JP2011089943A - Contact combustion type gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a contact combustion type gas sensor capable of improving sensitivity by increasing the amount of combustion of a gas to be detected without having to drive a heater so as to raise the temperature of the surface of a catalytic layer. <P>SOLUTION: A gas sensor unit 15 includes a heater 42 wired over a multi-layer insulating film 48 superposed over a substrate 41 and a catalytic sinter 43 provided over the multi-layer insulating film 48 so as to be superposed over the heater 42. The heater 42 is formed in such a way that a heating value of a part of the heater 42 wired at a section close to the center of the surface 430 of the catalytic sinter 43 in a unit area may be smaller than a heating value of a part of the heater 42 wired at a section farther from the center of the surface 430 of the catalytic sinter 43 so as to make the temperature of the surface 430 of the catalytic sinter 43 uniform when the heater 42 is driven. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a catalytic combustion type gas sensor having a heater and a catalyst layer provided on the heater.

  A conventionally known catalytic combustion type gas sensor has, for example, a sensitive element and a compensating element, burns a gas to be detected by the catalytic action of the sensitive element, and captures this combustion heat as a change in the resistance value of the platinum coil. It is configured. Among the gases to be detected, gases with high polarity and large adsorption power, such as toluene, acetic acid, and ethanol, are adsorbed when the gas molecules are adsorbed on the catalyst surface of the sensitive element when driven at low temperatures and when they are driven at high temperatures. Burns instantaneously and the catalytic combustion reaction occurs simultaneously, so that the sensor output has a peak waveform (mountain waveform) that reaches a peak in a short time and then gradually decreases. On the other hand, a nonpolar or small polarity gas such as methane, hydrogen, carbon monoxide or the like has a small adsorption power, so the above phenomenon does not occur, and the sensor output gradually increases until it stabilizes at a steady value.

  As described above, by utilizing a characteristic peak waveform in a specific type of gas such as toluene, gas detection such as gas concentration detection or gas type separation can be performed using a catalytic combustion gas sensor. Such a catalytic combustion type gas sensor that utilizes an adsorption phenomenon of a specific type of gas is also called an adsorption combustion type gas sensor.

  As the above-described catalytic combustion type gas sensor, for example, a conventional catalytic combustion type gas sensor 115 disclosed in Patent Document 1 is a catalyst that carries a heater 142 made of a platinum wire and a catalyst such as palladium as shown in FIG. And a sensitive element 111 having a layer 143. The heater 142 is arranged on the diaphragm D formed by the multilayer insulating films 148a, 148b, and 148c laminated on the silicon wafer 141 in a folded manner with thin thin wires, and has the same width over the entire length. The wirings are formed so as to have the same thickness and the intervals between the parallel parts are the same. The catalyst layer 143 is formed on the diaphragm D so as to overlap the heater 142 so as to be thermally connected to the heater 142. In such a catalytic combustion type gas sensor 115, the heater 142 is energized (that is, driven at a low temperature) so that the temperature of the surface 1430 of the catalyst layer 143 becomes a low temperature (adsorption temperature) for adsorbing the detection target gas, and subsequently the catalyst The heater 142 is energized (that is, driven at a high temperature) so that the temperature of the surface 1430 of the layer 143 becomes a high temperature (combustion temperature) at which the detection target gas is combusted. As a result, the detection target gas adsorbed on the catalyst layer surface 1430 during low temperature driving burns during high temperature driving.

JP 2005-83950 A

  However, in the catalytic combustion type gas sensor 115 of Patent Document 1, when the heater 142 is energized, the temperature near the center of the catalyst layer surface 1430 becomes higher than the temperature near the periphery of the catalyst layer surface 1430, and the temperature on the catalyst layer surface 1430 is increased. Unevenness had occurred.

This is because a portion of the heater 142 wired near the center of the catalyst layer surface 1430 (hereinafter referred to as the center portion Hc) is arranged on the inner side when viewed from the entire heater 142, and the periphery of the heater 142 is surrounded by the periphery of the heater 142. Since it is surrounded by other portions, it is difficult to dissipate heat, and a portion (hereinafter referred to as a peripheral portion He) wired at a location away from the center of the catalyst layer surface 1430 (that is, a location close to the edge of the catalyst layer surface 1430). Is located on the outer side of the heater 142 as a whole and is close to the outside of the heater 142 so that it is easy to dissipate heat. Therefore, the temperature of the central portion Hc of the heater 142 is higher than the peripheral portion He of the heater 142. Because. Further, when the central portion Hc becomes high temperature, the resistance value per unit length of the central portion Hc is increased due to the characteristics of the platinum wire, and the calorific value P of the platinum wire is a resistance value to the square of the current I. Since it is indicated by a value multiplied by R (P = I ² R), when the resistance value per unit length increases, the amount of heat generation increases, and accordingly, the region where the heater 142 is wired (diaphragm D) This is because the amount of heat generated per unit area increases in the central portion Hc, and the central portion Hc becomes even higher in temperature.

  When temperature unevenness occurs on the catalyst layer surface 1430, as shown in FIGS. 7A and 7B, for example, when the catalytic combustion gas sensor 115 is driven at a low temperature, the central portion 1430a of the catalyst layer surface 1430 is Since the temperature becomes higher than the adsorption temperature, the detection target gas cannot be burned and adsorbed, and the annular portion 1430b and the peripheral portion 1430c outside the central portion 1430a become the adsorption temperature to adsorb the detection target gas. Subsequently, when the contact combustion type gas sensor 115 is driven at a high temperature from this state, the central portion 1430a and the annular portion 1430b become the combustion temperature, and the detection target gas is combusted, but the peripheral portion 1430c outside the annular portion 1430b has a temperature. The adsorption temperature remains at the same level and does not burn the detection target gas. Therefore, only the detection target gas adsorbed on the annular portion 1430b is adsorbed and burned, that is, only a part of the catalyst layer surface 1430 can be used for the adsorption combustion, so that the amount of adsorption combustion of the detection target gas is small. There is a problem that the sensitivity of the gas sensor 115 decreases and the detection accuracy deteriorates. Further, the above describes the operation in the adsorption combustion, but the operation in the catalytic combustion also does not combust the detection target gas at the peripheral portion 1430c at the time of high temperature driving. There was a similar problem.

  Further, each drive control can be performed so that the central portion 1430a of the catalyst layer surface 1430 has an adsorption temperature during low temperature driving, and the peripheral portion 1430c of the catalyst layer surface 1430 has a combustion temperature during high temperature driving. For this purpose, it is necessary to drive to a lower temperature during low-temperature driving and to a higher temperature during high-temperature driving, so the temperature difference between the low-temperature driving and the high-temperature driving increases and the temperature It takes time to switch the battery, resulting in poor responsiveness, and driving at a higher temperature during high-temperature driving increases power consumption and shortens the usable time in a gas detection device that uses a battery as a power source. There was another problem such as.

  The present invention aims to solve the above problems. That is, an object of the present invention is to provide a catalytic combustion type gas sensor that can increase the combustion amount of the detection target gas and improve the sensitivity without driving the heater so that the temperature of the catalyst layer surface becomes higher. Yes.

  In order to achieve the above object, the invention described in claim 1 is a catalytic combustion type gas sensor having a heater wired on a plane and a catalyst layer provided on the plane so as to overlap the heater. In order to make the temperature of the catalyst layer surface uniform when the heater is driven, the heater has a calorific value per unit area of a portion wired near the center of the catalyst layer surface, The catalytic combustion type gas sensor is characterized in that it is formed to be smaller than a calorific value per unit area of a portion wired at a position far from the center of the surface of the catalyst layer.

  The invention described in claim 2 is the invention described in claim 1, wherein a resistance value per unit length of a portion of the heater wired near the center of the surface of the catalyst layer is the catalyst layer. The heater is formed so as to be lower than a resistance value per unit length of a portion wired at a location far from the center of the surface.

  The invention described in claim 3 is the invention described in claim 1 or 2, wherein the wiring density of a portion of the heater wired near the center of the catalyst layer surface is the center of the catalyst layer surface. The heater is formed so as to be lower than the wiring density of a portion wired at a location far from the heater.

  According to the first aspect of the present invention, the heater is wired near the center of the catalyst layer surface so that the temperature of the catalyst layer surface becomes uniform when the heater included in the catalytic combustion gas sensor is driven. Since the heat generation amount per unit area of the formed part is smaller than the heat generation amount per unit area of the part wired away from the center of the catalyst layer surface, the occurrence of temperature unevenness on the catalyst layer surface is prevented. Therefore, without increasing the temperature of the catalyst layer surface, the area where the detection target gas burns on the surface of the catalyst layer can be expanded and the amount of combustion of the detection target gas can be increased without driving the heater. And sensitivity can be improved.

According to the invention described in claim 2, the resistance value per unit length of the portion wired in the heater near the center of the catalyst layer surface is a portion wired in a location far from the center of the catalyst layer surface. Since the heater is formed so as to be lower than the resistance value per unit length, the heating value P of the heater is represented by a value obtained by multiplying the square of the current I by the resistance value R (P = I ^2). R) Therefore, when the resistance value per unit length decreases, the amount of heat generation also decreases. Therefore, the amount of heat generation per unit area of the portion wired near the center of the catalyst layer surface in the heater is reduced by the catalyst layer. The calorific value per unit area of the portion wired far from the center of the surface is smaller, and the temperature near the center of the catalyst layer surface can be prevented from becoming higher than the temperature near the periphery of the catalyst layer surface. Therefore, it is possible to make the temperature of the catalyst layer surface uniform by preventing the occurrence of temperature unevenness on the catalyst layer surface, thereby expanding the area where the detection target gas burns on the catalyst layer surface, and the amount of combustion of the detection target gas Can be increased, and the sensitivity can be improved. In addition, when the heater is made of a homogeneous material over its entire length, the resistance value per unit length is inversely proportional to the cross-sectional area, so the line width of the heater wired at a location near the center of the catalyst layer surface (or It is only necessary to form the heater so that (thickness) is larger than the line width (or thickness) of the heater wired at a location far from the center of the catalyst layer surface. can do.

  According to the invention described in claim 3, the wiring density of the portion wired near the center of the catalyst layer surface in the heater is lower than the wiring density of the portion wired away from the center of the catalyst layer surface. Since the heater is formed, the wiring interval of the portion wired near the center of the catalyst layer surface in the heater is wider than the wiring interval of the portion wired far from the center of the catalyst layer surface. As a result, the heat generation amount per unit area of the portion wired near the center of the catalyst layer surface of the heater is smaller than the heat generation amount per unit area of the portion wired far from the center of the catalyst layer surface. The temperature near the center of the catalyst layer surface can be prevented from becoming higher than the temperature near the periphery of the catalyst layer surface. Therefore, it is possible to make the temperature of the catalyst layer surface uniform by preventing the occurrence of temperature unevenness on the catalyst layer surface, thereby expanding the area where the detection target gas burns on the catalyst layer surface, and the amount of combustion of the detection target gas Can be increased, and the sensitivity can be improved. Moreover, since it is easy to form, a contact combustion type gas sensor can be easily manufactured.

(A), (B), and (C) are the sectional views which follow the AA line in a top view, a rear view, and a top view of a gas sensor unit which is one embodiment of the present invention, respectively. It is the elements on larger scale which expanded about the sensitive element with which the gas sensor unit of FIG. 1 (A) is equipped. (A) is a figure which shows typically the temperature distribution of the catalyst sintered compact (catalyst layer) surface when supplying with electricity to the heater with which the gas sensor unit of FIG. 1 is supplied, (B) is X- of (A). It is a figure which shows typically the temperature distribution along a X-ray. It is the elements on larger scale which show the structure of the modification of the gas sensor unit of FIG. It is a block diagram of a gas concentration detection apparatus provided with the gas sensor unit of FIG. (A), (B), and (C) are the sectional views which follow the BB line in the top view, back view, and top view of the conventional catalytic combustion type gas sensor, respectively. (A) is a figure which shows typically the temperature distribution of the catalyst layer surface when supplying with electricity to the heater with which the catalytic combustion type gas sensor of FIG. 6 is equipped, (B) follows the YY line of (A). It is a figure which shows temperature distribution typically.

  Hereinafter, a gas sensor unit as an embodiment of a catalytic combustion gas sensor according to the present invention will be described with reference to the drawings of FIGS.

  As shown in FIG. 1, the gas sensor unit 15 includes a substrate 41, and a sensitive element 11 and a compensating element 12 that are arranged adjacent to each other on the substrate 41.

  The substrate 41 is a rectangular plate-like member having a thickness of about 400 μm made of a silicon single crystal having a predetermined crystal orientation, and a multilayer insulating film 48 formed on one plane (hereinafter referred to as the upper surface). And two openings 46 and 47 provided on the other plane (hereinafter referred to as the lower surface).

The multilayer insulating film 48 includes, for example, a silicon oxide film (SiO ₂ ) 48c formed over the upper surface of the substrate 41, a silicon nitride (SiN) film 48b formed over the silicon oxide film 48c, and the nitride A hafnium oxide (HfO ₂ ) film 48a formed over the silicon film 48b. These insulating films are sequentially formed on the substrate 41 by, for example, PVD (Physical Vapor Deposition) processing, CVD (Chemical Vapor Deposition) processing, or the like. In this embodiment, the hafnium oxide film 48a is formed with a thickness of about 30 nm, the silicon nitride film 48b is formed with a thickness of about 250 nm, and the silicon oxide film 48c is formed with a thickness of about 600 nm. The multilayer insulating film 48 (that is, one plane of the substrate 41) corresponds to the plane in the claims.

  The openings 46 and 47 are recesses formed by digging down the substrate 41 from the lower surface side to the multilayer insulating film 48 by anisotropic etching or the like. By forming the openings 46 and 47, the diaphragms Ds and Dr including the multilayer insulating film 48 are formed.

  The sensitive element 11 includes a heater 42, terminals 51 and 52, and a catalyst sintered body 43 as a catalyst layer.

  The heater 42 is a platinum wire provided on the upper surface (surface opposite to the opening 46) of the diaphragm Ds, and is a member that generates heat when energized and changes its own resistance value according to its temperature. is there. The heater 42 is spirally wound from one end thereof toward the inside, and then folded back at the central portion, similarly wound spirally toward the outside, and the one end is sandwiched between the spiral portions. It is wired so as to reach the other end arranged so as to face the part. The heater 42 is formed so that the thickness is uniform (about 250 nm) over its entire length, and the line width is gradually increased from the outside of the spiral toward the inside (for example, about 12 to 18 μm). ing. In other words, the heater 42 is formed such that its cross-sectional area gradually increases from the outside to the inside of the spiral.

In general, the electrical resistance R [Ω] of a conductor is expressed by the following equation, where L [m] is the length of the conductor, S [m ² ] is the cross-sectional area of the conductor, and ρ is the resistivity. .
R = ρ (L / S) [Ω]

  As is clear from this equation, since the resistance value of the conductor decreases as the cross-sectional area increases, the resistance value per unit length of the heater 42 gradually decreases from the outside to the inside of the spiral. That is, the heater 42 is formed such that the resistance value per unit length of the portion near the center of the heater 42 is lower than the resistance value per unit length of the portion far from the center of the heater 42.

  In the present embodiment, the line width of the heater 42 is formed so as to gradually increase from the outside to the inside of the spiral, but the present invention is not limited to this. The line width is uniform over the entire length, and the thickness is gradually increased from the outside to the inside of the spiral, or the electrical resistance impurities contained in the material of the heater 42 are spiral. The resistance value per unit length of the portion near the center of the heater 42 becomes lower than the resistance value per unit length of the portion far from the center of the heater 42, such as gradually decreasing from the outside to the inside. In addition, as long as the heater 42 is formed, the configuration is arbitrary. In this embodiment, platinum is used as the heater 42. However, the present invention is not limited to this. For example, any metal or compound having a large temperature coefficient of resistance, such as tungsten, which is stable up to a high temperature is used. You may use something.

  The terminals 51 and 52 are platinum film portions formed in a substantially rectangular shape on the multilayer insulating film 48, arranged so as to face each other with the heater 42 interposed therebetween, and the terminal 51 is one of the heaters 42. The terminal 52 is connected to the other end of the heater 42. The terminals 51 and 52 are for electrically connecting the sensitive element 11 to an external electric circuit.

  The heater 42 and the terminals 51 and 52 perform sputtering on the multilayer insulating film 48 to form a platinum film, and further, on the platinum film, along the shape of the heater 42 and the terminals 51 and 52 by photolithography. After patterning, dry etching is performed to remove unnecessary platinum films, so that they are formed integrally with each other.

  The catalyst sintered body 43 corresponds to the catalyst layer of the claims, and a multilayer insulating film 48 (diaphragm) is formed so that a ceramic powder paste mixed with a palladium compound as a catalyst for accelerating the combustion of the detection target gas covers the entire heater 42. Ds) is applied with a thickness of about 1 to 40 μm to form a substantially hemispherical shape, and then heated to about 700 ° C. for sintering. The center of the surface 430 of the catalyst sintered body 43 is disposed so as to overlap the center portion 42 a of the heater 42, and the outer edge of the surface 430 is disposed slightly outside the peripheral edge portion 42 b of the heater 42 so as to be concentric with the heater 42. It is provided so that it may overlap. The catalyst sintered body 43 is thermally connected to the heater 42. In the present embodiment, the catalyst material is mixed with the catalyst sintered body 43 which is the catalyst layer, but the present invention is not limited to this. For example, only ceramic powder is formed in a substantially hemispherical shape, A catalyst material may be applied to the surface to form a catalyst film.

  The compensation element 12 includes a heater 44, terminals 53 and 54, and a sintered body 45 as a non-catalytic layer. The heater 44 is the same as the heater 42 except that it is provided on the diaphragm Dr. The terminals 53 and 54 are the same as the terminals 51 and 52 except that they are provided integrally with the heater 44. Therefore, detailed description thereof will be omitted.

  The sintered body 45 is the same as the catalyst sintered body 43 by applying a paste made of only ceramic powder on the multilayer insulating film 48 (diaphragm Dr) so as to cover the entire heater 44 with a thickness of about 1 to 40 μm. After forming into a hemispherical shape, it is sintered by heating at about 700 ° C. The sintered body 45 is disposed so that the center of the surface thereof is overlapped with the center of the heater 44 and the outer edge of the surface is disposed slightly outside the peripheral edge of the heater 44 so as to overlap the heater 44 concentrically. ing. The sintered body 45 is thermally connected to the heater 44.

  In a steady state in which the temperature change of the sensitive element 11 and the compensating element 12 converges after being driven at a low temperature and a high temperature in an atmosphere that does not include the detection target gas, the heater 42 and the compensating element 12 of the sensitive element 11 The heater 44 is formed to have the same resistance value.

  Further, since the sensitive element 11 includes the catalyst sintered body 43 and the compensating element 12 includes the sintered body 45 (that is, does not include a catalyst), when driven at a low temperature, the sensitive element 11 The gas to be detected is adsorbed by the catalyst sintered body 43, while the gas to be detected is not adsorbed by the sintered body 45 in the compensation element 12 and is driven by the catalyst in the sensitive element 11 when driven at a high temperature. On the other hand, the gas to be detected does not burn in the compensation element 12. That is, the sensitive element 11 is sensitive to the detection target gas, and the compensation element 12 is not sensitive to the detection target gas.

  As described above, according to the present embodiment, the catalyst sintered body 43 is concentrically overlapped with the heater 42, and the resistance value per unit length of the portion near the center of the heater 42 is the heater value. The heater 42 is formed so as to be lower than the resistance value per unit length of the portion far from the center of the 42, that is, wired at a location near the center of the surface 430 of the catalyst sintered body 43 in the heater 42. The heater 42 is formed so that the resistance value per unit length of the portion is lower than the resistance value per unit length of the portion wired at a location far from the center of the surface 430 of the catalyst sintered body 43. .

Next, the effect | action which concerns on this invention of the gas sensor unit 15 mentioned above is demonstrated with reference to FIG. 3 (A) and (B). The heater 42 of the sensitive element 11 has a resistance value per unit length of a portion wired near the center of the surface 430 of the catalyst sintered body 43 at a location far from the center of the surface 430 of the catalyst sintered body 43. The wiring portion is formed so as to be lower than the resistance value per unit length. The heat value P of the heater 42 is indicated by a value obtained by multiplying the square of the current I by the resistance value R (P = I ² R). Therefore, when the resistance value per unit length is reduced, the heat value is also increased. Therefore, when the heater 42 is energized, the temperature in the vicinity of the center of the surface 430 of the catalyst sintered body 43 does not become higher than the temperature in the vicinity of the periphery of the surface 430 of the catalyst sintered body 43. The entire surface 430 becomes a uniform temperature.

  Thereby, for example, when the heater 42 provided in the sensitive element 11 of the gas sensor unit 15 is energized (low temperature driving) so that the surface temperature of the catalyst sintered body 43 becomes the adsorption temperature, the entire surface 430 of the catalyst sintered body 43 is When energization (high temperature driving) is performed so that the adsorption temperature is uniform and the surface temperature of the catalyst sintered body 43 is equal to the combustion temperature, the entire surface 430 of the catalyst sintered body 43 is uniformly at the combustion temperature. Therefore, the detection target gas is adsorbed on the entire surface 430 of the catalyst sintered body 43, and the detection target gas is burned on the entire surface 430. That is, the heater 42 is a portion of the portion wired near the center of the surface 430 of the catalyst sintered body 43 so that the temperature of the surface 430 of the catalyst sintered body 43 becomes uniform when the heater 42 is driven. The amount of heat generated per unit area in the diaphragm Ds (that is, the plane on which the heater is wired) is formed smaller than the amount of heat generated per unit area of the portion wired away from the center of the surface 430 of the catalyst sintered body 43. Has been.

As described above, according to the present invention, the resistance value per unit length of the portion wired near the center of the surface 430 of the catalyst sintered body 43 in the heater 42 is the center of the surface 430 of the catalyst sintered body 43. Since the heater 42 is formed so as to be lower than the resistance value per unit length of the portion wired far from the heater, the heating value P of the heater 42 is obtained by multiplying the square of the current I by the resistance value R. (P = I ² R), the lower the resistance value per unit length, the smaller the amount of heat generated. Therefore, wiring is made near the center of the surface 430 of the catalyst sintered body 43. The amount of heat generated per unit area of the heater 42 becomes smaller than the amount of heat generated per unit area of the heater 42 wired near the center of the surface 430 of the catalyst sintered body 43, and the surface 430 of the catalyst sintered body 43. The temperature near the center of It is higher than the temperature in the vicinity of the peripheral surface 430 of the sintered body 43 can be prevented. Therefore, the occurrence of temperature unevenness on the surface 430 of the catalyst sintered body 43 can be prevented, and the temperature of the surface 430 of the catalyst sintered body 43 can be made uniform. The area where the detection target gas burns on the surface 430 of the catalyst sintered body 43 can be expanded without driving the heater 42 so as to be higher or lower, and the amount of combustion of the detection target gas can be increased. Can be improved.

  Further, the heater 42 has a line width of a portion wired near the center of the surface 430 of the catalyst sintered body 43, and a line width of a portion wired away from the center of the surface 430 of the catalyst sintered body 43. Since it is formed to be larger, it has a shape that can be easily formed, and therefore the gas sensor unit 15 can be easily manufactured.

  In the present embodiment, the resistance value per unit length of the portion wired in the heater 42 near the center of the surface 430 of the catalyst sintered body 43 is at a location far from the center of the surface 430 of the catalyst sintered body 43. Although the heater 42 is formed so as to be lower than the resistance value per unit length of the wired portion, it is not limited to this. For example, the sensitive element 11A of the gas sensor unit 15A shown in FIG. 4 has a wiring density of a portion wired near the center of the surface 430 of the catalyst sintered body 43 instead of the heater 42 described above. A heater 42 </ b> A is provided so as to be lower than the wiring density of a portion wired at a location far from the center of the surface 430 of 43.

  According to the gas sensor unit 15A, the wiring density of the portion wired near the center of the surface 430 of the catalyst sintered body 43 in the heater 42A is wired at a location far from the center of the surface 430 of the catalyst sintered body 43. Since the heater 42A is formed so as to be lower than the wiring density of the part, the wiring interval of the part wired near the center of the surface 430 of the catalyst sintered body 43 in the heater 42A is set as the catalyst sintered body. The amount of heat generated per unit area of the heater 42 wired near the center of the surface 430 of the catalyst sintered body 43 is increased by extending the wiring interval of the portion wired at a location far from the center of the surface 430 of the 43. The calorific value per unit area of the heater 42 wired near the center of the surface 430 of the catalyst sintered body 43 is smaller than the center of the surface 430 of the catalyst sintered body 43. It is possible to prevent the temperature of the near is higher than the temperature in the vicinity of the peripheral surface 430 of the catalyst sintered body 43. Therefore, the occurrence of temperature unevenness on the surface 430 of the catalyst sintered body 43 can be prevented, and the temperature of the surface 430 of the catalyst sintered body 32 can be made uniform, whereby the temperature of the surface 430 of the catalyst sintered body 43 can be reduced. The area where the detection target gas burns on the surface 430 of the catalyst sintered body 43 can be expanded without driving the heater 42A so as to be higher or lower, and the amount of combustion of the detection target gas can be increased. Can be improved. In addition, since the heater 42A is easily formed, the gas sensor unit 15A can be easily manufactured.

  Alternatively, the heaters 42 and 42A described above may be combined to form the heater of the sensitive element 11. Specifically, the cross-sectional area (that is, the line width, thickness, or line width and thickness) of the portion wired near the center of the surface 430 of the catalyst sintered body 43 in the heater is from the center of the surface 430. Location where the wiring density of the portion wired near the center of the surface 430 of the catalyst sintered body 43 in the heater is far from the center of the surface 430 so as to be larger than the cross-sectional area of the portion wired at a far location. The heater 42 is formed so that the temperature of the surface 430 of the catalyst sintered body 43 becomes uniform when the heater 42 is driven, such as being formed so as to be lower than the wiring density of the portion wired in The amount of heat generated per unit area of the portion wired near the center of the surface 430 of the sintered body 43 is the amount of heat generated per unit area of the portion wired far from the center of the surface 430 of the catalyst sintered body 43. Less than quantity If YES in Ku formed, the shape of the heater is optional. In FIG. 1A, FIG. 2, and FIG. 4, for the convenience of explanation, each heater is shown through the catalyst sintered body 43 and the sintered body 45.

  Next, a gas concentration detection apparatus including the gas sensor unit 15 described above will be described with reference to FIG. This gas concentration detection apparatus includes the gas sensor unit 15 described above and uses the gas sensor unit 15 as an adsorption combustion type gas sensor.

  As shown in FIG. 5, the gas concentration detection apparatus 1 includes a bridge circuit 2, a voltage supply source 5, an instrumentation amplifier 6, an A / D converter 7, a microcomputer 60, a gas storage chamber (not shown), And a display device (not shown).

  The bridge circuit 2 includes a first fixed resistor 13, a second fixed resistor 14, and the gas sensor unit 15 described above. The sensor circuit unit 10 is configured by connecting the second fixed resistor 14 and the sensitive element 11 in series, and the reference circuit unit 20 is configured by connecting the first fixed resistor 13 and the compensation element 12 in series. Is configured. Further, the bridge circuit 2 is configured by connecting the sensor circuit unit 10 and the reference circuit unit 20 in parallel to each other. A signal line connecting the first fixed resistor 13 and the second fixed resistor 14 in the bridge circuit 2 is connected to the voltage supply source 5. A signal line connecting the sensitive element 11 and the compensating element 12 in the bridge circuit 2 is connected to a ground point (GND).

  When the sensitive element 11 and the compensating element 12 included in the gas sensor unit 15 are driven at a high temperature after being driven at a low temperature in an atmosphere containing the detection target gas, the detection target gas adsorbed on the sensitive element 11 explosively burns. . Then, due to this combustion energy, the temperature of the sensitive element 11 becomes higher than the temperature of the compensating element 12, and a temperature difference corresponding to the concentration of the detection target gas occurs between the sensitive element 11 and the compensating element 12. There is a difference in resistance value between the heater 42 of the sensitive element 11 and the heater 44 of the compensating element 12. This difference in resistance value is the difference between the second fixed resistor 14 and the sensitive element 11 (that is, the middle point of the sensor circuit unit 10) and between the first fixed resistor 13 and the compensation element 12 (that is, in the reference circuit unit 20). Point), that is, as a potential difference between a pair of middle points in the bridge circuit 2. The potential difference between the pair of midpoints is referred to as a “midpoint potential difference Vc”, and the gas concentration is detected based on the midpoint potential difference Vc. This midpoint potential difference Vc becomes the output of the gas sensor unit 15.

  The gas sensor unit 15 is installed in a gas storage chamber (not shown). The gas storage chamber is filled with an atmosphere (test gas) for detecting the concentration of the detection target gas under the control of the microcomputer 60 described later.

  The first fixed resistor 13 and the second fixed resistor 14 are well-known electronic components that generate an electric resistance having a predetermined fixed value. The first fixed resistor 13 and the second fixed resistor 14 may be configured by combining a plurality of fixed resistors in series, in parallel, or in series and in parallel, or fixing the resistance value when measuring the gas concentration. For example, a variable resistor that can change the resistance value for balance adjustment may be used. The first fixed resistor 13 and the second fixed resistor 14 are the bridge circuit 2 configured by the first fixed resistor 13, the second fixed resistor 14, and the gas sensor unit 15 in an atmosphere not including the detection target gas. When a high temperature driving voltage is supplied to the voltage supply source 5, the change in the temperature of the sensitive element 11 and the temperature of the compensation element 12 are balanced in a convergent steady state, that is, between a pair of midpoints. Each resistance value is determined so that the midpoint potential difference Vc becomes zero. In the present embodiment, the resistance value of the first fixed resistor 13 is set to 200Ω, and the resistance value of the second fixed resistor 14 is set to 200Ω.

  The resistance value of the sensitive element 11 is Rs, the resistance value of the compensation element 12 is Rr, the resistance value of the first fixed resistor 13 is R1, the resistance value of the second fixed resistor 14 is R2, and the supply voltage to the bridge circuit 2 is Assuming Vbrg, the midpoint potential difference Vc is represented by the following equation.

  Vc = ((Rs / (R2 + Rs)) − (Rr / (R1 + Rr))) × Vbrg

  The voltage supply source 5 is a voltage supply circuit that supplies a predetermined voltage to the bridge circuit 2. The voltage supply source 5 is connected to an MPU 60 described later, and the temperature of the sensitive element 11 becomes a low temperature (adsorption temperature, for example, 200 degrees) at which the detection target gas is adsorbed according to a voltage control signal from the MPU 60. Bridge the pulsed supply voltage Vbrg such as a low temperature drive voltage and a high temperature drive voltage at which the temperature of the sensitive element 11 becomes a high temperature (combustion temperature, for example, 400 degrees) for burning the detection target gas adsorbed on the sensitive element 11 Supply to circuit 2. That is, the low temperature drive voltage is supplied as the low temperature drive control, and the high temperature drive voltage is supplied as the high temperature drive control. In the present embodiment, the voltage is supplied by the voltage supply source to drive the gas sensor unit 15 as a catalytic combustion type gas sensor. However, the present invention is not limited to this, and for example, the temperature of the sensitive element is increased by a current source or the like. The gas sensor unit 15 may be driven by energizing the current at the low temperature or the high temperature.

  The instrumentation amplifier 6 is a balanced input amplifier having a differential input and a single-ended output, and is a well-known amplifier having a feature that a common mode rejection ratio (CMRR) can be increased. The instrumentation amplifier 6 amplifies the potential difference between the signals input to the pair of differential inputs with high impedance, respectively, with a predetermined amplification factor, and outputs the amplified signal. A signal line between the second fixed resistor 14 of the sensor circuit unit 10 and the sensitive element 11 (middle point) is connected to one (V +) of the differential input terminal of the instrumentation amplifier 6, and the other (V− ) Is connected to the signal line between the first fixed resistor 13 and the compensation element 12 (middle point) of the reference circuit unit 20. In other words, the instrumentation amplifier 6 includes a midpoint potential of the sensor circuit unit 10 (hereinafter referred to as “first voltage V1”) and a midpoint potential of the reference circuit unit 20 (hereinafter referred to as “second voltage V2”). And the potential difference between the first voltage V1 and the second voltage V2 (that is, the midpoint potential difference Vc) is amplified with a predetermined amplification factor and output from the output terminal.

  The A / D converter 7 is a well-known analog-digital converter that converts an input analog signal into a digital signal and outputs the digital signal. The midpoint potential difference Vc amplified by the instrumentation amplifier 6 is input to the input portion of the A / D converter 7. The output unit of the A / D converter 7 is connected to the MPU 60, and the midpoint potential difference Vc converted into a digital signal is output toward the MPU 60.

  As is well known, a microcomputer (MPU) 60 includes a central processing unit (CPU) 61 that performs various processes and controls according to a predetermined program, a read-only memory that stores programs for the CPU 61 and various parameters. ROM 62, which stores various data and RAM 63, which is a readable / writable memory having an area necessary for processing operations of CPU 61, and can retain various stored data even when power supply is cut off. And an EEPROM 64 having various storage areas necessary for processing operations of the CPU 61.

  The ROM 62 stores in advance a program that causes the CPU 61 to function as various means such as a low temperature drive means, a high temperature drive means, an output measurement means, and a gas concentration detection means. The CPU 61 functions as these means by executing various programs stored in the ROM 62.

  The MPU 60 further includes an input / output port (not shown) and an external connection unit having various interface functions. The MPU 60 is connected to the A / D converter 7 and the voltage supply source 5 through the external connection unit. The MPU 60 receives the midpoint potential difference Vc converted into a digital signal from the A / D converter 7 and detects the gas concentration based on the midpoint potential difference Vc. The MPU 60 supplies a low temperature driving voltage (ie, low temperature driving control) over a predetermined low temperature driving time (adsorption time, non-adsorption time), for example, and then performs a predetermined high temperature driving time (adsorption combustion time, contact) depending on the processing. A voltage control signal is transmitted to the voltage supply source 5 so as to supply a high temperature drive voltage (ie, high temperature drive control) over the combustion time).

  The MPU 60 is connected to a display device (not shown) via the external connection unit, and transmits, for example, a display control signal including information on the detected concentration of the detection target gas to the display device. The display device displays information corresponding to the display control signal, that is, the concentration of the detection target gas. Further, the MPU 60 is connected to a gas storage chamber equipped with a pump or the like through this external connection portion, and fills the gas storage chamber with various gases according to processing.

  Next, an example of the gas concentration detection operation in the gas concentration detection apparatus 1 described above will be described.

  The gas concentration detection device 1 detects a low-temperature driving voltage at which the temperature of the sensitive element 11 becomes a low temperature (adsorption temperature) at which the gas to be detected is adsorbed after the gas containing chamber is filled with the gas to be detected. The detection target gas that has been supplied over the predetermined adsorption time during which the gas is adsorbed and subsequently has a high temperature driving voltage at which the temperature of the sensitive element 11 becomes a high temperature (combustion temperature) for burning the detection target gas Supply is performed over a predetermined adsorption combustion time for combustion, and the integrated value (adsorption combustion integral value) of the output of the gas sensor unit 15 during the adsorption combustion time at this time is measured.

  Subsequently, the low temperature driving voltage is supplied over a predetermined non-adsorption time (the non-adsorption time is shorter than the adsorption time) in which the detection target gas is not adsorbed to the sensitive element 11, and then the high temperature driving voltage is supplied to the predetermined temperature. Supply over the contact combustion time (the same length as the adsorption combustion time), and measure the integrated value (contact combustion integrated value) of the output of the gas sensor unit 15 during the contact combustion time.

  Then, a value obtained by subtracting the contact combustion integral value from the adsorption combustion integral value is calculated as a gas detection value (adsorption peak integral value), and is obtained in advance by an adsorption peak integral value that is the gas detection value and preliminary measurement or the like. The concentration of the detection target gas is obtained based on the relationship information between the adsorption peak integrated value and the concentration of the detection target gas.

  In addition, in order for a detection object gas to adsorb | suck to a sensitive element, appropriate time is required. The adsorption time for which the detection target gas is adsorbed to the above-described sensitive element is a time period sufficient for the detection target gas to be adsorbed to the sensitive element, and the detection target gas is adsorbed to the sensitive element. The non-adsorption time is a time that is less than the adsorption time and is insufficient for the detection target gas to be adsorbed to the sensitive element.

  Thus, the detection target gas adsorbed by subtracting the contact combustion output (contact combustion integral value) when the detection target gas is not adsorbed from the adsorption combustion output (adsorption combustion integral value) when the detection target gas is adsorbed. Therefore, it is possible to extract only the peak output related to the above, so that the characteristics related to the adsorption combustion of the detection target gas can be obtained more clearly.

  As described above, according to the gas concentration detection device 1, the heater 42 is configured so that the temperature of the surface 430 of the catalyst sintered body 43 becomes uniform when the heater 42 included in the sensitive element 11 of the gas sensor unit 15 is driven. The amount of heat generated per unit area of the portion wired near the center of the surface 430 of the catalyst sintered body 43 is per unit area of the portion wired away from the center of the surface 430 of the catalyst sintered body 43. Since the heat generation amount is smaller than the amount of heat generation, it is possible to prevent the occurrence of temperature unevenness on the surface 430 of the catalyst sintered body 43. Therefore, the heater 42 is set so that the temperature of the surface 430 of the catalyst sintered body 43 becomes higher. Without being driven, the detection target gas combustion area on the surface 430 of the catalyst sintered body 43 can be expanded to increase the amount of detection target gas combustion, thereby improving sensitivity. Can.

  Although the gas concentration detection device 1 described above includes the gas sensor unit 15 as an adsorption combustion type gas sensor, the present invention is not limited thereto, and may include a contact combustion type gas sensor that performs non-adsorption combustion. However, in the case of this catalytic combustion type gas sensor, adsorption combustion does not occur, so the adsorption combustion integral value is not measured, only the above-mentioned catalytic combustion integral value is measured, and the concentration of the detection target gas is detected from this catalytic combustion integral value. To.

  Further, in the gas concentration detection device 1 described above, the concentration of the detection target gas is detected. However, the present invention is not limited to this, and a gas type detection device that detects the type of gas contained in the target gas whose component is unknown. The present invention may be applied to other types of gas detection devices.

  In addition, embodiment mentioned above only showed the typical form of this invention, and this invention is not limited to embodiment. That is, various modifications can be made without departing from the scope of the present invention.

1 Gas concentration detector (gas detector)
2 Bridge circuit 5 Voltage supply source 6 Instrumentation amplifier 11 Sensing element 12 Compensation element 15 Gas sensor unit (contact combustion type gas sensor, adsorption combustion type gas sensor)
42, 44 Heater 43 Catalyst sintered body (catalyst layer)
45 Sintered body 60 MPU
61 CPU

Claims (3)

In a catalytic combustion type gas sensor having a heater wired on a plane, and a catalyst layer provided on the plane so as to overlap the heater,
The heater has a calorific value per unit area of a portion wired near the center of the catalyst layer surface so that the temperature of the catalyst layer surface becomes uniform when the heater is driven. A catalytic combustion type gas sensor characterized in that it is formed to be smaller than a calorific value per unit area of a portion wired at a location far from the center of the layer surface.   The resistance value per unit length of the portion wired near the center of the catalyst layer surface in the heater is greater than the resistance value per unit length of the portion wired far from the center of the catalyst layer surface. The catalytic combustion type gas sensor according to claim 1, wherein the heater is formed so as to be low.   The heater is formed such that the wiring density of the portion wired near the center of the catalyst layer surface of the heater is lower than the wiring density of the portion wired far from the center of the catalyst layer surface. The contact combustion type gas sensor according to claim 1 or 2, wherein the contact combustion type gas sensor is provided.

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