阅读说明：本技术 催化式气体传感元件、加工方法和催化式气体传感器 (Catalytic gas sensor element, processing method and catalytic gas sensor ) 是由 荆高山 樊晓华 于 2020-04-20 设计创作，主要内容包括：本发明涉及一种催化式气体传感元件,包括薄膜基底、检测元件、参考元件、多孔沉积层。薄膜基底的导热系数小、耐高温且绝缘；检测元件在薄膜基底上加工而成,包括检测元件加热电极、检测元件温度检测电极；参考元件在薄膜基底上加工而成,包括参考元件加热电极、参考元件温度检测电极；多孔沉积层包括沉积在检测元件上的含有催化剂的多孔载体、沉积在参考元件上的不含催化剂的多孔载体。薄膜基底上加工有隔离检测元件和参考元件的镂空区域。本发明还涉及上述催化式气体传感元件的加工方法以及应用其的催化式气体传感器。本发明具有高性能、低成本、高可靠性的优点,还具备高灵敏、良好的气体选择性、低功耗、良好的长期稳定性。(The invention relates to a catalytic gas sensing element, which comprises a film substrate, a detection element, a reference element and a porous deposition layer. The film substrate has small heat conductivity coefficient, high temperature resistance and insulation; the detection element is processed on the film substrate and comprises a detection element heating electrode and a detection element temperature detection electrode; the reference element is processed on the film substrate and comprises a reference element heating electrode and a reference element temperature detection electrode; the porous deposition layer includes a porous support containing a catalyst deposited on the detection element, and a porous support containing no catalyst deposited on the reference element. A hollow-out area for isolating the detection element and the reference element is processed on the film substrate. The invention also relates to a processing method of the catalytic gas sensing element and a catalytic gas sensor using the catalytic gas sensing element. The invention has the advantages of high performance, low cost and high reliability, and also has the advantages of high sensitivity, good gas selectivity, low power consumption and good long-term stability.)

1. A catalytic gas sensor element, characterized by: the catalytic gas sensing element comprises:

a film substrate having a thermal conductivity of less than 5.0W/m^.k, the thickness is less than 30 μm, and the insulating material can resist the high temperature of more than 500 ℃;

the detection element is processed on the film substrate and comprises a detection element heating electrode used for heating the detection element to a required ignition temperature and a detection element temperature detection electrode used for detecting the temperature of the detection element;

the reference element is processed on the film substrate and comprises a reference element heating electrode used for heating the reference element to a required ignition temperature and a reference element temperature detection electrode used for detecting the temperature of the reference element;

a porous deposition layer comprising a catalyst-containing porous support deposited on the detection element, a catalyst-free porous support deposited on the reference element.

2. The catalytic gas sensor element according to claim 1, wherein: the film substrate is made of ceramic, glass or metal oxide.

3. The catalytic gas sensor element according to claim 1, wherein: and a hollow area for isolating the detection element and the reference element is processed on the film substrate.

4. A method of manufacturing a catalysed gas sensor element according to claim 1, wherein: the processing method of the catalytic gas sensing element comprises the following steps:

step 1: preparing the film substrate, and processing the detection element and the reference element on the film substrate;

step 2: depositing the catalyst-free porous support over the reference element;

and step 3: depositing the catalyst-containing porous support over the detection element.

5. The method of manufacturing a catalytic gas sensor element according to claim 4, wherein: in the step 1, the detection element and the reference element are processed on the surface of the film substrate by photolithography, metal evaporation/sputtering, and etching processes, or the detection element and the reference element are processed on the surface of the film substrate by photolithography, metal evaporation/sputtering, and stripping processes.

6. The method of manufacturing a catalytic gas sensor element according to claim 4, wherein: in the step 1, the film substrate is placed on the surface of a support, and the support is a silicon wafer.

7. The method of manufacturing a catalytic gas sensor element according to claim 4, wherein: in the step 2, depositing the porous carrier without the catalyst above the reference element and drying the surface by using a high-precision screen printing process, and in the step 3, depositing the porous carrier with the catalyst above the detection element and drying the surface by using a high-precision screen printing process; and then forming a stable porous structure by using a high-temperature sintering process for the catalyst-free porous carrier and the catalyst-containing porous carrier.

8. A method of manufacturing a catalysed gas sensor element according to claim 3, wherein: the processing method of the catalytic gas sensing element comprises the following steps:

step 1: preparing the film substrate, and processing the detection element and the reference element on the film substrate;

step 2: depositing the catalyst-free porous support over the reference element;

and step 3: depositing the catalyst-containing porous support over the detection element;

and 4, step 4: and processing the hollow area.

9. The method of manufacturing a catalytic gas sensor element according to claim 8, wherein: and 4, processing the hollow area by using high-power laser or high-precision machining process.

10. A catalytic gas sensor, characterized by: the catalytic gas sensor includes:

a catalytic gas sensing element according to any one of claims 1 to 3;

the constant power output circuit is respectively connected with the detection element heating electrode in the detection element and the reference element heating electrode in the reference element, and is used for applying the same power to the detection element heating electrode and the reference element heating electrode so as to enable the detection element heating electrode and the reference element heating electrode to reach the same ignition temperature;

and a wheatstone bridge differential detection circuit which is respectively connected with the detection element temperature detection electrode in the detection element and the reference element temperature detection electrode in the reference element, and is used for enabling the detection element temperature detection electrode and the reference element temperature detection electrode to form a wheatstone bridge and outputting an electric signal capable of reflecting the concentration of the combustible gas based on the wheatstone bridge.

Technical Field

The invention relates to the technical field of gas sensing, in particular to a catalytic gas sensing element, a processing method of the catalytic gas sensing element and a catalytic gas sensor based on the catalytic gas sensing element.

Background

Alkane gases are a common class of gases in daily life and include methane, ethane, propane, butane, pentane, and isomers thereof. Among them, methane gas is the most common alkane gas in national production and life. As a main fuel and a raw material for industry and civil use, methane widely exists in a plurality of fields such as energy, chemical industry, municipal administration and the like, and has important application value. Methane is a combustion and explosion gas and a greenhouse gas, and people need to detect the methane in real time and distribution when developing and utilizing the methane.

The mainstream combustible gas sensing detection technology and method for explosive gases including methane, ethane, propane, butane, pentane and isomers thereof, hydrogen and carbon monoxide mainly comprise a catalytic combustion type, a metal oxide semiconductor type, an optical absorption type, a thermal conduction type and an electrochemical type, and further comprise a resonance type, a mass spectrum ion spectrum analysis type and a biological detection type. The catalytic combustion sensor has the advantages of simple structure, low manufacturing cost, high detection precision, strong harsh environment resistance, small volume, simple subsequent circuit and the like, and is widely applied. Over a million worldwide markets each year, catalytic combustion sensors have significant demand in the field of gas detection.

The catalytic combustion type sensor utilizes the thermal effect principle of catalytic combustion, and a measuring bridge is formed by pairing a detection element and a reference element. Under the condition of a certain ignition temperature, the combustible gas is flameless combusted on the surface of the carrier of the detection element and under the action of the catalyst, the temperature of the carrier of the detection element is increased, and the resistance of the platinum wire passing through the carrier is correspondingly increased. The carrier temperature of the reference element is not changed, so that the balance bridge is out of balance, and an electric signal which is in direct proportion to the concentration of the combustible gas is output. By measuring the magnitude of the resistance change of the detection element, the concentration of the combustible gas is known.

Alkane gas detection has specificity. The light-off temperature of different alkane gases is different, and the material selection requirement of the light-off temperature sensor is high. Taking methane gas as an example, the strong bond of the single saturated CH bond of methane stabilizes methane chemically, which is much more difficult to detect than other alkanes. The catalytic light-off temperature of methane is typically above 400 deg.f^oThe catalytic light-off temperature of C, hydrogen, carbon monoxide or other alkanes is generally less than 260 deg.C^oC. At different ignition temperatures, gasThe reaction efficiency is different. Also, for many materials, 250 f^oC is the critical point at which material degradation occurs, for example, at 300 for thin film metal electrodes commonly used in MEMS devices^oDiffusion degradation occurs above C, the polymer substrate is at 200^oSoftening and decomposing of C and high efficiency noble metal catalyst material of 300^oSintering deactivation begins above C and these factors limit the materials available for alkane gas catalysis. Among them, the bond energy of methane single saturated CH bond is very high, and methane detection is more challenging compared with other combustible gases, and more demanding on high temperature activity and stability of the sensor.

There are four important parameters for evaluating the performance of a catalytic combustion sensor: sensitivity, gas selectivity, power consumption, long-term stability. For a catalytic combustion sensor, the effects of light-off temperature, catalytic material and its structure on the above four parameters are as follows:

(1) the sensor sensitivity is dependent on the light-off temperature, catalyst material and structure. The higher the light-off temperature, the higher the sensor sensitivity; the better the gas-sensitive catalytic property of the catalytic material, the larger the specific surface area, the higher the sensitivity of the sensor.

(2) Gas selectivity is determined by detecting differences in gas sensitivity. Different alkane gases have different detection sensitivities at the same ignition temperature. Under the same ignition temperature, the bond energy of the CH bond of the methane gas is the largest, and the detection sensitivity is the lowest. The difference in the detection sensitivity of different gases is a criterion for gas selectivity. The stability of the sensor light-off temperature determines the stability of the sensitivity of the gas to be detected, and thus the gas selectivity of the sensor,

(3) the power consumption is dependent on the sensor light-off temperature. The higher the light-off temperature, the greater the sensor power consumption.

(4) The long term stability of the sensor is determined by the light-off temperature. The higher the light-off temperature, the poorer the long-term stability of the sensor.

The ideal catalytic combustion sensor has high gas sensitivity, good gas selectivity, low power consumption and good long-term stability. On the premise that the catalytic material and the structure are definite, the ignition temperature is a key parameter and is proper and stable, and the catalytic combustion type sensor has high enough gas sensitivity, good gas selectivity, low power consumption and good long-term stability. Thus, the thermal conductivity and structure of the catalytic combustion sensor base material/support material have a significant impact on the above performance parameters.

(1) The traditional wire-wound sensor adopts platinum wire as heating element, and the carrier containing catalyst is porous alumina (thermal conductivity: 25W/m)^.k) In that respect The traditional wire winding type sensor process is manually operated, the uniformity is poor, the heat load of a carrier containing a catalyst is large, and various performances of the sensor need to be improved.

(2) Silicon-based MEMS catalytic combustion gas sensor, since silicon is an excellent thermal conductor (149W/m)^.k) The thermal load is too large, so that a suspended thin film structure needs to be designed and processed to reduce the thermal load and power consumption of the sensor. In addition, conventional silicon wafers are conductors, whereas catalytic combustion sensor substrates need to be insulators. Therefore, it is necessary to deposit an insulating film on the surface of the silicon wafer. The design and processing technology of the silicon-based MEMS catalytic combustion type gas sensor is complex, and the process needs to be realized by utilizing a precise MEMS processing technology, and the related technologies comprise thermal oxidation growth, low-stress silicon nitride deposition, physical vapor deposition, photoetching, dry etching, wet etching and the like. Therefore, the film structure of the silicon-based MEMS catalytic combustion type gas sensor is complex, the processing cost is high, and the wide application of the sensor is not facilitated.

(3) Researchers developed MEMS catalytic combustion gas sensors based on quartz substrates due to the small thermal conductivity of quartz (1.1W/m)^.k) In that respect Compared with a silicon material, a suspended film structure does not need to be designed and processed, the processing technology of the sensor is relatively simplified, and the catalytic combustion type gas sensor is processed on the surface of a quartz substrate with the thickness of 100 microns only by adopting photoetching and screen printing technologies. However, compared with a silicon-based thin film sensor, the thermal load is still too large, the sensitivity is too low, and the practicability is poor.

Therefore, the defects of the above several existing catalytic combustion type gas sensors are as follows:

(1) the substrate material of the sensor also needs to be preferred. The existing silicon wafer (with too large heat conduction coefficient) needs to be processed into a thin film structure; the quartz substrate material, although having a small thermal conductivity, is subject to excessive thermal loading at conventional thicknesses (about 100 microns).

(2) The existing catalytic combustion type gas sensor simultaneously takes two functions and is heated to the ignition temperature; the gas concentration is detected by a change in temperature.

The detection of alkane gas, especially methane gas, urgently needs a high-performance, low-cost and high-reliability gas sensor, has high sensitivity, good gas selectivity, low power consumption and good long-term stability, and is widely applied to the daily life of the people.

Disclosure of Invention

The invention aims to provide a low-power consumption catalytic gas sensing element which has good performance, low cost, high reliability, stability and sensitivity and good gas selectivity, and a catalytic gas sensor based on the same.

In order to achieve the purpose, the invention adopts the technical scheme that:

a catalytic gas sensing element comprising:

a film substrate having a thermal conductivity of less than 5.0W/m^.k, the thickness is less than 30 μm, and the insulating material can resist the high temperature of more than 500 ℃;

the detection element is processed on the film substrate and comprises a detection element heating electrode used for heating the detection element to a required ignition temperature and a detection element temperature detection electrode used for detecting the temperature of the detection element;

the reference element is processed on the film substrate and comprises a reference element heating electrode used for heating the reference element to a required ignition temperature and a reference element temperature detection electrode used for detecting the temperature of the reference element;

a porous deposition layer comprising a catalyst-containing porous support deposited on the detection element, a catalyst-free porous support deposited on the reference element.

The film substrate is made of ceramic, glass or metal oxide.

And a hollow area for isolating the detection element and the reference element is processed on the film substrate.

The processing method of the catalytic gas sensing element comprises the following steps:

step 1: preparing the film substrate, and processing the detection element and the reference element on the film substrate;

step 2: depositing the catalyst-free porous support over the reference element;

and step 3: depositing the catalyst-containing porous support over the detection element.

In the step 1, the detection element and the reference element are processed on the surface of the film substrate by photolithography, metal evaporation/sputtering, and etching processes, or the detection element and the reference element are processed on the surface of the film substrate by photolithography, metal evaporation/sputtering, and stripping processes.

In the step 1, the film substrate is placed on the surface of a support, and the support is a silicon wafer.

In the step 2, depositing the porous carrier without the catalyst above the reference element and drying the surface by using a high-precision screen printing process, and in the step 3, depositing the porous carrier with the catalyst above the detection element and drying the surface by using a high-precision screen printing process; and then forming a stable porous structure by using a high-temperature sintering process for the catalyst-free porous carrier and the catalyst-containing porous carrier.

Another method for manufacturing the catalytic gas sensor element comprises the following steps:

step 1: preparing the film substrate, and processing the detection element and the reference element on the film substrate;

step 2: depositing the catalyst-free porous support over the reference element;

and step 3: depositing the catalyst-containing porous support over the detection element;

and 4, step 4: and processing the hollow area.

And 4, processing the hollow area by using high-power laser or high-precision machining process.

The present invention also provides a catalytic gas sensor comprising:

a catalytic gas sensor element, the catalytic gas sensor element being the aforementioned catalytic gas sensor element;

the constant power output circuit is respectively connected with the detection element heating electrode in the detection element and the reference element heating electrode in the reference element, and is used for applying the same power to the detection element heating electrode and the reference element heating electrode so as to enable the detection element heating electrode and the reference element heating electrode to reach the same ignition temperature;

and a wheatstone bridge differential detection circuit which is respectively connected with the detection element temperature detection electrode in the detection element and the reference element temperature detection electrode in the reference element, and is used for enabling the detection element temperature detection electrode and the reference element temperature detection electrode to form a wheatstone bridge and outputting an electric signal capable of reflecting the concentration of the combustible gas based on the wheatstone bridge.

Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages: the invention has the advantages of high performance, low cost and high reliability, has high sensitivity, good gas selectivity, low power consumption and good long-term stability, can be widely applied to the daily life of the people, and is particularly suitable for alkane gas detection, such as methane gas detection.

Drawings

FIG. 1 is a schematic structural diagram of a catalytic gas sensor element according to the present invention.

FIG. 2 is a process flow diagram of a catalytic gas sensor element of the present invention.

Fig. 3 is a schematic diagram of the operation of the catalytic gas sensor of the present invention.

In the above drawings: 1. a film substrate; 2. a detection element heating electrode; 3. a detection element temperature detection electrode; 4. a reference element heating electrode; 5. a reference element temperature detection electrode; 6. a porous support containing a catalyst; 7. a porous support free of catalyst; 8. a hollowed-out area; 9. a constant power output circuit; 10. wheatstone bridge differential detection circuit.

Detailed Description

The invention will be further described with reference to examples of embodiments shown in the drawings to which the invention is attached.