Tungsten-Based SOI Microhotplates for Smart Gas Sensors

• Published in: Journal of microelectromechanical systems Vol. 17; no. 6; pp. 1408 - 1417
• Main Authors: Ali, S.Z., Udrea, F., Milne, W.I., Gardner, J.W.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.12.2008; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Analytical models; Costs; Design engineering; Devices; Electrothermal effects; Etching; Exact sciences and technology; Fabrication; Gas detectors; Gas sensors; Heaters; Heating equipment; High temperature; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Integrated circuit interconnections; Mechanical instruments, equipment and techniques; microhotplates; Micromechanical devices and systems; Operating temperature; Physics; Sensors; silicon on insulator (SOI); Silicon on insulator technology; Temperature sensors; Three dimensional; Tungsten; Wafers; tungsten; Gas sensors; microhotplates; silicon on insulator (SOI); Energy consumption; Transient response; Great depth; Silicon-on-insulator; Electrothermics; High temperature; Experimental study; Thermal stability; Reactive ion etching; Complementary MOS technology; Tungsten; Heating elements; Ion beam etching; Microelectromechanical device; Gas detector; Intelligent system; Production process
• ISSN: 1057-7157; 1941-0158
• DOI: 10.1109/JMEMS.2008.2007228

This paper is concerned with the design, fabrication, and characterization of novel high-temperature silicon on insulator (SOI) microhotplates employing tungsten resistive heaters. Tungsten has a high operating temperature and good mechanical strength and is used as an interconnect in high temperature SOI-CMOS processes. These devices have been fabricated using a commercial SOI-CMOS process followed by a deep reactive ion etching (DRIE) back-etch step, offering low cost and circuit integration. In this paper, we report on the design of microhotplates with different diameters (560 and 300 mum) together with 3-D electrothermal simulation in ANSYS, electrothermal characterization, and analytical analysis. Results show that these devices can operate at high temperatures (600 deg C ) well beyond the typical junction temperatures of high temperature SOI ICs (225 deg C), have ultralow dc power consumption (12 mW at 600 deg C), fast transient time (as low as 2-ms rise time to 600 deg C), good thermal stability, and, more importantly, a high reproducibility both within a wafer and from wafer to wafer. We also report initial tests on the long-term stability of the tungsten heaters. We believe that this type of SOI microhotplate could be exploited commercially in fully integrated microcalorimetric or resistive gas sensors.