CN117825455A - MEMS gas sensor chip based on two-dimensional aluminum nitride material and preparation method thereof - Google Patents
MEMS gas sensor chip based on two-dimensional aluminum nitride material and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a MEMS gas sensor chip based on a two-dimensional aluminum nitride material and a preparation method thereof. The gas sensor chip comprises an MEMS micro-hotplate electrode chip and a two-dimensional functionalized aluminum nitride (AlN) gas-sensitive material. During preparation, in the aspect of an electrode chip, sputtering Pt metal on a glass sheet, and then adopting ion beam etching to obtain an interdigital electrode with a heating function; in the aspect of the gas-sensitive material, precious metal Rh atoms are modified on the two-dimensional AlN, and the two-dimensional AlN gas-sensitive material modified by Rh single atoms is obtained. The gas sensor provided by the invention has the advantages of simple structure and good heating performance, and can be used for formaldehyde gas detection.
Description
Technical Field
The invention relates to the field of harmful gas detection, in particular to a MEMS gas sensor chip based on a two-dimensional aluminum nitride material and a preparation method thereof.
Background
With the rapid development of economic and technological levels, environmental problems become more serious, and people are more concerned about environmental problems in living places and human health problems caused by the environmental problems while living matters are improved. Air is a necessary condition for people to live, and air pollution is most prominent in environmental problems. Formaldehyde (HCHO) is a toxic, irritating, volatile Organic Compound (VOCs). Excessive formaldehyde gas inhaled in a short time can irritate the mouth and nose and respiratory tract, causing cough and even asthma. The long-term life in the environment with formaldehyde exceeding the standard can cause potential health problems such as allergic dermatitis, lung injury, immune system disorder, cancer and the like. At the same time, formaldehyde was also listed by the international cancer institute as a list of carcinogens, and the World Health Organization (WHO) and National Institute for Occupational Safety and Health (NIOSH) set the maximum safe exposure concentration of formaldehyde to 0.08 ppm and 1 ppm, respectively. Several methods of detecting formaldehyde have been developed, including gas chromatography, liquid chromatography and colorimetry. These methods require high precision test instrumentation and must be performed in a fixed test environment, which is not suitable for real-time testing in the field. Therefore, there is a need to equip portable systems to detect formaldehyde gas molecules in indoor air to maintain human health.
The gas sensor is used as an important branch of the sensor, plays a role in environmental monitoring, medical diagnosis and the like, has various types at present, and has the characteristics of simple manufacture, direct measurement and the like, wherein the resistance type gas sensor analyzes and calculates the gas concentration along with the change of resistance under the interaction with the detected gas through the direct test sensor. In the aspect of gas-sensitive materials, the gas-sensitive material has the remarkable characteristics that the gas-sensitive material has an ultrahigh specific surface area and a special planar structure is two-dimensional graphene. However, graphene has difficulty in adjusting the band gap, which limits graphene as a gas-sensitive material with excellent sensing performance. In contrast, group III-V2D materials exhibit a significantly tunable band gap and have a honeycomb structure similar to graphene. Wherein, the single-layer aluminum nitride with novel performance has wide application prospect in the field of gas sensing. Unlike the common three-dimensional structure (4-fold coordination), the N and Al atoms of the two-dimensional AlN surface undergo 3-fold coordination through dangling bonds, yielding more gas-molecule adsorption active sites. The electronegativity difference drives electrons to transfer from Al atoms to N atoms, so that Al-N bonds generate dipole moment, and gas adsorption is facilitated. It has been reported that gas molecules can interact with AlN. However, to detect with better sensitivity and selectivity, alN needs to be modified to improve the adsorption performance of AlN to achieve better sensing performance.
Disclosure of Invention
The invention aims to provide a MEMS gas sensor chip based on a two-dimensional aluminum nitride material.
Still another object of the present invention is: the preparation method of the MEMS gas sensor chip based on the two-dimensional aluminum nitride material is provided.
The invention aims at realizing the following scheme: a MEMS gas sensor chip based on two-dimensional aluminum nitride material comprises an MEMS micro-hotplate electrode chip and a two-dimensional functional aluminum nitride (AlN) gas-sensitive material, wherein the electrode chip comprises a micro heater surrounding an interdigital electrode, pt metal is sputtered on a glass sheet, and then the interdigital electrode with a heating function is obtained by adopting ion beam etching; the gas-sensitive material is a two-dimensional functionalized AlN gas-sensitive material modified by noble metal Rh atoms on two-dimensional AlN to obtain Rh single-atom modification.
The MEMS gas sensor chip based on the two-dimensional aluminum nitride material can be obtained by dripping the two-dimensional functionalized AlN dispersion liquid onto interdigital electrodes of an MEMS micro-hotplate chip and drying at normal temperature. The sensitivity of the sensor to gas can be remarkably improved due to the adoption of the Rh noble metal monoatomically modified two-dimensional AlN; the MEMS micro-thermal plate chip comprises a micro heater surrounding the interdigital electrode, has a heating function, and can remarkably reduce the response time and recovery time of the sensor to gas.
The invention adopts Rh monoatomic modified two-dimensional aluminum nitride as a gas-sensitive material. It is reported that after Rh modification, the adsorption of aluminum nitride to formaldehyde gas can be obviously promoted, and the surface specific area of the material can be obviously improved by combining a two-dimensional framework, more gas reaction sites are provided, so that the responsiveness of the material to formaldehyde can be obviously improved. Compared with the common interdigital electrode, the micro-thermal plate with the heating function can remarkably improve the response time and the recovery time of the functionalized aluminum nitride to the gas under the heating condition, and can reduce the influence of the environmental humidity on the operation of the sensor when the heating temperature exceeds 100 ℃.
Preferably, the interdigital electrodes of the MEMS micro-hotplate chip and the main body material of the micro-heater are Pt metal, and Cr or Ti metal for increasing adhesion is further contained.
Preferably, the thickness of the Cr or Ti metal layer is 1-20 nm, and the thickness of Pt is 20-300 nm.
Preferably, the outline of the peripheral connecting line of the interdigital electrode and the outline of the micro-heater wire of the MEMS micro-hotplate chip are arc-shaped, the radius of the peripheral connecting line of the interdigital electrode is 150-1150 mu m, and the arc-shaped radius of the micro-heater is 150-1550 mu m.
Preferably, each electrode width of the interdigital electrode of the MEMS micro-hotplate chip is 5-40 μm, the electrode spacing is 10-30 μm, the micro-heater line width is 10-50 μm, and the line spacing is 10-50 μm.
Preferably, the two-dimensional aluminum nitride material is an Rh single-atom modified aluminum nitride two-dimensional material.
Preferably, the aluminum nitride has a structure similar to that of graphene, and the Al atom and the N atom are each in sp 2 The hybridization forms bond, al-N bond length is 1.780-1.850A.
Preferably, the Rh modification mode is physical adsorption doping or chemical bond doping instead of Al atoms.
Preferably, the molar content ratio of Rh modification is 0.1% -50%.
Preferably, the Rh-modified aluminum nitride two-dimensional material is dropped on the interdigital electrode in an amount of 0.1-100 μg.
The invention provides a preparation method of the MEMS gas sensor chip based on the two-dimensional aluminum nitride material, which comprises the following steps:
(1) MEMS micro-hotplate chip preparation
Sequentially ultrasonically cleaning glass sheets in acetone, alcohol and deionized water for 10 min, then drying by nitrogen, and baking in a 180 ℃ oven for 2 hours; subsequently sputtering a metal layer of 20 nm Cr/300 nm Pt on the glass sheet; spin-coating HJ6030 photoresist on the metal layer with thickness of 5 μm, and baking 120 s on a hot plate at 90deg.C; subsequently exposing 20 to s with a UV lithography machine and finally developing 50 to s; then an electrode wire is obtained by adopting an ion beam etching method;
(2) Preparation of gas-sensitive materials
Preparing an AlN film on a monocrystalline Ag (111) substrate by adopting a plasma assisted molecular beam epitaxy technology, sputtering Ar ions of 1.5keV at a speed of 5 multiplied by 10 < -5 > millibar in vacuum for 30 min before deposition, cleaning the silver substrate, and then performing heat treatment in vacuum at 500 ℃ for 30 min to repair sputtering damage of the Ar ions on the Ag surface, thereby obtaining a flat and orderly surface monitored by a stripe RHEED graph and a (1 multiplied by 1) reconstructed surface; to obtain a clean surface free of carbon and oxygen contaminants, the anneal-sputter cycle was repeated multiple times, which was verified using in-situ XPS; evaporating Al metal from the cold lip pool with a pyrolytic boron nitride crucible to deposit AlN at a deposition temperature of 650 c, a deposition rate of 0.22A per second, and an aluminum nitride thickness of sub-milliliters to 20 milliliters after the presence or exposure of a reactive atomic nitrogen beam generated by a remote radio frequency (rf) plasma source to achieve the desired stoichiometry and structure while minimizing residual oxygen on the surface; after two-dimensional aluminum nitride is obtained, modifying Rh metal atoms with required molar content on the surface of the aluminum nitride by utilizing an atomic layer deposition technology to obtain Rh single-atom modified two-dimensional aluminum nitride;
(3) Gas sensor chip preparation
Spin-coating a PVA film on an Ag substrate, spin-coating a PMMA film on the PVA film, heating and drying the PVA film, stripping Rh-modified two-dimensional aluminum nitride material, immersing the PVA film in deionized water, dissolving the PVA film, floating PMMA carrying the two-dimensional material on the water surface, adsorbing the PMMA film by a transparent glass sheet, transferring the PMMA film to an interdigital electrode of a MEMS micro-hotplate under a microscope, heating and removing deionized water, immersing the whole sample in acetone to remove PMMA, cleaning the PMMA film by using ethanol and deionized water, drying the PMMA film at normal temperature, controlling the Rh-modified two-dimensional aluminum nitride content to be 0.1-100 mu g, and finally obtaining the gas sensor chip
The beneficial effects of the invention are as follows:
(1) The two-dimensional aluminum nitride has adjustable band gap and extremely large specific surface area, and has advantages in the aspect of gas sensing.
(2) Rh modification can remarkably enhance the adsorption of two-dimensional aluminum nitride to formaldehyde, so that the gas responsiveness is improved.
(3) The heating function of the micro-hotplate can obviously reduce the response time and recovery time of the sensor to formaldehyde, and achieve quick response.
Drawings
FIG. 1 is a topographical view of the MEMS micro-hotplate chip product obtained in example 1;
FIG. 2 is a graph showing interactions of formaldehyde molecules with Rh-modified aluminum nitride;
FIG. 3 is a graph showing the density of material states before and after Rh-modified aluminum nitride;
FIG. 4 is a graph showing the change of the system density before and after Rh-modified aluminum nitride is adsorbed by formaldehyde molecules;
fig. 5 is a schematic diagram of the present invention.
Detailed Description
The following describes in detail the examples of the present invention, which are implemented on the premise of the technical solution of the present invention, and detailed embodiments and specific operation procedures are given, but the scope of protection of the present invention is not limited to the following examples.
Example 1
A MEMS gas sensor chip based on two-dimensional aluminum nitride material is prepared by the following steps:
(1) MEMS micro-hotplate chip preparation
Sequentially ultrasonically cleaning glass sheets in acetone, alcohol and deionized water for 10 min, then drying by nitrogen, and baking in a 180 ℃ oven for 2 hours; subsequently sputtering a metal layer of 20 nm Cr/300 nm Pt on the glass sheet; spin-coating HJ6030 photoresist on the metal layer with thickness of 5 μm, and baking 120 s on a hot plate at 90deg.C; subsequently exposing 20 to s with a UV lithography machine and finally developing 50 to s; then an electrode wire is obtained by adopting an ion beam etching method;
(2) Preparation of gas-sensitive materials
Preparing an AlN film on a monocrystalline Ag (111) substrate by adopting a plasma assisted molecular beam epitaxy technology, sputtering Ar ions of 1.5keV at a speed of 5 multiplied by 10 < -5 > millibar in vacuum for 30 min before deposition, cleaning the silver substrate, and then performing heat treatment in vacuum at 500 ℃ for 30 min to repair sputtering damage of the Ar ions on the Ag surface, thereby obtaining a flat and orderly surface monitored by a stripe RHEED graph and a (1 multiplied by 1) reconstructed surface; to obtain a clean surface free of carbon and oxygen contaminants, the anneal-sputter cycle was repeated multiple times, which was verified using in-situ XPS; evaporating Al metal from a cold lip pool with a pyrolytic boron nitride crucible to deposit AlN at a deposition temperature of 650 ℃ at a deposition rate of 0.22A/s and an aluminum nitride thickness of sub-milliliters to 20 milliliters after the existence or exposure of reactive atomic nitrogen beams generated by a remote radio frequency (rf) plasma source to obtain a required stoichiometric ratio and structure, preferably, a Rh modified molar content ratio of 0.1% -50%; at the same time, residual oxygen on the surface is minimized; after two-dimensional aluminum nitride is obtained, modifying Rh metal atoms with required molar content on the surface of the aluminum nitride by utilizing an atomic layer deposition technology to obtain Rh single-atom modified two-dimensional aluminum nitride;
(3) Gas sensor chip preparation
Spin-coating a PVA film on an Ag substrate, spin-coating a PMMA film on the Ag substrate, heating and drying, peeling Rh-modified two-dimensional aluminum nitride material, immersing the Ag substrate in deionized water, dissolving the PVA, floating PMMA carrying the two-dimensional material on the water surface, adsorbing the PMMA film by using a transparent glass sheet, transferring the PMMA film onto an interdigital electrode of a MEMS micro-hotplate under a microscope, heating to remove deionized water, immersing the whole sample in acetone to remove PMMA, washing by using ethanol and deionized water, drying at normal temperature, controlling the content of Rh-modified two-dimensional aluminum nitride to be 0.1-100 mu g, and finally obtaining the gas sensor chip.
The appearance and morphology diagram of the obtained MEMS micro-hotplate chip product is shown in figure 1, the outline of the interdigital electrode peripheral connecting line and the outline of the micro-heater line of the MEMS micro-hotplate chip are arc-shaped, the radius of the interdigital electrode peripheral connecting line is 150-1150 mu m, and the arc radius of the micro-heater is 150-1550 mu m.
The width of each electrode of the interdigital electrode of the MEMS micro-hotplate chip is 5-40 mu m, the electrode spacing is 10-30 mu m, the line width of the micro-heater is 10-50 mu m, and the line spacing is 10-50 mu m.
FIG. 2 is a graph showing interactions of formaldehyde molecules with Rh-modified aluminum nitride.
The aluminum nitride has a similar structure to graphene, and Al atoms and N atoms are sp 2 The hybridization forms bond, al-N bond length is 1.780-1.850A.
The change chart of the state density of the material before and after the Rh modified aluminum nitride is shown in figure 3, the change chart of the state density of the system before and after the Rh modified aluminum nitride is adsorbed by formaldehyde molecules is shown in figure 4, the Rh single-atom modified two-dimensional aluminum nitride is adopted as a gas-sensitive material, the adsorption of the Rh to formaldehyde gas can be obviously promoted after the Rh modification, and the surface area of the material can be obviously improved by combining with a two-dimensional framework, so that more gas reaction sites are provided, and the responsiveness of the material to formaldehyde can be obviously improved. Compared with the common interdigital electrode, the micro-thermal plate with the heating function can remarkably improve the response time and the recovery time of the functionalized aluminum nitride to the gas under the heating condition, and can reduce the influence of the environmental humidity on the operation of the sensor when the heating temperature exceeds 100 ℃.
The principle of the invention is shown in figure 5, the adoption of Rh single-atom modified two-dimensional aluminum nitride as a gas-sensitive material can obviously promote the adsorption of the aluminum nitride to formaldehyde gas, and the combination of the two-dimensional architecture can obviously improve the surface area of the material and provide more gas reaction sites, so that the responsiveness of the material to formaldehyde can be obviously improved; compared with the common interdigital electrode, the micro-thermal plate with the heating function can remarkably improve the response time and the recovery time of the functionalized aluminum nitride to gas under the heating condition, and particularly can reduce the influence of environmental humidity on the operation of the sensor when the heating temperature exceeds 100 ℃.
Claims (10)
1. The MEMS gas sensor chip based on the two-dimensional aluminum nitride material is characterized by comprising an MEMS micro-hotplate electrode chip and a two-dimensional functionalized aluminum nitride (AlN) gas-sensitive material, wherein the electrode chip comprises a micro heater surrounding an interdigital electrode, and the interdigital electrode with a heating function is obtained by sputtering Pt metal on a glass sheet and then adopting ion beam etching; the gas-sensitive material is a two-dimensional functionalized AlN gas-sensitive material modified by noble metal Rh atoms on two-dimensional AlN to obtain Rh single-atom modification.
2. The MEMS gas sensor chip of claim 1, wherein the interdigital electrode of the MEMS micro-hotplate electrode chip and the bulk material of the micro-heater are Pt metal, and further comprise Cr or Ti metal for increasing adhesion.
3. A MEMS gas sensor chip based on two-dimensional aluminum nitride material according to claim 2, wherein the Cr or Ti metal layer has a thickness of 1-20 nm and the pt has a thickness of 20-300 nm.
4. The MEMS gas sensor chip of claim 2, wherein the peripheral connecting lines of the interdigital electrodes and the micro heater wires of the MEMS micro-hotplate chip have an arc shape, the radius of the peripheral connecting lines of the interdigital electrodes is 150-1150 μm, and the arc radius of the micro heater is 150-1550 μm.
5. The MEMS gas sensor chip of claim 2, wherein each of the interdigital electrodes of the MEMS micro-hotplate chip has a width of 5-40 μm, an electrode pitch of 10-30 μm, a micro-heater line width of 10-50 μm, and a line pitch of 10-50 μm.
6. The MEMS gas sensor chip based on the two-dimensional aluminum nitride material according to claim 1, wherein the Rh single-atom modified two-dimensional functionalized AlN gas-sensitive material is prepared into discrete droplets and added onto interdigital electrodes of the MEMS micro-hotplate chip, and the MEMS gas sensor chip based on the two-dimensional aluminum nitride material is obtained after normal-temperature drying; wherein, the two-dimensional AlN modified by Rh noble metal monoatoms is adopted to improve the sensitivity of the sensor to gas; the MEMS micro-hotplate electrode chip can reduce the response time and recovery time of the sensor to gas.
7. The MEMS gas sensor chip based on two-dimensional aluminum nitride material according to claim 6, wherein in the Rh-modified aluminum nitride two-dimensional material, aluminum nitride has a structure similar to graphene, and Al atoms and N atoms are sp 2 Hybridization to form bond, al-N bond length is 1.780-1.850A; the Rh modification mode is physical adsorption doping or chemical bond doping instead of Al atoms.
8. A MEMS gas sensor chip based on a two-dimensional aluminum nitride material according to claim 1 or 6, wherein the Rh-modified aluminum nitride two-dimensional material has a molar content ratio of Rh modification of 0.1% to 50%.
9. A MEMS gas sensor chip based on a two-dimensional aluminum nitride material according to claim 1 or 6, wherein the Rh-modified aluminum nitride two-dimensional material is present on the interdigital electrodes in an amount of 0.1-100 μg.
10. A method for manufacturing a MEMS gas sensor chip based on a two-dimensional aluminium nitride material according to any one of claims 1-9, characterized in that it comprises the steps of:
(1) MEMS micro-hotplate chip preparation
Sequentially ultrasonically cleaning glass sheets in acetone, alcohol and deionized water for 10 min, then drying by nitrogen, and baking in a 180 ℃ oven for 2 hours; subsequently sputtering a metal layer of 20 nm Cr/300 nm Pt on the glass sheet; spin-coating HJ6030 photoresist on the metal layer with thickness of 5 μm, and baking 120 s on a hot plate at 90deg.C; subsequently exposing 20 to s with a UV lithography machine and finally developing 50 to s; then an electrode wire is obtained by adopting an ion beam etching method;
(2) Preparation of gas-sensitive materials
Preparing an AlN film on a monocrystalline Ag (111) substrate by adopting a plasma assisted molecular beam epitaxy technology, sputtering Ar ions of 1.5keV at a speed of 5 multiplied by 10 < -5 > millibar in vacuum for 30 min before deposition, cleaning the silver substrate, and then performing heat treatment in vacuum at 500 ℃ for 30 min to repair sputtering damage of the Ar ions on the Ag surface, thereby obtaining a flat and orderly surface monitored by a stripe RHEED graph and a (1 multiplied by 1) reconstructed surface; to obtain a clean surface free of carbon and oxygen contaminants, the anneal-sputter cycle was repeated multiple times, which was verified using in-situ XPS; evaporating Al metal from the cold lip pool with a pyrolytic boron nitride crucible to deposit AlN at a deposition temperature of 650 c, a deposition rate of 0.22A per second, and an aluminum nitride thickness of sub-milliliters to 20 milliliters after the presence or exposure of a reactive atomic nitrogen beam generated by a remote radio frequency (rf) plasma source to achieve the desired stoichiometry and structure while minimizing residual oxygen on the surface; after two-dimensional aluminum nitride is obtained, modifying Rh metal atoms with required molar content on the surface of the aluminum nitride by utilizing an atomic layer deposition technology to obtain Rh single-atom modified two-dimensional aluminum nitride;
(3) Gas sensor chip preparation
Spin-coating a PVA film on an Ag substrate, spin-coating a PMMA film on the Ag substrate, heating and drying, peeling Rh-modified two-dimensional aluminum nitride material, immersing the Ag substrate in deionized water, dissolving the PVA, floating PMMA carrying the two-dimensional material on the water surface, adsorbing the PMMA film by using a transparent glass sheet, transferring the PMMA film onto an interdigital electrode of a MEMS micro-hotplate under a microscope, heating and removing deionized water, immersing the whole sample in acetone to remove PMMA, washing by using ethanol and deionized water, drying at normal temperature, controlling the content of Rh-modified two-dimensional aluminum nitride to be 0.1-100 mu g, and finally obtaining the gas sensor chip.
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