JP2017102131A - Thin film type gas sensor, and checkup method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin film type gas sensor that can maintain over a long period its detecting performance regarding a gas to be checked, and a checkup method enabling such a thin film type gas sensor to be selected in an early stage of a product.SOLUTION: A thin film type gas sensor comprises a sensor element having: a gas detecting layer whose electric characteristics change upon contact with methane gas; a selective combustion layer formed from a catalyst-doped porous body so as to be in contact with the gas detecting layer to prevent gas other than methane gas from reaching the gas detecting layer; and a heater layer that can heat the gas detecting layer. The thin film type gas sensor enables the methane gas to be detected on the basis of the resistance value of the gas detection layer heated by the heater layer. A prescribed indicator value calculated by using a gas concentration X of the methane gas and a resistance level R of the gas detecting layer measured with the thin film type gas sensor in its initial state satisfies a preset standard. A thin film type gas sensor checkup method comprises determining whether or not the gas sensor is satisfactory on the basis of such a standard.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a thin film gas sensor that detects a detection target gas using a sensor element having a gas detection layer and a heater layer capable of heating the gas detection layer, the electrical characteristics of which change due to contact with the detection target gas. It relates to the inspection method.

In general, a gas sensor is used in a gas detection device or the like, and a specific detection target gas such as carbon monoxide (CO), methane gas (CH ₄ ), propane gas (C ₃ H ₈ ), methanol vapor (CH ₃ OH) and the like. Gas sensors are required to have high sensitivity, high selectivity, high response, high reliability, and low power consumption due to their characteristics.

  Among gas detectors using such gas sensors, household gas leak alarms are for the purpose of detecting flammable gases for city gas and propane gas, and for incomplete combustion gases in combustion equipment. Some exist for the purpose of detection, or some have both of these functions. However, none of the gas leak alarms are widely used due to high cost and difficulty of installation. In order for gas leak alarms to become widespread, it is particularly desirable to improve the installation. In order to meet such a demand, it is conceivable to provide a compact gas sensor by using a battery as a driving source and making it cordless. When a battery is used as the drive source, it is particularly important to reduce the power consumption of the gas sensor. However, the catalytic combustion type or semiconductor type gas sensor detects gas in a state of being heated to a high temperature of 400 ° C to 500 ° C. Therefore, it is necessary to consume a large amount of power in order to maintain a high temperature state, which is a problem in reducing the power consumption of the gas sensor.

As for such a gas sensor, for example, Patent Document 1 discloses a thin film gas sensor that is intermittently driven. As shown in FIG. 2, the sensor element 2 of the thin film gas sensor has a substantially plate-like silicon (Si) substrate 10. A through-hole 10a extending in the thickness direction is formed in the silicon substrate 10. A thin film-like support layer 11 is disposed on the silicon substrate 10. In the support layer 11, a thermally oxidized SiO ₂ (silicon dioxide) layer 11 a is disposed on the silicon substrate 10, and a CVD-Si ₃ N ₄ (silicon nitride) layer 11 b is superimposed on the thermally oxidized SiO ₂ layer 11 a. The CVD-SiO ₂ layer 11c is placed on the CVD-Si ₃ N ₄ layer 11b. Furthermore, a heater layer 12 is disposed in the center on the support layer 11, and an electrical insulating layer 13 is disposed on the support layer 11 so as to cover the heater layer 12. A gas detection layer 14 is disposed at the center on the electrical insulating layer 13. In the gas detection layer 14, a pair of bonding layers 14a is disposed at the center of the electrical insulating layer 13, and the sensing layer electrodes 14b are disposed on the pair of bonding layers 14a, respectively. A sensing layer 14c is disposed on the electrical insulating layer 13 so as to connect them. Further, a selective combustion layer 14d is disposed on the electrical insulating layer 13 so as to cover the sensing layer electrode 14b and the sensing layer 14c. Therefore, the thin-film gas sensor of Patent Document 1 is excellent in high heat insulation and low heat capacity due to a diaphragm structure using a microfabrication process.

With regard to intermittent driving of the heater layer 12 performed in the thin film gas sensor, for example, conventionally, when a combustible gas such as methane gas or propane gas is detected, the temperature of the heater layer 12 is set to a high temperature of 400 ° C. to 500 ° C. In addition, the heater layer 12 is energized for a fixed time of 50 msec to 500 msec (High state), the resistance value of the sensing layer 14c is measured by the sensing layer electrode 14b, and combustible gas such as methane gas and propane gas is measured from the change in the resistance value. The concentration is detected. In the selective combustion layer 14d under a high temperature, by burning a reducing gas such as carbon monoxide and hydrogen (H ₂ ) and other miscellaneous gases, a combustible gas such as inert methane gas and propane gas is selectively burned. As a result of diffusion through the layer 14d and reaching the sensing layer 14c and reacting with the tin dioxide (SnO ₂ ) of the sensing layer 14c, the resistance value of tin dioxide changes. It detects the concentration of flammable gases such as methane gas and propane gas generated when gas leaks from equipment. Further, a state where the heater layer 12 is not energized (Off state) is set for a certain period of time. Such intermittent driving is called high-off driving, and the high state and the off state are repeated at a predetermined cycle (for example, 60 sec cycle).

  Further, when detecting carbon monoxide generated during incomplete combustion, the heater layer 12 is energized for a certain period of time of 50 msec to 500 msec so that the temperature of the heater layer 12 is once set to a high temperature state of 400 ° C. to 500 ° C. (High state) After cleaning the thin film gas sensor, energization is performed so that the temperature of the heater layer 12 is lowered to a low temperature state of about 100 ° C. (Low state), and carbon monoxide is detected in this low temperature state. . At this time, it is known that sensitivity to carbon monoxide (hereinafter referred to as “CO sensitivity”) and selectivity are increased. Further, a state where the heater layer 12 is not energized (Off state) is set for a certain period of time. Such intermittent driving is called high-low-off driving, and the high state, the low state, and the off state are repeated in a predetermined cycle (for example, 150 sec cycle).

  In addition to detecting carbon monoxide in the low state and performing methane detection in addition to cleaning the thin film gas sensor in the high state, there is one that can detect both methane and carbon monoxide in one thin film gas sensor doing.

JP 2003-270185 A

Here, the atmosphere of the installation environment of the gas sensor includes nitrogen, carbon dioxide gas, water vapor and the like in addition to the detection target gas. However, while the heater layer 4 is in the OFF state in the intermittent driving described above, the temperature of the heater layer 12 is lowered to the ambient temperature. In such a state, since the gas sensor is exposed to high-concentration water vapor for a long time, the characteristics of the gas sensor are easily changed. In particular, for a gas sensor that senses methane gas (CH ₄ ), the resistance in an atmosphere containing methane gas is likely to change, and the threshold value of a parameter for detecting methane gas is likely to change. This is a problem in considering the long-term use of the gas sensor.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a thin film gas sensor capable of maintaining the detection performance of the detection target gas over a long period of time. It is another object of the present invention to provide an inspection method that makes it possible to select such a thin film gas sensor at an early stage of the product.

In order to solve the problem, a thin film gas sensor according to one embodiment of the present invention includes a gas detection layer whose electrical characteristics change due to contact with methane gas, and a gas other than the methane gas that reaches the gas detection layer. A sensor element having a selective combustion layer formed of a porous body to which a catalyst is added and formed to cover the gas detection layer, and a heater layer capable of heating the gas detection layer. A thin-film gas sensor configured to be able to detect the methane gas based on a resistance value of the gas detection layer heated by the heater layer, wherein the initial state when the gas concentration X of the methane gas is 2000 ppm The resistance value R ₂₀₀₀ of the gas detection layer measured by the thin film gas sensor and the thin film gas sensor in the initial state when the gas concentration X is 0 ppm. When the gas sensitivity S, which is a ratio with the measured resistance value R ₀ of the gas detection layer, is defined by the following (formula 1):
S = R ₂₀₀₀ / R ₀ (Formula 1)
The gas sensitivity S is 12 or less. Therefore, the thin film type gas sensor can maintain the detection performance of the detection target gas for a long period of time by satisfying such conditions in the initial state.

In order to solve the problem, an inspection method for a thin film gas sensor according to one embodiment of the present invention includes a gas detection layer whose electrical characteristics change due to contact with methane gas, and a gas other than the methane gas in the gas detection layer. A sensor having a selective combustion layer formed of a porous body to which a catalyst is added so as to prevent the gas from reaching, and a heater layer capable of heating the gas detection layer, and a heater layer capable of heating the gas detection layer A thin film gas sensor inspection method comprising an element and configured to detect the methane gas based on a resistance value of the gas detection layer heated by the heater layer, wherein the thin film gas sensor in an initial state A predetermined index value is calculated using the resistance value R of the gas detection layer and the gas concentration X of the methane gas measured in Step 1, and the threshold value of the index value set in advance is used as a reference. In the inspection method of quality determining thin film type gas sensor of Formula gas sensor, and the resistance value R ₂₀₀₀ of the gas sensing layer, which is measured by a thin film type gas sensor of the initial state when the gas concentration X is 2000 ppm, the gas concentration X The gas sensitivity S, which is a ratio with the resistance value R ₀ of the gas detection layer measured by the thin film gas sensor in the initial state when is 0 ppm, is defined by the following (Equation 2):
S = R ₂₀₀₀ / R ₀ (Formula 2)
When the gas sensitivity S is set as the index value, the threshold value of the gas sensitivity S is set to 12, and when the gas sensitivity S is 12 or less of the threshold value, it is determined that the measured thin film gas sensor is a non-defective product. To do. The thin film gas sensor selected by such determination can maintain the detection performance of the detection target gas over a long period of time. Therefore, a thin film gas sensor that can maintain the detection performance of the detection target gas over a long period of time can be selected at the initial stage of the product.

  According to the thin film gas sensor according to one aspect of the present invention, the detection performance of the detection target gas can be maintained over a long period of time. In addition, according to the method for inspecting a thin film gas sensor according to one aspect of the present invention, a thin film gas sensor that can maintain reliability over a long period of time can be selected at the initial stage of the product.

It is sectional drawing which shows typically the thin film type gas sensor which concerns on embodiment and reference form of this invention. It is sectional drawing which shows typically the sensor element used with the thin film type gas sensor which concerns on embodiment and reference form of this invention. It is a figure which shows an example about the relationship between the resistance value of the gas detection layer and the gas concentration of methane gas in the thin film type gas sensor which concerns on embodiment and reference form of this invention. In the reference example 1 of this invention, it is a figure which shows the relationship between the gradient coefficient computed with the some thin film type gas sensor, and an alarm concentration fluctuation ratio. In the Example of this invention, it is a figure which shows the relationship between the gas sensitivity computed with the several thin film type gas sensor, and an alarm concentration fluctuation ratio. In the reference example 2 of this invention, it is a figure which shows the relationship between the zero gas density | concentration calculated with the some thin film type gas sensor, and an alarm density fluctuation ratio.

[First Reference Form]
The thin film gas sensor and its inspection method according to the first reference embodiment of the present invention will be described below. As shown in FIG. 1, a thin-film gas sensor 1 used in a gas detection device has a sensor element 2 that detects a detection target gas. The sensor element 2 is disposed on the table 3, and the bottom of the sensor element 2 and the top surface of the table 3 are in contact with each other. The table 3 is supported by a plurality of stems 4. The stem 4 is formed in a bar shape extending in the vertical direction. A cap 5 is disposed on the table 3 so as to surround the sensor element 2. The cap 5 is formed in a cylindrical shape extending in the vertical direction. A bottom opening 5 a is provided at the bottom of the cap 5, and the top surface of the table 3 is in contact with the peripheral edge of the bottom opening 5 a of the cap 5. . A top opening 5b is provided at the top of the cap 5, and a net-like upper net 6 is attached to the top of the cap 5 so as to cover the top opening 5b. Inside the cap 5, a net-like lower net 7 is arranged below the upper net 6 with a gap. A filter 8 made of activated carbon is arranged between the upper net 6 and the lower net 7. The thin film gas sensor 1 includes a housing 9 that houses a sensor element 2, a table 3, a stem 4, a cap 5, an upper net 6, a lower net 7, and a filter 8, and the housing 9 extends in the vertical direction. It is formed in a cylindrical shape. A ventilation opening 9 a is provided at the top of the housing 9.

  In such a thin film gas sensor 1, the external gas passes through the ventilation opening 9 a of the housing 9 and then passes through the filter 8 and is sent into the cap 5. Thus, the sensor element 2 reacts to the gas sent into the cap 5.

The sensor element 2 of the thin film gas sensor 1 will be described. As shown in FIG. 2, the sensor element 2 of the thin film gas sensor 1 has a substantially plate-like silicon (Si) substrate 10. In such a silicon substrate 10, a through hole 10a extending in the thickness direction is formed. A thin film-like support layer 11 is disposed on the silicon substrate 10. In the support layer 11, a thermally oxidized SiO ₂ (silicon dioxide) layer 11 a is disposed on the silicon substrate 10, and a CVD-Si ₃ N ₄ (silicon nitride) layer 11 b is superimposed on the thermally oxidized SiO ₂ layer 11 a. The CVD-SiO ₂ layer 11c is placed on the CVD-Si ₃ N ₄ layer 11b.

A heater layer 12 is disposed in the center of the support layer 11 so as to correspond to the position of the through hole 10a. An electrical insulating layer 13 is disposed on the support layer 11 so as to cover the heater layer 12. A gas detection layer 14 is disposed in the center of the electrical insulating layer 13 so as to correspond to the position of the through hole 10a. In the gas detection layer 14, a pair of bonding layers 14a is disposed at the center of the electrical insulating layer 13 so as to correspond to the positions of the through holes 10a, and sensing layer electrodes 14b are disposed on the pair of bonding layers 14a, respectively. The sensing layer 14c is disposed on the electrical insulating layer 13 so as to connect the pair of sensing layer electrodes 14b. The sensing layer 14c has electrical characteristics when selectively sensitive to, for example, carbon monoxide (CO), methane gas (CH ₄ ), propane gas (C ₃ H ₈ ), methanol vapor (CH ₃ OH), and the like. Is configured to change. Further, a selective combustion layer 14d is disposed on the electrical insulating layer 13 so as to cover the sensing layer electrode 14b and the sensing layer 14c. The selective combustion layer 14d is composed of a porous body to which a catalyst is added, and is configured to prevent a gas other than the gas to be detected from reaching the sensing layer 14c.

  The portions corresponding to the through holes 10 a of the silicon substrate 10 in the support layer 11, the heater layer 12, and the electrical insulating layer 13 (hereinafter referred to as “diaphragm portions”) are not supported by the silicon substrate 10. The sensor element 2 of the thin film gas sensor 1 has a diaphragm structure.

Furthermore, although an example of the preferable structure of the sensor element 2 is demonstrated, the structure of the sensor element 2 is not limited to this. The silicon substrate 10 is preferably a silicon wafer with a thermal oxide film. The heater layer 12 is formed by superposing a second heater layer made of platinum / tungsten (PtW) on a first heater layer made of tungsten (Ta), and on the second heater layer. It is preferable to have a laminated structure (Ta / PtW / Ta) in which a third heater layer made of tungsten is disposed. The electrically insulating layer 13 is preferably made of silicon dioxide. The sensing layer electrode 14b preferably has a stacked structure (Pt / Ta) in which a second electrode layer made of tungsten is stacked on a first electrode layer made of platinum. The sensing layer 14c is preferably made of tin dioxide (SnO ₂ ). The selective combustion layer 14d is preferably made of a sintered material in which palladium (Pd) is supported on aluminum oxide (Al ₂ O ₃ ) as a catalyst.

Here, although the preferable example of the manufacturing method of the sensor element 2 used for the gas detection apparatus which concerns on this reference form is demonstrated, the manufacturing method of the sensor element 2 is not limited to this. A thermally oxidized SiO ₂ layer 11 a is formed on the front and back surfaces of the silicon substrate 10. Next, a CVD-Si ₃ N ₄ layer 11b and a CVD-SiO ₂ layer 11c are sequentially formed on the thermally oxidized thermally oxidized SiO ₂ layer 11a by a plasma CVD method. Further, a heater layer 12 and an electrical insulating layer 13 made of silicon dioxide are sequentially formed by sputtering. Next, in order to form the gas detection layer 14, a bonding layer 14a, a sensing layer electrode 14b, and a sensing layer 14c made of silicon dioxide doped with antimony (Sb) are sequentially sputtered on the electrical insulating layer 13. To form. In this embodiment, as an example, an RF magnetron sputtering apparatus is preferably used for film formation by sputtering. Regarding the film forming conditions, for example, in the case of the bonding layer 6a made of tungsten (Ta) or titanium (Ti) and the sensing layer electrode 14b made of platinum (Pt) or gold (Au), the argon (Ar) gas pressure Is 1 Pa, the substrate temperature is 300 ° C., the RF power is 2 W / cm ² , and the thicknesses of the bonding layer 14a and the sensing layer electrode 14b are preferably 500 mm and 2000 mm, respectively. The selective combustion layer 14d is applied by a screen printing method so as to sufficiently cover the sensing layer electrode 14b, and then baked at a temperature of 500 ° C. for 1 hour or more. Next, silicon is removed from the back surface of the silicon substrate 10 by etching to form a through hole 10a.

  Next, an inspection method for the thin film gas sensor 1 according to the present embodiment will be described. The relationship between the resistance value R of the gas detection layer measured by the thin film gas sensor 1 in the initial state and the gas concentration X of the detection target gas is defined by the following (formula 7).

R = aX ^b (Expression 7)

  As shown in FIG. 3, in the orthogonal coordinate system composed of the resistance value R and the gas concentration X, the above-described (2) using the two measurement points composed of the resistance value R and the gas concentration X in the region where the gas concentration X is 4000 ppm or more ( The coefficient a and the coefficient b are calculated by Expression 7). This coefficient (hereinafter referred to as “gradient coefficient”) b represents the slope of a straight line passing through the two measurement points in a state where both the resistance value R and the gas concentration X are logarithmically displayed. Of the coefficient a and the gradient coefficient b calculated in this way, the gradient coefficient b is used as an index value. Furthermore, when the threshold value of the gradient coefficient b is set to −0.8 in advance, and the gradient coefficient b is −0.8 or less, it is determined that the measured thin film gas sensor 1 is a non-defective product.

  In FIG. 3, as an example, in the thin film gas sensor 1 in the initial state, the first measurement point D1 measured when the gas concentration X of methane gas is 0 ppm, the first measurement point D1 measured when the gas concentration X of methane gas is 500 ppm. The second measurement point D2, the third measurement point D3 measured when the gas concentration X of methane gas is 1000 ppm, the fourth measurement point D4 measured when the gas concentration X of methane gas is 2000 ppm, and the gas concentration X of methane gas are A fifth measurement point D5 measured at 5500 ppm and a sixth measurement point D6 measured when the gas concentration X of methane gas is 12500 ppm are shown. In FIG. 3, the two measurement points used in the above-described inspection method are the fifth measurement point D5 and the sixth measurement point D6, and pass through the fifth measurement point D5 and the sixth measurement point D6. The slope of the straight line L1 (shown by a broken line) corresponds to the value of the gradient coefficient b.

  As described above, according to the thin film gas sensor 1 and the inspection method thereof according to the present embodiment, the resistance value R of the gas detection layer 14 measured by the thin film gas sensor 1 in the initial state and the gas concentration X of the detection target gas are used. The gradient coefficient b is calculated by the above (formula 7), and the quality of the thin film gas sensor 1 is determined based on a preset threshold value of the gradient coefficient b. The thin film gas sensor 1 selected by such determination can maintain the detection performance of the detection target gas over a long period of time, as shown in Reference Example 1 described later. Therefore, the thin film gas sensor 1 that can maintain the detection performance of the detection target gas over a long period of time can be selected at the initial stage of the product.

[Embodiment]
A thin film gas sensor and an inspection method thereof according to an embodiment of the present invention will be described below. The present embodiment is basically the same as the first reference embodiment. Elements similar to those in the first reference embodiment will be described using the same reference numerals and names as those in the first reference embodiment. Here, a configuration different from the first reference embodiment will be described.

In the thin film gas sensor and the inspection method thereof according to the present embodiment, the thin film gas sensor 1 similar to the first reference embodiment is an inspection target, and the thin film gas sensor 1 and the inspection method thereof will be described. The resistance value R ₂₀₀₀ of the gas detection layer 14 when the gas concentration X of the detection target gas measured by the thin film gas sensor 1 in the initial state is 2000 ppm, and the resistance value R ₂₀₀₀ of the gas detection layer 14 when the gas concentration X is 0 ppm. The ratio with the resistance value _R0 is defined as gas sensitivity S, and the gas sensitivity S is defined by the following (formula 8).

S = R ₂₀₀₀ / R ₀ (Formula 8)

  The gas sensitivity S calculated in this way is used as an index value. Furthermore, when the threshold value of the gas sensitivity S is set to 12 in advance and the gas sensitivity S is 12 or less, the measured thin film gas sensor 1 is determined to be a non-defective product.

  As described above, according to the thin film gas sensor 1 and the inspection method thereof according to the present embodiment, the resistance value R of the gas detection layer 14 and the gas concentration X of the detection target gas measured by the thin film gas sensor 1 in the initial state are used. The gas sensitivity S is calculated by the above (Expression 8), and the quality of the thin film gas sensor 1 is determined based on a preset threshold value of the gas sensitivity S. The thin-film gas sensor 1 selected by such determination can maintain the detection performance of the detection target gas over a long period of time, as shown in an example described later. Therefore, the thin film gas sensor 1 that can maintain the detection performance of the detection target gas over a long period of time can be selected at the initial stage of the product.

[Second Reference Form]
A thin film gas sensor and an inspection method thereof according to the second reference embodiment of the present invention will be described below. The second reference form is basically the same as the first reference form. Elements similar to those in the first reference embodiment will be described using the same reference numerals and names as those in the first reference embodiment. Here, a configuration different from the first reference embodiment will be described.

  In the thin film gas sensor and the inspection method thereof according to the present reference embodiment, the thin film gas sensor 1 similar to that of the first reference embodiment is an inspection target, and the thin film gas sensor 1 and the inspection method thereof will be described. The relationship between the resistance value R of the gas detection layer 14 measured by the thin film gas sensor 1 in the initial state and the gas concentration X of the detection target gas is defined by the following (formula 9).

R = aX ^b (Formula 9)

As shown in FIG. 3, in the orthogonal coordinate system composed of the resistance value R and the gas concentration X, the above-mentioned (2) using the two measurement points composed of the resistance value R and the gas concentration X in the region where the gas concentration X is 4000 ppm or more The coefficient a and the gradient coefficient b are calculated according to Equation 9). Using the calculated coefficient a and gradient coefficient b and the resistance value R ₀ measured when the gas concentration X is 0 ppm in the thin film gas sensor 1 in the initial state, the gas concentration (hereinafter referred to as “Equation 9”) is obtained. to calculate the) X ₀ of "zero gas concentration". The zero gas concentration X ₀ calculated in this way as an index value. Further, it is determined that the 150ppm threshold of zero gas concentration _{X 0,} if zero gas concentration _{X 0} is more than 150ppm, the measured thin film gas sensor 1 is good.

In FIG. 3, as an example, a straight line L1 (shown by a broken line) described in the first reference embodiment and a straight line L2 (shown by a one-dot chain line) representing the resistance value _R0 of the first measurement point D1 are drawn. and which, the gas concentration X at the intersection P of these lines L1, L2 has a zero gas concentration X ₀ of the index value.

As described above, according to the thin film gas sensor 1 and the inspection method thereof according to the present embodiment, the resistance value R of the gas detection layer 14 measured by the thin film gas sensor 1 in the initial state and the gas concentration X of the detection target gas are used. The zero gas concentration X ₀ is calculated by the above (Equation 9), and the quality of the thin film gas sensor 1 is determined based on a preset threshold value of the zero gas concentration X ₀ . The thin film gas sensor 1 selected by such determination can maintain the detection performance of the detection target gas over a long period of time, as shown in Reference Example 2 described later. Therefore, the thin film gas sensor 1 that can maintain the detection performance of the detection target gas over a long period of time can be selected at the initial stage of the product.

  Although the embodiments and reference embodiments of the present invention have been described so far, the present invention is not limited to the above-described embodiments and reference embodiments, and various modifications and changes can be made based on the technical idea of the present invention. It is.

[Reference Example 1]
Reference Example 1 of the present invention will be described. In Reference Example 1, a plurality of thin film gas sensors 1 are inspected using the inspection method for thin film gas sensors 1 according to the first reference embodiment of the present invention. The thin-film gas sensor 1 to be inspected has a sensor element 2 in an example of a preferable configuration of the sensor element 2 described in the first reference embodiment, and the sensor element 2 corresponds to the sensor element 2 described in the first reference embodiment. It is produced as a preferred example of the manufacturing method. Further, for the thin film gas sensor 1, the resistance value (hereinafter referred to as “alarm resistance value”) of the gas detection layer 14 serving as a reference for issuing a gas leak alarm is set to a predetermined value.

The slope coefficient b was calculated by (Formula 7) of the first reference form using the resistance value R of the gas detection layer and the gas concentration X of methane gas measured by the plurality of thin film gas sensors 1 in the initial state. Further, the plurality of thin-film gas sensor 1 in the initial state was measured gas concentration X ₁ methane reaching the alarm resistance. Next, a two-year equivalent acceleration test was performed on the plurality of thin film gas sensors 1. A plurality of thin-film gas sensor 1 after 2 years equivalent accelerated test were measured gas concentration X ₂ methane reaching the alarm resistance. For each thin film gas sensor 1, the ratio of the gas concentration X ₂ that reaches the alarm resistance value in the state after the 2-year equivalent acceleration test to the gas concentration X ₁ that reaches the alarm resistance value in the initial state (hereinafter referred to as “alarm concentration fluctuation ratio”) ) T (= X ₂ / X ₁ ) was calculated.

  As a result, the relationship between the gradient coefficient b and the alarm concentration fluctuation ratio T in each thin film gas sensor 1 is as shown in FIG. In FIG. 4, in most thin film gas sensors 1, the alarm concentration fluctuation ratio T in the range where the gradient coefficient b is −0.8 or less is 1.5 or less, and the gradient coefficient b is larger than −0.8. By excluding the thin film type gas sensor 1, it was confirmed that the thin film type gas sensor 1 having the alarm concentration fluctuation ratio T larger than 1.5 could be almost excluded. Therefore, according to the inspection method of the thin film gas sensor 1 according to the first reference embodiment, it was confirmed that the thin film gas sensor 1 capable of maintaining the detection performance of the detection target gas for a long period of time can be selected at the initial stage of the product.

[Example]
Examples of the present invention will be described. In the examples, a plurality of thin film gas sensors 1 are inspected using the inspection method of the thin film gas sensors 1 according to the embodiment of the present invention. The thin film gas sensor 1 to be inspected has a sensor element 2 similar to that in Reference Example 1, and the sensor element 2 is manufactured in the same manner as in Reference Example 1. As for the thin film gas sensor 1, the alarm resistance value is set to a predetermined value as in the first reference example.

The gas sensitivity S was calculated by (Equation 8) of the embodiment using the resistance value R of the gas detection layer measured by the plurality of thin film gas sensors 1 in the initial state and the gas concentration X of methane gas. Further, the gas concentration X ₁ ′ of methane gas reaching the alarm resistance value was measured for the plurality of thin film gas sensors 1 in the initial state. Next, a two-year equivalent acceleration test was performed on the plurality of thin film gas sensors 1. The gas concentration X ₂ ′ of methane gas reaching the alarm resistance value was measured for a plurality of thin film gas sensors 1 after the 2-year equivalent acceleration test. For each thin film gas sensor 1, the alarm density variation ratio T '(= X gas concentration X ₁ which initially reaches the alarm _resistance' gas concentration X ₂ in a state after two years equivalent accelerated test for reaching the alarm resistance _{' 2} ′ / X ₁ ′) was calculated.

  As a result, the relationship between the gas sensitivity S and the alarm concentration fluctuation ratio T ′ in each thin film gas sensor 1 is as shown in FIG. In FIG. 5, in most thin film gas sensors 1, the alarm concentration fluctuation ratio T ′ in the range where the gas sensitivity S is 12 or less is 1.7 or less. It was confirmed that the thin-film gas sensor 1 having the alarm concentration fluctuation ratio T ′ larger than 1.7 can be almost excluded by the exclusion. Therefore, according to the inspection method of the thin film type gas sensor 1 according to the embodiment, it was confirmed that the thin film type gas sensor 1 capable of maintaining the detection performance of the detection target gas over a long period of time can be selected at the initial stage of the product.

[Reference Example 2]
Reference Example 2 of the present invention will be described. In Reference Example 2, a plurality of thin film gas sensors 1 are inspected using the inspection method for thin film gas sensors 1 according to the second embodiment of the present invention. The thin film gas sensor 1 to be inspected has a sensor element 2 similar to that in Reference Example 1, and the sensor element 2 is manufactured in the same manner as in Reference Example 1. As for the thin film gas sensor 1, the alarm resistance value is set to a predetermined value as in the first reference example.

It was calculated zero gas concentration X ₀ by using the resistance value of the gas sensing layer is measured by a plurality of thin-film gas sensor 1 in the initial state R and the gas concentration X of methane gas of the second reference embodiment (Equation 9). Further, the gas concentration X ₁ ″ of methane gas reaching the alarm resistance value was measured for the plurality of thin film gas sensors 1 in the initial state. Next, a two-year equivalent acceleration test was performed on the plurality of thin film gas sensors 1. With respect to the plurality of thin film gas sensors 1 after the 2-year equivalent acceleration test, the gas concentration X ₂ ″ of methane gas reaching the alarm resistance value was measured. For each thin film gas sensor 1, the alarm concentration fluctuation ratio T ″ of the gas concentration X ₂ ″ reaching the alarm resistance value in the state after the 2-year equivalent acceleration test with respect to the gas concentration X ₁ ″ reaching the alarm resistance value in the initial state. (= X ₂ ″ / X ₁ ″) was calculated.

As a result, the relationship between the alarm density variation ratio T '' and zero gas concentration X ₀ in each of the thin film gas sensor 1, now shown in FIG. In FIG. 6, in most thin film gas sensors 1, the alarm concentration fluctuation ratio T ″ in the range where the zero gas concentration X ₀ is 150 ppm or more is 1.5 or less, and the thin film gas sensor whose zero gas concentration X ₀ is smaller than 150 ppm. By excluding the gas sensor 1, it was confirmed that the thin film gas sensor 1 with the alarm concentration fluctuation ratio T ″ larger than 1.5 can be almost excluded. Therefore, according to the inspection method of the thin film gas sensor 1 according to the second reference embodiment, it was confirmed that the thin film gas sensor 1 capable of maintaining the detection performance of the detection target gas for a long period of time can be selected at the initial stage of the product.

DESCRIPTION OF SYMBOLS 1 Thin film type gas sensor 2 Sensor element 12 Heater layer 14 Gas detection layer R, R ₀ Resistance value X Gas concentration X _{0 Zero} gas concentration D1 1st measurement point D2 2nd measurement point D3 3rd measurement point D4 4th measurement Point D5 Fifth measurement point D6 Sixth measurement point L1, L2 Straight line b Gradient coefficient T, T ′, T ″ Alarm concentration fluctuation ratio S Gas sensitivity

Claims (5)

A gas detection layer whose electrical characteristics change due to contact with methane gas, and a porous body to which a catalyst is added so as to prevent a gas other than the methane gas from reaching the gas detection layer, and the gas A sensor element having a selective combustion layer formed to cover the detection layer and a heater layer capable of heating the gas detection layer;
A thin film gas sensor configured to be able to detect the methane gas based on a resistance value of the gas detection layer heated by the heater layer,
When the gas concentration X of the methane gas is 2000 ppm, the resistance value R ₂₀₀₀ of the gas detection layer measured with the thin film gas sensor in the initial state, and when the gas concentration X is 0 ppm, with the thin film gas sensor in the initial state When the gas sensitivity S, which is a ratio with the measured resistance value R ₀ of the gas detection layer, is defined by the following (formula 1):
S = R ₂₀₀₀ / R ₀ (Formula 1)
A thin film gas sensor, wherein the gas sensitivity S is 12 or less.   The sensor element is disposed on the support layer, a plate-shaped silicon substrate having a through-hole, a thin-film support layer formed on the silicon substrate so as to cover the opening of the through-hole. The thin film gas sensor according to claim 1, further comprising an electrical insulating layer formed on the support layer so as to cover the heater layer, and having a diaphragm structure. The sensor element further includes two electrodes formed on the electrical insulating layer at a distance from each other corresponding to the position of the through hole,
The gas detection layer is formed on the electrical insulating layer so as to connect the two electrodes,
The selective combustion layer is formed so as to cover the two electrodes and the gas detection layer on the electrical insulating layer corresponding to the position of the through hole,
The thin film gas sensor according to claim 2, wherein the heater layer is formed on the support layer corresponding to the position of the through hole. A gas detection layer whose electrical characteristics change due to contact with methane gas, and a porous body to which a catalyst is added so as to prevent a gas other than the methane gas from reaching the gas detection layer, and the gas A sensor element having a selective combustion layer formed to cover the detection layer and a heater layer capable of heating the gas detection layer;
An inspection method for a thin film gas sensor configured to detect the methane gas based on a resistance value of the gas detection layer heated by the heater layer,
A predetermined index value is calculated using the resistance value R of the gas detection layer measured by the thin film gas sensor in the initial state and the gas concentration X of the methane gas, and a threshold value of the preset index value is used as a reference In the inspection method of the thin film type gas sensor for judging the quality of the thin film type gas sensor,
When the gas concentration X is 2000 ppm, the resistance value R ₂₀₀₀ of the gas detection layer measured by the thin film gas sensor in the initial state, and when the gas concentration X is 0 ppm, the resistance value R ₂₀₀₀ is measured by the thin film gas sensor in the initial state. Further, a gas sensitivity S which is a ratio with the resistance value R ₀ of the gas detection layer is defined by the following (formula 2),
S = R ₂₀₀₀ / R ₀ (Formula 2)
The gas sensitivity S is the index value,
A threshold of the gas sensitivity S is set to 12,
A method for inspecting a thin film gas sensor, wherein the measured thin film gas sensor is determined to be a non-defective product when the gas sensitivity S is 12 or less of the threshold. The sensor element is disposed on the support layer, a plate-shaped silicon substrate having a through-hole, a thin-film support layer formed on the silicon substrate so as to cover the opening of the through-hole. An electric insulating layer formed on the support layer so as to cover the heater layer, and two electrodes formed on the electric insulating layer so as to be spaced from each other corresponding to the positions of the through holes. And it has a diaphragm structure,
The gas detection layer is formed on the electrical insulating layer so as to connect the two electrodes,
The selective combustion layer is formed so as to cover the two electrodes and the gas detection layer on the electrical insulating layer corresponding to the position of the through hole,
The thin film type gas sensor inspection method according to claim 4, wherein the heater layer is formed on the support layer corresponding to the position of the through hole.

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