JP2002333426A - Gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To heighten the reliability of a gas sensor, and to realize power saving. SOLUTION: In this gas sensor, plural solid electrolyte coatings 6 equipped with a pair of electrodes are formed on a board equipped with a heating element through an insulating film, and porous oxidation catalysts 7 are provided on the surface of each one electrode 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a gas sensor mounted on a flammable gas alarm of carbon monoxide or the like used in ordinary households, and has an object to be applied to a battery-driven type having a high degree of freedom in installation. . Also, as a gas alarm,
The goal is to achieve high reliability and low power consumption.

[0002]

2. Description of the Related Art Gases to be detected from the viewpoint of safety and security in realizing comfortable living at home include methane and propane due to fuel gas leakage, and carbon monoxide due to incomplete combustion. Gas leak alarms for preventing gas leak accidents have become widespread because gas leak explosion accidents have increased as fuel gas demand has increased and housing has become more airtight. With the spread of gas leak alarms, gas leak explosion accidents are decreasing. Current gas leak alarms are powered by household AC power. It is desired that a gas leak alarm be driven by a battery having a superior degree of freedom in installation, rather than an AC power supply having a degree of freedom in installation. The sensors currently used for alarms are:
90% or more are of the semiconductor type, and the remaining several percent are of the catalytic combustion type.

On the other hand, as for carbon monoxide, no effective sensor has been proposed for the purpose of warning of incomplete combustion at home, and the number of accidents is not easily reduced. Therefore, there is a strong demand for a low power consumption type carbon monoxide gas detection sensor which is inexpensive, inexpensive, small and highly reliable, and can be driven by a battery.

As a conventionally proposed gas sensor, particularly a chemical sensor for detecting a flammable gas such as carbon monoxide, an electrode is provided which absorbs and oxidizes carbon monoxide in an electrolytic solution, and is proportional to the concentration of carbon monoxide. Method to detect the concentration of carbon monoxide from the current value to be applied (constant-potential electrolytic gas sensor), using a sintered body type such as an N-type semiconductor oxide sensitized by adding a trace metal element such as a noble metal, for example, tin oxide Then, a method of detecting gas by using the property that electric conductivity changes when these semiconductors come in contact with combustible gas (semiconductor type gas sensor), alumina is attached to a thin platinum wire of about 20 μm, A method of detecting a difference in heat generated when a combustible gas is brought into contact with this element to perform a catalytic oxidation reaction by using a pair of comparison elements of a supported element and a non-supported element. Burn gas sensor), and the like are known. For example, [Reference 1] Supervised by Toyoaki Omori: "Sensor Practical Encyclopedia": Fuji Techno System [Chapter 14 Basics of Gas Sensors (Masatoshi Haruta), P112-130 (1986)
Has a detailed description.

Further, a zirconia electrochemical cell is constituted,
An electromotive force-type solid electrolyte type carbon monoxide sensor that detects carbon monoxide by forming a platinum / alumina catalyst layer on one side of an electrode has also been proposed [eg, H.OKAMOTO, H.OBAYASI
AND T. KUDO, Solid State Ionics, 1, 319 (198
0)].

The principle of the solid electrolyte type carbon monoxide sensor is based on the fact that a kind of oxygen concentration cell can be formed on the catalyst layer side and the bare side electrode, and oxygen reaches the catalyst layer side electrode as it is. On the bare electrode, both oxygen and carbon monoxide reach, while carbon oxide does not reach.
This carbon monoxide reduces oxygen, an oxygen concentration cell is formed between both electrodes, and an electromotive force output appears.

[0007]

All of these chemical sensors have the following disadvantages. That is, even if a constant potential electrolytic gas sensor, a semiconductor type gas sensor, and a catalytic combustion type gas sensor in principle react indiscriminately to a reducing gas (combustible gas), even if various measures are taken, basically, carbon monoxide (CO ) Has the property of detecting hydrogen, alcohol, etc. That is, there is a disadvantage that the selectivity of CO is poor.

[0008] In addition, any of the sensors requires a temperature for operation and thus requires driving energy. For example, in the semiconductor type, basically, the operation at the measurement temperature at which the high-temperature operation and the low-temperature operation are repeated is repeated. The operation at the measurement temperature differs depending on the type of the target gas. At least 450, regardless of
Heating of about ° C is required. This results in a large energy consumption when a battery drive requiring power saving is intended.

In order to save power, the sensor is made thinner,
In the case of miniaturization and low power consumption, power consumption for heating the surrounding air provided with the sensor is large, and it is difficult to reduce power consumption. Although a method of reducing power consumption by performing a pulse-like operation or an intermittent operation has been proposed, at most one kind of gas sensor can be used at most within a range of an economical battery power supply. It is only capable of operating for about a year, and does not have the ability to have two or more gases for several years.

[0010] In addition, there is a problem in durability of the entire chemical sensor. That is, there is a problem that the sensitivity of the sensor decreases over time. This is due to the deterioration of the electrodes and catalysts, which play a central role in the chemical sensor, over time with the progress of the reaction. This deterioration is caused by the hydrocarbon-based reducing gas present in trace amounts in the general atmosphere. , The catalyst is reduced, or a sulfur-based compound or the like is strongly adsorbed on the electrode surface, thereby inhibiting the detection reaction of carbon monoxide.

[0011] The original demand for a gas sensor in the home is that the conventional gas leak alarm is a low power consumption type gas sensor which can be driven by a battery having a high degree of freedom in installation, and has a large number of malfunctions. There is a need for a gas sensor.

[0012]

In order to solve the above problems, a gas sensor according to the present invention comprises a substrate provided with a heating element and a plurality of solid electrolyte films provided with a pair of electrodes interposed on a substrate provided with an insulating film. Each of the electrode surfaces is provided with a porous oxidation catalyst.

The gas sensor according to the present invention has a configuration in which the size and thickness of the gas sensor are reduced for the purpose of realizing high reliability and low power consumption. As a means for reducing the size of the thin film, a semiconductor fine processing technology such as photolithography, electron beam evaporation, or sputtering is used. Further, in order to save power, a pulse driving means for operating the sensor in a very short time on the order of milliseconds is used. In addition, gas sensor elements manufactured using microfabrication technology, whether a single element or a plurality of elements, are basically subject to patterning problems in process, and have little effect on productivity and cost. I have. The basic idea is that one heating element is pulse-driven to operate a plurality of solid electrolyte gas sensor elements or the like at a time as a heat source for driving the sensor.

The operation of gas detection will be described below.
The energization of the heating element heats the solid electrolyte element to a temperature of 400 to 500 ° C. necessary for its operation.

Further, the porous oxidation catalyst formed on one electrode surface is activated. In this situation, when placed in an environment of air that does not contain a gas to be detected such as carbon monoxide, no electromotive force output is generated because the oxygen concentration reaching the interface between the electrode and the solid electrolyte is equivalent. On the other hand, in an environment of air that does not contain a gas to be detected, such as carbon monoxide, on the electrode provided with the porous oxidation catalyst, the gas to be detected, such as carbon monoxide, is oxidized by the porous oxidation catalyst and the electrode surface , The interface between the electrode and the solid electrolyte is at a high oxygen level, whereas the other electrode receives a gas to be detected such as carbon monoxide. On the electrode surface, oxygen is reduced by the gas to be detected such as carbon monoxide, and the interface between the electrode and the solid electrolyte has a low oxygen level. As a result, an electromotive force output related to the concentration of the detected gas such as carbon monoxide is generated. The same phenomenon occurs simultaneously on other solid electrolyte elements. If the electromotive force output of the solid electrolyte element is taken in at an appropriate timing of energization in the order of milliseconds, a plurality of electromotive force data can be obtained simultaneously. By supplying electricity in the order of milliseconds, heat energy for excessively heating the air around the substrate and the sensor is unnecessary, and power is saved.

Since reading of output data from a plurality of solid electrolyte elements can be sufficiently performed on the order of 100 microseconds, the output data is read out by one amplifier circuit by sequentially shifting the output data reading timing by a switch. Therefore, it is not necessary to provide a plurality of signal processing circuits.

When the catalyst, electrodes, etc. are changed among a plurality of solid electrolyte elements, the output value of each element differs depending on the type and concentration of the gas. Can be qualitatively determined and the concentration can be determined. About two kinds of mixed gas composition,
By giving the equation of the output pattern for the gas composition obtained in advance, the simultaneous equations can be solved and the gas composition can be accurately estimated. Thereby, even if it is a mixed gas of carbon monoxide and methane, it is possible to accurately obtain the carbon monoxide concentration and the methane concentration. With three types of mixed gases, the same can be achieved with three solid electrolyte output patterns.

Further, by repeating this pulse driving operation periodically, a power-saving and highly reliable battery-driven composite gas alarm can be realized.

Even when one kind of gas is generated, for example, when carbon monoxide gas is generated, carbon monoxide as a gas sensor is obtained by adding the electromotive force outputs generated by the plurality of solid electrolyte elements. Sensitivity to gas can be improved. In addition to the above-described sensitivity improvement, by comparing the electromotive force output values with each other, it is possible to judge an abnormality of a sensor related to a failure such as an abnormality at a zero point or a deterioration state of a catalyst, so that reliability is expected to be improved.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION In a first embodiment of the present invention, a plurality of solid electrolyte films having a pair of electrodes are formed on a substrate having a heating element via an insulating film, and each of the solid electrolyte films is formed on one side. The electrode surface is provided with a porous oxidation catalyst.

As the heating element, noble metals and metal oxides can be applied, but their volume resistivity is appropriate.
A platinum film that is stable in a high-temperature oxidizing atmosphere and has excellent chemical resistance is desirable. The platinum film can be formed by a dry process such as sputtering or electron beam evaporation and a wet process typified by electroless plating, but it is desirable to apply the dry process because of the ease of patterning. The patterning is performed by a method such as PVD under a metal mask, etching using a photolithography technique, or lift-off processing using a patterned aluminum deposition film instead of a metal mask. Depending on the combination with the base material, the film may be formed through a pre-base treatment of titanium or chromium.

Since the process is the same, a pattern as a resistance thermometer capable of detecting the temperature of the heating element is formed together with the patterning film formation of the heating element.
Using this, an operating temperature detection pattern for detecting room temperature and checking the stability of the temperature of the sensor can be formed and used.

As the substrate, many substrates can be used as long as they are heat-resistant insulating substrates. However, from the viewpoint of a power saving operation as a gas sensor, extra heat is applied to the substrate surface during a millisecond pulse driving operation. Any material can be used as long as the material does not transmit heat, withstands thermal shock during driving, and has a coefficient of thermal expansion close to that of the oxygen ion conductive solid electrolyte. Although different in thermal expansion coefficient, various ceramics such as silica glass, alumina, sapphire, crystallized glass, forsterite, cordierite, zirconia, and silicon nitride having a heat-shielding glaze layer can be applied.

The insulating film is selected from heat-resistant insulating materials in consideration of bonding with the base material or the glaze layer and a difference in thermal expansion coefficient, and is made of silica or alumina. From the viewpoint of preventing internal stress from occurring, the insulating film is desirably thin at a level at which insulation can be ensured. Usually, the range is from 1 μm to several μm. The insulating film is formed by PVD such as sputtering, or
It is desirable to use a dry process such as CVD.

The solid electrolyte membrane can be applied to any of the fluoride ion conductors and the proton conductors, mainly the oxygen ion conductor, so that the output of the oxygen concentration cell can be taken out. As the oxygen ion conductor, bismuth oxide-molybdenum oxide, cerium oxide-samarium oxide and the like have good properties in addition to stabilized zirconia and zirconia. Is desirable. Among the stabilized zirconia, ytterbium-based or the like has excellent conductivity, but from the viewpoint of forming a film by PVD, a yttria-stabilized type or a scandia-stabilized type is preferable.

The solid electrolyte film is formed into a plurality of islands of about 1 to 2 μm by PVD film forming method such as sputtering using the patterning method described in the section of the heating element.

As the electrode, silver, platinum, palladium, ruthenium, perovskite oxide and the like can be applied in terms of oxygen ion adsorption and mobility to the solid electrolyte.
Platinum and perovskite oxides are desirable from the viewpoints of heat resistance and film forming properties. In each case, a film is formed on the solid electrolyte surface by sputtering or the like using the patterning method described in the section of the heating element.

The porous oxidation catalyst is prepared by applying a paste obtained by dispersing an oxidation catalyst in a crystallized glass or a sol-gel inorganic binder compounded in consideration of a porous means to a predetermined portion by a method such as screen printing and baking. Form. As an oxidation catalyst,
Any of precious metals such as palladium, platinum, rhodium and ruthenium and oxides and composite oxides of transition metals such as manganese, iron, nickel, cobalt, copper and chromium can be applied. Operating temperature is about 400-50 in solid electrolyte part
Since the temperature is 0 ° C., the temperature of the porous catalyst portion is lower than that of the temperature, but the temperature is still lower than the temperature required for oxidation of carbon monoxide.
There is a sufficient temperature margin as compared with 00 to 250 ° C.

As described above, a plurality of solid electrolyte elements are formed on a substrate provided with a heating element, and when the heating element is pulsed, the plurality of solid electrolyte elements are in a drivable state. Can be detected and quantified. By adding a plurality of output values, an increase in sensitivity can be obtained. By calculating and determining an output pattern, deterioration of the porous oxidation catalyst and electrodes can be estimated.

In a second embodiment of the present invention, the plurality of solid electrolyte films include a second solid electrolyte film and a second solid electrolyte film, and a pair of electrodes on the first solid electrolyte film and a second solid electrolyte film. The thickness of the pair of electrodes of the solid electrolyte film is changed by at least 50% or more. In the operation of the solid electrolyte elements having different film thicknesses, generally, the sensitivity and the output increase as the film thickness decreases. When the film thickness is large, the sensitivity and output are small, but the durability is excellent. When the thickness of the pair of electrodes on the first solid electrolyte coating and the pair of electrodes on the second solid electrolyte coating are changed by at least 50% or more,
The deterioration state of the electrode can be determined by looking at the ratio between the zero point and the output of the first and second solid electrolyte elements. Thinner one,
That is, if the zero point with the higher sensitivity shifts to the plus side and the output also decreases, it is possible to correct the electrode deterioration by increasing the amplification factor of the added output value. The output level of the electrode whose film thickness has been increased by 50% or more based on the film thickness that can sufficiently secure both the sensitivity and reliability is reduced,
The stability of the properties is greatly increased. Therefore, if the amplification factor of the output signal of the sensor is increased based on the determination of the state of deterioration of the electrode, the sensitivity as a gas sensor can be apparently maintained at a constant value for a long time, and the electrode is temporarily deteriorated. However, extremely reliable operation, in which the apparent sensitivity of the sensor does not change, becomes possible. Such a method of changing the film thickness of the electrode can be realized by repeatedly performing sputtering while changing the pattern. The electrode forming method may be changed, such as sputtering and electron beam evaporation.

According to a third embodiment of the present invention, the plurality of solid electrolyte films comprise a first solid electrolyte film and a second solid electrolyte film, and a pair of electrodes on the first solid electrolyte film and a second solid electrolyte film. The pair of electrodes of the solid electrolyte film are formed using different materials. In the second embodiment, the thickness of the electrode is changed by using the same type of material, but in the present embodiment, the type of the electrode is changed. As the electrode, silver, platinum, palladium, ruthenium, or a perovskite oxide among many metal oxides can be used in terms of oxygen adsorption and mobility to the solid electrolyte. Further, these can be mixed and stably dispersed to be used as an electrode. It has good properties such as platinum and perovskite oxide from the viewpoint of heat stability. A porous oxidation catalyst coating formed on one electrode of the first solid electrolyte coating and a porous oxidation catalyst coating formed on one electrode of the second solid electrolyte coating, for example, using a platinum-based catalyst in common, The electrode of the solid electrolyte film is, for example, platinum, and the electrode of the second solid electrolyte film is, for example, La.
_{1-x Ce x Co (Au} ) output when the perovskite type oxide of O ₃ to the mixed gas of carbon monoxide and methane characteristics are different, the first solid electrolyte, exhibit greater sensitivity of carbon monoxide On the other hand, in the second solid electrolyte element, an output dominant to methane is obtained. When the electrode of the second solid electrolyte element is a LaMnO ₃ perovskite oxide electrode, the first solid electrolyte element outputs a sum of hydrogen and carbon monoxide against a mixed gas of hydrogen and carbon monoxide. On the other hand, in the second solid electrolyte element, an output in which carbon monoxide is dominant is obtained. Thus, by solving simultaneous equations relating to the output characteristics of both solid electrolyte elements, the respective concentrations of the mixed gas of hydrogen and carbon monoxide can be known.

In the case where the first electrode is kept platinum and the material of the second pair of electrodes is changed without the porous oxidation catalyst, the combination of the inverted output corresponding to the gas type is included. A unique sensor output characteristic is obtained. Also in this case, it is possible to estimate the gas type by comparing the output characteristics of the two solid electrolyte elements.

The fourth embodiment of the present invention relates to a porous catalyst provided on one electrode on a first solid electrolyte film and a porous oxidation catalyst provided on one electrode on a second solid electrolyte film. Are configured using different catalysts. The porous oxidation catalyst is
A paste in which an oxidation catalyst is dispersed in a crystallized glass or a sol-gel inorganic binder compounded in consideration of a porous means is applied to a predetermined place by a method such as screen printing to form the paste. As the oxidation catalyst, palladium, platinum, rhodium,
Both oxides and composite oxides of noble metals such as ruthenium and transition metals such as manganese, iron, nickel, cobalt, copper and chromium can be applied. The porous catalyst provided on one electrode on the first solid electrolyte film and the porous oxidation catalyst provided on one electrode on the second solid electrolyte film are formed by changing the type of the porous oxidation catalyst The zero point of the sensor is the same because the same electrode is used for both the first and second elements, but the output level changes depending on the gas type. By changing the first element such that the porous catalyst is based on a noble metal and the second element based on a transition metal oxide, it is possible to slightly change the concentration dependency of the output with respect to the gas type. In many cases, noble metal based catalysts are Langmuir-
This is a Hinschel Wood type reaction mechanism, in which oxygen and gas are both adsorbed on the catalyst surface and then react.Therefore, the reactivity at low concentration with the detection gas is high, so a relatively high output at low concentration is obtained. Although the output characteristic is obtained but conversely saturates on the high concentration side, the metal oxide catalyst is a primary reaction type for the detection gas and hardly saturates with respect to the concentration. Is obtained. By utilizing this, it is possible to extend the high sensitivity detection range of the gas to be detected. This is a good complement to both carbon monoxide, which requires high output characteristics at low concentrations of several tens of PPM level, and methane and isobutane, which require high concentration gas detection near the lower limit of explosion on the order of%. This is a favorable characteristic for This is equivalent when both are used in combination with one catalyst, but by using them separately, their uniqueness can be emphasized and extracted. In addition, noble metal catalysts and metal oxide catalysts have different behaviors against poisoning substances in the air, which is advantageous in terms of ensuring durability.

In a fifth embodiment of the present invention, a solid electrolyte element and a semiconductor element are provided on a substrate provided with a heating element via an insulating film, and the solid electrolyte element is a solid electrolyte film having a pair of electrodes. The above-mentioned coating having a porous catalyst disposed on one of the electrode surfaces is provided, and the semiconductor element is constituted by providing a comb-shaped electrode and an oxide semiconductor sensitive film. In this embodiment, the semiconductor element is driven simultaneously with the solid electrolyte element by using a heating element that is a common heat source, and the detection characteristics for a plurality of gas types are exhibited. The solid electrolyte element is activated by pulse current supply to the heating element, but the semiconductor element is also operated. The operation of the solid electrolyte element is the same as in the previous embodiment. The operation of the semiconductor element will be described. The material of the comb electrode is
Gold, platinum and the like can be applied, but platinum is desirable from the viewpoint of process versatility and heat stability. In addition, it is desirable to form a film by PVD from the viewpoint of pattern accuracy.

N-type semiconductor oxides such as zinc oxide, tin oxide, and indium oxide have a surface potential of oxygen lower than the Fermi level of these oxides in a high-temperature oxidizing atmosphere, so that oxygen adsorbs negative charges and electron Is trapped by oxygen, a space charge layer having a low electron concentration is formed on the oxide surface, and a high resistance state is established. However, when reducing gas is present, adsorbed oxygen is consumed by the reducing gas on the oxide surface, electrons trapped in oxygen are returned to the oxide, and the electron deficient layer disappears,
The element enters a low resistance state. This is used to detect the reducing gas. The detection sensitivity is further increased by using a sensitizer such as palladium, gold, or silver in combination with an N-type semiconductor oxide such as zinc oxide, tin oxide, or indium oxide. At a temperature of 400 to 500 ° C. necessary for driving the solid electrolyte, a semiconductor gas sensor element using an N-type semiconductor oxide such as zinc oxide, tin oxide, and indium oxide in combination with a sensitizer such as palladium, gold, and silver is Since it has the highest sensitivity to methane in the same temperature range, it is possible to detect carbon monoxide with the solid electrolyte element by pulse driving and simultaneously detect methane with the semiconductor gas sensor element. When the pulse drive to the heating element on the order of milliseconds is stopped, the temperature of the entire gas sensor element drops according to its heat capacity and the surrounding temperature environment. Utilizing this, it is also possible to detect isobutane having a maximum sensitivity at 300 to 350 ° C. and carbon monoxide having a maximum sensitivity at 100 to 150 ° C.
However, the detection of carbon monoxide by a semiconductor gas sensor has a low temperature range in which the sensitivity is maximum, so that there is a problem in that the risk of false reports of water vapor and various miscellaneous gases in a high-humidity environment increases. For this reason, conventionally, a semiconductor type carbon monoxide sensor has not been easily accepted. However, when used in combination with a solid electrolyte element that does not operate on water vapor at all as in this embodiment, a composite sensor can be successfully complemented.

In a sixth embodiment of the present invention, a porous catalyst is disposed on one electrode surface by a solid electrolyte film having a pair of electrodes on a substrate having a heating element via an insulating film. A coating and a comb-shaped electrode and an oxide semiconductor sensitive film are provided, and particularly, as the oxide semiconductor sensitive film, palladium, platinum, rhodium, ruthenium and at least one noble metal supported thereon, zinc oxide, tin oxide, It is constituted by using at least one kind of oxide thin film of indium oxide.

First, after forming a comb-shaped electrode by film forming means such as sputtering, one or more oxides selected from the group of zinc oxide, tin oxide and indium oxide are formed by sputtering, and the oxide film is formed. Palladium, platinum, on the surface
An oxide semiconductor element portion is manufactured by supporting at least one noble metal selected from the group consisting of rhodium and ruthenium. One or more oxides selected from the group consisting of zinc oxide, tin oxide, and indium oxide form a film in the range of 1 μm to several μm.
When the film formation speed is increased and the film thickness is increased, columnar crystals grow in the oxide semiconductor film or cracks are generated due to a difference in thermal expansion with the base material, but it is rather advantageous from the viewpoint of gas detection sensitivity. . One or more noble metals selected from the group of palladium, platinum, rhodium and ruthenium used as a sensitizer are impregnated from the surface using a noble metal salt solution, and thermally decomposed to be supported. The oxide semiconductor sensitive film thus formed has good detection sensitivity to gases such as methane and isobutane.

[0038]

FIG. 1 to FIG. 6 show an embodiment of the present invention.
This will be described with reference to FIG.

(Embodiment 1) FIG. 1 is a conceptual sectional view of a gas sensor according to an embodiment of the present invention. In FIG. 1, a plurality of solid electrolyte elements 4A, 4B, and 4C are provided on a base material 2 having a heating element 1 with an insulating film 3 interposed therebetween. Although FIG. 1 shows an example in which three elements are formed, any number of elements may be used as long as two or more elements are formed. Since it is formed by patterning in order from the lower layer to the upper layer by a thin film process or the like, even if there are a plurality of solid electrolyte elements, the processing time is almost the same as that of a single solid electrolyte element. Each solid electrolyte element has a configuration in which a pair of electrodes 5 is provided on a solid electrolyte 6, and a porous oxidation catalyst film 7 is provided on one of the pair of electrodes.

The heating element 1 is formed on a substrate 2 by patterning a resistor into a zigzag or the like shape.

The patterning method is as follows under a metal mask.
Various methods, such as a method for forming a thin film, a dry or wet etching process, and a lift-off process, which are usually used in a semiconductor lithography process, can be applied. By using a heating element mainly composed of platinum-based noble metal as the heating element and forming a pattern by a thin film forming method such as electron beam evaporation or sputtering, the temperature rise required when applied to a gas sensor And a good heating element with excellent reliability can be obtained. An insulating film 3 is formed on the main part of the heating element by the same thin film process as that of the heating element. On the insulating film 3, a thin film 6 of a solid electrolyte is formed by patterning. Examples of the solid electrolyte 6 include an oxygen ion conductor such as stabilized zirconia,
Any of a fluoride ion conductor and a proton conductor can be applied. As for the pair of electrodes 5 formed by patterning on the solid electrolyte, silver, platinum, palladium, ruthenium, perovskite oxide, and the like can be applied in terms of adsorption of oxygen ions and mobility to the solid electrolyte. Platinum and perovskite oxides are desirable from the viewpoints of heat resistance and film forming properties. In each case, a film is formed on the solid electrolyte surface by sputtering or the like using the patterning method described in the section of the heating element. Also, the porous oxidation catalyst film 7
Is sufficient if it has a property of oxidizing a gas to be detected when a gas to be detected such as carbon monoxide permeates between the gas and the heat-resistant porous body. A catalyst carrying an oxidation catalyst can be used. This is also formed by patterning by a thin film or thick film printing method or the like.

The plurality of solid electrolyte gas sensor elements 4A, 4B, and 4C thus manufactured are required to operate.
A temperature of 0 to 500 ° C. is provided by energizing and heating the heating element 1. Since the configuration of the gas sensor is made very small by the micromachining technology, the temperature of each of the elements 4A, 4B, and 4C becomes operable by energization at the millisecond level. The operation of the 4A element will be described. Solid electrolyte 6
On the electrode 5 formed on the electrode, air containing a gas to be detected such as carbon monoxide is applied to one of the electrodes, and the other electrode is coated with a gas such as carbon monoxide by the porous oxidation catalyst film 7. The air from which the detection gas has been removed reaches, and an oxygen concentration cell type electromotive force output is obtained between the two electrodes corresponding to the gas to be detected such as the concentration of carbon monoxide. Thereby, the concentration of the gas to be detected such as carbon monoxide can be detected.

Exactly the same operation can be performed in different solid electrolyte elements 4B and 4C, and the present gas sensor can simultaneously obtain a plurality of sensor outputs by operating a common heating element. By adding a plurality of sensor outputs as they are, the apparent sensor sensitivity can be increased. Further, in a plurality of solid electrolyte devices, by changing the types and conditions of electrodes and catalysts, the sensitivity of each solid electrolyte device with respect to the gas type is changed, thereby enabling simultaneous detection of a plurality of gas types. In addition, gas sensors that have a low sensitivity by combining a high-sensitivity sensor and a low-sensitivity sensor generally have excellent durability. Therefore, by calculating the output ratio of both gas sensors, deterioration of the sensor can be achieved. It is also possible to grasp information and perform sensitivity correction.
In this way, the reliability of the sensor can be increased. By adopting the configuration of the present embodiment, it is possible to overcome the problems of the conventional gas sensor, such as the problem of energy saving, the problem of false alarm, and the problem of fail-safe, which are the basic problems of the gas sensor.

(Embodiment 2) FIG. 2 is a conceptual sectional view of a main part of a gas sensor according to another embodiment of the present invention. FIG.
Shows the configuration of two types of solid electrolyte gas sensor elements of 4A and 4B. Although not shown in FIG. 2, each element in FIG. 2 is formed on a base material 2 provided with a heating element 1 via an insulating film 3. The first solid electrolyte element 4A includes a pair of electrodes 5A on a solid electrolyte 6A, and a porous oxidation catalyst film 7A on one of the electrodes. The second solid electrolyte element 4B includes a pair of electrodes 5B on a solid electrolyte 6B, and a porous oxidation catalyst film 7B on one of the electrodes. In the present embodiment, the difference between the first solid electrolyte element 4A and the second solid electrolyte element 4B is that the pair of electrodes on the first solid electrolyte coating and the pair of electrodes on the second solid electrolyte coating are different. The thickness is changed by at least 50% or more. The solid electrolyte coating and the porous oxidation catalyst coating of the other elements are the same. In view of the pattern, the porous oxidation catalysts of the first solid electrolyte element and the second solid charge element may be formed over both.

As in the first embodiment, the gas sensor of this embodiment can be manufactured by sequentially patterning and laminating a heating element to a porous oxidation catalyst on a substrate. For the electrode of the first solid electrolyte element and the electrode of the second solid electrolyte element, for example, by changing the film forming conditions such as the film forming time, electrodes having different film thicknesses, that is, electrodes having a film thickness different by 50% or more are formed. Make it. If a film thickness level capable of functioning as an electrode is realized, the characteristics as a gas sensor differ between an electrode having a smaller film thickness and an electrode having a film thickness more than twice as large. In the case of a thin electrode, the diffusion of oxygen is rapid and the electrode becomes relatively porous, so the oxygen adsorption is high, so the response and sensitivity of the gas sensor are high, but the sensitivity is relatively low. It becomes a gas sensor that is easily lowered. On the other hand, an electrode having a large film thickness is relatively inferior in responsiveness and sensitivity, but has extremely high durability. As a characteristic of the gas concentration of the output of the gas sensor with respect to the gas to be detected, the thin electrode sensor has a high output on the low concentration side, but has a tendency to saturate the output at the high concentration, but has a large output. On the electrode side, the output at a low concentration is small, but the characteristic is such that the output can be obtained at a high concentration. Thus, by using both of them in combination, the detection concentration range of the gas concentration can be expanded.

The solid-charged gas sensors having different electrode thicknesses for two types of mixed gases have different output characteristics depending on the gas type. It is known that the gas ratio is approximately 2: 1. Also, by preparing a calibration curve in advance, and solving the simultaneous equations, a mixed gas of carbon monoxide and hydrogen gas can be obtained. Thus, the respective gas concentrations can be estimated and calculated almost exactly. This is a method for detecting gas concentration, which could not be performed with a conventional single gas sensor.

Regarding the durability, the sensitivity of a gas sensor element having a small film thickness is apt to be reduced due to the high sensitivity, whereas the sensitivity of the electrode having a large film thickness is poor, but the gas sensor element over time has a poor sensitivity. It has excellent stability and has tough characteristics that the sensitivity is not easily reduced. For example, by obtaining the ratio of the sensor outputs of both the solid electrolyte gas sensor elements, it is possible to evaluate a decrease in the sensitivity of a highly sensitive sensor and correct the sensor output value. As a result, the sensitivity and durability of the gas sensor can be well balanced. As described above, with the configuration as in the present embodiment, with a single gas sensor, a highly reliable and safe operation can be continued even with a decrease in sensitivity that could not be achieved with the conventional technology. .

In this embodiment, two solid electrolyte elements have been described, but the same effect can be expected when three elements are used.

As described above, according to the configuration of this embodiment, it is possible to improve the problem of reliability deterioration due to deterioration with time,
It enables simultaneous detection of mixed gases, and overcomes several problems that were impossible with conventional gas sensors.
Further, since the micromachining process is used, these functions can be provided at extremely low cost.

(Embodiment 3) FIG. 3 is a conceptual sectional view of a main part of a gas sensor according to another embodiment of the present invention.

FIG. 3 shows a part of the configuration of a gas sensor provided with two types of solid electrolyte gas sensor elements 4A and 4C. Although not shown in FIG. 3, each element of FIG. 3 is formed on a base material 2 provided with a heating element 1 via an insulating film 3. The first solid electrolyte element 4A includes a solid electrolyte 6A
A pair of electrodes 5A is provided thereon, and a porous oxidation catalyst film 7A is provided on one of the electrodes. The second solid electrolyte element 4C includes a pair of electrodes 5C on a solid electrolyte 6C, and a porous oxidation catalyst film 7C on one of the electrodes. In the present embodiment, the difference between the first solid electrolyte element 4A and the second solid electrolyte element 4C is that the pair of electrodes on the first solid electrolyte film and the pair of electrodes on the second solid electrolyte film are different. It is formed by changing the material. The solid electrolyte coating and the porous oxidation catalyst coating of the other elements are the same.

Since the materials of the electrodes of the first solid-state charge element and the second solid-state electrolyte element are different, both sensors have completely different characteristics as gas sensors.

The process of the gas sensor of this embodiment is also as follows.
Although one electrode forming step is added in the process, there is almost no difference even if one step is added in the entire micromachining process for manufacturing the gas sensor. In view of the pattern, the porous oxidation catalysts of the first solid electrolyte element and the second solid charge element may be formed over both.

For two types of solid electrolyte elements, when the gas to be detected is a mixed gas of two types, the sensor output characteristics when the gas concentration of the first solid electrolyte element is changed and the second solid electrolyte element And have completely different characteristics,
By solving the simultaneous equations by creating a calibration curve in advance,
The composition can be inferred. This is because the characteristic composition is possible and the gas composition can be estimated more accurately than in the case of the same electrode of Example 2 in which the film thickness is changed by 50% or more. For example, if the electrodes are changed from a noble metal type to a metal oxide type, gas adsorption characteristics, oxygen transfer characteristics, catalytic oxidation characteristics, etc. will significantly change between the two electrodes. This is advantageous because a large difference in selectivity for the gas type can be realized. Further, even if the sensitivity of the electrode of one of the solid electrolyte elements is slightly inferior, by using a material having extremely high durability stability, the correction operation for the decrease in sensitivity described in the second embodiment can be similarly performed. For example, platinum alloyed with rhodium is an example. Compared with a platinum electrode, the sensitivity decrease due to heat sintering when operated continuously is extremely small.

As described above, according to the configuration of this embodiment, it is possible to improve the problem of the decrease in reliability due to the deterioration over time, to enable the simultaneous detection of the mixed gas, and to achieve the conventional gas sensor. Can overcome various issues. Further, since the micromachining process is used, these functions can be provided at extremely low cost.

(Embodiment 4) FIG. 4 is a conceptual sectional view of a main part of a gas sensor according to another embodiment of the present invention.

FIG. 4 shows a part of the configuration of a gas sensor provided with two types of solid electrolyte gas sensor elements of 4A and 4D. Although not shown in FIG. 4, each element in FIG. 4 is formed on a base material 2 provided with a heating element 1 via an insulating film 3. The first solid electrolyte element 4A includes a solid electrolyte 6A
A pair of electrodes 5A is provided thereon, and a porous oxidation catalyst film 7A is provided on one of the electrodes. The second solid electrolyte element 4D includes a pair of electrodes 5D on a solid electrolyte 6D, and a porous oxidation catalyst film 7D on one of the electrodes. In the present embodiment, the difference between the first solid electrolyte element 4A and the second solid electrolyte element 4D is the difference between the first solid electrolyte element 4A and the second solid electrolyte element 4D.
It is formed by changing the porous oxidation catalyst film. The porous oxidation catalyst coatings 4A and 4B include the type of catalyst,
By changing the binder, the porous means, the film forming means, the film forming method, and the like, a porous oxidation catalyst film having different characteristics can be obtained. Important characteristics as a porous oxidation catalyst film are the oxidation activity of gas and the diffusion characteristics of oxygen. These have different characteristics by changing the type, thickness, porosity, etc. of the catalyst. As the catalyst, noble metals such as platinum, palladium, and rhodium have different characteristics from transition metal oxides such as iron, manganese, copper, nickel, and cobalt. For example,
Transition metal oxide or composite oxide catalysts often have selectively good oxidation activity for hydrocarbon oxidation. In this case, even if the sensitivity is low for carbon monoxide, the characteristics have good sensitivity for hydrocarbons. Also zinc oxide,
Oxides such as indium oxide and tin oxide also often have special selectivity to gas in combination with precious metals. Further, even with the same porous oxidation catalyst film, the oxidation characteristics with respect to gas species are different by changing the film thickness. With the porous catalyst side gas concentration, oxygen / electrode / solid electrolyte / electrode / gas concentration, and oxygen concentration cell configuration, changing the porous oxidation catalyst results in different gas sensor output characteristics for different gas types. By changing the porous oxidation catalyst in this way, a unique sensor sensitivity is obtained for the composite gas, and thus two equations of output characteristics are obtained.
When the type of coexisting gas is clear, the composition ratio can be accurately estimated using the output characteristics of the two solid electrolyte elements. Further, by forming a different porous catalyst film on an electrode having no porous catalyst, gas sensors having different output characteristics can be formed and can be utilized.

Since the micromachining process is used as a method for manufacturing the gas sensor, the above functions can be provided at extremely low cost.

(Embodiment 5) FIG. 5 is a conceptual sectional view of a main part of a gas sensor according to another embodiment of the present invention.

FIG. 5 shows a solid electrolyte element 4 and a semiconductor element 10 on a substrate 2 provided with a heating element 1 via an insulating film 3.
Are formed. That is, the solid electrolyte element 4 includes the pair of electrodes 5 on the solid electrolyte coating 6 via the insulating film 3, and the porous oxidation catalyst coating 7 on one of the electrodes 5. On the other hand, the semiconductor element 10 includes the oxide semiconductor sensitive film 9 on the comb-shaped electrode 8 via the insulating film 3.
The operation of the solid electrolyte element 4 heated to a temperature environment of 400 to 500 ° C. by the pulsed power of the heating element is the same as that of the previous embodiment. That is, when the gas to be detected exists, an oxygen concentration cell is formed, and an electromotive force output according to the concentration of the gas to be detected is obtained between the pair of electrodes 5.

On the other hand, in the oxide semiconductor sensitive film formed on the comb-shaped electrode 8, the electrons of the oxide semiconductor are trapped by the oxygen adsorbed by the negative charge and the electron concentration of A low space charge layer is formed and the device goes into a high resistance state. Gas to be detected (reducing gas)
Is present, the adsorbed oxygen is consumed by the combustion reaction with the gas to be detected, the electrons trapped by oxygen are returned to the oxide semiconductor, the electron deficient layer disappears, and the element enters a low resistance state. Thus, the resistance value of the oxide semiconductor sensitive film changes according to the presence of the gas to be detected. By tracking the resistance value of the comb-shaped electrode, a change in resistance value due to the presence of the gas to be detected can be detected. The temperature at which the sensitivity is maximized differs depending on the type of the gas to be detected depending on the material configuration of the oxide semiconductor sensitive film. For example, generally for methane, 400 to 50
It is known that a high sensitivity is obtained at 0 ° C, 300-400 ° C for isobutane, and 100-200 ° C for carbon monoxide. The oxide semiconductor element is heated to a temperature of 400 to 500 ° C. and changes to a high resistance state by pulse current supply to the heating element of this embodiment. And equilibrate. If the temperature at which the resistance value between the comb-shaped electrodes is detected is set to a temperature at which the sensitivity of the gas to be detected is maximized, the target gas to be detected can be detected with high sensitivity.

By combining the solid electrolyte element formed on the insulating film and the oxide semiconductor element in this manner, simultaneous detection of a plurality of gas types becomes possible. By combining the features of the solid electrolyte element and the features of the oxide semiconductor element, the advantages of both can be effectively utilized while complementing the weak points. By preparing a regression equation for the mixed gas in advance, it is possible to calculate the composition of the mixed gas by combining these two elements and solving the simultaneous equations, as in the previous embodiment. It is. There is also a method of detecting a plurality of gases using the difference in sensitivity to temperature with only the oxide semiconductor element, but in this case, excessive selectivity occurs, and the detection of carbon monoxide is increased. 5 for
It is necessary to set the temperature to a low temperature such as 0 to 100 ° C., which may cause a false report due to miscellaneous gases such as alcohol and a risk of a false report due to water vapor. On the other hand, the configuration of the present embodiment is operated on the high temperature side, and therefore, there is almost no risk of such false alarm.

The process labor for manufacturing the gas sensor of this embodiment is almost the same as the case where one or a plurality of solid electrolyte elements are arranged. Thus, an inexpensive and highly reliable gas sensor can be realized.

(Embodiment 6) FIG. 6 is a conceptual sectional view showing a principal part of an oxide semiconductor sensitive film of a gas sensor according to another embodiment of the present invention. In FIG. 6, the coating fragments 9 are formed to include pores 13 of voids through which gas diffuses and carry one or more noble metals 11 selected from the group of palladium, platinum, rhodium, and ruthenium. It is formed as a thin film containing at least one oxide 12 selected from the group consisting of zinc oxide, tin oxide, and indium oxide. Zinc oxide,
At least one oxide selected from the group consisting of tin oxide and indium oxide has properties as an N-type semiconductor oxide.
At least one noble metal selected from the group consisting of palladium, platinum, rhodium, and ruthenium has active d-electrons, adsorbs gas species in a molecular form, and changes the electronic state of the semiconductor oxide. Thereby, the gas species is spilled over to increase the reactivity of the N-type semiconductor oxide with the adsorbed oxygen, or to increase the resistance change accompanying the reduction reaction with the gas, thereby achieving a sensitizing effect.

Thus, the gas to be detected can be effectively detected. In addition, the film is formed by zinc oxide, tin oxide,
A thin film of one or more oxides selected from the group of indium oxide is formed. When a thin film is formed at a level of μm or more, a columnar crystal film grows, so that pores of voids are formed well. A solution containing at least one noble metal selected from the group consisting of palladium, platinum, rhodium, and ruthenium on a thin film of at least one oxide selected from the group consisting of zinc oxide, tin oxide, and indium oxide. , A part of one or more oxide thin films selected from the group consisting of zinc oxide, tin oxide, and indium oxide dissolves, and voids are effectively formed. One or more oxide thin films selected from the group of zinc oxide, tin oxide, and indium oxide formed by a thin film process were prepared by sintering oxide powder or thermally decomposing metal salts. It is much finer than an oxide and has excellent activity as an oxide semiconductor. Thus, a highly active oxide semiconductor sensitive film is formed. In terms of process, the gas sensor is manufactured by a consistent thin film process technology, so that the characteristics are stable, the reliability is high, and the gas sensor can be manufactured at low cost.

The results of experiments relating to the effects of the present invention are described below.

(Prototype sensor 1) A 3 mm square quartz substrate having a thickness of 0.5 mm was used as a substrate, and a 0.5 μm thick film having a film thickness of 0.5 μm and a central portion of about 0.5 mm square was formed thereon. A platinum resistance film having a resistance value of 20 Ω was formed by patterning the region, and a silica coating having a thickness of 2 μm was formed on the surface of the platinum resistance film by sputtering in a region of about 1 mm square as an insulating film. In this state, heat aging was performed at 1000 ° C. for 2 hours to stabilize the coating. As a result of aging, the resistance value was about 10Ω. Furthermore, the central portion is spaced apart by 100 μm in a portion corresponding to the heater film on the above, and 0.2 mm × 0.5 m
m Two solid electrolyte coating patterns were formed. That is,
The solid electrolyte was formed by sputtering a yttria-stabilized zirconia (8Y product), which is an oxygen ion conductor, to a thickness of about 2 μm with the above dimensions. Further, a pair of electrodes having a thickness of 0.5 μm and dimensions of 100 μm × 50 μm were formed on the respective sputtering films by sputtering in the same manner, and then 700
Aged at 1 ° C. for 1 hour to stabilize the coating. For each solid electrolyte element, a 150 μm × 70 μm porous oxidation catalyst film was formed on one electrode of the element using a γ-alumina sol-based paste containing 1 wt% each of platinum and palladium with a fired film thickness of about 10 μm. A platinum lead wire was joined to this and welded to a nickel pin to obtain a gas sensor.

(Trial sensor 2) Using the same substrate as above, two solid electrolyte coating patterns were formed in the same procedure as the prototype element 1, and the electrode film had the same pattern, but one of the film thicknesses Is formed with a thickness of 0.5 μm and the other layer with a thickness of 1.2 μm, similarly to the element 1.
A gas sensor was manufactured in the same configuration as the element 1.

(Prototype Sensor 3) Using the same substrate as above, two solid electrolyte coating patterns were prepared in the same procedure as the prototype element 1, and the electrode films were also the same pattern. The film thickness of both is 0.5μ
The electrode of one element was a platinum electrode, and the electrode of the other element was formed by patterning a LaCoO ₃ perovskite oxide electrode by sputtering. The other processes were the same as in the case of the element 1 to produce a gas sensor.

(Prototype Sensor 4) Using the same substrate as above, two solid electrolyte coating patterns were prepared in the same procedure as in Prototype Element 1, and up to the electrode film in the same procedure as in Prototype Element 1. After the formation, for one of the solid electrolyte elements, about 150 μm × 70 μm with a fired film thickness of about 10 μm using a γ-alumina sol-based paste containing 1 wt% each of platinum and palladium on one of the electrodes. A porous oxidation catalyst film is formed, and for the other element,
Using a γ-alumina sol-based paste containing 5 wt% of LaCoO _3, with a fired film thickness of about 10 μm, 150 μm × 70 μm
m porous oxidation catalyst film was formed. A platinum lead wire was joined to this and welded to a nickel pin to obtain a gas sensor.

(Prototype element 5) The same base material as described above was used, and the procedure was the same as that of Prototype element 1. However, only one solid electrolyte membrane, a pair of 0.5 μm-thick platinum electrodes and a porous An oxidation catalyst was formed to form an element. On the other hand, a platinum comb-shaped electrode having a thickness of 0.5 μm was formed in an area of 0.2 mm × 0.5 mm, and about 2 μm was formed by sputtering.
Then, a tin oxide film was formed with a film thickness of, and a gas sensor having a structure in which 0.5% by weight of palladium was supported on the surface was produced.

Each of the above sensor prototypes was installed in a flow-through test apparatus, and a test gas was flowed under atmospheric conditions and energized for 10 milliseconds once every 25 seconds to control the operating temperature to 450 ° C. Table 1 shows the results of evaluating the output characteristics of the sensor by measuring the average output value for 100 microseconds after 9.9 milliseconds. Of each of the prototype gas sensors, the electromotive force output was measured as it was for the solid electrolyte element, and the resistance change was measured for the oxide semiconductor element by voltage conversion. In the case of oxide semiconductor elements, the same timing is used for measurement of methane, and the same timing is used for isobutane.
It was measured when cooled to 50 ° C.

(Prototype Sensor 1) The output of the prototype sensor 1 was evaluated by passing 500 ppm of carbon monoxide, and the output was evaluated as 20.5 mV for the element 1 and 23.5 mV for the element 2.
Was obtained. When this is added, the output becomes 44 mV, and an extremely sensitive sensor output can be obtained.

(Prototype Sensor 2) Regarding the prototype sensor 2,
Similarly, the output was evaluated at an initial stage by passing 500 ppm of carbon monoxide, and the output was 19.6 mV in the element 1 and 5.3 mV in the element 2. Next, 100pp
After a similar test was performed after 100 m of sulfur dioxide gas was passed, the output of the device 1 was reduced to 12.2 mV, but the output of the device 2 was not changed. By using the ratio of the sensor output of the element 2 and the sensor output of the element 2 to reduce the output of the element 1 and then to output an alarm signal, even if the sensitive element has a reduced sensitivity, this can be corrected. Can be.

(Prototype Sensor 3) With respect to the prototype sensor 3,
In test 1, 500 ppm of carbon monoxide was aerated alone.
In Test 2, 250 ppm of hydrogen was used alone, and in Test 3, the mixed gas of both gases was ventilated.

[0076]

[Table 1]

Although the output is not necessarily additive, Test 3
Since the element 2 has a high selectivity for carbon monoxide, the output of the element 2 indicates that carbon monoxide is almost 50%.
0 ppm, and from the output of element 1,
By calculating based on the regression equation, it can be estimated that 250 ppm of hydrogen is contained. Although the element 2 happened to show extremely excellent selectivity, even if it is not an element having high selectivity like the element 2, the simultaneous calculation based on the respective regression output equations can be used to calculate the composition. Can be guessed.

(Prototype Sensor 4) Regarding the prototype sensor 4,
In test 4, 500 ppm of carbon monoxide was aerated alone,
In Test 5, methane was evaluated by 2,000 ppm alone, and in Test 6, the mixed gas of both was ventilated.

[0079]

[Table 2]

Methane is a gas that is difficult to oxidize. The methane is a platinum group catalyst of the element 1 and a perovskite-based composite oxide catalyst of the element 2, and its concentration, dispersibility, matching with the carrier, etc. are also concerned. It is considered that No. 1 was a catalyst having remarkable oxidizing property of carbon monoxide and element 2 was a catalyst having remarkable oxidizing property of methane, and the difference appears in the sensor output. Also in this case, the composition of the element 1 and the element 2 can be estimated using the difference in the output characteristics with respect to the mixed gas of carbon monoxide and methane, similarly to the prototype sensor 4.

(Prototype Sensor 5) Regarding the prototype sensor 5,
The solid electrolyte element output about 24 mV with respect to 500 ppm of carbon monoxide. On the other hand, on the side of the oxide semiconductor element, a change in resistance value of about 80 times with respect to 2000 ppm of methane with respect to methane. 2000ppm
Also showed about 115-fold change in resistance. For the mixed gas of Test 6, the device 1
The element 2 showed an output of mV, and the element 2 showed a change in resistance value of 85 times. This is probably because the element 2 has a little sensitivity to carbon monoxide. Thus, the composition of the mixed gas can be detected.

[0082]

The gas sensor of the present invention has the following effects.

(1) By adding the sensor outputs of a plurality of elements to the gas to be detected, a large detection sensitivity can be obtained, and highly reliable gas detection can be performed.

(2) A gas sensor can be manufactured inexpensively by using a micro-machining technique applied in the semiconductor industry or the like in terms of process, with excellent productivity. Further, since the sensor is formed of a small thin film, remarkable power saving can be expected as compared with the related art. As a result, a battery-driven composite gas sensor having a high degree of freedom in installation as a gas alarm can be realized.

(3) This is a major problem of the conventional gas sensor. To compensate for the problem of output drop due to deterioration of the sensor function part after long-term use, that is, the problem of fail-safe operation, correct the drop in sensitivity of high-sensitivity sensors based on the characteristics of sensors with stable characteristics. Thus, it is possible to substantially avoid a decrease in sensitivity during long-term use.

(4) It is possible to estimate and detect the composition of a coexisting gas of carbon monoxide and hydrogen, which is difficult to separate. Can be detected.

As described above, as the gas sensor, a highly practical sensor which largely solves the problems of the conventional chemical sensor can be obtained.

[Brief description of the drawings]

FIG. 1 is a conceptual sectional view of a gas sensor according to a first embodiment of the present invention.

FIG. 2 is a conceptual sectional view of a gas sensor according to a second embodiment of the present invention.

FIG. 3 is a conceptual sectional view of a gas sensor according to a third embodiment of the present invention.

FIG. 4 is a conceptual sectional view of a gas sensor according to a fourth embodiment of the present invention.

FIG. 5 is a conceptual sectional view of a gas sensor according to a fifth embodiment of the present invention.

FIG. 6 is a conceptual sectional view of a main part of a gas sensor according to a sixth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating element 2 Substrate 3 Insulating film 4A, 4B, 4C Solid electrolyte element 5 Electrode 6 Solid electrolyte 7 Porous oxidation catalyst film

Continuing on the front page (72) Inventor Takashi Niwa 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Person Takahiro Umeda 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture (72) Inside the Matsushita Electric Industrial Co., Ltd. 1006 Kadoma, Matsushita Electric Industrial Co., Ltd. FB04 FE15 FE29 FE31 FE33 FE34 FE39 FE48 FE49

Claims (6)

[Claims] 1. A gas sensor comprising: a plurality of solid electrolyte films provided with a pair of electrodes formed on a substrate provided with a heating element via an insulating film; and a porous oxidation catalyst provided on one of the electrode surfaces. 2. A plurality of solid electrolyte membranes comprising a first solid electrolyte membrane and a second solid electrolyte membrane, a pair of electrodes on the first solid electrolyte membrane and a pair of electrodes of the second solid electrolyte membrane. 2. The gas sensor according to claim 1, wherein the film thickness is changed by at least 50% or more. 3. A plurality of solid electrolyte films comprising a first solid electrolyte film and a second solid electrolyte film, wherein a pair of electrodes on the first solid electrolyte film and a pair of electrodes of the second solid electrolyte film. 2. The gas sensor according to claim 1, wherein said gas sensor is made of a different material. 4. A plurality of solid electrolyte membranes comprising a first solid electrolyte membrane and a second solid electrolyte membrane, wherein a porous catalyst provided on one electrode on the first solid electrolyte membrane and a second solid electrolyte membrane are provided. The gas sensor according to claim 1, wherein a catalyst different from the porous oxidation catalyst provided on one electrode on the electrolyte coating is used. 5. A solid electrolyte element and a semiconductor element are provided on a substrate provided with a heating element via an insulating film, and the solid electrolyte element is a solid electrolyte film having a pair of electrodes and a porous catalyst is provided on one electrode surface. A gas sensor provided with a comb-shaped electrode and an oxide semiconductor sensitive film as a semiconductor element. 6. An oxide semiconductor sensitive film using at least one oxide thin film of zinc oxide, tin oxide and indium oxide carrying at least one noble metal of palladium, platinum, rhodium and ruthenium. The gas sensor according to claim 5, wherein