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Review
. 2022 Mar 21;13(3):491.
doi: 10.3390/mi13030491.

Research Progress on Coating of Sensitive Materials for Micro-Hotplate Gas Sensor

Zhenyu Yuan  1   2   3   4 , Fan Yang  1 , Fanli Meng  1   2   3   4
Affiliations
Review

Research Progress on Coating of Sensitive Materials for Micro-Hotplate Gas Sensor

Zhenyu Yuan et al. Micromachines (Basel). .

Abstract

Micro-hotplate gas sensors are widely used in air quality monitoring, identification of hazardous chemicals, human health monitoring, and other fields due to their advantages of small size, low power consumption, excellent consistency, and fast response speed. The micro-hotplate gas sensor comprises a micro-hotplate and a gas-sensitive material layer. The micro-hotplate is responsible for providing temperature conditions for the sensor to work. The gas-sensitive material layer is responsible for the redox reaction with the gas molecules to be measured, causing the resistance value to change. The gas-sensitive material film with high stability, fantastic adhesion, and amazing uniformity is prepared on the surface of the micro-hotplate to realize the reliable assembly of the gas-sensitive material and the micro-hotplate, which can improve the response speed, response value, and selectivity. This paper first introduces the classification and structural characteristics of micro-hotplates. Then the assembly process and characteristics of various gas-sensing materials and micro-hotplates are summarized. Finally, the assembly method of the gas-sensing material and the micro-hotplate prospects.

Keywords: MEMS; micro-hotplate gas sensor; sensitive material coating.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Silicon micro-hotplate [34].
Figure 2
Figure 2
Structure of AlN ceramic micro-hotplate [42].
Figure 3
Figure 3
Microhotplates with different LTCC structures: (A) PdAg as temperature sensor; (B) Pt as temperature sensor [27].
Figure 4
Figure 4
Structure diagram of glass-based micro-hotplate [46].
Figure 5
Figure 5
(a) The overall structure of the micro-hotplate, (b–e) Micro-hotplates with four different structures [32].
Figure 6
Figure 6
Process of sensor preparation by drop coating method [56].
Figure 7
Figure 7
(a) PicoTipTM emit image. (b) Schematic of the emitter in combination with injector [61].
Figure 8
Figure 8
(a) Structural diagram of the micro-hotplate; (b,c) ZnO nanowires synthesized by hydrothermal method; (d,e) locally synthesized ZnO nanowires replaced by SnO2 nanotubes (PH = 4) by liquid deposition method or SnO2/ZnO composite structure (PH = 6) [64].
Figure 9
Figure 9
WO3@SnO2 deposition process [65].
Figure 10
Figure 10
Assembly of nanowire on a micro-hotplate [55].
Figure 11
Figure 11
Schematic diagram of nanowire integration: ① nanowire drop-casting; ② DEP device connection; ③ nanowire row; ④ nanowire bonding; ⑤ sensor oxidation; ⑥ obtaining the final sensor [71].
Figure 12
Figure 12
Schematic diagram of spray pyrolysis process [72].
Figure 13
Figure 13
Diagram of spray pyrolysis unit [73].
Figure 14
Figure 14
(a) Micro-hotplate structure, (b) MEMS sensor with sputtered ZnO-CuO thin film [35].
Figure 15
Figure 15
Schematic diagram of gas-phase vulcanization technology [78].
Figure 16
Figure 16
Diagram of the preparation process of in-situ growth of ZnO on FTO gas-sensing electrode [80].
Figure 17
Figure 17
Structure of the micro-hotplate gas sensor with ZnO nanowire [82].
Figure 18
Figure 18
The growth process of ZnO nanowire [83].
Figure 19
Figure 19
(a) EHD inkjet printing system. (b) Finished EHD printed micro hotplate surface [85].
Figure 20
Figure 20
Inkjet printing of an optical image of SnO2 nanoparticle ink deposited on a micro-hotplate [86].
Figure 21
Figure 21
Screen-printing process [87].
Figure 22
Figure 22
Sensor array, (a) front, (b) back [88].
Figure 23
Figure 23
(i) Glass plate covered with PS colloid immersed in the solution. (ii) Monolayer of colloid floating on the surface of the solution. (iii) Pick up with glass rod. (iv) Drying. (v) Calcination to remove the PS microspheres [90].
Figure 24
Figure 24
PS microspheres preparation of SnO2 porous membrane [91].
Figure 25
Figure 25
Sensor wafer-level array film formation [49].
See this image and copyright information in PMC

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