CN108844652B - MEMS gas sensor chip, sensor and preparation method of sensor - Google Patents

MEMS gas sensor chip, sensor and preparation method of sensor Download PDF

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CN108844652B
CN108844652B CN201810400193.8A CN201810400193A CN108844652B CN 108844652 B CN108844652 B CN 108844652B CN 201810400193 A CN201810400193 A CN 201810400193A CN 108844652 B CN108844652 B CN 108844652B
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刘宇航
刘立滨
李平
许诺
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Beijing Machinery Equipment Research Institute
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/28—Electrolytic cell components
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    • G01N27/333—Ion-selective electrodes or membranes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K7/00—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements
    • G01K7/16—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements
    • G01K7/18—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements the element being a linear resistance, e.g. platinum resistance thermometer
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D23/00—Control of temperature
    • G05D23/19—Control of temperature characterised by the use of electric means
    • G05D23/20—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature
    • G05D23/22—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature the sensing element being a thermocouple

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Abstract

The invention relates to an MEMS gas sensor chip, a sensor and a preparation method of the sensor, belongs to the technical field of gas detection, and solves the problems of high price, long response time and poor environmental stability in the prior art. The MEMS gas sensor chip comprises a gas sensitive unit, a temperature sensitive unit, a sensitive structure substrate and a temperature control unit. The MEMS gas sensor comprises an MEMS gas sensor chip and a control circuit; the control circuit comprises a microcontroller, an N-type MOSFET, a P-type MOSFET and a positive and negative power supply. The microcontroller compares the actual temperature acquired by the temperature sensitive unit with a preset temperature, outputs a control signal according to a comparison result, controls the on-off of the N-type MOSFET and the P-type MOSFET, further controls the direction and the magnitude of current flowing through the temperature control unit, and changes the temperature of the surface of the sensitive structure substrate. The MEMS gas sensor has the advantages of simple operation, strong universality, capability of simultaneously measuring the concentration of various gases, cost saving, short response time and good environmental stability.

Description

MEMS gas sensor chip, sensor and preparation method of sensor
Technical Field
The invention relates to the technical field of gas detection, in particular to an MEMS gas sensor chip, a sensor and a preparation method of the sensor.
Background
The gas detection is used as an important environmental parameter acquisition means, and has higher application value in the fields of atmospheric pollutant prevention and control, industrial harmful gas monitoring, Internet of things and the like. Currently, gas detection is mainly achieved by gas sensors, and commonly used gas sensors can be classified into electrochemical type, metal oxide type, contact combustion type, semiconductor type, MEMS gas sensors, and the like according to the operating principle and the structure thereof.
MEMS gas sensors have received much attention in recent years due to their small size, low cost, and simple structure. However, the sensitive structure of the existing MEMS gas sensor is greatly affected by environmental stress, has low performance, and has poor stability (especially, adaptability to temperature, which is one of the most important indicators in sensor stability) in long-term use, so that the related requirements of gas detection in a severe environment cannot be completely met.
In domestic and foreign research, the main approaches for improving the performance of the MEMS gas sensor are to improve the specificity of a gas sensitive material, increase the contact area between a gas sensitive structure and gas and the like, but the improvement of the specificity of the gas sensitive material is only suitable for detecting partial gas, and the increase of the contact area between the gas sensitive structure and the gas brings about the improvement of complexity, cost and micromachining realization difficulty. Currently, a technical way for improving the performance of the MEMS gas sensitive structure on the premise of not increasing the structural complexity is lacked.
Disclosure of Invention
In view of the foregoing analysis, embodiments of the present invention provide a MEMS gas sensor chip, a sensor and a method for manufacturing the sensor, so as to solve the problems of the prior art, such as high price, long response time and poor environmental stability.
The embodiment of the invention provides an MEMS gas sensor chip, which comprises a gas sensitive unit, a temperature sensitive unit, a sensitive structure substrate and a temperature control unit, wherein the gas sensitive unit is arranged on the substrate;
the gas sensitive unit and the temperature sensitive unit are positioned on the same layer, are respectively arranged above the sensitive structure substrate, and the bottom surfaces of the gas sensitive unit and the temperature sensitive unit are in direct contact with the upper surface of the sensitive structure substrate;
the temperature control unit is arranged below the sensitive structure substrate and used for controlling the temperature of the surface of the sensitive structure substrate.
The beneficial effects of the above technical scheme are as follows: the sensitive structure substrate has good heat conduction performance, the temperature sensitive unit is used for collecting the ambient temperature of the MEMS gas sensor chip, and when the measured ambient temperature is higher than the preset temperature, the temperature control unit cools the sensitive structure substrate, otherwise, the temperature is increased. The temperature control unit can realize rapid heat transfer and lower steady-state temperature difference based on the Peltier effect, so that the gas sensitive unit always works in a constant temperature environment, the influence of the ambient temperature on the MEMS gas sensor chip is eliminated or weakened, and the response time is short and the environmental stability is good. In addition, the invention can realize the detection of the concentration of various gases simultaneously by arranging a plurality of gas sensitive units in the sensitive structure substrate or the package, and compared with the prior discrete gas sensor which directly adopts various gases, the cost is reduced.
In another embodiment based on the above method, in the MEMS gas sensor chip, the gas sensitive unit includes a metal electrode and a gas sensitive film; the gas sensitive film covers the surface of the metal electrode;
the gas sensitive unit is used for converting the concentration change of specific gas components in the environment atmosphere into the change of self resistance;
the temperature sensitive unit comprises at least one group of metal broken line type structures and is used for converting the change of the ambient temperature into the change of the self resistance.
The beneficial effect of adopting above-mentioned technical scheme is: the gas sensitive unit and the temperature sensitive unit are all static structures, and no movable part exists, so that the gas sensitive unit and the temperature sensitive unit have higher reliability. The scheme can realize smaller thickness of the metal electrode and the gas sensitive film, and gas molecules are easy to penetrate into the gas sensitive film, so that the conductivity of the gas sensitive unit is changed, and the sensitivity to target gas is improved. In addition, the gas sensitive unit and the temperature sensitive unit have simple structures, easy realization of processing technology and good stability.
Furthermore, the metal electrode is a complementary symmetrical comb-tooth structure, the interdigital width of the comb-tooth structure is 5-30 μm, the interdigital distance is 5-30 μm, and the thickness of the metal electrode is 1000-2000A;
the temperature sensitive unit is made of platinum materials, and the resistance of the temperature sensitive unit is in direct proportion to the length of a broken line of the metal broken line type structure and in inverse proportion to the width and the thickness of the section of the broken line.
The beneficial effect of adopting the further scheme is that: platinum has good environmental stability, and the linearity of the resistivity of platinum in a larger temperature range is generally better, so that the temperature detection precision of the temperature sensitive unit is higher. In addition, the preparation process of the temperature sensitive unit and the preparation process of the metal electrode in the gas sensitive unit can both adopt a magnetron sputtering process, namely the preparation of the metal electrode of the gas sensitive unit and the temperature sensitive unit can be completed in the same process, thereby being beneficial to reducing the manufacturing cost of the whole MEMS gas sensor. Because the resistance of the temperature sensitive unit has a fixed relation with the structure size, the resistance value of the temperature sensitive unit can be adjusted within a certain range by changing the size parameter of the fold line.
Further, the temperature control unit is a flat plate type structure based on the Peltier effect and made of semiconductor materials, and comprises an upper N-type semiconductor and a lower P-type semiconductor which are directly connected; the length and the width of the temperature control unit are larger than those of the sensitive structure substrate, and the thickness of the temperature control unit is about 1000 mu m;
and the upper surface of the upper N-type semiconductor layer is connected with the bottom surface of the sensitive structure substrate through colloidal silicone grease.
The beneficial effect of adopting the further scheme is that: the temperature control unit is in mm level, the temperature response speed is in ms level, and the sizes of the gas sensitive unit and the temperature sensitive unit are both in um to mm level, so that the heat transfer process among the temperature control unit, the gas sensitive unit and the temperature sensitive unit has the characteristics of short transfer path, high balance speed and the like.
Further, the thickness of the sensitive structure substrate is about 200 μm, and the distance between the gas sensitive unit and the temperature sensitive unit is about 100 μm.
The beneficial effect of adopting the further scheme is that: on the premise of ensuring the heat transfer effect, the thickness of the sensitive structure substrate can ensure the electrical insulation between the gas sensitive unit and the temperature sensitive unit and the outside. Moreover, the thickness of the sensitive structure substrate is thin, so that the heat transfer performance is good. The gas sensitive unit and the temperature sensitive unit are not in contact, so that the gas sensitive unit and the temperature sensitive unit can be tested independently. The distance is about 100 mu m, so that the influence of the temperature sensitive unit on the gas sensitive unit can be well eliminated.
The embodiment of the invention also provides an MEMS gas sensor, which comprises the MEMS gas sensor chip and a control circuit;
the input end of the control circuit receives two paths of input signals, one path is the measured temperature output by the temperature sensitive unit, and the other path is the preset temperature; the control circuit compares the two paths of input signals and outputs a control signal according to a comparison result; the control signal changes the temperature of the surface of the sensitive structure substrate by controlling the direction and the magnitude of the current flowing through the temperature control unit.
The beneficial effect who adopts above-mentioned scheme is: by controlling the direction and the magnitude of the current flowing through the temperature control unit, heating and cooling can be realized only by adopting a single temperature control unit, namely, the temperature rise and the temperature drop of the gas sensitive unit and the temperature sensitive unit are realized. When the preset temperature is lower than the temperature collected by the temperature sensitive unit, the control signal enables the heat of the upper surface of the temperature control unit to be transferred to the lower surface, so that the temperature of the upper surface can be reduced, and the MEMS gas sensor is cooled. Otherwise, the temperature rise is realized.
Further, the control circuit comprises a microcontroller, an N-type MOSFET, a P-type MOSFET and a positive power supply and a negative power supply;
the input end of the microcontroller receives the two paths of input signals, the output end of the microcontroller is respectively connected with the grids of the N-type MOSFET and the P-type MOSFET, and the on-off of the N-type MOSFET and the P-type MOSFET is controlled by utilizing the temperature deviation result of the two paths of input signals;
the source electrode of the N-type MOSFET is connected with the source electrode of the P-type MOSFET; the drain electrode of the N-type MOSFET is connected with a positive power supply, and the drain electrode of the P-type MOSFET is connected with a negative power supply;
one electrical interface of the temperature control unit is respectively connected with the source electrode of the N-type MOSFET and the drain electrode of the P-type MOSFET, and the other electrical interface is directly grounded.
The beneficial effect of adopting the further scheme is that: comparing the two paths of input signals through a microcontroller, and outputting a control signal according to a comparison result; the control signal controls the on-off of the N-type MOSFET and the P-type MOSFET so as to control the direction and the magnitude of current flowing through the temperature control unit, change the temperature of the surface of the sensitive structure substrate and further stabilize the temperature of the gas sensitive unit around the preset temperature at a higher speed. Through the rapid control of the temperature of the gas sensitive unit, the influence of the change of the ambient temperature on the self sensitivity of the gas sensitive unit can be reduced, and the environmental adaptability and the environmental stability of the MEMS gas sensor are further improved.
The embodiment of the invention also provides a method for preparing the MEMS gas sensor, which comprises the following steps:
after cleaning the semiconductor wafer, growing an oxide layer on the surface of the semiconductor wafer through a thermal oxidation process;
preparing a gas sensitive unit on the surface of the oxidation layer;
preparing a temperature sensitive unit on the surface of the oxide layer;
thinning the semiconductor wafer;
scribing the semiconductor wafer to form a sensitive structure substrate, wherein the sensitive structure substrate comprises a complete structure of a gas sensitive unit and a temperature sensitive unit;
preparing a temperature control unit in a flat plate shape;
bonding the sensitive structure substrate and the temperature control unit through heat-conducting silicone grease to obtain an MEMS gas sensor chip;
and building a control circuit, and connecting the MEMS gas sensor chip to the control circuit to obtain the MEMS gas sensor.
The beneficial effect who adopts above-mentioned scheme is: on the basis of the chip-level size, the system-level integration of the gas sensitive unit, the temperature sensitive unit and the temperature control unit is realized, and the temperature of the gas sensitive unit and the temperature sensitive unit can be controlled and adjusted at any time. Moreover, the processing technology of the MEMS gas sensor is a common technology, is easy to realize, and a plurality of gas sensitive units and temperature sensitive units aiming at different gases can be prepared on the surface of the oxidation layer.
Further, the step of preparing the gas sensitive unit on the surface of the oxidation layer comprises,
generating a nickel single layer on the surface of the oxide layer by adopting a sputtering process;
generating a gold single-layer on the nickel single-layer by adopting a sputtering process;
transferring the two-dimensional pattern of the metal electrode in the gas sensitive unit to the surface of the simple substance gold layer by adopting a photoetching process;
removing redundant metal materials and photoresist through a corrosion process to form a metal electrode;
after a sensitive material aiming at specific gas is dissolved in an organic solvent, a gas sensitive film is prepared on the metal electrode through a spin coating process.
The beneficial effect of adopting the further scheme is that: by repeating the steps, a plurality of gas sensitive units aiming at different specific gases can be manufactured on the sensitive structure substrate, and the detection of the same sensor on the concentration of a plurality of different gases is realized.
The step of preparing the temperature sensitive unit on the surface of the oxidation layer comprises the following steps,
generating a platinum single-layer on the oxide layer through a sputtering process;
transferring the two-dimensional structure of the temperature sensitive unit to the surface of the platinum simple substance layer by a photoetching process;
and removing the redundant metal material and the photoresist by using a corrosion process to form a fold line type platinum metal structure.
The beneficial effect of adopting the further scheme is that: by repeating the steps, a plurality of temperature sensitive units can be manufactured on the sensitive structure substrate, the temperature distribution of the surface of the substrate can be obtained, and the environment temperature can be obtained more accurately. The temperature sensitive unit is used for accurately measuring the ambient temperature of the gas sensitive unit.
In the invention, the technical schemes can be combined with each other to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.
FIG. 1 is a schematic structural diagram of a MEMS gas sensor chip according to embodiment 1 of the present invention;
FIG. 2 is a schematic structural diagram of a MEMS gas sensor chip according to embodiment 2 of the present invention;
FIG. 3 is a schematic structural diagram of a gas sensing unit in embodiment 2 of the present invention;
FIG. 4 is a schematic structural diagram of a temperature-sensitive unit in accordance with embodiment 2 of the present invention;
FIG. 5 is a schematic structural diagram of a temperature control unit according to embodiment 2 of the present invention;
FIG. 6 is a schematic diagram showing the composition of a MEMS gas sensor in accordance with embodiment 3 of the present invention;
FIG. 7 is a schematic diagram of a method for manufacturing a MEMS gas sensor according to embodiment 4 of the present invention;
FIG. 8 is a schematic view of a method for preparing a gas sensing unit according to example 4 of the present invention;
FIG. 9 is a schematic view of a method for preparing a temperature sensitive unit according to example 4 of the present invention;
reference numerals:
a, B-metal electrodes; l-the length of the gas-sensitive cell; d-width of the gas sensitive cell;
d-the spacing between adjacent fingers; w-finger width; M1-N type MOSFET; M2-P type MOSFET;
v + -positive power supply, V-negative power supply, M, N-interface of temperature control unit.
Detailed Description
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate preferred embodiments of the invention and together with the description, serve to explain the principles of the invention and not to limit the scope of the invention.
Example 1
As shown in fig. 1, an embodiment of the present invention discloses a MEMS gas sensor chip, which includes a gas sensitive unit, a temperature sensitive unit, a sensitive structure substrate, and a temperature control unit.
The gas sensitive unit and the temperature sensitive unit are arranged on the same layer, are respectively arranged above the sensitive structure substrate, and the bottom surfaces of the gas sensitive unit and the temperature sensitive unit are in direct contact with the upper surface of the sensitive structure substrate.
The temperature control unit is arranged below the sensitive structure substrate and comprises two electrical interfaces. The temperature control unit is used for controlling the temperature of the surface of the sensitive structure substrate.
In operation, one electrical interface of the temperature control unit is grounded and the other is connected to a control signal. When the actual temperature that the temperature sensitive unit gathered is higher than the preset temperature of sensor work, the temperature control unit cools down, and the heat of temperature control unit upper surface shifts to the lower surface promptly, realizes the cooling. When the actual temperature collected by the temperature sensitive unit is lower than the preset temperature of the sensor, the temperature sensitive unit generates heat to realize temperature rise.
Compared with the prior art, the MEMS gas sensor chip provided by the embodiment integrates the temperature control unit and the gas sensitive structure, and the temperature control unit has a refrigerating/heating effect, controls the direction and the size of current passing through the temperature control unit, can effectively and rapidly control the refrigerating/heating of the temperature control unit, namely, realizes the rapid switching of the cold end and the hot end, further controls the temperature of the gas sensitive structure to be around the preset temperature, and improves the environmental adaptability and the environmental stability of the MEMS gas sensor. By adopting MEMS design, the heat transfer process is short, the balance speed is high, and the cost of mass production is low.
Example 2
As shown in fig. 2, optimized on the basis of the above embodiment, the MEMS gas sensor further includes a colloidal silicone grease with good thermal conductivity, the upper surface of the temperature control unit is connected to the bottom surface of the sensitive structure substrate through the colloidal silicone grease with good thermal conductivity, and the thickness of the colloidal silicone grease layer is not more than 50 μm. The better thermal conductivity means that the thermal conductivity coefficient of the heat-conducting silicone grease reaches more than 2.0W/(m K), the temperature range of the working environment is-40 ℃ to 200 ℃, the thickness of the heat-conducting silicone grease is generally 1-5mm, and the thickness can be controlled through the coating process. The existing heat-conducting silicone grease for CPU heat dissipation can generally meet the requirements.
Preferably, there may be one or more gas sensitive units and temperature sensitive units above the sensitive structure substrate, as the sensitive structure of the MEMS gas sensor, the whole sensitive structure has only one sensitive structure substrate. The distance between the gas sensitive unit and the temperature sensitive unit is about 100 mu m.
The gas sensitive unit is a micron-scale structure with the physical characteristics related to specific gas concentration, and consists of a metal electrode and a gas sensitive film, wherein the gas sensitive film covers the surface of the metal electrode. The gas-sensitive cell is capable of converting a change in the concentration of a particular gas component in the ambient atmosphere into a change in its own conductive properties (resistance).
Since different gas-sensitive materials are sensitive to different gases, e.g. metal phthalocyanine compounds to NO2Gas has higher sensitivity, while SnO2To H2S gas has higher sensitivity, and a plurality of gas sensitive units are formed by preparing a plurality of gas sensitive films (containing sensitive materials) based on different gases, so that detection of different gases and concentration thereof can be realized.
The most typical principle (the principle used in the present embodiment) among the principles of gas-sensitive units detecting a certain gas is: adsorption between the gas-sensitive film and a specific gas (i.e., target gas) molecule may occur, and in this process, there is charge transfer between the gas-sensitive film material molecule and the target gas molecule, and thus a higher or lower concentration of electrons/holes is formed inside the gas-sensitive film, accordingly. The charge transfer process becomes more remarkable gradually as target gas molecules gradually penetrate into the gas sensitive material, the conductivity of the gas sensitive film can generate remarkable and quantitative change after a period of time, and the measurement of the target gas concentration can be realized by detecting the change of the conductivity of the gas sensitive film.
The gas-sensitive film resistance and the target gas concentration in the environment generally satisfy the following relationship:
Figure BDA0001645514470000101
wherein R (t) represents a resistance value at time t, R0Representing the resistance, K, of the gas-sensitive film in the absence of the target gas in the environmentTDenotes a temperature coefficient, K denotes a sensitivity of the gas sensitive film to the target gas, the larger K denotes the more sensitive the gas sensitive film is to a change in the concentration of the target gas, T denotes a time constant of the gas sensitive film, generally T is a value of several seconds or more, CgasRepresenting the target gas concentration.
When the time is long enough, i.e. T > > T:
R(t)＝KTR0(1+KCgas) (2)
preferably, the metal electrodes are A, B two sets of complementary symmetric comb-tooth structures, as shown in FIG. 3, each set includes a plurality of fingers, the finger width w is 5-30 μm, the finger pitch d is 5-30 μm, and the metal electrode thickness is 1000-2000A. The length L and width D of the whole gas sensitive structure range from 2000-. The metal electrode is made of a metal material having good electrical conductivity and environmental stability, such as gold. The gas sensitive film covers the surface of the metal electrode and extends into the gaps among the fingers, and the thickness of the gas sensitive film is similar to that of the metal electrode layer. The gas sensitive film material is a mixture formed by mixing a substance sensitive to a specific gas in self conductivity and an organic solvent such as trichloromethane.
The temperature sensitive unit is a micron-scale structure with physical characteristics related to the temperature of the environment in which the temperature sensitive unit is located, and consists of one or more groups of metal broken line type structures, as shown in fig. 4, and is used for converting the change of the temperature of the environment into the change of self resistance. Preferably, the temperature sensitive unit is made of platinum metal material with good stability of resistivity and temperature characteristics, and the resistance of the temperature sensitive unit is in direct proportion to the length of the broken line of the metal broken line type structure and in inverse proportion to the width and the thickness of the cross section of the broken line. Therefore, by changing the size parameter of the folding line, the resistance value of the temperature sensitive unit can be adjusted within a certain range.
The sensitive structure substrate is a planar structure formed by a wafer made of semiconductor materials such as monocrystalline silicon through processes of oxidation, thinning and the like, is used for providing a processing starting point of the gas sensitive unit and the temperature sensitive unit, provides mechanical support and structural interconnection for the gas sensitive unit and the temperature sensitive unit, and provides necessary electrical insulation for the whole sensitive structure. Preferably, the sensitive structure substrate has a thickness of about 200 μm.
The temperature control unit is made of Bi2Te3Flat plate-type structures based on the Peltier (Peltier) effect, made of semiconductor materials, as shown in fig. 5, include N-type semiconductors, P-type semiconductors, and ceramic cases. The N-type semiconductor material and the P-type semiconductor material are manufactured by adopting a doping process and are directly connected to form a thermocouple structure, and the outer surface of the thermocouple structure is integrally packaged by a ceramic shell. Preferably, its length and width are greater than those of the sensitive structure substrate, and its thickness is about 1000 μm. When current flows through the interior of the refrigerator, the heat of the cold end of the refrigerator can be transferred to the hot end, so that the refrigeration function of the cold end can be realized. By switching the direction of the current through the temperature control unit, i.e. by switching the respective cold and hot ends accordingly, i.e. by controlling the direction and magnitude of the current through the temperature control unit, cooling and heating of a surface thereof can be achieved, changing the temperature of the surface. Preferably, in this embodiment, the temperature control unit is MPC-D404 of Miropelt.
During implementation, the temperature control unit is used for maintaining the temperature of the MEMS gas sensor chip at a preset temperature, namely realizing constant temperature, eliminating or weakening the influence of the ambient temperature on the MEMS gas sensor chip, and improving the adaptability of the MEMS gas sensor to the ambient temperature.
Example 3
As shown in fig. 6, the present embodiment provides a MEMS gas sensor including a MEMS gas sensor chip and a control circuit. The control circuit comprises a microcontroller, an N-type MOSFET, a P-type MOSFET and a power supply.
The input end of the microcontroller receives two paths of input signals, one path is the measured temperature output by the temperature sensitive unit, and the other path is the preset temperature, and the input signals are set by a user according to the working requirements of the sensor. The output end of the microcontroller is respectively connected with the grids of the N-type MOSFET and the P-type MOSFET.
The source electrode of the N-type MOSFET is connected with the source electrode of the P-type MOSFET; the drain of the N-type MOSFET is connected with a positive power supply, and the drain of the P-type MOSFET is connected with a negative power supply.
One electrical interface of the temperature control unit is respectively connected with the source electrode of the N-type MOSFET and the drain electrode of the P-type MOSFET through leads, and the other electrical interface is directly grounded.
Preferably, the microcontroller compares the two input signals and outputs a control signal according to the comparison result. The control signal controls the on-off of the N-type MOSFET and the P-type MOSFET so as to control the direction and the magnitude of the current flowing through the temperature control unit and change the temperature of the surface of the sensitive structure substrate.
The temperature control realization process of the MEMS gas sensor comprises the following steps: the temperature control unit is connected with a peripheral microcontroller and a bipolar direct current power supply (V +, V-) through an interface M, the interface N is directly grounded, M1 is an N-type MOSFET, and M2 is a P-type MOSFET. When M1 is turned on by the control signal output by the microcontroller, since M1 and M2 are complementary, M2 is turned off, current flows from interface M to interface N, and heat on the upper surface of the temperature control unit is transferred to the lower surface, so that the temperature of the upper surface can be reduced. When M2 is turned on by the control signal output by the microcontroller, M1 is turned off, current flows from interface N to interface M, and heat from the lower surface of the temperature control unit is transferred to the upper surface, thereby increasing the temperature of the upper surface. Because of the voltage signal amplification of the MOSFET, the magnitude of the current flowing between the interface M and the interface N can be controlled by the control signal output by the microcontroller, so that the microcontroller can not only increase the temperature of the upper surface of the temperature control unit, but also reduce the temperature of the upper surface of the temperature control unit.
In addition, the upper surface of the temperature control unit and the sensitive structure substrate are connected together through the silicone grease with good heat conductivity, so that the heat resistance of the heat transfer process from the upper surface of the temperature control unit to the gas sensitive unit and the temperature sensitive unit is small, namely the temperature difference between the upper surfaces of the gas sensitive unit and the temperature control unit is small. The temperature (actual temperature) measured by the temperature sensitive unit is input to the microcontroller as a feedback signal, the microcontroller can compare the actual temperature with the preset temperature, and when the actual temperature is higher than the preset temperature, the output control signal enables the M1 to be conducted, so that the temperature of the upper surface of the temperature control unit is reduced. When the actual temperature is lower than the preset temperature, the control signal output by the microcontroller turns on M2 to raise the temperature of the upper surface of the temperature control unit. Therefore, by the method, the temperature of the sensitive structure can be stabilized at the preset temperature, the influence of the ambient temperature on the sensitive structure is reduced, and the environmental adaptability of the sensitive structure is improved.
Compared with the prior art, the MEMS gas sensor provided by this embodiment can stabilize the temperature of the gas sensitive unit around the preset temperature (preset temperature) at a faster speed through the microcontroller. Through the rapid control of the temperature of the gas sensitive unit, the influence of the change of the ambient temperature on the self sensitivity of the gas sensitive unit can be reduced, and the environmental adaptability and the environmental stability of the MEMS gas sensor can be improved.
Example 4
As shown in fig. 7, the present embodiment provides a process for preparing the MEMS gas sensor of embodiment 3, which comprises the following steps:
1. cleaning a semiconductor wafer made of a monocrystalline silicon material, and growing an oxide layer with the thickness of 500A on the surface of the semiconductor wafer through a thermal oxidation process;
2. preparing a gas sensitive unit on the surface of the oxide layer;
3. preparing a temperature sensitive unit on the surface of the oxide layer;
4. thinning the semiconductor wafer to enable the thickness of the semiconductor wafer to reach 200 mu m;
5. scribing a semiconductor wafer to form a sensitive structure substrate, wherein the sensitive structure substrate comprises a complete structure of a gas sensitive unit and a temperature sensitive unit;
6. preparing a temperature control unit in a flat plate shape;
7. the sensitive structure substrate and the temperature control unit are jointed through the heat conduction silicone grease, and the preparation process of the MEMS gas sensitive structure aiming at various gases such as nitrogen oxide and the like is completed after the temperature control unit is solidified;
8. and building a control circuit, and connecting the MEMS gas sensor chip to the control circuit to obtain the MEMS gas sensor.
Repeating the steps 2-3, a plurality of gas sensitive units aiming at different gases and a plurality of temperature sensitive units can be manufactured on the same substrate.
Further, as shown in fig. 8, the step of preparing the gas sensing unit on the surface of the oxide layer includes:
1. a nickel single layer with the thickness of 50A is grown on the surface of the oxide layer by adopting a PVD (physical vapor deposition) process such as sputtering and the like;
2. forming a gold single-layer with the thickness of 1000-2000A on the nickel single-layer by adopting a PVD (physical vapor deposition) process such as sputtering and the like;
3. transferring the two-dimensional pattern of the metal electrode in the gas sensitive unit to the surface of the gold simple substance layer by adopting a photoetching process;
4. removing redundant metal materials and photoresist through a corrosion process to form a metal electrode;
5. after a sensitive material aiming at specific gas is dissolved in an organic solvent, a gas sensitive film is prepared on the metal electrode through a spin coating process, and the preparation of the gas sensitive unit is completed through the step.
Repeating the steps 3-5, and adopting the sensitive materials aiming at different gases in the step 5, namely, a plurality of gas sensitive units aiming at different specific gases can be manufactured on the sensitive structure substrate.
Further, as shown in fig. 9, the step of preparing the temperature sensitive unit on the surface of the oxide layer includes:
1. generating a platinum single-layer with the thickness of 1000A on the oxide layer through a PVD (physical vapor deposition) process such as sputtering;
2. transferring the two-dimensional structure of the temperature sensitive unit to the surface of a platinum simple substance layer by a photoetching process;
3. and removing redundant metal materials and photoresist by a corrosion process to form a fold line type platinum metal structure, and completing the preparation of the temperature sensitive unit.
And repeating the steps 2-3 to manufacture a plurality of temperature sensitive units on the sensitive structure substrate.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.

Claims (10)

1. An MEMS gas sensor chip is characterized by comprising a gas sensitive unit, a temperature sensitive unit, a sensitive structure substrate and a temperature control unit;
the gas sensitive unit and the temperature sensitive unit are positioned on the same layer, are respectively arranged above the sensitive structure substrate, and the bottom surfaces of the gas sensitive unit and the temperature sensitive unit are in direct contact with the upper surface of the sensitive structure substrate;
the temperature control unit is arranged below the sensitive structure substrate and used for controlling the temperature of the surface of the sensitive structure substrate;
the length and width of the temperature control unit are greater than the length and width of the sensitive structure substrate.
2. The MEMS gas sensor chip of claim 1, wherein the gas-sensitive cell comprises a metal electrode and a gas-sensitive film; the gas sensitive film covers the surface of the metal electrode;
the gas sensitive unit is used for converting the concentration change of specific gas components in the environment atmosphere into the change of self resistance;
the temperature sensitive unit comprises at least one group of metal broken line type structures and is used for converting the change of the ambient temperature into the change of the self resistance.
3. The MEMS gas sensor chip of claim 2, wherein the metal electrode is a complementary symmetric comb-tooth structure, the finger width of the comb-tooth structure is 5-30 μm, the finger pitch is 5-30 μm, and the metal electrode thickness is 1000-2000A;
the temperature sensitive unit is made of platinum materials, and the resistance of the temperature sensitive unit is in direct proportion to the length of a broken line of the metal broken line type structure and in inverse proportion to the width and the thickness of the section of the broken line.
4. The MEMS gas sensor chip according to one of claims 1 to 3, wherein the temperature control unit is a flat plate type structure based on peltier effect made of a semiconductor material, comprising an upper N-type semiconductor and a lower P-type semiconductor, the upper N-type semiconductor and the lower P-type semiconductor being directly connected; the thickness of the temperature control unit is about 1000 mu m;
and the upper surface of the upper N-type semiconductor layer is connected with the bottom surface of the sensitive structure substrate through colloidal silicone grease.
5. The MEMS gas sensor chip of claim 4, wherein the thickness of the sensitive structure substrate is about 200 μm, and the distance between the gas sensitive unit and the temperature sensitive unit is about 100 μm.
6. A MEMS gas sensor comprising a MEMS gas sensor chip as claimed in any one of claims 1 to 5, and control circuitry;
the input end of the control circuit receives two paths of input signals, one path is the measured temperature output by the temperature sensitive unit, and the other path is the preset temperature; the control circuit compares the two paths of input signals and outputs a control signal according to a comparison result; the control signal changes the temperature of the surface of the sensitive structure substrate by controlling the direction and the magnitude of the current flowing through the temperature control unit.
7. The MEMS gas sensor of claim 6, wherein the control circuit comprises a microcontroller, an N-type MOSFET, a P-type MOSFET, a positive and negative power supply;
the input end of the microcontroller receives the two paths of input signals, the output end of the microcontroller is respectively connected with the grids of the N-type MOSFET and the P-type MOSFET, and the on-off of the N-type MOSFET and the P-type MOSFET is controlled by utilizing the temperature deviation result of the two paths of input signals;
the source electrode of the N-type MOSFET is connected with the source electrode of the P-type MOSFET; the drain electrode of the N-type MOSFET is connected with a positive power supply, and the drain electrode of the P-type MOSFET is connected with a negative power supply;
one electrical interface of the temperature control unit is respectively connected with the source electrode of the N-type MOSFET and the drain electrode of the P-type MOSFET, and the other electrical interface is directly grounded.
8. A method of making the MEMS gas sensor of claim 6 or 7, comprising the steps of:
after cleaning the semiconductor wafer, growing an oxide layer on the surface of the semiconductor wafer through a thermal oxidation process;
preparing a gas sensitive unit on the surface of the oxidation layer;
preparing a temperature sensitive unit on the surface of the oxide layer;
thinning the semiconductor wafer;
scribing the semiconductor wafer to form a sensitive structure substrate, wherein the sensitive structure substrate comprises a complete structure of a gas sensitive unit and a temperature sensitive unit;
preparing a temperature control unit in a flat plate shape;
bonding the sensitive structure substrate and the temperature control unit through heat-conducting silicone grease to obtain an MEMS gas sensor chip;
and building a control circuit, and connecting the MEMS gas sensor chip to the control circuit to obtain the MEMS gas sensor.
9. The method for manufacturing a MEMS gas sensor according to claim 8, wherein the step of manufacturing the gas sensitive unit on the surface of the oxide layer comprises,
generating a nickel single layer on the surface of the oxide layer by adopting a sputtering process;
generating a gold single-layer on the nickel single-layer by adopting a sputtering process;
transferring the two-dimensional pattern of the metal electrode in the gas sensitive unit to the surface of the simple substance gold layer by adopting a photoetching process;
removing redundant metal materials and photoresist through a corrosion process to form a metal electrode;
after a sensitive material aiming at specific gas is dissolved in an organic solvent, a gas sensitive film is prepared on the metal electrode through a spin coating process.
10. The method of manufacturing a MEMS gas sensor according to claim 8 or 9, wherein the step of manufacturing a temperature sensitive unit on the surface of the oxide layer comprises,
generating a platinum single-layer on the oxide layer through a sputtering process;
transferring the two-dimensional structure of the temperature sensitive unit to the surface of the platinum simple substance layer by a photoetching process;
and removing the redundant metal material and the photoresist by using a corrosion process to form a fold line type platinum metal structure.
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