JP2002350391A - Gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor capable of being used stably for a long time, the electrode of which is surely connected even in the case the sensor is a gas sensor of solid electrolyte type used at a high temperature. SOLUTION: Lead electrodes 17, 18 of a sensing element 10 and an electrode terminal of a base body 19 are connected by a contacting member 23, and the variation of resistance caused by the diffusion of metal at the connection region and the deterioration of the bond strength are prevented, and thereby the gas sensor capable of being used stably for a long time is obtained. The contacting member 23 is integrally formed on a cover body 24, and adsorbent 26 and a volatile material 27 are disposed on an aperture of the cover body 24, and disturbing gas, toxic gas and moisture are thus removed using a simple structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining lead wires of a gas sensor for detecting gas leakage from gas-fired equipment, carbon monoxide generated by incomplete combustion of indoor-fired equipment, and various toxic gases and odors. It is about.

[0002]

2. Description of the Related Art There are various types and shapes of conventional gas sensors, one of which uses a solid electrolyte as shown in FIG. 3 as an example. In FIG. 3, reference numeral 1 denotes an insulator made of a ceramic plate such as alumina, and a heater 2 is set on the back surface. A solid electrolyte 3 is provided on the insulating plate 1 and has a pair of platinum electrodes 4a and 4b formed on the upper surface. Reference numeral 5 denotes a porous body having a large number of minute air holes of about 10 to 100 degrees inside. An oxidation catalyst 6 is provided on the porous body 5 at a position corresponding to one platinum electrode 4a.
Reference numeral 7 denotes a sealing material for integrally fixing the insulating plate 1, the solid electrolyte 3, and the porous body 5, and for sealing a gap between the solid electrolyte 3 and the porous body 5, and fixing the three members on the outer periphery thereof. Reference numeral 8 denotes a lead wire, which is joined to the electrodes 4a and 4b and the heater 2 with a conductive paste.

[0003] In general, gas sensors use carbon monoxide, methane,
Sensitive to propane, hydrogen, odor, etc., it is used for applications such as gas leak alarms, CO alarms, and odor sensors. The solid electrolyte type sensor shown in FIG. 3 detects gas based on the following principle. In the following description, the case where the detection gas is carbon monoxide (hereinafter referred to as CO) will be described. In FIG. 7, power is supplied from a power supply (not shown) to the heater 2 to bring the solid electrolyte 3 to a predetermined temperature (400 ° C. to 500 ° C.).
(° C.), electrons are transferred at the interface between the electrode 4, the solid electrolyte 2, and the air, and oxygen ions are generated. Here, when CO is present, C 4 is present at the electrode 4 ′ on which the catalyst 6 is mounted.
O is oxidized by the catalyst 6, and CO does not reach the electrode 4 '. In the other electrode 4, CO is CO on the surface of the electrode 4.
It is oxidized to 2. As a result, a difference occurs in the electrode reactions between the two electrodes, the equilibrium of oxygen ions is disrupted, and a potential difference occurs between the two electrodes. The potential difference is led to a detection circuit (not shown) by the lead wire 8, and the CO concentration can be detected.

[0004]

In recent years, there has been a remarkable trend toward miniaturization and power saving of gas sensors, which has spurred development for battery driving. However, in the above-mentioned conventional method, the insulator 1, the solid electrolyte 3, and the porous body 5 are plate-shaped, and several hundred mW to several W of electric power are required to heat them to a predetermined temperature. As a countermeasure, if a semiconductor process technology is used, it is possible to form a gas-sensitive film in a region of, for example, 1 mm square or less, thereby achieving miniaturization and power saving. In the case of joining the lead wires, the conventional joining method using a conductive paste requires a large joining area, and cannot cope with the problem because the heat dissipation area becomes large. It is a well-known fact that gold wire bonding is widely used in semiconductor manufacturing processes as a method for joining lead wires.However, wire bonding is limited to gold wire or aluminum wire, and it is possible to use a platinum electrode or platinum heater on a platinum heater. Is difficult to join directly. There is also a method of forming a thick gold film on a part of a platinum electrode or heater and bonding a gold wire to it.However, in a sensor operated at high temperature, gold diffuses into platinum and the resistance value changes. In some cases, the joining strength was weakened. In addition, the aluminum wire has a low melting point and cannot be used in a high-temperature atmosphere, and in addition, has a problem that an oxide film is formed and the resistance value changes. In addition, gas sensors, especially in a home environment, contain various gases generated from combustion equipment, gases other than for detection purposes such as housework, cooking, cosmetics, insecticides, and gases that are likely to harm the sensor. Must be able to be used stably for a long time even in the presence of. An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide a gas sensor in which a lead electrode and an electrode terminal are securely joined and can be used stably for a long period of time.

[0005]

According to the present invention, there is provided a gas sensor comprising: a heater formed on a substrate; a sensitive film formed on the heater via an insulating film; A detection electrode formed on a sensitive film, a sensor element including a lead electrode formed by extending the detection electrode and the heater on the substrate, a base body for housing the sensor element, and a base body for storing the sensor element. It is configured to include the provided electrode terminal, a contact member for bringing the lead electrode and the electrode terminal into contact with each other to conduct the current, and a lid covering an upper portion of the base body.

Accordingly, the lead electrode and the electrode terminal of the sensor element are physically joined to each other by the contact member so as to conduct, so that even if the lead electrode, the electrode terminal and the contact member are made of different materials, diffusion between different metals is performed. Since the resistance value does not change and the heater resistance is always kept constant, the gas sensor can be used stably for a long period of time.

[0007]

2. A gas sensor according to claim 1, wherein the heater is formed on a substrate, a sensitive film is formed on the heater via an insulating film, and a detection electrode is formed on the sensitive film. A sensor element including a lead electrode formed by extending from the detection electrode and the heater on the substrate, a base body for housing the sensor element, an electrode terminal provided on the base body, and the lead By having a contact member for bringing an electrode into contact with the electrode terminal to conduct, and a lid covering the upper part of the base body, the lead electrode of the sensor element and the electrode terminal are physically joined by the contact member to conduct electricity. Therefore, even if the lead electrodes, electrode terminals, and contact members are made of different materials, diffusion between different metals does not occur, the resistance value does not change, and a constant heater resistance is always maintained. It is possible to use a gas sensor in stably for a long period of time.

According to a second aspect of the present invention, in the first aspect of the invention, the substrate is formed of a material having a lower thermal conductivity than the sensitive film, so that the sensitive film can be heated to a predetermined temperature in a short time. As well as greatly reduce heat dissipation due to heat conduction to the board, greatly reducing power consumption,
The gas sensor can be driven by a battery.

According to a third aspect of the present invention, in the first and second aspects of the present invention, the sensitive film is made of a solid electrolyte having oxygen ion conductivity, and a pair of detection electrodes formed on the sensitive film is provided. Since the sensor is composed of an oxidation catalyst installed on the detection electrode, even in a solid electrolyte membrane type gas sensor used at a relatively high temperature, the lead electrode and the electrode terminal of the sensor element are physically joined by a contact member. Even if the lead electrodes, electrode terminals, and contact members are made of different materials, they do not diffuse between different metals, and the resistance value does not change. The gas sensor can be used stably for a long period of time, and the temperature of the sensitive film can be raised to a predetermined temperature in a short time, and the heat dissipation due to heat conduction to the substrate is greatly reduced. It also becomes possible to drive by a battery.

[0010] The invention described in claim 4 is the invention according to claims 1 to 3.
In the described invention, the contact member is formed integrally with the lid, so that a separate member for fixing the contact member is unnecessary, and a gas sensor can be obtained with a simple configuration.

According to a fifth aspect of the present invention, since the air intake is formed at a position corresponding to the sensitive portion of the lid in the fourth aspect of the invention, gas diffusion to the sensor element is facilitated. It is possible to detect the target gas in a short time.

According to a sixth aspect of the present invention, since an adsorbent is set in the space between the air intake and the sensor element in the fifth aspect of the invention, various types of interference mainly occurring in a home are provided. Since gas and poisoning gas are adsorbed and removed, a gas sensor that is stable for a long time can be obtained.

According to a seventh aspect of the present invention, since a breathable water-repellent member is attached to the air intake side of the adsorbent in the sixth aspect of the present invention, a large amount of water is used particularly in kitchens and bathrooms. Water can be prevented from entering the sensor in the environment in which it is used, and a long-term stable gas sensor can be obtained.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view of a gas sensor according to a first embodiment of the present invention. In this embodiment, a solid electrolyte type CO sensor will be described.

In FIG. 1, reference numeral 10 denotes a sensor element.
Reference numeral 11 denotes a substrate, which is made of quartz glass of about 2 mm × 2 mm × 0.3 mm. Reference numeral 12 denotes a platinum heater whose resistance is set to a predetermined temperature by a sputtering method, an electron beam evaporation method, or the like. Reference numeral 13 denotes an insulating film formed of a thin film of an insulating material such as alumina, silica, or silicon nitride so as to cover the heater 12 by a sputtering method, an electron beam evaporation method, or the like. Numeral 14 denotes a solid electrolyte film which is a sensitive film formed on the insulating film 13 and has a size of about 0.5 mm × 0.5 mm by sputtering a solid electrolyte having oxygen ion conductivity (8% yttria stabilized zirconia). Formed. In addition to the solid electrolyte membrane 14, a semiconductor such as tin oxide or zinc oxide which is generally used as a gas sensor can be used as the sensitive membrane. 15a and 15b are detection electrodes, and platinum is formed on the sensitive film by a sputtering method. Precious metals such as palladium, ruthenium, and rhodium may be partially mixed with platinum. Reference numeral 16 denotes a catalyst set on one of the detection electrodes 15a. The catalyst 16 may be any catalyst that can oxidize and decompose the gas to be measured. Oxides are available. The catalyst 16 is formed by a screen printing method, or by impregnating a porous material in the form of a nitrate or the like, followed by firing. 17 and 18 are the heater 12 and the detection electrode 15
a and 15b are a heater lead electrode and a detection lead electrode extended from 15b. Heater 12 and detection electrodes 15a, 15
It is integrally formed of the same material as b. Reference numeral 19 denotes a base body for housing the sensor element 10, on which an electrode terminal 20 is mounted. The electrode terminal 20 detects the output from the heater terminal 21 and the detection electrodes 15a and 15b for supplying electric power to the heater 12 from a power supply (not shown) and a detection circuit (not shown).
And a detection terminal 22 for transmitting the signal to the terminal. 2
Reference numeral 3 denotes a contact member for connecting the heater lead electrode 17 and the detection lead electrode 18 to the electrode terminal 20. Reference numeral 24 denotes a lid provided so as to cover the upper portion of the base body 19, and the contact member 23 is formed by integral molding, welding, fitting, or the like.
4 are integrally formed. An air intake port 25 is provided at a position facing the sensor element 10 above the lid 24. Reference numeral 26 denotes an adsorbent which is mounted in a space between the air intake 25 and the sensor element 10. 27 is an adsorbent 26
Is a gas-permeable, water-repellent member provided on the upstream side and made of a porous sheet such as PTFE. 28 is a wire mesh for holding the adsorbent 26 and the water repellent member 27.

In the above configuration, a heater terminal 21, a contact member 23, and a heater lead electrode 17 are supplied from a power source (not shown).
Power is supplied to the heater 12 through the heater to heat the solid electrolyte 13 to a predetermined temperature (400 ° C. to 500 ° C.). When the solid electrolyte membrane 14 reaches a predetermined temperature, the detection electrodes 15a, 15b
Transfer of electrons is performed at the interface between the solid electrolyte membrane 14 and the air, and oxygen ions are generated. The air flows from the air inlet 25 by diffusion and reaches the sensor element. Here, if CO exists in the air, the detection electrode 1 on which the catalyst 16 is mounted
In 5a, CO is oxidized by the catalyst 16 and the detection electrode 1
CO does not reach up to 5a. The other detection electrode 15b
Then, CO is oxidized to CO2 on the surface of the detection electrode 15. As a result, a difference occurs in the electrode reactions between the two electrodes, the equilibrium of oxygen ions is disrupted, and a potential difference occurs between the two electrodes. By detecting this potential difference, the CO concentration can be detected.
The quartz glass used for the substrate 11 has a thermal conductivity of 1.5 W /
mK and insulating film 13 (35-45W / mK) and sensitive film 14 (6W /
mK), and when heated by the heater 12, the temperature of the substrate 11 can be increased only in the region of the solid electrolyte membrane 14 immediately above the heater 12 without substantially increasing the temperature of the substrate 11. Power consumption can be greatly reduced. Further, since the thermal shock strength is high, it is possible to raise the temperature to a predetermined temperature in a short time. With the above configuration, it was possible to raise the temperature up to 450 ° C. with a power amount of 15 mWsec. Therefore, since the power consumption can be greatly reduced by driving the heater 12 in a pulsed manner, driving with a battery power supply is also possible. In the first embodiment, the case where the solid electrolyte membrane 14 is used as the sensitive membrane is shown. However, when the operating temperature is higher (400 ° C. to 500 ° C.) than the normal semiconductor sensor operating temperature (150 ° C. to 300 ° C.). Also in the solid electrolyte type, the heater lead electrode 17 and the heater terminal 2
1. The detection lead electrode 18 and the detection terminal 22 are
Physically, the conductive members are electrically connected to each other, so that even if each constituent member is made of a different material, diffusion between different metals does not occur, the resistance value does not change, and a constant heater resistance is always maintained. Therefore, the gas sensor can be used stably for a long period of time. Further, since the contact member 23 is formed integrally with the lid 24, a separate member for fixing the contact member 23 is unnecessary, and positioning is performed simultaneously when the lid 24 is fixed to the base body 19. And contact member 2
3 also fixes the contact member 23 between the heater lead electrode 17 and the heater terminal 21 and the detection lead electrode 18 and the detection terminal 22 at the same time, so that a gas sensor can be easily configured.
Further, since the air intake 25 is formed at a position corresponding to the sensor element 10 on the lid 24, the gas can be easily diffused into the sensor element 10 and the target gas can be detected in a short time. It is. The adsorbent 26 is generally made of activated carbon, zeolite, or the like in a honeycomb, granular, or fibrous form. Considering the use of gas sensors at home, there are various interfering gases and poisoning gases such as SO2 and NO2 generated from combustion equipment, various seasonings generated during cooking, food odor, hair styling and insecticides, The damage that these cause to the sensor element 10 cannot be ignored. By passing the entire amount of gas reaching the sensor element 10 through the adsorbent 26 to adsorb and remove these gases, a long-term stable gas sensor can be obtained. Further, in a home, it is conceivable that the sensor is used in a place where a large amount of water is used, such as a kitchen or a bathroom, or that the sensor body (not shown) is cleaned with water when the sensor body (not shown) becomes dirty. Sensor element 10
When water enters the heater, the heater 12 may be short-circuited or an abnormal potential may be detected, thereby causing a problem in the sensor. By providing a gas-permeable water-repellent material, it is possible to obtain a stable gas sensor for a long period of time by preventing water from entering while passing gas.

[0018]

As described above, according to the first to seventh aspects of the present invention, the heater lead electrode and the heater terminal, and the detection lead electrode and the detection terminal are physically joined by the contact member and made conductive. Even when the operating temperature is high as in the equation, even if each component is made of a different material, diffusion between different metals does not occur, the resistance value does not change, and a constant state heater resistance is always maintained. . Further, by forming the lid and the contact member integrally, a gas sensor can be obtained with a simple configuration. Further, by providing a gas-permeable diffusion water-repellent member or activated carbon in the gas diffusion path, moisture, various interfering gases and poisoning gas are removed, so that the gas sensor can be used stably for a long period of time.

[Brief description of the drawings]

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

FIG. 2 is an assembled perspective view of the gas sensor according to the first embodiment of the present invention.

FIG. 3 is a perspective view of a conventional gas sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Substrate 12 Heater 13 Insulating film 14 Sensitive film 15a, 15b Detection electrode 16 Catalyst 17 Heater lead electrode 18 Detection lead electrode 19 Base body 20 Electrode terminal 21 Heater terminal 22 Detection terminal 23 Contact member 24 Cover 25 Air intake 26 Adsorbent 27 Water repellent material

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. (72) Inventor Mitsuhiro Shibao 1006 Kadoma Kadoma City, Osaka Pref. Matsushita Electric Industrial Co., Ltd. BH15 BJ02 BM04 ZA04

Claims (7)

[Claims] 1. A heater formed on a substrate, a sensitive film formed on the heater via an insulating film, a detection electrode formed on the sensitive film, and a detection electrode formed on the substrate. A sensor element composed of a lead electrode connected to the heater, a base body for housing the sensor element, an electrode terminal provided on the base body, and contact between the lead electrode and the electrode terminal for conduction. A gas sensor having a contact member to be made and a lid for covering an upper portion of the base. 2. The gas sensor according to claim 1, wherein the substrate is formed of a material having a lower thermal conductivity than the sensitive film. 3. The sensitive membrane comprises an oxygen ion conductive solid electrolyte, and comprises a pair of detection electrodes formed on the sensitive membrane, and an oxidation catalyst provided on one of the detection electrodes. 2. The gas sensor according to 2. 4. The gas sensor according to claim 1, wherein the contact member is formed integrally with the lid. 5. The gas sensor according to claim 4, wherein an air intake is formed at a position corresponding to the sensitive portion of the lid. 6. The gas sensor according to claim 5, wherein an adsorbent is set in a space between the air intake and the sensor element. 7. The gas sensor according to claim 6, wherein a gas-permeable water-repellent member is mounted on the air intake side of the adsorbent.