JP2007064865A - Gas sensor and gas sensor manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly sensitive gas sensor and a manufacturing method for efficiently manufacturing the gas sensor.
A hydrogen sensor is a hydrogen sensor that converts heat generated by a catalytic reaction between hydrogen gas and a catalyst material into an electrical signal by a bridge circuit and detects it as a detection signal.
A substrate 20 that is insulative and inert to hydrogen and a platinum film 30 as a catalyst material formed on the main surface of the substrate 20 are provided. The platinum film 30 is formed in a zigzag shape, and is removed except for the joint portions 31 and 32 of the platinum film, and a bridging portion is provided to form a space where hydrogen gas flows on both the front and back surfaces of the platinum film 30. In addition, the contact area with the hydrogen gas is increased and the heat capacity is reduced to achieve high sensitivity. In addition, the platinum film 30 is subjected to a recrystallization process by supplying an electric current, thereby increasing the temperature coefficient.
[Selection] Figure 1

Description

The present invention relates to a gas sensor and a method for manufacturing the gas sensor. More specifically, the present invention relates to a structure of a contact combustion type gas sensor that detects a gas concentration and a preferable manufacturing method of the gas sensor.

In recent years, various gas sensors have been proposed. In particular, with the spread of fuel cells and the like, a hydrogen sensor that accurately measures the concentration of combustible gas, particularly hydrogen gas, is required for safety. However, the hydrogen sensors that have been commercially available from the past have the problems of slow response speed, large size, and high cost, which hinders widespread use.

Therefore, in order to solve these problems, a pressure film of thermoelectric conversion oxide material is formed on the surface of the substrate, and several to several platinum films as catalyst materials are formed on half of the surface of the pressure film of thermoelectric conversion oxide material. There is a hydrogen sensor that is formed with a thickness of 10 nm, converts a local temperature difference generated from catalyst heat generation of hydrogen gas and a platinum catalyst into a voltage signal by a thermoelectric conversion oxide material, and measures the hydrogen gas concentration. It has been proposed (see, for example, Patent Document 1).

JP 2003-156461 A (Page 4, FIG. 1)

In such Patent Document 1, since the platinum film as the catalyst material is formed on the surface of the pressure film of the thermoelectric conversion oxide material, the contact range between the platinum film and the hydrogen gas is one of the exposed platinum films. Therefore, it is predicted that the contact area with hydrogen gas is small, the generation of catalyst heat is small, and a sufficient temperature difference cannot be obtained. Also, in order to increase the catalyst heat, it is necessary to increase the contact area with hydrogen gas, and the area of the platinum film must be increased. In this way, the heat capacity of the platinum film increases, and the detection response It is considered that the speed, that is, the detection sensitivity cannot be increased.

In addition, since the entire flat area of the surface of the platinum film is bonded to the thermoelectric conversion oxide material film, the catalyst heat generated in the platinum film is transferred to the thermoelectric conversion oxide material film, so that the heat capacity increases as a whole. There is a problem that the response speed cannot be increased.

Furthermore, the local temperature difference generated from the catalyst heat generation of hydrogen gas and platinum catalyst is converted into a voltage signal by the thermoelectric conversion oxide material, and the hydrogen concentration is measured. This is a difficult material to form, and is generally difficult to form a pressure film, and requires several film forming steps.

An object of the present invention is to provide a highly sensitive gas sensor and a manufacturing method for efficiently manufacturing the gas sensor with a small number of steps, which is intended to solve the above-described problems.

The gas sensor of the present invention is a gas sensor that converts heat generated by a catalytic reaction between a gas and a catalyst material into an electric signal by a thermoelectric conversion circuit and detects it as a detection signal. And an inert substrate, and the catalyst material formed on the main surface of the substrate,
The substrate is characterized in that a lower portion of the catalyst material is removed except for a joint surface with the catalyst material, and a space in which a gas flows is formed on the back surface of the catalyst material.
At this time, the catalyst material has a cross-linked shape by forming a space through which the gas flows.

According to the present invention, since the portion other than the joint portion with the catalyst material is removed from the substrate, the gas to be detected contacts both the front and back surfaces of the catalyst material, so that only one surface of the catalyst material described above is present. Compared with the structure in which the gas is in contact with the gas, the contact area with the gas is increased, the rising rate of the catalyst heat is increased, and the response is improved.

In addition, since a large range of the catalyst material (a range other than the junction with the substrate) is configured not to be bonded to the substrate, the heat capacity of the gas sensor as a whole is reduced, and the response, that is, the detection sensitivity can be further improved. it can.

Further, the catalyst material includes a connection portion with the thermoelectric conversion circuit provided at both ends, a joint portion with the substrate, and a continuous portion in which the connection portion and the joint portion are continuous in a zigzag shape, The planar shape is a single zigzag shape.

Thus, since the catalyst material is formed into a thin and long shape, the resistance of the catalyst material is increased, the catalyst heat due to the gas is easily increased, the temperature increase rate of the catalyst material is increased, and the sensitivity can be increased.
Furthermore, as described above, since the gas is in contact with both the front and back surfaces of the catalyst material, the sensitivity can be further enhanced in combination with the zigzag shape of the catalyst material.

Further, the catalyst material is formed of a platinum or palladium film having a selective catalytic action on hydrogen.
As a catalyst material for hydrogen gas detection, platinum (Pt) or palladium (Pd) is suitable, and platinum and palladium have selectivity to respond only to hydrogen gas.
Only hydrogen gas exhibits a catalytic reaction at 00 ° C. or lower, and excellent selectivity to hydrogen gas can be realized.

Moreover, it is preferable that a metal film having higher electrical conductivity than the catalyst material is further formed at the interface between the catalyst material and the substrate.
Here, when the catalyst material is platinum or palladium, examples of the metal film include Au,
Is selected.

In this manner, by forming an Au film between platinum or palladium and the substrate, it is possible to promote the heat generation of only the catalyst material in the space region having a high specific resistance and perform the recrystallization process.

In addition, when the metal film is an Au thin film, it is desirable that a metal film made of Cr, Ni, Ti, or an alloy thereof is further formed to increase the bonding strength between the Au thin film and the substrate.

In this way, since the bonding strength between the Au thin film and the substrate can be increased, it is possible to prevent peeling of the Au thin film and realize a highly reliable gas sensor.

Moreover, it is preferable that the space is formed by a through hole formed in the substrate, and a part of the back surface of the catalyst material is exposed.

If it does in this way, it will become easy to flow gas on the back surface of a catalyst material, and a catalyst reaction can be promoted. Furthermore, the through hole can be formed using a general manufacturing method such as dry etching or wet etching.

The space is preferably formed by a recess provided by removing the sacrificial layer after the sacrificial layer is formed on the substrate, and a part of the back surface of the catalyst material is exposed.
Here, as the sacrificial layer, for example, when the substrate is silicon (Si), it is a selective oxidation layer by element isolation, and can be formed in a range of a space to be formed.

By forming the space in which the gas flows in this way, it is possible to obtain almost the same sensitivity as the structure in which the above-described through hole is opened, and it is possible to increase the structural strength of the substrate compared to the structure in which the through hole is provided. effective.

In the present invention, the catalyst material is subjected to a recrystallization treatment by a heat treatment.
Here, the recrystallization treatment means, for example, that the catalyst material is heated to increase the crystallinity of the catalyst material. This recrystallization treatment may be referred to as annealing.
According to the present invention, since the crystallinity of the catalyst material is increased by recrystallization, the thermal conductivity is improved and the sensitivity can be increased.
Further, the recrystallization increases the strength of the catalyst material formed into a film, and the structural strength of the catalyst material having a crosslinked shape can be increased by providing the above-described space.

The thermoelectric conversion circuit is preferably a bridge circuit in which the catalyst material is connected as a resistance temperature detector.
Here, the bridge circuit means a circuit based on a Wheatstone bridge circuit.

Thus, by using one of the four resistors constituting the bridge circuit as a catalyst material, a highly sensitive gas sensor can be realized with a simple circuit configuration.

Moreover, it is desirable that the measurement temperature environment of the catalyst material is variable.
As described above, if the catalyst material is platinum, platinum has a high selectivity to hydrogen gas even in a room temperature environment region, but when catalyst heat is generated, water vapor is generated from a mixed gas of hydrogen and air. It is known to do. When this water vapor adheres to the catalyst material (condensation), an accurate detection value may not be obtained. Therefore, by making the measurement temperature environment of the thermoelectric conversion circuit variable, the measurement temperature environment can be set within a predetermined temperature range.
If the temperature is set in the vicinity of ° C., condensation of the generated water vapor can be prevented, and accurate hydrogen gas concentration can be detected.

Furthermore, it is preferable that heating power is supplied to the catalyst material connected to the thermoelectric conversion circuit, and a predetermined measurement temperature environment is set.

By supplying electric power to the catalyst material in this way, heat is generated by the resistance of the catalyst material, and the measurement temperature environment can be arbitrarily set. Thus, the gas concentration can be detected in a desired measurement temperature environment.
Since the heating power may be supplied from an external power source to both ends of the catalyst material connected to the thermoelectric conversion circuit, it can be realized without changing the configuration of the gas sensor including the thermoelectric conversion circuit.

In addition, it is desirable to detect heat generated by the catalytic reaction as a change in resistance value of the material constituting the catalyst material.

Such a gas sensor can perform gas detection with a simple configuration including a measuring device,
In addition, since the gas is detected by catalytic heat, it is possible to provide a highly reliable gas sensor that can be repeatedly measured.

The gas sensor manufacturing method of the present invention is a gas sensor manufacturing method for detecting heat generated by a catalytic reaction between a gas and a catalyst material as a detection signal by converting the heat generation into an electric signal by a thermoelectric conversion circuit. A step of forming a catalyst material on the main surface of the substrate that is inert to the gas to be detected; and removing the lower portion of the catalyst material except for a bonding surface with the catalyst material; The method includes a step of forming a space in which a gas flows on the back surface of the material, and a step of recrystallizing the catalyst material.

According to such a manufacturing method, the shape of the catalyst material can be accurately formed in a small number of steps by means of forming a metal film or the like that has been conventionally used, opening a hole by etching or the like, and forming a recess. The substrate shape can be molded.

Furthermore, in the present invention, it is preferable that the step of recrystallizing the catalyst material is a resistance heating step of supplying current to the catalyst material and heating the catalyst material.

According to the present invention, the temperature of the catalyst material can be raised to the recrystallization temperature by supplying current to the catalyst material and resistance heating due to the resistance of the catalyst material. Further, by appropriately adjusting the supply current, the temperature can be increased to a desired temperature, and the temperature can be freely set within the range from the temperature at which recrystallization of the catalyst material starts to less than the transformation point temperature.

Moreover, according to this method, compared with the method of heating a conventional catalyst material in a constant temperature bath, equipment such as a constant temperature bath is unnecessary, and it can be heated to a desired temperature in a short time.

In the gas sensor manufacturing method of the present invention, when a recrystallization process is performed by supplying current to the catalyst material, a metal film having a higher electrical conductivity than the catalyst material is provided between the catalyst material and the substrate. And forming a resistance value at the interface between the catalyst material and the metal film lower than that of the catalyst material in the space region, and promoting heat generation of only the catalyst material in the space region to perform a recrystallization process. It is preferable.

In this way, heat generation concentrates only on the catalyst material in the space region, and thus the heat generation rate can be increased, so that the recrystallization rate increases and efficient recrystallization can be performed.

Furthermore, it is desirable that the method for forming the planar shape of the catalyst material is performed using a lift-off technique.

When the pattern of the catalyst material is formed, if the catalyst material is platinum, it is considered that an accurate pattern (shape) cannot be formed with a general etching solution (sometimes referred to as an etchant). By using it, accurate and efficient pattern formation can be performed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention can be applied to the detection of various gases. In the embodiments described below, a hydrogen sensor that detects hydrogen gas will be described as an example of a combustible gas.
1 to 4 show a hydrogen sensor and a method of manufacturing the hydrogen sensor according to Embodiment 1 of the present invention, FIG. 5 is Embodiment 2, FIG. 6 is a modification of Embodiment 1, and FIG. 7 is Embodiment 3. Is shown.
(Embodiment 1)

FIG. 1 is a perspective view showing a hydrogen sensor 10 according to the first embodiment, and FIG. 2 is a cross-sectional view schematically showing a cross section taken along the line AA of FIG. In the present embodiment, a hydrogen sensor chip as a resistance temperature detector is represented as a hydrogen sensor 10. 1 and 2, the hydrogen sensor 10 has a platinum film 30 as a catalyst material formed on the main surface of a substrate 20 and patterned into a predetermined shape. In the substrate 20, through holes 24 and 25 are formed below a partial region of the platinum film 30.
In addition, although platinum can be employ | adopted as a catalyst material other than platinum, platinum is illustrated and demonstrated in this embodiment.

The substrate 20 can be formed of silicon (Si), ceramics, quartz, quartz glass, or the like, and a material having an insulating property and inert to hydrogen is selected. In the substrate 20, rectangular through holes 24 and 25 are respectively opened in parallel, and are provided in a region where a back surface of a continuous portion 32 of a platinum film 30 having a zigzag shape described later is exposed. The peripheral portions of the through holes 24 and 25 are joined surfaces 21, 22 and 23 with the platinum film 30, and are provided on the same plane.

The platinum film 30 includes a connection portion 35 and a connection portion 36 that are connected to a bridge circuit 50 (see FIG. 3) formed at a larger area than the other at both ends, and the space between the connection portions 35 and 36 is between The planar shape is formed to be one zigzag shape. This zigzag shape corresponds to the substrate 20
It is comprised by the continuous part 32 which continues the junction part 31 and the junction part 33 currently joined. The shape of the platinum film 30 is axisymmetric with respect to the center line P of the substrate 20 shown in the drawing.

In the hydrogen sensor 10 exemplified in the present embodiment, the thickness of the platinum film 30 is 3 μm, and the continuous portion 3
The width of 2 is 140 μm, and the size of the hydrogen sensor 10 (hydrogen sensor chip) is 5 mm.
, W is 8 mm and H is 0.1 mm.

The cross-sectional shape will be described in more detail with reference to FIG. 2. An Au thin film 40 is formed between the platinum film 30 and the substrate 20. The Au thin film is provided in order to improve the adhesion between the substrate 20 and the platinum film 30 and is formed in a rectangular shape between the joint portions 31 and 33 of the platinum film 30, and each is electrically separated. . In addition, the Au thin film 40 is formed in the substrate 20 during the recrystallization process.
The upper platinum film 30 is devised so that the current concentrates on the Au thin film 40 at the interface between the platinum film 30 and the Au film 40. That is, the substrate 20 is heated by the heat generation of the platinum film 30 and the continuous portion (cross-linked portion) is not sufficiently heated by the catalyst heat, so that recrystallization is not performed. Further, in order to increase the bonding strength between the Au thin film 40 and the insulating substrate 20, a metal film (not shown) that is oxidized and stabilized is often used. In this embodiment, chromium (Cr) is used, but nickel (Ni), titanium (Ti), or the like may be used.

The platinum film 30 is bonded to the substrate 20 at the bonding portions 31 and 33 via the Au thin film 40, but the back surface of the continuous portion 32 is exposed because the through holes 24 and 25 of the substrate 20 are opened. Thus, a space in which hydrogen gas can flow is formed, and the entire surface of the platinum film 30 and the exposed portion of the back surface become a contact region with the hydrogen gas.

In addition, since the substrate 20 is left on the lower surfaces of the connection portions 35 and 36 at both ends of the platinum film 30, wire bonding or the like is used when connecting to the bridge circuit 50 (see FIG. 3) as a thermoelectric conversion circuit. It is suitable for connecting with.

A frame 39 made of a platinum film is provided around the zigzag platinum film 30. The frame 39 is a lift-off process for forming the platinum film 30 in a zigzag shape (see FIG. 4). Is the remaining lift-off portion. This leaves an unnecessary processing portion in order to shorten the processing time in the lift-off process.

Next, the bridge circuit 50 as a thermoelectric conversion circuit in the present embodiment will be described with reference to the drawings. The hydrogen sensor according to the present embodiment detects heat generated by a catalytic reaction caused by contact of hydrogen gas with the platinum film 30 serving as a catalyst material as a change in the resistance value of the platinum film 30. Detect value changes.
FIG. 3 is a circuit diagram showing a basic circuit configuration of the bridge circuit 50. In FIG. 3, since the configuration of the bridge circuit 50 is well known, detailed description thereof is omitted, but four resistors R1 to R1 are omitted.
4 are connected in series, and a DC power source 51 and a voltmeter 52 for applying a constant voltage are connected to the positions shown in the figure.

Here, one resistor R4 among the four resistors R1 to R4 is the hydrogen sensor 1 described above.
Zero platinum film 30 is connected as a resistance temperature detector. When there is no hydrogen gas, the respective resistors are balanced in the state of R4 × R1 = R2 × R3, and no current flows through the voltmeter 52. When air mixed with hydrogen gas comes into contact with the platinum film 30 as the catalyst material, catalyst heat is generated, the resistance value of the resistor R4 increases, the balance of the bridge circuit is broken, and an unbalanced current flows through the voltmeter. The difference between the values is detected and output to a microcomputer (not shown).

Since the voltage difference described above depends on the temperature and hydrogen concentration of the catalyst material, the microcomputer refers to a correlation table between the voltage difference and the hydrogen concentration in a predetermined measurement temperature environment recorded in advance in an internal storage device. Output in terms of hydrogen concentration.

The hydrogen sensor of the present invention uses the hydrogen gas concentration as the combustible gas from the viewpoint of safety, and can accurately detect the hydrogen gas concentration from about 0.05% to the lower explosion limit concentration of 5%. The alarm is issued when a predetermined hydrogen concentration is reached.

Accordingly, the thickness of the platinum film 30 and the minimum width and length of the zigzag-shaped continuous portion 32 are freely set to optimum specifications in order to achieve the above object.

The platinum film 30 is formed in a zigzag shape and then recrystallized. The recrystallization process is performed by heating the platinum film 30 (specifically, by a method for manufacturing a hydrogen sensor described later). Since the crystallinity of the platinum film 30 is increased by the recrystallization treatment, the resistance value of the platinum film as the catalyst material is 21 under the conditions of the platinum film 30 of the present embodiment described above.
The resistance value decreases from 0Ω to 150Ω, and the temperature coefficient increases from 2000 ppm / ° C. to 2800.
Change to ppm / ° C.

In particular, the higher temperature coefficient indicates that the amount of change in the resistance value has increased with respect to the temperature change of the platinum film 30, that is, the change in the hydrogen concentration, which means that the detection sensitivity has increased. Yes.

Therefore, according to the configuration of the first embodiment described above, the joint portion 21 of the substrate 20 with the platinum film 30,
Since the portions other than 22 and 23 are removed by the through holes 24 and 25, the hydrogen gas contacts both the entire surface of the platinum film 30 and the back surface of the continuous portion 32. Compared with the structure in which only hydrogen gas contacts, the contact area with the hydrogen gas increases, the catalyst heat rises faster and the responsiveness is enhanced.

In addition, since the region other than the junctions 31 and 33 region of the platinum film 30 with the substrate 20 is not bonded to the substrate 20, the heat capacity of the entire hydrogen sensor is reduced, and the response, that is, the detection sensitivity can be further improved. it can.

Further, since the platinum film 30 is formed in a zigzag shape, the platinum film 30 can be formed into a thin and long shape, so that the resistance of the platinum film 30 is increased, the catalyst heat due to hydrogen gas is increased, and the temperature measuring resistor is used. The temperature of the platinum film 30 is increased and the sensitivity can be increased.
Furthermore, as described above, since the hydrogen gas is in contact with both the front and back surfaces of the platinum film 30, the sensitivity can be further enhanced in combination with the zigzag shape.

Further, since the catalyst material is formed of a platinum film that is excellent in selectivity against hydrogen gas, a hydrogen sensor having a simple configuration in which the platinum film 30 is formed on the surface of the substrate 20 can be realized.

Moreover, in this invention, thermal conductivity improves by recrystallizing the platinum film | membrane 30, From this, a sensitivity can be raised.
Furthermore, the strength of the formed platinum film 30 is increased by recrystallization, and the structural strength of the platinum film 30 having a crosslinked shape can be increased by providing the above-described space.

Further, by providing the Au film 40 between the platinum film 30 and the substrate 20, a space (through-hole 2
4), the heat generation of only the platinum film 30 (crosslinked portion) having a high specific resistance in the region 4) is promoted, and the recrystallization treatment can be performed efficiently.

Furthermore, since a Cr thin film is formed between the Au film 40 and the substrate 20, the Au film 4
It is possible to realize a highly reliable hydrogen sensor that prevents 0 peeling.

Further, the bridge circuit 50 is adopted as the thermoelectric conversion circuit, and the bridge circuit 50 is configured 4
A highly sensitive hydrogen sensor can be realized with a simple circuit configuration by using one of the resistors R1 to R4 as the platinum film 30 as a temperature measuring resistor.
(Method for Manufacturing Hydrogen Sensor of Embodiment 1)

Then, the manufacturing method of the hydrogen sensor 10 of the structure by Embodiment 1 mentioned above is demonstrated with reference to drawings.
FIG. 4 is a cross-sectional view schematically showing main manufacturing steps of the hydrogen sensor 10 according to the first embodiment. This sectional view shows the AA section of FIG. First, the Au thin film 40 is formed.
FIG. 4A shows a process for forming the Au thin film 40. First, the main surface of the substrate 20 is subjected to CMP (
A smooth surface is finished by chemical and mechanical polishing, etc., and a Cr thin film (not shown) is formed in a predetermined shape and range by a film forming means such as sputtering, and then an Au thin film 40 is formed on the surface of the Cr thin film. In the present embodiment, the platinum film 3 described above.
It forms so that the junction parts 31 and 33 of 0 may be connected.
Subsequently, a platinum film 30 is formed on the surface of the Au thin film.

FIG. 4B shows a film forming process of the platinum film 30. A platinum film 30 is formed on the entire main surface of the substrate 20 including the Au thin film 40 using a film forming means such as vapor deposition or sputtering. On this occasion,
The thickness of the platinum film 30 is 3 μm.
Next, resist coating is performed.

FIG. 4C shows a coating process of the resist 60. In this step, the resist 60 is applied to the entire surface of the platinum film 30. At this time, the upper surface of the resist 60 becomes substantially the same plane.
Next, the platinum film 30 is formed into a predetermined zigzag shape by a lift-off process.

FIG. 48D shows a lift-off process. The resist 60 and the platinum film 30 are removed into a predetermined shape by a lift-off process using a mask having an opening in a predetermined zigzag shape, that is, a shape to be removed, on the surface of the resist 60. Thereafter, the resist 60 is removed,
A catalyst material made of the zigzag platinum film 30 is formed.

FIG. 4E shows a resist coating process on the back surface of the substrate 20. First, substrate 2
A resist 65 is applied to the back surface of 0, and the shape corresponding to the through holes 24 and 25 is patterned into an open shape.
Subsequently, the through holes 24 and 25 are opened.

FIG. 4F shows a through hole opening process. The through holes 24 and 25 remove portions corresponding to the through holes 24 and 25 of the substrate by wet etching or dry etching.
Thus, after forming the shape of the hydrogen sensor 10, a recrystallization process is performed.

FIG. 4G shows a resistance heating process as a recrystallization process (annealing). After the shape of the hydrogen sensor 10 is formed, a heating power source 70 is connected to the connecting portions 35 and 36 (see FIG. 1) at both ends of the platinum film 30 to supply heating power. In this embodiment, the voltage is 110V.
The electric current of 42 mA is supplied, and the platinum film 30 is heated to 500 ° C. by the resistance heating generated at this time.
It was possible to heat to the vicinity. In order to lower the resistance value of the catalyst material, which is the gist of the present invention for performing the recrystallization treatment, and to increase the structural strength, the range of 500 ° C. to 900 ° C. is suitable, and the supplied current, applied voltage, and The desired crystallinity can be obtained by appropriately adjusting the time.
The recrystallization treatment step can also be performed after the platinum film 30 is formed or formed in a zigzag shape.

After the hydrogen sensor 10 is completed as a hydrogen sensor chip, the bridge circuit 5 described above is used.
The connecting portions 35 and 36 are connected to 0 (see FIG. 3) by wire bonding.
Further, even when palladium is employed as the catalyst material, it can be manufactured along the manufacturing process described above.

Therefore, according to the method for manufacturing the hydrogen sensor 10 described above, the formation of the platinum film 30 as a catalyst material by sputtering or vapor deposition as a commonly used means for forming a metal film, penetration by dry etching or wet etching, etc. The opening of the holes 24 and 25 can be formed with few steps and with high accuracy.

Further, by supplying heating power to the platinum film 30 and resistance heating by the resistance of the platinum film 30, the temperature of the platinum film 30 can be quickly raised to the recrystallization temperature. Moreover, it can be easily raised to a desired temperature by appropriately adjusting the supply current and voltage.
According to this method, compared with a method of heating a catalyst material that has been conventionally used in a thermostat, etc., there is no need for equipment such as a thermostat, and it is possible to heat to a desired temperature in a short time. There is.

Furthermore, since the lift-off technique is used as a method for forming the pattern (shape) of the platinum film 30 as the catalyst material, the pattern can be formed accurately and efficiently.
(Embodiment 2)

Subsequently, a hydrogen sensor according to Embodiment 2 of the present invention will be described with reference to the drawings. The second embodiment is realized by forming a space in which hydrogen gas flows on the back surface side of the platinum film 30 instead of the through hole instead of the through-hole as compared with the first embodiment described above. The description of common parts is omitted because it is the same as 1.
FIG. 5 is a cross-sectional view showing the hydrogen sensor 10 according to the second embodiment. In FIG.
At 0, concave portions 26 and 27 are formed in the back surface of the zigzag-shaped continuous portion 32 of the platinum film 30, and the back surface 32A of the continuous portion 32 is exposed. The planar shapes of the recesses 26 and 27 are substantially the same as those of the first embodiment (see FIG. 1).

The recesses 26 and 27 are formed by removing the sacrificial layer after a sacrificial layer is formed in a portion corresponding to the recesses 26 and 27 of the substrate 20. As the sacrificial layer, for example, the substrate is silicon (S
In the case of i), it is a selective oxidation layer by element isolation, and this sacrificial layer can be easily removed by dry etching or wet etching. In this way, a space in which hydrogen gas flows can be formed.
The sacrificial layer is formed in the state of the first substrate (bulk) in the manufacturing process of Embodiment 1 (see FIG. 4), and the sacrificial layer is removed after the platinum film 30 is formed in a zigzag shape. Done.

Therefore, according to the second embodiment described above, by forming the space through which the hydrogen gas flows in this way, the sensitivity that is substantially the same as the structure of opening the through hole in the space described above can be obtained, and the through hole is provided. There is an effect that the structural strength of the substrate can be increased rather than the structure.
(Modification)

Subsequently, a modification of the first embodiment of the present invention will be described with reference to the drawings. This modification is characterized in that the shape of the platinum film 30 according to Embodiment 1 described above is changed, and accordingly, has a feature in which one through hole is formed, and only the changed portion will be described. .
6A and 6B show a hydrogen sensor 100 according to this modification, in which FIG. 6A is a perspective view thereof, and FIG. 6B is a cross-sectional view schematically showing a BB cut surface of FIG. 6A and 6B, the platinum film 130 as the catalyst material is formed in a zigzag shape on the upper surface of the substrate 120.

The substrate 120 is provided with a rectangular through-hole 124 at substantially the center, and the platinum film 13 on both ends thereof.
Bonding surfaces 121 and 122 for bonding 0 are provided, and a through hole 124 is opened between the bonding surfaces 121 and 122.

The platinum film 130 is connected to the bridge circuit 50 (see FIG. 3) at both ends.
136 are formed in a zigzag shape between the connecting portions 135 and 136 by a continuous portion 132 that continues between the joint portions 131. This zigzag shaped platinum film 13
Although there is a frame portion 139 on the outer peripheral portion of 0, the frame portion 139 exists for the same reason as the frame portion 39 of the first embodiment.

Therefore, the through hole 124 is formed in the substrate 120 on the back side of the continuous portion 132 of the platinum film 130 as the catalyst material, and the back side 132A of the platinum film 130 is exposed.

The manufacturing method of the hydrogen sensor 100 according to the second embodiment is the same as the first and second embodiments described above.
The same process can be used.
Moreover, the through-hole opened in the board | substrate 120 is good also as a structure which provides an additional joining surface near the center so that the continuous part 132 may be skewered.

The above-described modification shows an example in which a space in which hydrogen gas can flow is formed on the front surface of the platinum film 130 as a catalyst material and the back surface of the platinum film 130, and the catalyst which is the gist of the present invention. The platinum film can be formed by appropriately combining the shape of the space and the shape of the space as long as the temperature coefficient can be increased and the heat capacity can be decreased.

Therefore, the effect obtained by the above-described first embodiment can be achieved even by the modified example in which the shape of the platinum film is simplified.
(Embodiment 3)

Next, the configuration of the hydrogen sensor according to Embodiment 3 of the present invention will be described with reference to the drawings. This embodiment is characterized in that the structure of the hydrogen sensor 10 (hydrogen sensor chip) described above is kept as it is, and the measurement temperature environment is variable.
FIG. 7 shows a bridge circuit 50 as a thermoelectric conversion circuit according to the third embodiment. As described in the recrystallization process described above, the platinum film can be heated by resistance by passing an electric current. A heating power supply 53 is connected to both ends of the platinum film 30 as a resistance temperature detector, and measurement is performed. It becomes possible to change the temperature environment.

Platinum has high selectivity for hydrogen gas even in a room temperature environment region, but it is known that water vapor is generated from a mixed gas of hydrogen and air when catalyst heat is generated. If this water vapor is condensed on the catalyst material, it is considered that an accurate detection value cannot be obtained. Therefore, by making the measurement temperature environment of the bridge circuit 50 variable, a desired measurement temperature environment can be set. If the temperature is set near 100 ° C., condensation of the generated water vapor can be prevented and accurate Hydrogen gas concentration can be detected.

Furthermore, since the heating power can be supplied to the platinum film 30 as a resistance temperature detector connected to the bridge circuit 50 and the measurement temperature environment can be arbitrarily set, the configuration of the hydrogen sensor including the thermoelectric conversion circuit can be changed. It can be realized without.
Since the hydrogen concentration can be detected by the temperature difference of the platinum film 30, that is, the voltage difference output from the bridge circuit 50, if the temperature after heating is kept constant, the accurate hydrogen concentration can be detected from this voltage difference. Can be done.

It should be noted that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.
That is, the present invention has been particularly illustrated and described with respect to an embodiment of a hydrogen sensor for detecting hydrogen gas, but the above-described implementation has been made without departing from the scope of the technical idea and object of the present invention. Various modifications can be made by those skilled in the art in the shape, material, combination, other detailed configuration, and processing method between manufacturing processes corresponding to the type of gas to be detected. Is.

Therefore, the description limited to the shape, material, manufacturing process and the like disclosed above is an example for easy understanding of the present invention, and does not limit the present invention. Descriptions of the names of members from which some or all of the limitations such as materials and combinations are removed are included in the present invention.

For example, in the above-described embodiment, the platinum film as the catalyst material is formed in a zigzag shape, but it can be formed in a simple flat plate shape, and can be formed in a mesh shape, and unevenness is formed in the cross-sectional direction in the platinum film. This is also included in the scope of the present invention, and the shape can be freely selected by combining with the exchange of hydrogen flowing on the back side of the platinum film.

Moreover, the bridge circuit as a thermoelectric conversion circuit has resistors R1 to R1 outside the hydrogen sensor chip.
A bridge circuit may be formed on the substrate 20 by providing R3 and connecting a platinum film as a resistance temperature detector (resistor R4) by wire bonding.

Therefore, according to the above-described first to third embodiments, it is possible to provide a highly sensitive hydrogen sensor and a manufacturing method for efficiently manufacturing the hydrogen sensor with fewer steps.

The perspective view which shows the hydrogen sensor which concerns on Embodiment 1 of this invention. Sectional drawing which shows typically the AA cut surface of FIG. 1 of the hydrogen sensor which concerns on Embodiment 1 of this invention. The circuit diagram which shows the basic circuit structure of the bridge circuit as a thermoelectric conversion circuit which concerns on Embodiment 1 of this invention. Sectional drawing which shows typically the manufacturing process of the hydrogen sensor by Embodiment 1 of this invention. Sectional drawing which shows the hydrogen sensor which concerns on Embodiment 2 of this invention. The hydrogen sensor which concerns on the modification of Embodiment 1 of this invention is shown, (a) is the perspective view, (b) is sectional drawing which shows typically the BB cut surface of Fig.6 (a). The circuit diagram which shows the bridge circuit as a thermoelectric conversion circuit which concerns on Embodiment 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Hydrogen sensor, 20 ... Board | substrate, 24, 25 ... Through-hole, 30 ... Platinum film as a catalyst material,
31, 32... Junction with a platinum film substrate, 50... Bridge circuit as a thermoelectric conversion circuit.

Claims (16)

A gas sensor that converts heat generated by a catalytic reaction between a gas and a catalyst material into an electric signal by a thermoelectric conversion circuit and detects it as a detection signal,
A substrate that is insulative and inert to the gas to be detected;
The catalyst material formed on the main surface of the substrate,
The gas sensor according to claim 1, wherein a lower portion of the catalyst material is removed except for a joint surface with the catalyst material, and a space in which a gas flows is formed on the back surface of the catalyst material. The gas sensor according to claim 1,
The catalyst material includes a connection portion with the thermoelectric conversion circuit provided at both ends, a joint portion with the substrate, and a continuous portion in which the connection portion and the joint portion are continuous in a zigzag shape, and has a planar shape. Is formed in a single zigzag shape. The gas sensor according to claim 1 or 2,
The gas sensor according to claim 1, wherein the catalyst material is formed of a platinum or palladium film having a catalytic action selectively on hydrogen. The gas sensor according to claim 3, wherein
A gas sensor, wherein a metal film having higher electrical conductivity than the catalyst material is further formed at an interface between the catalyst material and the substrate. The gas sensor according to claim 3 or 4,
When the metal film is an Au thin film, a gas film further comprising a metal film made of Cr, Ni, Ti, or an alloy thereof for increasing the bonding strength between the Au thin film and the substrate is formed. . The gas sensor according to any one of claims 1 to 5,
The gas sensor according to claim 1, wherein the space is formed by a through hole formed in the substrate, and a part of the back surface of the catalyst material is exposed. The gas sensor according to any one of claims 1 to 6,
The gas sensor is characterized in that the space is formed by a recess provided by removing the sacrificial layer after the sacrificial layer is formed on the substrate, and a part of the back surface of the catalyst material is exposed. The gas sensor according to any one of claims 1 to 7,
A gas sensor, wherein the catalyst material is recrystallized by heat treatment. The gas sensor according to claim 1,
The gas sensor, wherein the thermoelectric conversion circuit is a bridge circuit in which the catalyst material is connected as a resistance temperature detector. The gas sensor according to claim 1 or 9,
A gas sensor, wherein a measurement temperature environment of the thermoelectric conversion circuit is variable. The gas sensor according to claim 10, wherein
A gas sensor, wherein heating power is supplied to the catalyst material connected to the thermoelectric conversion circuit, and a predetermined measurement temperature environment is set. The gas sensor according to any one of claims 1 to 11,
A gas sensor that detects heat generation due to a catalytic reaction as a change in resistance value of a material constituting the catalyst material. A gas sensor manufacturing method for detecting heat generated by a catalytic reaction between a gas and a catalyst material as a detection signal by converting it into a voltage signal by a thermoelectric conversion circuit,
Forming a catalyst material on the main surface of the substrate that is insulative and inert to the gas to be detected;
Removing the catalyst material except for the joint surface with the catalyst material, and forming a space in which gas flows on the back surface of the catalyst material;
Recrystallizing the catalyst material by heat treatment;
The method for manufacturing a gas sensor according to any one of claims 1 to 7, wherein In the manufacturing method of the gas sensor according to claim 13,
The method of manufacturing a gas sensor, wherein the step of recrystallizing the catalyst material is a resistance heating step of supplying current to the catalyst material and heating the catalyst material. In the manufacturing method of the gas sensor according to claim 14,
When supplying a current to the catalyst material and performing a recrystallization treatment, a metal film having a higher electrical conductivity than the catalyst material is formed between the catalyst material and the substrate,
The resistance value at the interface between the catalyst material and the metal film is set lower than the catalyst material in the space region,
A method of manufacturing a gas sensor, wherein recrystallization is performed by promoting heat generation of only the catalyst material in the space region. In the manufacturing method of the gas sensor according to any one of claims 12 to 15,
A method for producing a gas sensor, wherein the method for forming a planar shape of the catalyst material is performed using a lift-off technique.

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