JP2009079907A - Catalytic combustion type gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an easily-mountable catalytic conversion type gas sensor capable of storing a detection element and a compensation element in one chip without damaging gas sensitivity and shock resistance. <P>SOLUTION: Two or more heater parts are formed on a hole penetrating both surfaces of an insulating substrate, and each sintered body comprising a catalyst material is exposed from both surfaces of the substrate, while covering each whole heater part and a part of the hole, and detection object gas can be circulated from a gap of the penetrating hole. The finally formed gas sensor has improved shock resistance and response speed to the detection object gas, and can be mounted easily by summarizing on the surface, electrodes to be conducted to each element. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a catalytic combustion type gas sensor.

Combustible gas sensors that detect hydrogen gas, methane gas, and the like include contact combustion type gas sensors, semiconductor type gas sensors, and the like, all of which incorporate a heat source that is used for detection of combustible gases.
For example, the catalytic combustion type gas sensor element has a heater part, and the resistance value change of the heater part due to the contact combustion heat of the combustible gas generated on the combustion catalyst equipped in the heater part is output as a voltage change. It detects the presence of gas.

  As shown in FIG. 14, a conventional contact combustion type gas sensor is composed of a combustion catalyst material 3 and a heat conduction layer material 2 that efficiently transmits the combustion heat of the gas to the heater coil 1 in order to burn the detection target gas. It consists of a sintered body and a heater coil 1 whose electrical characteristic value changes with the combustion heat of gas, and has a structure in which the heater coil 1 is embedded in the sintered body.

  Both end portions of the heater coil 1 are connected to and supported by electrode pins for external connection.

  As a contact combustion type gas sensor, there is also a silicon chip type gas sensor for the purpose of downsizing and low power consumption. For the purpose of reducing heat capacity and increasing sensitivity, for example, there is a gas sensor having a structure in which a platinum film is bridged and supported in a zigzag manner on a silicon substrate having a through hole (see, for example, Patent Document 1).

Japanese Patent Laying-Open No. 2007-64865 (page 14, FIG. 1)

  In a contact combustion type gas sensor, if the gas concentration is the same, it is better that the amount of change in voltage output from the sensing element is large. A large change in the output voltage means high gas sensitivity. For this reason, the gas to be detected causes catalytic combustion on the catalyst surface, and the combustion heat must be efficiently transmitted to the heater section while suppressing loss as much as possible.

  Further, in the contact combustion type gas sensor, it is preferable that the voltage output from the detection element is stabilized in the shortest possible time if the gas concentration is the same. The short time required to stabilize the output voltage means that the response speed is fast. In order to increase the response speed, it is only necessary that the heater part, which is a heat source, in the sintered body efficiently receives the combustion heat so that the resistance value changes efficiently.

  However, in the case of the gas sensor disclosed in Patent Document 1, the platinum films 31, 32, and 35 as the catalyst material, that is, the platinum film 30 are used as a resistance temperature detector as shown in FIG. For example, even when air is blown onto the surface of the platinum film, the resistance value changes and there is a risk of malfunction.

  Further, in the case of the gas sensor disclosed in Patent Document 1, since the platinum film 30 as a catalyst has a structure in which the through hole is cross-linked in a zigzag manner, the impact resistance is weak, and it is difficult to use for a vehicle. It is.

In order to solve the above-mentioned problems, the contact combustion type gas sensor according to the present invention changes the electrical characteristic value of the heater part by the combustion heat generated by the combustion of the gas in contact with the sintered body, and the change of the characteristic value. A gas sensor for detecting the presence of a combustible gas based on the above, characterized in that it has a sintered body on both surfaces of a heater portion provided on an insulating substrate and has a hole penetrating the insulating substrate.

  Moreover, in the catalytic combustion type gas sensor of the present invention, it is preferable that the heater part bridges the hole.

  In the contact combustion gas sensor of the present invention, the sintered body is preferably exposed on the insulating substrate.

  According to the contact combustion type gas sensor according to the present invention, the heater part itself has a structure that bridges the through hole provided in the insulating substrate, so that both surfaces of the heater part are covered with the sintered body and can be effectively used. In addition, since there is no base film directly under the heater section, the heat capacity can be reduced.

  Further, the porous sintered body formed in the holes is exposed on the insulating substrate, and can respond quickly even when the detection target gas comes from both sides of the insulating substrate.

  In addition, two or more heater parts are formed by bridging the holes, and when the sintered body is formed, the gas to be detected can flow in the gaps between the sintered bodies. Will improve.

  Further, since the slurry made of the catalyst material covers the heater portion and is filled along the side wall of the hole and baked, the impact resistance of the heater portion is improved.

  Since the catalyst material is a sintered body and is fixed to the side wall of the hole, it has a structure that is difficult to peel off from the silicon substrate, and the impact resistance is improved.

  Exemplary embodiments of a catalytic combustion gas sensor according to the present invention will be described below in detail with reference to the drawings.

  FIG. 1A shows the surface of a catalytic combustion type gas sensor according to an embodiment of the present invention, and FIG. Here, the surface that is in contact with the heater portion is the surface of the insulating substrate, and the surface that is not in contact with the heater portion is the back surface. Also, the front and back surfaces are combined to make both sides.

  The sintered body 11 on the surface of FIG. 1 (a) is filled in the side wall of the hole in a slurry state before sintering.

  FIG. 2 shows a contact combustion type gas sensor before forming a sintered body. There is a hole 10 penetrating the front and back surfaces of the insulating film 5 which is an insulating substrate. By forming the sintered body on the side wall of the hole 10, it is possible to suppress the heat loss generated when the detection target gas burns on the surface of the sintered body and transmit it to the heater unit 9.

Two or more heater portions 9 are formed, and the top of the hole 10 is cross-linked. If the zigzag structure is used to repeat the cross-linking as in this embodiment, the wiring length can be increased. Further, the heater unit 9 may be bridged in parallel with the long axis direction of the hole 10.

  Since the present invention can use the front surface and the back surface of the heater unit 9, the gas sensitivity to the detection target gas is improved as compared with the structure using one side of the heater unit as in the prior art.

  By forming two or more heater parts, the detection target gas flows in the through holes formed between the heater parts. In addition, by forming a plurality of heater sections, each heater section can be shared as a sensing element, a compensation element, or a fixed resistance, and finally functions as a contact combustion type gas sensor in one substrate. be able to.

  There are electrode parts 12 at both ends of the heater part 9 so as to be electrically connected to the outside of the sensor.

  FIG. 3 is a plan view of the catalytic combustion gas sensor according to the embodiment of the present invention as seen from the back side. The sintered body 11 is also exposed on the back surface. The insulating film 5 and the silicon substrate 4 are stepped and concave when viewed from the back. This can remove a part of the silicon substrate 4 by etching to reduce the overall heat capacity, and can suppress heat loss caused by combustion of the detection target gas.

  As shown in FIG. 1B, the sintered body 11 is formed so as to be fixed to the side wall of the hole, and has a structure that is difficult to peel off from the chip.

  The heater section 9 is preferably formed of two layers of a hard film 6 made of a tungsten film or a titanium film and platinum or a platinum alloy film 7 containing platinum. The heater portion may be made of gold, platinum, rhodium, or a material obtained by selectively alloying them, but may be formed of any single material.

  Assembling and detecting the above-mentioned contact combustion type gas sensor having a through hole and a sintered body (hereinafter referred to as Example 1) and a contact combustion type gas sensor having no through hole but having a sintered body (hereinafter referred to as Comparative Example 1) The response performance to the target gas was evaluated. Moreover, the comparative example 1 is assembled with reference to the Example of patent document 1. FIG.

  In all of the above evaluation examples, after forming a heat conductive layer mainly composed of alumina, a slurry-like combustion catalyst material mainly composed of tin oxide and platinum is applied and subjected to electric firing to form a sintered body. Evaluation was made as a catalytic combustion type gas sensor element.

  Assembling as a catalytic combustion type gas sensor with the above configuration, the arrival time (hereinafter referred to as response time) of the output signal of the gas sensor with respect to hydrogen as a detection target gas and 4000 ppm of methane gas to a stable value was evaluated.

  As a result of the response time evaluation, the response time was the shortest for hydrogen and methane as detection target gases in Example 1, 1.1 seconds for hydrogen, and 2.1 seconds for methane. Second. Comparative Example 1 was 2 seconds for hydrogen and 3 seconds for methane. Example 1 showed a faster response time than Comparative Example 1 in hydrogen and methane.

  The reason why the response time of Example 1 is shorter than that of Comparative Example 1 is that the gas to be detected is easily adsorbed on the surface of the sintered body and the combustion reaction easily proceeds by having the through holes and the sintered body. As a result, it is considered that the combustion heat generated from the detection target gas burned on the catalyst surface is transmitted to both surfaces of the heater part while suppressing heat loss in the middle. Moreover, since the sintered body is exposed on both sides of the sensor, it is possible to capture the detection target gas on both sides.

  The manufacturing method will be described based on the AA cross section shown in FIG.

  As shown in FIG. 4, a silicon oxide film, a silicon nitride film, or an insulating film 5 made of a combination of these is laminated on the surface of the silicon substrate 4.

  As shown in FIG. 5, after the insulating film 5 is laminated, tungsten or titanium is laminated by sputtering to form the hard film 6.

  As shown in FIG. 6, after the hard film 6 is laminated, platinum or an alloy containing platinum is laminated by sputtering to form a platinum film 7.

  As shown in FIG. 7, the recess 8 is formed from the back surface by dry etching using the resist pattern as a mask by photolithography or the like until the insulating film 5 is exposed. By etching the silicon substrate 4 to leave the insulating film 5, the hard film 6, and the platinum film 7, the heat capacity of the entire gas sensor can be lowered, and the gas sensitivity is improved.

  As shown in FIG. 8, the heater part 9 and the electrode part are formed from the surface side by dry etching with the platinum film 7 and the hard film 6 as a mask by a photolithography method or the like.

  As shown in FIG. 9, holes 10 are formed by etching a part of the insulating film 5 from the back surface to the position where the heater portion 9 is exposed by dry etching using a resist pattern as a mask by photolithography or the like.

  The shape of the hole 10 is not limited to a quadrangle, and may be an ellipse, a corner portion may be curved, a T-shape as shown in FIG. 11 may be formed, and the heater portions 9 may be formed at both ends thereof. Good. When dry etching is performed by the method described above, a structure in which the heater portion meanders over the hole is completed.

  Although not particularly limited as shown in FIG. 10, for example, a slurry made of a catalyst material containing tin oxide, platinum, palladium, and alumina is filled in the holes while covering each heater portion 9. The electrode portion is connected to an external power source, and the slurry is blown away while being energized to be completely fired. The combustion catalyst material filling and firing are divided into 3 to 5 times and fired to form the sintered body 11 and the through-holes 16. By dividing and firing, it becomes easy to configure a desired shape. At this time, the characteristics as the detection element or the compensation element are determined depending on the selection of the catalyst material covering each heater section.

  As shown in FIG. 12, three or more heater sections 9 and sintered bodies 11 may be formed, and holes 16 penetrating between the sintered bodies may be provided. By providing two or more through holes, the fluidity of the detection target gas is improved.

  In this embodiment, the first series circuit in which the sensing element and the compensation element are connected in series and the second series circuit in which two fixed resistors having the same resistance value are connected in series are connected in parallel to Wheatstone. A bridge circuit is configured, a DC voltage is applied between the connection points of the first series circuit and the second series circuit, and the connection point between the detection element and the compensation element and the connection point of the two fixed resistors The voltage between them is output as a detection signal. A sensor configuration in which a fixed resistor is formed on an insulating film to form a single chip may be used.

In the above, the present invention is not limited to the above-described embodiment, and various modifications can be made. For example, the line width, thickness, length, layout on the substrate, etc. of the heater part can be changed as appropriate.

  A plurality of the present invention can be combined and can be changed as appropriate.

  As described above, the catalytic combustion type gas sensor according to the present invention is useful for a gas leak detection device for home use or industrial use, and is particularly suitable for a device for detecting a combustible gas used in a fuel cell.

(A) is the top view seen from the surface of the contact combustion type gas sensor concerning the embodiment of the present invention, and (b) is a sectional view cut from AA. It is the top view seen from the surface of the contact combustion type gas sensor concerning the embodiment of the present invention. It is the top view seen from the back surface of the contact combustion type gas sensor concerning the embodiment of the present invention. It is sectional drawing in the manufacturing process of the contact combustion type gas sensor concerning embodiment of this invention. It is sectional drawing in the manufacturing process of the contact combustion type gas sensor concerning embodiment of this invention. It is sectional drawing in the manufacturing process of the contact combustion type gas sensor concerning embodiment of this invention. It is sectional drawing in the manufacturing process of the contact combustion type gas sensor concerning embodiment of this invention. It is sectional drawing in the manufacturing process of the contact combustion type gas sensor concerning embodiment of this invention. It is sectional drawing in the manufacturing process of the contact combustion type gas sensor concerning embodiment of this invention. It is sectional drawing in the manufacturing process of the contact combustion type gas sensor concerning embodiment of this invention. It is the top view seen from the surface of the contact combustion type gas sensor concerning the embodiment of the present invention. It is the top view seen from the surface of the contact combustion type gas sensor concerning the embodiment of the present invention. It is a perspective view of a silicon chip type gas sensor element. It is sectional drawing of the conventional catalytic combustion type gas sensor element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heater coil 2 Heat conductive layer material 3 Combustion catalyst material 4 Silicon substrate 5 Insulating film 6 Hard film 7 Platinum film 8 Recessed part 9 Heater part 10 Hole 11 Sintered body 12 Electrode part 13 Heating resistor 14 Thin film insulator 15 Crosslinking support part 16 hole 17 sintered body 30 platinum film 31 platinum film 32 platinum film 35 platinum film

Claims (3)

A contact combustion type gas sensor that detects the presence of a flammable gas based on the change in the electrical characteristic value of the heater section due to the combustion heat generated by the combustion of the gas in contact with the sintered body, and the change in the characteristic value. ,
Sintered bodies on both sides of the heater section provided for the insulating substrate,
A contact combustion type gas sensor having a hole penetrating the insulating substrate.   The catalytic combustion gas sensor according to claim 1, wherein the heater section bridges the hole.   The catalytic combustion gas sensor according to claim 1, wherein the sintered body is exposed on the insulating substrate.

Images