5 to 7, characterized in that the H _{2 O} (water).

The high boiling point liquid was H ₂ O which was inexpensive and easy to use.

According to the invention of claim 9,
8. The method of manufacturing a thin film gas sensor according to claim 7, wherein the filling step is a step of using a high boiling point liquid as the same component as the organic solvent contained in the printing paste.

  The high boiling point liquid was made the same component as the organic solvent contained in the printing paste, and the temperature control was facilitated by vaporizing at the same temperature as the firing temperature of the gas selective combustion layer.

According to the invention of claim 10,
The method for producing a thin film gas sensor according to claim 9, wherein the filling step is characterized in that the high boiling point liquid is diethylene glycol monoethyl ether.

  Of the organic solvents contained in the printing paste as a high boiling liquid, diethylene glycol monoethyl ether was found to be good.

  According to the first aspect of the present invention, the gas sensitive layer is a layer in which a plurality of micropores, a plurality of mesopores and a plurality of macropores communicate with the outside world. It is possible to provide a thin-film gas sensor that reliably changes the value.

  Further, according to the invention of claim 2, it is an aggregate of columnar crystals having a plurality of gaps between the columnar crystals, and having a plurality of pores on the surface and inside of the columnar crystals. The gas-sensitive layer has micropores, mesopores, and macropores in the gaps and a plurality of pores, so the gas is greatly increased in contact area so that oxygen adsorption and contact with the gas to be detected can be reliably performed. It can be a thin film gas sensor that reliably changes its conductivity depending on the concentration.

Further, according to the invention of claim 3, when SnO ₂ is selected as the gas sensitive layer, the gas contact area is greatly increased so that the adsorption of oxygen and the contact with the detection target gas are surely performed. It can be a thin film gas sensor that reliably changes its conductivity depending on the concentration.

Further, according to the invention of claim 4, when a gas selective combustion layer of Al ₂ O ₃ sintered material supporting Pd (palladium) or Pt (platinum) as a catalyst is further provided, oxygen adsorption and detection It is possible to provide a thin film gas sensor in which the contact area is greatly increased so that the contact with the target gas is reliably performed and the conductivity is reliably changed according to the gas concentration.

Further, according to the invention of claim 5, since silica sol (silica colloid, SiO ₂ fine particles) does not precipitate in the gaps and pores filled with the high boiling point liquid in the gas sensitive layer, many silica sols (silica colloids) , SiO ₂ fine particles) are used for adhesion to increase the adhesion strength between the gas sensitive layer and the gas selective combustion layer and the adhesion strength between the electrical insulating layer and the gas selective combustion layer, and SiO _{2 which} is well-suited with moisture. Since the finest particle / SnO ₂ outermost surface is not formed, the generation of OH groups by interacting with moisture in the air, the condensation of moisture is promoted, and the occurrence of R _air (resistance in the air) of the gas sensitive layer may also occur. It can be set as the manufacturing method of the thin film gas sensor which makes it difficult to occur.

Further, according to the invention of claim 6, the filling of small pores such as micropores and mesopores in the porous gas-sensitive layer is performed by using a high-boiling liquid in a gaseous state to capillarize the pores. A thin-film gas sensor that prevents the precipitation of silica sol (silica colloid, SiO ₂ fine particles) by reliably filling the pores and gaps with a high-boiling liquid, as in the case of macropores. It can be set as a manufacturing method.

According to the seventh aspect of the invention, more specifically, in the gas selective combustion film forming step of forming a gas selective combustion layer (screen printing) using a printing paste, high-boiling liquid is surely provided in the pores and gaps. The thin film gas sensor manufacturing method can prevent the silica sol (silica colloid, SiO ₂ fine particles) from being deposited.

According to the eighth aspect of the present invention, when the high boiling point liquid is made of H ₂ O which is inexpensive and convenient to use, the high boiling point liquid is surely filled in the pores and gaps, and silica sol (silica colloid, SiO ₂ It can be a method for manufacturing a thin film gas sensor that prevents the precipitation of fine particles).

  Further, according to the invention according to claim 9, the high boiling point liquid is made the same component as the organic solvent contained in the printing paste, the material is made common to reduce the cost, and the same temperature as the firing temperature of the gas selective combustion layer It is possible to provide a method for manufacturing a thin film gas sensor that facilitates temperature management by vaporizing.

  Further, according to the invention of claim 10, the high boiling point liquid is diethylene glycol monoethyl ether, the material is made common to reduce the cost, and it is vaporized at the same temperature as the firing temperature of the gas selective combustion layer. It can be set as the manufacturing method of the thin film gas sensor which makes temperature management easy.

In general, according to the present invention as described above, even in a porous gas-sensitive layer (SnO ₂ layer) covered by a gas selective combustion layer containing silica sol as a binder, silica sol (silica colloid, SiO ₂ fine particles) in pores and gaps are covered. ) And a thin film gas sensor that can improve both the mechanical strength of the gas selective combustion layer and the detection performance of the gas sensitive layer, and a method of manufacturing such a thin film gas sensor can be provided. .

  Hereinafter, the thin film gas sensor of the best mode for carrying out the present invention and a method of manufacturing the thin film gas sensor will be described with reference to the drawings. The thin film gas sensor of this embodiment is mainly characterized in that the structure of the gas sensitive layer and the manufacturing method thereof are improved. The entire structure of the thin film gas sensor itself is the same as that of the conventional thin film gas sensor 10 shown in FIG. The same.

That is, as shown in FIG. 6, the thin film gas sensor 10 includes a Si substrate 1, a heat insulating support layer 2, a heater layer 3, an electric insulating layer 4, and a gas detection layer 5. Specifically, the heat insulating support layer 2 has a three-layer structure of a thermally oxidized SiO ₂ layer 21, a CVD-Si ₃ N ₄ layer 22, and a CVD-SiO ₂ layer 23. The gas detection layer 5 includes a bonding layer 51, a sensing electrode layer 52, a gas sensitive layer 53, and a gas selective combustion layer 54 in detail. The gas sensitive layer 53 is an SnO ₂ layer doped with Sb, and the gas selective combustion layer 54 is a catalyst-supported Al ₂ O ₃ sintered material. The heater layer 3 and the gas detection layer 5 (specifically, the gas sensitive layer 53 via the sensing electrode layer 52) are connected to a driving / processing unit (not shown).

Next, the configuration of each part will be described.
The Si substrate 1 is formed of silicon (Si) and has a through hole.
The thermal insulating support layer 2 is stretched over the opening of the through hole and formed in a diaphragm shape, and is provided on the Si substrate 1.

Specifically, the heat insulating support layer 2 has a three-layer structure of a thermally oxidized SiO ₂ layer 21, a CVD-Si ₃ N ₄ layer 22, and a CVD-SiO ₂ layer 23.
The thermally oxidized SiO ₂ layer 21 is formed as a heat insulating layer and has a function of reducing the heat capacity by preventing heat generated in the heater layer 3 from being conducted to the Si substrate 1 side. The thermally oxidized SiO ₂ layer 21 exhibits high resistance to plasma etching, and facilitates formation of a through hole in the Si substrate 1 by plasma etching, which will be described later.
The CVD-Si ₃ N ₄ layer 22 is formed above the thermally oxidized SiO ₂ layer 21.
The CVD-SiO ₂ layer 23 improves adhesion with the heater layer 3 and ensures electrical insulation. The SiO ₂ layer formed by CVD (chemical vapor deposition) has a small internal stress.

The heater layer 3 is a thin-film Ni—Cr film (nickel-chromium film), and is provided on the upper surface at substantially the center of the heat insulating support layer 2. A power supply line (not shown) is also formed. This power supply line is connected to a driving / processing unit (not shown).
The electrical insulating layer 4 is formed of a sputtered SiO ₂ layer that ensures electrical insulation, and is provided so as to cover the heat insulating support layer 2 and the heater layer 3. Electrical insulation is ensured between the heater layer 3 and the sensing electrode layer 52, and the electrical insulating layer 4 improves adhesion with the gas sensitive layer 53.

The bonding layer 51 is made of, for example, a Ta film (tantalum film) or a Ti film (titanium film), and is provided on the electrical insulating layer 4. The bonding layer 51 has a function of increasing the bonding strength by being interposed between the sensing electrode layer 52 and the electrical insulating layer 4.
The sensing electrode layers 52 are made of, for example, a Pt film (platinum film) or an Au film (gold film), and are provided in a pair on the left and right sides so as to serve as the sensing electrodes of the gas sensitive layer 53. The bonding layer 51 may be omitted, and the pair of sensing electrode layers 52 are provided on the electrical insulating layer 4 directly through the bonding layer 51 or without the bonding layer 51. .
The gas sensitive layer 53 is made of an SnO ₂ layer doped with Sb, and is formed on the electrical insulating layer 4 so as to pass the pair of sensing electrode layers 52 and 52.

The gas selective combustion layer 54 is a sintered body supporting a catalyst of platinum (Pt) or palladium (Pd), and is a catalyst-supported Al ₂ O ₃ sintered material as described above. The gas selective combustion layer 54 is provided on the surface of the gas sensitive layer 53. Since Al ₂ O ₃ is a porous body, it increases the chance that the detection gas passing through the holes comes into contact with the catalyst and promotes the combustion reaction. The gas selective combustion layer 54 is provided so as to cover the surfaces of the electrical insulating layer 4, the bonding layer 51, the pair of sensing electrode layers 52 and 52, and the gas sensitive layer 53.

Such a thin film gas sensor has a highly heat insulating and low heat capacity structure by a diaphragm structure.
Although not shown, the driving / processing unit is configured by integrally forming the driving unit and the processing unit, and is connected so as to drive the heater layer 3 by electricity. Further, the gas-sensitive layer is connected via the sensing electrode layer 52. 53 are connected to detect a change in the sensor resistance value. Gas detection driving is performed by the driving / processing section.
The configuration of the thin film gas sensor 10 is as described above.

Next, details of the gas sensitive layer 53 and the gas selective combustion layer 54 which are characteristic parts of the thin film gas sensor of the present invention will be described with reference to the drawings. FIG. 1 is a detailed view of a gas sensitive layer and a gas selective combustion layer of the thin film gas sensor of this embodiment.
The gas sensitive layer 53 is an aggregate of a large number of columnar crystals 531. The diameter of the columnar crystal 531 is about 10 nm to 100 nm. A plurality of gaps 532 of 5 nm to 50 nm are formed between these many columnar crystals. Further, as shown in the circle, a plurality of pores 533 are formed on the surface and inside of the columnar crystal 531. The plurality of gaps 532 and the plurality of pores 533 are layers containing micropores, mesopores, and macropores.

In such a gas sensitive layer 53, gaps and pores without silica sol (silica colloid, SiO ₂ fine particles) are formed, that is, the outermost surface of SiO ₂ fine particles / SnO ₂ that is well-adapted to moisture is not formed. The generation of OH groups and the condensation of moisture are promoted by interacting with moisture, and the occurrence of a situation where R _air (in-air resistance) of the gas sensitive layer 53 is reduced is less likely to occur. Further, since the surface area of the gas sensitive layer 53 is increased, the adsorption of oxygen and the contact with the detection target gas are reliably performed, and the detection performance is enhanced.

Next, a method for manufacturing the thin film gas sensor of this embodiment will be schematically described with reference to the drawings. 2 is an explanatory diagram of the gas sensitive film forming process, FIG. 3 is an explanatory diagram of the first filling process, FIG. 4 is an explanatory diagram of the second filling process, and FIG. 5 is an explanatory diagram of the gas selective combustion film forming process.
A thermal insulating support layer is formed on the substrate (thermal insulating layer forming step).
First, thermal oxidation is performed on one surface (or both front and back surfaces) of a substrate, which is a plate-like silicon wafer (not shown), to form a thermally oxidized SiO ₂ film, and finally a thermally oxidized SiO ₂ layer. 21.
Subsequently, a CVD-Si ₃ N ₄ film is deposited and formed on the upper surface of the thermally oxidized SiO ₂ layer 21 by a plasma CVD method, and finally becomes a CVD-Si ₃ N ₄ layer 22.
Subsequently, a CVD-SiO ₂ film is deposited and formed on the upper surface of the CVD-Si ₃ N ₄ layer 22 by a plasma CVD method, and finally becomes a CVD-SiO ₂ layer 23.

Subsequently, a heater layer is formed on the heat insulating support layer (heater layer forming step).
A Ni—Cr film is vapor-deposited in a predetermined pattern on the upper surface of the CVD-SiO ₂ layer 23 by sputtering, and finally becomes the heater layer 3.

Subsequently, an electrical insulating layer is formed on the heat insulating support layer and the heater layer (electrical insulating layer forming step).
A SiO ₂ film is deposited on the upper surfaces of the CVD-SiO ₂ layer 23 and the heater layer 3 by a sputtering method, and finally becomes the electrical insulating layer 4.

Subsequently, a sensing electrode layer is formed on the electrically insulating layer (sensing electrode layer forming step).
A Ta film or a Ti film is deposited on the upper surface of the electrical insulating layer 4 by a sputtering method, and finally becomes the bonding layer 51. When the bonding layer 51 is not formed, this bonding layer formation is omitted.
Similarly, a Pt film or an Au film is deposited on the upper surface of the bonding layer 51 by sputtering, and finally becomes the sensing electrode layer 52.
The bonding layer 51 and the sensing electrode layer 52 are formed by an ordinary sputtering method using an RF magnetron sputtering apparatus. The film forming conditions are the same for the bonding layer (Ta or Ti) 51 and the sensing electrode layer (Pt or Au) 52, Ar gas (argon gas) pressure 1 Pa, substrate temperature 300 ° C., RF power 2 W / cm ² , film thickness Bonding layer 51 / sensing electrode layer 52 = 500/2000 mm.

Subsequently, a gas sensitive film is formed on the electrical insulating layer (gas sensitive film forming step).
A porous Sb-doped SnO ₂ film is deposited on the upper surface of the electrical insulating layer 4 so as to be passed between the pair of sensing electrode layers 52 and 52 by sputtering. The gas-sensitive film is a gas-sensitive layer 53 that is formed only after the gas selective combustion film covering the gas-sensitive film is formed and then both are fired, and is referred to as a gas-sensitive film for convenience until firing.
Film formation is performed by a reactive sputtering method using an RF magnetron sputtering apparatus. For the target, SnO ₂ containing 0.5 wt% Sb and 6.0 wt% Pt is used. The film forming conditions are Ar + O ₂ gas pressure 2 Pa, substrate temperature 150 to 300 ° C., RF power 2 W / cm ² , and film thickness 5000 mm. The size of the gas sensitive film (the gas sensitive layer 53 after firing) is preferably about 50 to 200 μm square and the thickness is preferably about 0.2 to 1.6 μm. In this gas sensitive film, a plurality of columnar crystals are erected as shown in FIG. 2, and a plurality of gaps 532 and a plurality of pores 533 are formed.

The high-boiling liquid is filled into the plurality of gaps and the plurality of pores of the gas sensitive membrane (filling step).
This filling step is divided into two steps. Specifically, a step in which the substrate formed up to the gas sensitive film is exposed for a certain period of time in an atmosphere higher than the saturated vapor pressure of the high boiling point liquid (first filling step), and then a step in which the substrate is immersed in the high boiling point liquid (first step). Two filling step). Specifically, water is adopted as the high boiling point liquid of this embodiment.

First, the first filling step is performed. More specifically, the substrate (wafer) formed up to the porous gas sensing film (SnO ₂ film) is left in a sealed container together with a beaker filled with water for 24 hours. The temperature of the sealed container may be any temperature as long as it is 1 ° C. or higher and 99 ° C. or lower, but the relative humidity in the sealed container is a saturated vapor pressure of H ₂ O. Under such an atmosphere, the micropores in the pores and gaps of the gas sensing film (SnO ₂ film) and the mesopores having a relatively small diameter have a capillary condensation action, and as shown in FIG. The inside of the mesopore having a relatively small diameter is filled with water (H ₂ O) which is the high boiling point liquid 60.

Subsequently, the second filling step is performed. More specifically, the substrate (wafer) subjected to the first filling step is immersed in water (H ₂ O), which is a high boiling point liquid, at room temperature for 60 minutes (impregnation with H ₂ O). . Then, as shown in FIG. 4, water (H ₂ O), which is a high boiling point liquid, reaches the inside of a relatively large diameter mesopore or macropore and is filled with water (H ₂ O), which is a high boiling point liquid 60. Is done. Then, the surface of the substrate (wafer) taken out from the water is blown with N ₂ gas to blow off moisture adhering to the surface. As shown in FIG. 4, the state of the gas sensitive film after this is such that most of the micropores, mesopores and macropores are filled with the high boiling point liquid 60. In FIG. 4, the high boiling point liquid 60 is illustrated in a mesh pattern and a black background pattern, but this is a separate illustration of the high boiling point liquid 60 filled in the first and second filling steps. After all, it is the same high boiling point liquid 60 and is united.

The reason why the first and second filling steps are performed in this way is that only the second filling step (only H ₂ O impregnation) is affected by surface tension and internal residual gas (air). Although it is difficult to fill with H ₂ O, the first filling step (capillary condensation action) is performed in advance to fill the micropores and the mesopores, and then the second filling step (H ₂ O impregnation) is performed. Thus, almost all of the large number of micropores, mesopores, and macropores contained in the plurality of gaps 532 and the plurality of pores 533 on the surface and inside of the columnar crystal 531 are surely filled with water as the high-boiling point liquid 60. . The filling process is performed in this way.

Subsequently, a gas selective combustion film is formed (gas selective combustion film forming step).
For a substrate having a gas sensitive film filled with water which is a high boiling point liquid in the first and second filling steps, a gas selective combustion layer printing paste prepared in advance is 30 μm thick immediately above the gas sensitive film. A gas selective combustion film is formed by screen printing so that In this way, the thickness is reduced by screen printing. As shown in FIGS. 5 and 6, the gas selective combustion film covers the electrical insulating layer 4, the bonding layer 51, the pair of sensing electrode layers 52 and 52, and the gas sensitive film. This gas selective combustion layer printing paste is kneaded by adding the same weight of diethylene glycol monoethyl ether and 20 wt% of silica sol as a binder to γ-alumina (average particle diameter of 2 to 3 μm) to which 7.0 wt% of Pd is added. This is a paste. Note that the gas selective combustion film is a gas selective combustion layer 54 only after the gas sensitive film and the gas selective combustion film are fired, and is referred to as a gas selective combustion film for convenience until firing.

Subsequently, the gas sensitive film and the gas selective combustion film are fired to form a gas sensitive layer and a gas selective combustion layer (firing step).
The substrate on which the gas sensitive film and the gas selective combustion film are formed is dried at room temperature and then baked at 500 ° C. for 1 hour. At this time, the gas sensitive membrane and the gas selective combustion membrane are heated to a temperature higher than the boiling point of the high-boiling liquid to evaporate the high-boiling liquid in the gaps and pores to form gaps and pores in the gas-sensitive membrane. Thus, the gas sensitive layer 53 and the gas selective combustion layer 54 as shown in FIG. 1 are formed. Water becomes water vapor at 100 ° C. or higher, and has no influence on the gas sensitive layer 53 and the gas selective combustion layer 54 through the gaps 532 and the pores 533 of the porous gas sensitive membrane and the porous gas selective combustion membrane. It scatters without.

Finally, the silicon wafer (not shown) is removed from the back surface by etching as a microfabrication process to form the Si substrate 1 in which the through holes are formed. Thus, the thin film gas sensor 10 having a diaphragm structure is obtained. The heater layer 3 and the sensing electrode layer 52 are connected so as to be electrically communicable with the driving / processing unit.
The manufacturing method of the thin film gas sensor 10 is as described above.

In the thin film gas sensor of the present embodiment described above, even in the porous gas-sensitive layer 53 (SnO ₂ layer) covered with the gas selective combustion layer 54 containing silica sol as a binder, silica sol (silica colloid, SiO ₂ ) in the pores and gaps is covered. A thin film gas sensor that reduces both the penetration of the fine particles) and realizes an improvement in mechanical strength of the gas selective combustion layer 54 and an improvement in detection performance of the gas sensitive layer 53. And it was set as the manufacturing method which implement | achieves such a thin film gas sensor.

  Next, another type of thin film gas sensor will be described. Compared to the previously described form (hereinafter referred to as the first form) thin film gas sensor, it differs in that only the high boiling point liquid is changed. In the first mode, water is used as the high boiling point liquid, whereas in this mode (hereinafter referred to as the second mode), the organic solvent contained in the gas selective combustion layer printing paste, that is, diethylene glycol monoethyl ether, is used as the high boiling point liquid. The point of adoption is different. Except for this, the structure and manufacturing method of the thin film gas sensor 10 having a large number of micropores, mesopores, and macropores described with reference to FIGS. 1 and 6 are the same, and redundant description is omitted.

Only the differences of the second embodiment will be described.
The high-boiling liquid is filled into the plurality of gaps and the plurality of pores of the gas sensitive membrane (filling step).
This filling step is divided into two steps. Specifically, a step in which the substrate formed up to the gas sensitive film is exposed for a certain period of time in an atmosphere higher than the saturated vapor pressure of the high boiling point liquid (first filling step), and then a step in which the substrate is immersed in the high boiling point liquid (first step). Two filling step). Specifically, the high boiling point liquid of this embodiment is diethylene glycol monoethyl ether.

First, the first filling step is performed. More specifically, the substrate (wafer) formed up to the porous gas sensing film (SnO ₂ film) is left in a closed container for 24 hours together with a beaker filled with diethylene glycol monoethyl ether. . Diethylene glycol monoethyl ether is about 200 ° C., and any temperature can be used as long as the temperature of the sealed container is 1 ° C. or more and 199 ° C. or less, but the relative humidity in the sealed container is the saturated vapor pressure of diethylene glycol monoethyl ether. Under such an atmosphere, the micropores in the pores and gaps of the gas sensing membrane (SnO ₂ membrane) and the mesopores having a relatively small diameter have a capillary condensing action, so as compared with the micropores as shown in FIG. The inside of the mesopore having a small target diameter is filled with diethylene glycol monoethyl ether (liquid).

Subsequently, the second filling step is performed. More specifically, the substrate (wafer) subjected to the first filling step is immersed (diluted with an organic solvent) for 60 minutes in diethylene glycol monoethyl ether which is a high boiling point liquid at room temperature. Then, as shown in FIG. 4, diethylene glycol monoethyl ether, which is a high boiling point liquid, reaches the inside of the relatively large mesopores and macropores and is filled with the high boiling point liquid 60. Then, the substrate (wafer) surface taken out from diethylene glycol monoethyl ether is blown with N ₂ gas to blow off the diethylene glycol monoethyl ether adhering to the surface. As shown in FIG. 4, the gas sensitive membrane after this is filled with a high-boiling liquid 60, which is diethylene glycol monoethyl ether, in most of the micropores, mesopores and macropores.

Subsequently, a gas selective combustion film is formed (gas selective combustion film forming step).
The gas selective combustion layer printing paste prepared in advance is applied directly above the gas sensitive film to the substrate having the gas sensitive film filled with diethylene glycol monoethyl ether which is a high boiling point liquid in the first and second filling processes. A gas selective combustion film is formed by screen printing to a thickness of 30 μm. As shown in FIG. 5, the gas selective combustion film covers the electrical insulating layer 4, the bonding layer 51, the pair of sensing electrode layers 52 and 52, and the gas sensitive film. This gas selective combustion layer printing paste is kneaded by adding the same weight of diethylene glycol monoethyl ether and 20 wt% of silica sol as a binder to γ-alumina (average particle diameter of 2 to 3 μm) to which 7.0 wt% of Pd is added. This is a paste.

Subsequently, the gas sensitive film and the gas selective combustion film are fired to form a gas sensitive layer and a gas selective combustion layer (firing step).
The substrate on which the gas sensitive film and the gas selective combustion film are formed is dried at room temperature and then baked at 500 ° C. for 1 hour. At this time, the gas sensitive membrane and the gas selective combustion membrane are heated to a temperature higher than the boiling point of the high-boiling liquid to evaporate the high-boiling liquid in the gaps and pores to form gaps and pores in the gas-sensitive membrane. Thus, the gas sensitive layer 53 and the gas selective combustion layer 54 as shown in FIG. 1 are formed. Diethylene glycol monoethyl ether becomes a vapor at about 200 ° C. or higher and passes through the pores and gaps of the porous gas-sensitive membrane and the porous gas-selective combustion membrane, and has no effect on the gas-sensitive layer 53 and the gas-selective combustion layer 54. Spatter without giving. The following is the same, and a duplicate description is omitted.

The thin film gas sensor of the present embodiment described above is different in that the organic solvent contained in the gas selective combustion layer printing paste, that is, diethylene glycol monoethyl ether, is used as the high boiling point liquid, but even in this place, the silica sol is contained as the binder. Even in the porous gas-sensitive layer 53 (SnO ₂ layer) covered by the gas selective combustion layer 54, the penetration of silica sol (silica colloid, SiO ₂ fine particles) in the pores and gaps is reduced. The thin film gas sensor achieves improved mechanical strength and improved detection performance of the gas sensitive layer. And it was set as the manufacturing method which implement | achieves such a thin film gas sensor.

Next, the characteristics of the thin film gas sensor previously produced as the first form and the second form will be shown. Here, the thin film gas sensor created in the first form (form in which water is adopted as the high boiling point liquid) is referred to as an element A. Further, a thin film gas sensor created in the second form (a form in which diethylene glycol monoethyl ether is adopted as the high boiling point liquid) is referred to as an element B. All treatments with diethylene glycol monoethyl ether were performed at room temperature. In addition, a thin film gas sensor of the prior art manufactured by a conventional method (SiO ₂ fine particles / SnO ₂ outermost surface is formed and interacts with moisture in the _air to promote generation of OH groups and condensation of moisture to promote R _air (in air The element C is a thin film gas sensor that is presumed to promote a decrease in resistance. These elements A, B, and C are subjected to a high-temperature and high-humidity test to examine changes in R _air (resistance in air). The results are shown in the following table.

Table 1 shows R _air (resistance in air) before and after energization for 30 days in high temperature and high humidity (60 ° C., 80% RH). In the element C according to the prior art, the resistance value is reduced by almost a half digit, but there is no change in the characteristics of the elements A and B with respect to the detection gas such as CH ₄ before and after the test. That is, it can be seen that there is no change in the elements A and B. In this way, a large number of micropores, mesopores, and macropores were formed by filling the gas-sensitive layer with a large number of micropores, mesopores, and macropores and then firing them together with the gas selective combustion layer. It can be a gas sensitive layer, and stable sensor characteristics can be obtained even when energized in high humidity.

The thin film gas sensor and the manufacturing method thereof according to the present invention have been described above. According to the present invention, the silica sol (silica colloid, SiO ₂ fine particles) component in the gas selective combustion film printed on the gas sensitive membrane is preliminarily filled in the pores and gaps of the gas sensitive membrane. It does not penetrate into the pores or gaps of the porous gas-sensitive membrane (SnO ₂ membrane) and remains only on the outermost surface of the gas selective combustion membrane. Therefore, silica sol (silica colloid, SiO ₂ fine particles) does not precipitate inside the pores of the porous gas sensing film (SnO ₂ film) even when heat-treated at a high temperature to burn the gas selective combustion film. At this time, there is no problem because the high boiling point liquid filling the pores and gaps is vaporized and scattered from the porous gas sensing film. The silica sol (silica colloid, SiO ₂ fine particle) component remaining on the outermost surface of the gas selective combustion film contributes to adhesion with the porous gas sensing film (SnO ₂ film). Silica sol (silica colloid, SiO ₂ fine particles) present at a high concentration on the surface is aggregated (not highly dispersed) by heat treatment and becomes relatively large silica particles, and therefore hardly contributes to generation of OH groups and aggregation of moisture.
According to the above, a thin film gas sensor having a gas selective combustion layer containing a silica sol having a good long-term reliability, which has good adhesive strength and does not change characteristics such as a reduction in R _air (resistance in air) even under high temperature and high humidity. be able to. Moreover, it can be set as the manufacturing method of such a thin film gas sensor.

1 is a detailed view of a gas sensitive layer and a gas selective combustion layer of a thin film gas sensor of the best mode for carrying out the present invention. It is explanatory drawing of a gas sensitive film formation process. It is explanatory drawing of a 1st filling process. It is explanatory drawing of a 2nd filling process. It is explanatory drawing of a gas selective combustion film formation process. It is a longitudinal cross-sectional view which shows the thin film gas sensor of a prior art schematically. It is explanatory drawing explaining the large amount adsorption | suction of the water | moisture content with respect to a silica sol. It is explanatory drawing explaining the large amount adsorption | suction of the water | moisture content with respect to a silica sol.

Explanation of symbols

10: thin film gas sensor 1: Si substrate 2: insulating support layer 21: thermally oxidized SiO ₂ layer 22: CVD-Si ₃ N ₄ layer 23: CVD-SiO ₂ layer 3: heater layer 4: electrical insulating layer 5: gas detection layer 51: Bonding layer 52: Sensing electrode layer 53: Gas sensitive layer (SnO ₂ layer)
531: Columnar crystals 532: Gaps 533: Pore 54: Gas selective combustion layer (Pd-supported Al ₂ O ₃ sintered material)
60: High boiling point liquid

Claims (10)

A Si substrate having a through hole;
A diaphragm-like heat insulating support layer stretched over the opening of the through hole;
A heater layer provided on the thermally insulating support layer;
An electrically insulating layer provided to cover the heat insulating support layer and the heater layer;
A pair of sensing electrode layers provided on the electrically insulating layer;
A gas sensitive layer provided on the electrically insulating layer so as to pass a pair of sensing electrode layers;
A gas selective combustion layer covering the gas sensitive layer;
With
The gas sensitive layer is a thin film gas sensor characterized in that a plurality of micropores, a plurality of mesopores and a plurality of macropores communicate with the outside world.   The gas sensitive layer is an aggregate of columnar crystals having a cross-sectional diameter of 10 nm to 100 nm, having a plurality of gaps of 5 nm to 50 nm between the columnar crystals, and having a plurality of pores on the surface and inside of the columnar crystals. The thin film gas sensor according to claim 1, wherein the thin film gas sensor is a layer including micropores, mesopores, and macropores in the plurality of gaps and the plurality of pores. The thin film gas sensor according to claim 1, wherein the gas sensitive layer is a layer formed of SnO ₂ (tin dioxide). The gas selective combustion layer is a layer made of an Al ₂ O ₃ (alumina) sintered material supporting Pd (palladium) or Pt (platinum) as a catalyst. The thin film gas sensor according to one item. It is a manufacturing method of the thin film gas sensor according to any one of claims 1 to 4,
Forming the gas sensitive layer and the gas selective combustion layer on a substrate;
A gas sensitive film forming step of forming a gas sensitive film on the electrical insulating layer;
A filling step of filling a plurality of gaps and a plurality of pores of the gas sensitive membrane with a high boiling point liquid;
A gas selective combustion film forming step of forming a gas selective combustion film so as to cover the gas sensitive film;
The gas sensitive membrane and the gas selective combustion membrane are heated above the boiling point of the high boiling point liquid to evaporate the high boiling point liquid in the gaps and pores to form gaps and pores in the gas sensitive membrane, and the gas sensitive membrane and gas A firing step of firing the selective combustion film to form a gas sensitive layer and a gas selective combustion layer;
A method of manufacturing a thin film gas sensor, comprising:   The filling step is a step of immersing the substrate in the high boiling point liquid after exposing the substrate formed up to the gas sensitive film in an atmosphere having a saturated vapor pressure or higher of the high boiling point liquid for a predetermined time. Item 6. A method for manufacturing a thin film gas sensor according to Item 5.   The gas selective combustion film forming step is a step of forming a gas selective combustion film having a predetermined shape by screen printing or the like on a gas sensitive film using a printing paste formed by mixing an organic solvent mainly composed of catalyst powder and silica sol binder. The method for manufacturing a thin film gas sensor according to claim 5, wherein the method is a thin film gas sensor. The filling step, the method of manufacturing a thin film gas sensor according to any one of claims 5 to 7, a high-boiling liquid is characterized by a H _{2 O} (water).   8. The method of manufacturing a thin film gas sensor according to claim 7, wherein the filling step is a step of using a high boiling point liquid as the same component as the organic solvent contained in the printing paste.   The method for producing a thin film gas sensor according to claim 9, wherein in the filling step, the high boiling point liquid is diethylene glycol monoethyl ether.