An Integrated Surface Micromachined Convex Microhotplate Structure for Tin Oxide Gas Sensor Array

This paper describes the fabrication process for a novel convex microhotplate (MHP) structure using surface micromachining technology. The process is used to fabricate an integrated 4times4 tin oxide gas sensor array. Surface micro-machining is selected for its simplified process and CMOS compatibil...

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Bibliographic Details
Published in:IEEE sensors journal 2007-12, Vol.7 (12), p.1720-1726
Main Authors: Bin Guo, Bermak, A., Chan, P.C.H., Gui-Zhen Yan
Format: Article
Language:English
Subjects:
Annealing
Arrays
CMOS technology
Convex microhotplates (MHPs)
Curvature
Energy consumption
Fabrication
Gas detectors
gas sensor array
Gas sensors
Mathematical analysis
membrane stress
Micromachining
Sensor arrays
Sensors
Studies
Temperature sensors
Thermal efficiency
Thermal stresses
Tin
tin oxide
Tin oxides
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Summary:This paper describes the fabrication process for a novel convex microhotplate (MHP) structure using surface micromachining technology. The process is used to fabricate an integrated 4times4 tin oxide gas sensor array. Surface micro-machining is selected for its simplified process and CMOS compatibility. However, limited sacrificial layer thickness usually leads to higher power consumption. In this work, a convex MHP structure is developed to increase the thermal efficiency, which is critical for large dimension and low-power gas sensor array integration. Before the structure release process, 700degC-950degC annealing process was carried out on the 190 times190 mum 2 MHP with 2.8 mum polysilicon sacrificial layer. It is shown that higher annealing temperature leads to lower tensional stress of the MHP membrane and larger curvature of the released structure, which enables higher thermal efficiency. Among the four annealing temperatures, the 950degC annealed MHP has the largest curvature of 2.438 cm -1 and the highest thermal efficiency of 13degC/mW. Experimental results showing the responses of the sensor array to different combustible gases are also illustrated in this paper. Comparison of power consumption with other designs reported in the literature illustrates the effectiveness of the proposed process.
ISSN:1530-437X
1558-1748
DOI:10.1109/JSEN.2007.908919