CN111443114A - Catalytic gas sensor element, processing method and catalytic gas sensor - Google Patents
Catalytic gas sensor element, processing method and catalytic gas sensor Download PDFInfo
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- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/14—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of an electrically-heated body in dependence upon change of temperature
- G01N27/16—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of an electrically-heated body in dependence upon change of temperature caused by burning or catalytic oxidation of surrounding material to be tested, e.g. of gas
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Abstract
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.
Description
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.foThe catalytic light-off temperature of C, hydrogen, carbon monoxide or other alkanes is generally less than 260 deg.CoC. At different ignition temperatures, gasThe reaction efficiency is different. Also, for many materials, 250 foC is the critical point at which material degradation occurs, for example, at 300 for thin film metal electrodes commonly used in MEMS devicesoDiffusion degradation occurs above C, the polymer substrate is at 200oSoftening and decomposing of C and high efficiency noble metal catalyst material of 300oSintering 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.
The first embodiment is as follows: as shown in fig. 1, the catalytic gas sensing element comprises a film substrate 1, a detection element, a reference element and a porous deposition layer.
(1) Film substrate
Low selective thermal conductivity (less than 5.0W/m).k) And insulating film material with small thickness (less than 30 μm) and high temperature resistance (more than 500 ℃), including ceramic, glass or metal oxide, etc. to manufacture the film substrate 1, and the heat conductivity coefficient of the film substrate 1 is less than 5.0W/m.k, less than 30 μm thick, capable of withstanding high temperatures above 500 ℃ and insulating. The material has small thermal conductivity coefficient, small thickness and small thermal load of the sensor; the material is high temperature resistant and can withstand the high temperature processing technology of the sensor.
(2) Detection element and reference element
The detection element is formed by processing on a film substrate 1, and includes a detection element heating electrode 2 for heating the detection element to a desired light-off temperature, and a detection element temperature detection electrode 3 for detecting the temperature of the detection element. The reference element is processed on the film substrate 1, and includes a reference element heating electrode 4 for heating the reference element to a desired light-off temperature, and a reference element temperature detecting electrode 5 for detecting the temperature of the reference element. The two ends of each detection electrode form the connecting end by the electrode slice, and a square wave-shaped electrode body is formed between the connecting ends.
(3) Porous deposition layer
The porous deposition layer comprises a porous support 6 containing a catalyst deposited on the detection element, a porous support 7 containing no catalyst deposited on the reference element. The catalyst-containing porous support 6 covers at least the electrode body portion of the detection element heating electrode 2 and the electrode body portion of the detection element temperature-detecting electrode 3, and the catalyst-free porous support 7 covers at least the electrode body portion of the reference element heating electrode 4 and the electrode body portion of the reference element temperature-detecting electrode 5.
Compared with the traditional catalytic combustion gas sensor (the detection element and the reference element are both single electrodes), the scheme isolates the heating function and the detection function, namely the detection element and the reference element are both composed of two electrodes, a porous carrier 6 material containing a catalyst is deposited above the detection element, and a porous carrier 7 material containing no catalyst is deposited above the reference element.
On the basis of the scheme, a hollow-out area 8 for isolating the detection element from the reference element can be processed on the film substrate 1, so that the thermal load of the sensor is further reduced, and the power consumption of the sensor is reduced.
(4) Optimization of processing technology of catalytic gas sensing element
The high-uniformity catalytic combustion type gas sensing element can be obtained only by photoetching, high-precision screen printing, high-temperature sintering and laser/mechanical processing.
As shown in fig. 2, the processing method of the catalytic gas sensor element comprises the following steps:
step 1: a film substrate 1 is prepared, and a detection element and a reference element are processed on the film substrate 1.
Specifically, on the surface of a thin film material used as a substrate, high-precision electrode structures (including a heating electrode and a temperature detection electrode) of a detection element and a reference element are processed by utilizing photoetching, metal evaporation/sputtering and etching processes. High-precision electrode structures (including heating electrodes and temperature detection electrodes) of the detection element and the reference element can also be processed by utilizing photoetching, metal evaporation/sputtering and stripping processes. Because the film material is small in thickness and soft, the film material can be placed on the surface of a bearing object such as a silicon wafer in advance for convenient operation, and the processing is convenient.
Step 2: a porous support 7 without catalyst is deposited over the reference element using a high precision screen printing process and the surface is baked.
And step 3: a porous carrier 6 containing a catalyst is deposited over the sensing element using a high precision screen printing process and the surface is dried.
And 4, step 4: the porous carrier 7 without the catalyst on the surface of the reference element and the porous carrier 6 with the catalyst on the surface of the detection element form a stable porous structure by using a high-temperature sintering process (more than 400 ℃). The high-temperature sintering temperature is higher than the ignition temperature of the sensor, so that the long-term stability of the sensor is improved.
And 5: and processing the hollow-out area 8 by using a high-power laser or high-precision machining process so as to further reduce the thermal load of the sensor and reduce the power consumption of the sensor.
Based on the method, the gas sensing element with high performance, low cost and high reliability can be realized, and the device has high sensitivity, good gas selectivity, low power consumption and good long-term stability.
As shown in fig. 3, a catalytic gas sensor includes the catalytic gas sensing element, a constant power output circuit 9, and a wheatstone bridge differential detection circuit 10.
The constant power output circuit 9 is respectively connected with the detection element heating electrode 2 in the detection element and the reference element heating electrode 4 in the reference element, and the constant power output circuit 9 is used for applying the same power to the detection element heating electrode 2 and the reference element heating electrode 4 so as to enable the detection element heating electrode 2 and the reference element heating electrode 4 to reach the same ignition temperature. That is, the constant power output circuit 9 functions to apply the same energy to the sensing element and the reference element regions, which are initially at the same temperature.
The wheatstone bridge differential detection circuit 10 is connected to the detection element temperature detection electrode 3 of the detection element and the reference element temperature detection electrode 5 of the reference element, respectively, and the wheatstone bridge differential detection circuit 10 is configured to configure the detection element temperature detection electrode 3 and the reference element temperature detection electrode 5 into a wheatstone bridge and output an electric signal capable of reflecting the concentration of the combustible gas based on the wheatstone bridge.
The working principle of the catalytic gas sensor is as follows: the same power is applied to the detection element heating electrode 2 and the reference element heating electrode 4 through the constant power output circuit 9. The sensing element and heating element are thermally loaded very closely by precision machining processes, so that the same amount of power brings the sensing element and reference element to the same light-off temperature. In the presence of combustible gas, the combustible gas undergoes flameless combustion in the detection element region, the combustion energy raises the temperature in the detection element region, and the resistance of the detection element heating electrode 2 is raised. The external constant power output circuit 9 can also adjust the output power in a feedback manner according to the resistance value change, so that the power applied to the heating electrode 2 of the detection element is still kept constant, namely, the energy required by the ignition temperature is generated. While the reference element area has no temperature change with respect to the light-off temperature. The difference in resistance values between the detection element temperature detection electrode 3 and the reference element temperature detection electrode 5 increases and the wheatstone bridge is out of balance. The difference between the resistance values of the two can represent the concentration of the combustible gas, so that the Wheatstone bridge differential detection circuit 10 can output an electric signal reflecting the concentration of the combustible gas.
According to the scheme, the energy-temperature change caused by the combustible gas can be accurately detected through the heating electrode, the detection electrode, the constant power output and the Wheatstone bridge differential detection of the sensor, so that the concentration of the combustible gas in the environment can be accurately measured. Another advantage of constant power output is that the light-off temperature is stable, resulting in a gas sensor with good gas selectivity. A catalytic gas sensor is designed and processed on the surface of a high-temperature-resistant film material with low thermal conductivity coefficient and a porous alkane gas-sensitive material with high precision deposition and patterning, and can realize low-power consumption, high sensitivity, high reliability and low cost detection on alkane gases such as methane and the like.
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (10)
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.
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