JP4852283B2 - Gas sensor - Google Patents

Description

  The present invention relates to a gas sensor that detects heat generated by a gas and a catalyst medium as a temperature.

Conventionally, a gas sensor for detecting a gas corresponding to a use has been put into practical use. In particular, a gas sensor that detects flammable gas is positioned as an important sensor for ensuring safety in use.
For example, in recent years, fuel cells have been developed for automobiles and households in order to reduce the environmental load. Since a fuel cell uses hydrogen as a fuel, detecting a gas leak of hydrogen gas is an important matter when using the fuel cell safely. This gas leak is detected by a hydrogen sensor, and a hydrogen sensor that responds only to hydrogen gas and quantitatively detects a hydrogen concentration of about 0.05% to 5% is required.

Currently, metal oxide sintered semiconductor sensors, contact combustion sensors, and the like are known as hydrogen sensors.
The metal oxide sintered semiconductor sensor utilizes a change in electrical resistance due to gas adsorption on the semiconductor surface, forms a bridge circuit paired with a fixed resistance, and detects this change as a voltage.
In addition, the contact combustion type sensor uses heat generated by the contact combustion phenomenon on the surface of a substance having a gas detection function, and detects a change in electrical resistance from this temperature change as a voltage from a bridge circuit paired with a fixed resistance. Is.

For example, as shown in Patent Document 1 as an example of a contact combustion type hydrogen sensor, a hydrogen reaction catalyst layer as a catalyst medium and a thin film thermistor for detecting the heat generation temperature of the hydrogen reaction catalyst layer are stacked via an insulating layer, A bridge circuit is configured using this element, and the hydrogen concentration can be detected by detecting the bridge voltage.

JP 2005-98742 A

However, the conventional gas sensor such as a hydrogen sensor has a problem that the gas concentration cannot be detected with high sensitivity because the voltage detected from the bridge circuit or the like is very small.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a gas sensor capable of detecting a gas concentration with high sensitivity.

In order to solve the above-mentioned problems, the present invention is a gas sensor for detecting heat generated by a gas and a catalyst medium as a temperature, wherein the gas detection part is constituted by a mechanical vibrator whose natural frequency changes depending on the temperature, and the catalyst A medium is provided on the mechanical vibrator, and heat generated by the catalytic effect of the gas and the catalyst medium is transmitted to the mechanical vibrator to cause a temperature rise, thereby changing a natural frequency of the mechanical vibrator. Features.

According to this configuration, the heat generated by the catalyst medium and the gas provided on the mechanical vibrator is transmitted to the mechanical vibrator, and the temperature of the mechanical vibrator rises. Since this mechanical vibrator has a characteristic that the natural frequency changes with temperature, the natural frequency changes as the temperature of the mechanical vibrator increases. By detecting the change in the natural frequency, it is possible to detect the presence of gas or the concentration of gas.
As described above, the gas sensor of the present invention can detect the gas by detecting the frequency signal caused by the temperature of the mechanical vibrator. Therefore, compared with the conventional method of detecting the gas by detecting the voltage, the gas is detected. A gas sensor capable of detecting with high sensitivity can be provided.
Here, as a material used for the mechanical vibrator, a single crystal piezoelectric material, a polycrystalline piezoelectric material, or a magnetostrictive material is employed. Examples of the single crystal piezoelectric material include α crystal, lithium niobate, and lithium tantalate, and examples of the polycrystalline piezoelectric material include PZT and barium titanate. Examples of the magnetostrictive material include nickel and amorphous ferromagnet.

In addition, the gas sensor of the present invention preferably includes a temperature control means for controlling the temperature of the mechanical vibrator and the portion of the catalyst medium in order to control the catalytic effect.

According to this configuration, by providing the temperature control means for controlling the temperature of the mechanical vibrator and the catalyst medium portion, both temperatures can be used at a temperature higher than the gas atmosphere temperature. In this way, the catalytic effect of the catalyst medium is improved, and a temperature change of heat generation can be detected efficiently, and a gas sensor with excellent sensitivity can be provided.

In the gas sensor of the present invention, it is desirable that current is passed through the catalyst medium as the temperature control means, and temperature control is performed by the heat generation effect.

In this way, by passing an electric current through the catalyst medium itself, it is possible to generate heat due to its resistance and raise the temperature of the mechanical vibrator. By appropriately controlling the magnitude of the electric current and the energizing time, the mechanical vibration The child temperature can be controlled. From this, it is possible to eliminate the influence of the change in the atmospheric temperature or the water that reacts with the gas and generates heat when the catalyst medium generates heat, and it is possible to provide a gas sensor with excellent sensitivity.

The gas sensor of the present invention is a gas sensor mainly composed of hydrogen gas as a detection gas. The piezoelectric vibration piece has a main surface on both sides and excites a vibration mode of thickness sliding, and the main surface of the piezoelectric vibration piece. Formed excitation electrode and connection electrode, at least a hydrogen reaction catalyst film formed on the excitation electrode and generating heat in response to hydrogen gas, an oscillation circuit for exciting the piezoelectric vibrating piece,
And a temperature change of the piezoelectric vibrating piece due to heat generation of the hydrogen reaction catalyst film is detected as a frequency signal.

A piezoelectric vibrating piece that excites a thickness-shear vibration mode generally has a frequency-temperature characteristic and oscillates at a frequency corresponding to the temperature. Further, when air containing hydrogen is brought into contact with the hydrogen reaction catalyst film, there is a property of generating catalytic combustion and generating heat. The gas sensor of the present invention is configured using these characteristics and properties.
First, air containing hydrogen comes into contact with the hydrogen reaction catalyst film to generate heat, the heat is transmitted to the piezoelectric vibrating piece, and the temperature of the piezoelectric vibrating piece rises. The piezoelectric vibrating piece oscillates at a frequency corresponding to this temperature.
The hydrogen concentration can be detected based on the detected frequency signal or the temperature derived from the frequency signal.
Thus, since the gas sensor of the present invention can detect the concentration of hydrogen gas by detecting the frequency signal resulting from the temperature of the piezoelectric vibrating piece, the conventional method of detecting the concentration of hydrogen gas by detecting the voltage Compared to the above, it is possible to provide a gas sensor that can detect the hydrogen concentration with high sensitivity.

In the gas sensor of the present invention, the hydrogen reaction catalyst film is preferably formed of a material selected from platinum or palladium.

According to this configuration, by using platinum or palladium as the hydrogen reaction catalyst membrane, a hydrogen reaction catalyst membrane having high hydrogen selectivity and hardly responding to other combustible gases can be configured.

In the gas sensor of the present invention, it is preferable that the piezoelectric vibrating piece is a quartz vibrating piece.

According to this configuration, the crystal has good workability and is suitable for mass production, and has an advantage that the temperature sensitivity coefficient of the crystal vibrating piece can be adjusted by appropriately selecting the cut angle (cutting orientation) of the main surface of the crystal. That is, by appropriately selecting the cut angle of the main surface of the crystal, it is possible to obtain a good sensitivity to temperature, and thus to provide a gas sensor that can detect the hydrogen concentration with high sensitivity and is excellent in mass productivity. .

The gas sensor of the present invention is a gas sensor that detects heat generated by a gas and a catalyst medium as a temperature, wherein the gas detection portion includes a crystal vibrating piece whose natural frequency varies with temperature, and the catalyst medium includes the crystal vibration. The heat generated by the catalytic effect of the gas and the catalyst medium is transmitted to the quartz crystal vibrating piece and the temperature rises to change the natural frequency of the quartz crystal vibrating piece. The electrical axis of the crystal is the X-axis, the mechanical axis is the Y-axis, the optical axis is the Z-axis, the X-axis is rotated clockwise around the Z-axis by an angle φ °, and the Z-axis is Is rotated clockwise around the X ′ axis by an angle θ ° to be a Z ′ axis, a plane including the X ′ axis and the Z ′ axis is a main surface of the quartz crystal vibrating piece, and φ = 7˜ 14 (°), θ = 14 ± 3 (°) it is Desirable.

According to this configuration, a quartz crystal vibrating piece with a temperature sensitivity coefficient of 30 to 60 ppm / ° C. can be configured, a heat sensor corresponding to the hydrogen concentration can be detected efficiently, and a hydrogen sensor excellent in hydrogen concentration detection sensitivity is provided. can do. In particular, this cut angle can provide a gas sensor that is less susceptible to changes in temperature with respect to θ and is excellent in mass productivity.

Further, in the gas sensor of the present invention, the gas sensor detects heat generated by the gas and the catalyst medium as a temperature, and the gas detection part is constituted by a quartz crystal vibrating piece whose natural frequency changes with temperature, and the catalyst medium is The heat generated by the catalytic effect of the gas and the catalyst medium is transmitted to the crystal vibrating piece, the temperature rises, and the natural frequency of the crystal vibrating piece is changed. The electrical axis of the crystal of the crystal is the X axis, the mechanical axis is the Y axis, the optical axis is the Z axis, the X axis is rotated around the Z axis by an angle φ ° clockwise to be the X ′ axis, and The Z axis is rotated clockwise around the X ′ axis by an angle θ ° to form a Z ′ axis, a plane including the X ′ axis and the Z ′ axis is defined as a main surface of the quartz crystal vibrating piece, and φ = 0 (°), be θ = 28 ± 2 (°) , which is Masui.

According to this configuration, a quartz crystal vibrating piece with a temperature sensitivity coefficient of 30 to 60 ppm / ° C. can be configured, a heat sensor corresponding to the hydrogen concentration can be detected efficiently, and a hydrogen sensor excellent in hydrogen concentration detection sensitivity is provided. can do. This cut angle is particularly good for crystal etching.
A gas sensor excellent in mass productivity can be provided.

Hereinafter, an embodiment of a gas sensor embodying the present invention will be described with reference to the drawings, taking a hydrogen sensor as an example.
(First embodiment)

FIG. 1 is a schematic plan view showing a configuration of a hydrogen reaction detecting element according to the hydrogen sensor of the present embodiment. FIG. 2 is a schematic cross-sectional view taken along the line AA in FIG.
The hydrogen reaction detecting element 5 includes a quartz crystal vibrating piece 10 as a piezoelectric vibrating piece made of quartz. The quartz crystal vibrating piece 10 excites a vibration mode with a thickness shear. Excitation electrodes 15 and connection electrodes 16 are formed on the front and back main surfaces 17 of the quartz crystal vibrating piece 10, respectively. The excitation electrode 15 is provided in the vicinity of the center of the crystal vibrating piece 10 and is formed at a position facing the front and back of the crystal vibrating piece 10. A connection electrode 16 is connected to the excitation electrode 15 so that the electrode is drawn out to the outer periphery of the quartz crystal vibrating piece 10.

The excitation electrode 15 and the connection electrode 16 are composed of a base film 11 such as Cr and an electrode film 12 such as Au, and are formed by a technique such as vacuum deposition or sputtering.
Further, a hydrogen reaction catalyst film 13 made of platinum (Pt) is formed on the excitation electrodes 15 on the front and back surfaces of the quartz crystal vibrating piece 10 with a thickness of 300 nm to 600 nm by a technique such as vacuum deposition or sputtering.

A lead penetrates the support body 20, and an inner lead 21 extending from one side of the support body 20 and the connection electrode 16 of the crystal vibrating piece 10 are bonded and fixed via a conductive adhesive 23. Further, the outer lead 22 extending from the other side of the support 20 is connected to an oscillation circuit (not shown) that excites the quartz crystal vibrating piece 10.

Here, the cut angle (cutting direction) of the crystal vibrating piece 10 will be described in detail. Quartz has a frequency-temperature characteristic that depends on the cut angle, and a desired temperature sensitivity coefficient can be obtained by appropriately selecting the cut angle. In this embodiment, a crystal vibrating piece that excites a vibration mode of thickness sliding is used. This is because, since the hydrogen reaction detecting element 5 is arranged at normal pressure, in a quartz crystal vibrating piece that excites bending vibration, the air resistance affects the vibration, and the resistance value becomes high, and good vibration cannot be maintained. It is.

FIG. 3 is an explanatory diagram for explaining the cut angle of the quartz crystal vibrating piece 10 used in the present embodiment.
In three crystal axes orthogonal to each other of the quartz crystal 1 which is α crystal, the electric axis is the X axis, the mechanical axis is the Y axis, and the optical axis is the Z axis.
First, the X axis is rotated around the Z axis by a predetermined angle φ ° in the clockwise direction to obtain the X ′ axis. Further, the Z axis is rotated around the X ′ axis by an angle θ ° in the clockwise direction to obtain the Z ′ axis. At the same time, the Y axis is also rotated twice. In the figure, the axis that can be rotated by the angle φ ° is the Y ′ axis, and the axis that can be rotated by the subsequent angle θ ° is the Y ″ axis. The crystal plate 2 is obtained by cutting out from the raw quartz crystal 1 with the plane including the X ′ axis and the Z ′ axis formed by this new rotation as the main surface. Then, a crystal vibrating piece is formed using the crystal plate 2.
In the present embodiment, the clockwise direction around the crystal axis means the positive direction of the crystal axis (+
Side).

In the present embodiment, the rotated angles (rotation angles) φ and θ are set so as to satisfy the following expressions (1) and (2).
φ = 7-14 (°) (1)
θ = 14 ± 3 (°) (2)

Further, the cut angle may satisfy the following formulas (3) and (4). This cut angle is a cut angle belonging to the AT cut.
φ = 0 (°) (3)
θ = 28 ± 2 (°) (4)

Next, how the angles φ and θ are set so as to satisfy the expressions (1) and (2) will be described.
Since the hydrogen sensor of the present invention is a contact combustion type, it uses heat generated when hydrogen gas containing air contacts the hydrogen reaction catalyst film. Since the amount of heat generated by this heat generation is very small, it is necessary to efficiently detect a temperature change, and a quartz crystal resonator element having a high temperature dependency in frequency is desired.
The temperature dependence of the natural frequency of the quartz crystal resonator piece is related to the change in the shape of the quartz crystal resonator piece due to thermal expansion, the temperature dependence of the elastic constant, and the density change due to thermal expansion. Was determined by

Furthermore, the following points were considered in selecting the crystal cut angle. First, when the detection sensitivity of the hydrogen concentration is 0.1% or less, the temperature change when detecting the hydrogen concentration of 5% is 2 to 3
The temperature change is 0.04 to 0.06 ° C. per hydrogen concentration of 0.1%. Here, the detection limit of the frequency is about 1 ppm, and the temperature sensitivity (temperature sensitivity coefficient) of the crystal vibrating piece is 30 p.
If it is pm / ° C. or more, a frequency change of 1.2 ppm or more per hydrogen concentration of 0.1% can be obtained. Here, a value representing a frequency change by a frequency deviation at a temperature change of 1 ° C. is called a temperature sensitivity coefficient (ppm / ° C.).
On the other hand, increasing the temperature sensitivity coefficient improves the detection sensitivity of the hydrogen concentration. However, if the temperature sensitivity coefficient is large, the variation in frequency increases, and there is a concern about coupling with spurious. In general, if the fluctuation is about ± 5000 ppm with respect to the main vibration, a design that can avoid spurious is possible. If the operating temperature range of the hydrogen sensor is 50 to 220 ° C., the frequency fluctuation of about 10000 ppm with a temperature change of 170 ° C. The temperature sensitivity coefficient of 60 ppm / ° C. is considered to be the upper limit.
From this, it can be said that selecting a crystal cut angle with a temperature sensitivity coefficient of 30 to 60 ppm / ° C. is suitable for a crystal vibrating piece used in a hydrogen sensor.

FIG. 4 is a graph showing temperature characteristics when φ = 9 ° at the cut angle of the quartz crystal vibrating piece and θ is changed from 7 to 18 °.
From this graph, it can be seen that the temperature characteristic is approximated to a linear function at each cut angle, and the slope increases as the value of θ increases. This inclination corresponds to the temperature sensitivity coefficient described above.

Further, in the application of the hydrogen sensor, it is desirable that this temperature characteristic is excellent in linearity in a wide range. FIG. 5 is a graph showing how much the approximate straight line of the temperature characteristic at the cut angle of the crystal deviates from the standard deviation.
Here, the closer the standard deviation is to 1, the better the linearity, and it can be seen from FIG. 5 that the linearity is best around θ = 14 °. If an attempt is made to obtain a standard deviation of 0.9995 or more, θ = 1
Application is possible within a range of 4 ± 3 °.

Similarly, when a cut angle with a linear temperature characteristic was investigated in the range of φ = 0 to 16 ° in the crystal cut angle, it was confirmed that the vicinity of θ = 14 ° had the most excellent linearity.
A standard deviation of 0.9995 or more can be obtained in the range of 14 ± 3 °.
Table 1 below shows the selected rotation angles φ and θ and the temperature sensitivity coefficient. Here, for convenience, the respective cut angles are referred to as CA-1 to CA-5.

FIG. 6 shows the relationship between θ and the temperature sensitivity coefficient at the cut angles (CA-1 to CA-5) in Table 1.
Shown in
Cut angles (CA-1 to CA-4) are 30 to 30 when φ = 7 to 14 ° and θ = 14 ± 3 °.
It has a temperature sensitivity coefficient of 60 ppm / ° C. and is suitable for detecting temperature changes due to heat generated by the hydrogen reaction catalyst membrane. Further, since the cut angle (CA-1 to CA-4) has a small change in the temperature sensitivity coefficient with respect to the variation of θ, it is easy to cut out the quartz plate from the quartz crystal and is excellent in mass productivity. It can be said.

Further, it may be a crystal vibrating piece having a cutting orientation such as a cut angle (CA-5). This cut angle (CA-5) is a cut angle belonging to the AT cut, and the temperature sensitivity coefficient is 30 to 60.
The value of θ was set so as to fall within the range of ppm / ° C.
The cut angle (CA-5) has a large temperature sensitivity coefficient with respect to the variation of θ, but the crystal etching processability is good, and it is effective in the external shape processing of the crystal vibrating piece using etching and the frequency adjustment. The cut angle.

Returning to FIG. 1, in the hydrogen sensor configured as described above, air containing hydrogen contacts the hydrogen reaction catalyst film 13 to generate heat, and the heat is transmitted to the crystal vibrating piece 10, and the temperature of the crystal vibrating piece 10 rises. To do. The quartz crystal vibrating piece 10 excited by the oscillation circuit oscillates at a frequency corresponding to this temperature. For example, the hydrogen concentration can be detected from the difference (frequency shift) between the detected frequency and the frequency excited in the absence of hydrogen.
FIG. 7 is an explanatory diagram for explaining the correlation between the frequency shift of the crystal vibrating piece 10 and the hydrogen concentration.
FIG. 7A shows the case where the operating temperature is 29 ° C., and FIG. 7B shows the case where the operating temperature is 100 ° C. FIG. 7 shows an example when the temperature sensitivity coefficient of the quartz crystal vibrating piece 10 is 40 ppm / ° C.

Thus, the frequency shift is substantially proportional to the hydrogen concentration, and the hydrogen concentration can be detected from the frequency shift.
As another method, the hydrogen concentration can also be detected based on the temperature derived from the detected frequency.

As described above, since the hydrogen sensor of the present invention can detect the concentration of hydrogen gas by detecting the frequency caused by the temperature of the crystal vibrating piece 10, it detects the concentration of hydrogen gas by detecting the conventional voltage. Compared with the method, a hydrogen sensor capable of detecting the hydrogen concentration with high sensitivity can be obtained.
In particular, the hydrogen sensor according to the present embodiment selects the cut angle of the quartz crystal vibrating piece 10 to select the quartz crystal vibrating piece 1.
If the temperature sensitivity of 0 is set in the range of 30 to 60 ppm / ° C., the spurious of the crystal vibrating piece 10 can be avoided, and the heat generation of the hydrogen reaction catalyst film 13 can be detected with high sensitivity.

In addition to platinum (Pt), palladium (Pd) can be used as the hydrogen reaction catalyst film. Palladium also has a high hydrogen selectivity like platinum and hardly responds to other combustible gases, so that it can be configured as a good hydrogen reaction catalyst membrane, and the same effect as platinum can be obtained.

Next, an example of a hydrogen concentration detection system using the hydrogen sensor of this embodiment will be described.
FIG. 8 is a schematic configuration diagram showing a configuration of a hydrogen concentration detection system using a hydrogen sensor.
The hydrogen sensor 31 includes a hydrogen reaction detection element 5 and an oscillation circuit 30. A feedback resistor 6 and an inverter 7 are connected in parallel to the hydrogen reaction detecting element 5, a gate capacitor 8 is connected to the gate side, and a drain capacitor 9 is connected to the drain side to excite the crystal vibrating piece of the hydrogen reaction detecting element 5. An oscillation circuit 30 is configured.
The oscillation circuit 30 of the hydrogen sensor 31 is connected to a rectifier 32, and the rectifier 32 is connected to a frequency counter 33. Further, the frequency counter 33 is connected to the computing unit 34 and the computing unit 3
4 outputs a desired signal.

In the hydrogen concentration detection system having such a configuration, the frequency signal of the hydrogen reaction detection element 5 is output to the rectifier 32 by the oscillation circuit 30. The frequency signal is rectified in the rectifier 32 and output to the frequency counter 33. The frequency is measured by the frequency counter 33 and the arithmetic unit 3
4 is output. The calculator 34 calculates, for example, the hydrogen concentration from the measured frequency and the reference frequency, and generates and outputs a hydrogen concentration value, an alarm signal when the standard value is exceeded, a solenoid valve control signal, and the like. To do.
Thus, in the hydrogen concentration detection system, the hydrogen concentration can be detected using the frequency signal output from the hydrogen sensor 31, and a control signal or the like is output to various devices based on the obtained hydrogen concentration. be able to.

A part of the above circuit can be integrated into an IC, and the frequency counter 33 and the arithmetic unit 34 can be configured as a one-chip microcomputer. The signal processing can be performed using either analog processing or digital processing.

Note that the hydrogen sensor of this embodiment may include temperature control means for controlling the temperature of the quartz crystal vibrating piece and the hydrogen reaction catalyst film. For example, when a hydrogen reaction catalyst film is provided in a portion other than the excitation electrode of the crystal vibrating piece and the hydrogen reaction catalyst film is energized, heat is generated and the temperature of the crystal vibrating piece rises. From this, the temperature of the quartz crystal vibrating piece can be controlled at a temperature higher than the gas ambient temperature by appropriately controlling the magnitude of the current and the energization time.
In this way, it is possible to eliminate the influence of water generated when the gas medium temperature changes or the catalyst medium generates heat when it reacts with the gas, and a gas sensor with excellent sensitivity can be provided.

Further, in the hydrogen sensor of the present embodiment, crystal is used as the piezoelectric vibrating piece. However, the piezoelectric vibrating piece may be configured using a piezoelectric material such as lithium tantalate or lithium niobate.

The schematic plan view which shows the structure of the hydrogen reaction detection element of this embodiment. The schematic cross section which shows the electrode structure of the crystal vibrating piece as a piezoelectric vibrating piece. Explanatory drawing which shows the cut angle of a crystal vibrating piece. The graph which shows the temperature characteristic of a crystal vibrating piece. The graph which shows how much the temperature characteristic in the cut angle of quartz has deviated from the standard deviation from the straight line approximation line. The graph which shows the relationship between rotation angle (theta) and temperature sensitivity coefficient in cut angle CA-1 to CA-5. It is explanatory drawing which shows an example of the relationship between hydrogen concentration and a frequency shift, (a) is a graph in operating temperature 29 degreeC, (b) is a graph in operating temperature 100 degreeC. Explanatory drawing which shows an example of the hydrogen concentration detection system using a hydrogen sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Crystal gemstone, 2 ... Quartz plate, 5 ... Hydrogen reaction detection element, 10 ... Crystal oscillation piece as a piezoelectric oscillation piece, 13 ... Hydrogen reaction catalyst film, 15 ... Excitation electrode, 16 ... Connection electrode, 30 ... Oscillation circuit, 31
... hydrogen sensor as gas sensor, 32 ... rectifier, 33 ... frequency counter, 34 ... calculator.

Claims (6)

A gas sensor for detecting heat generated by a gas and a catalyst medium as a temperature,
Natural frequency is composed of a crystal resonator element that changes the detection portion temperature of the gas, the catalyst medium is provided on the quartz crystal resonator element, heat generated by the catalytic effect of the catalyst medium and the gas is the crystal The temperature rise is transmitted to the resonator element , the natural frequency of the crystal resonator element is changed ,
The quartz crystal resonator element has an electric axis of crystal of crystal as an X axis, a mechanical axis as a Y axis, and an optical axis as a Z axis.
The X axis is rotated around the Z axis by an angle φ ° clockwise to form an X ′ axis,
And the Z axis is rotated around the X ′ axis by an angle θ ° clockwise to form the Z ′ axis,
A plane including the X ′ axis and the Z ′ axis is a main surface of the quartz crystal vibrating piece, and
φ = 7-14 (°),
θ = 14 ± 3 (°),
The gas sensor characterized by being. A gas sensor for detecting heat generated by a gas and a catalyst medium as a temperature,
  The gas detection portion is composed of a quartz crystal vibrating piece whose natural frequency changes with temperature, the catalyst medium is provided on the quartz crystal vibrating piece, and the heat generated by the catalytic effect of the gas and the catalyst medium is generated by the quartz crystal vibration. The temperature rise is transmitted to the piece, the natural frequency of the crystal vibrating piece is changed,
  The quartz crystal resonator element has an electric axis of crystal of crystal as an X axis, a mechanical axis as a Y axis, and an optical axis as a Z axis.
  The X axis is rotated around the Z axis by an angle φ ° clockwise to form an X ′ axis,
  And the Z axis is rotated around the X ′ axis by an angle θ ° clockwise to form the Z ′ axis,
  A plane including the X ′ axis and the Z ′ axis is a main surface of the quartz crystal vibrating piece, and
    φ = 0 (°),
    θ = 28 ± 2 (°),
The gas sensor characterized by being. 3. The gas sensor according to claim 1 , further comprising temperature control means for controlling temperatures of the quartz crystal vibrating piece and the catalyst medium in order to control a catalytic effect. The gas sensor according to claim 3, wherein the current flows into the catalyst medium as a temperature control means, a gas sensor, characterized in that the temperature control by the heating effect. The gas sensor according to any one of claims 1 to 4,
The quartz crystal vibrating piece excites a vibration mode of thickness sliding,
An excitation electrode and the connection electrode formed on the main surface of the quartz crystal resonator element,
A hydrogen reaction catalyst film that is formed on at least the excitation electrode and generates heat in response to hydrogen gas; and an oscillation circuit that excites the quartz crystal vibrating piece,
A gas sensor, wherein a temperature change of the quartz crystal vibrating piece due to heat generation of the hydrogen reaction catalyst film is detected as a frequency signal. The gas sensor according to claim 5 , wherein
The gas sensor, wherein the hydrogen reaction catalyst film is formed of a material selected from platinum or palladium.

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