Tungsten-Based SOI Microhotplates for Smart Gas Sensors

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 (600degC ) well beyond the typical junction temperatures of high temperature SOI ICs (225degC), have ultralow dc power consumption (12 mW at 600degC), fast transient time (as low as 2-ms rise time to 600degC), 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.

[1]  Matteo Ferroni,et al.  Thin-film gas sensor implemented on a low-power-consumption micromachined silicon structure , 1998 .

[2]  Angeliki Tserepi,et al.  Thermal properties of suspended porous silicon micro-hotplates for sensor applications , 2003 .

[3]  Pisana Placidi,et al.  Thermal characterization of a microheater for micromachined gas sensors , 2004 .

[4]  W. Eichenauer,et al.  Thermophysical Properties of Matter. Volume 4: Specific Heat, Metallic Elements and Alloys. Herausgeber: Y. S. Touloukian und C. Y. Ho, IFI/Plenum, New York‐Washington 1970. Vertrieb in Europa: Heyden & Son, Ltd., London. 830 Seiten, Preis: DM 260,–. , 1971 .

[5]  U. Dibbern,et al.  A substrate for thin-film gas sensors in microelectronic technology , 1990 .

[6]  A. Bermak,et al.  An Integrated Surface Micromachined Convex Microhotplate Structure for Tin Oxide Gas Sensor Array , 2007, IEEE Sensors Journal.

[7]  Gregory Benn,et al.  Design of a silicon carbide micro-hotplate geometry for high temperature chemical sensing , 2001 .

[8]  P.C.H. Chan,et al.  An integrated gas sensor technology using surface micro-machining , 2001 .

[9]  Péter Fürjes,et al.  Thermal characterisation of micro-hotplates used in sensor structures , 2004 .

[10]  M. Graf,et al.  A Digital CMOS Architecture for a Micro-Hotplate Array , 2007, IEEE Journal of Solid-State Circuits.

[11]  Florin Udrea,et al.  Design and simulations of SOI CMOS micro-hotplate gas sensors , 2001 .

[12]  Danilo Vrtačnik,et al.  Mechanical stress in thin film microstructures on silicon substrate , 2005 .

[13]  O. Rorato,et al.  Batch fabrication of metal oxide sensors on micro-hotplates , 2008 .

[14]  O. Paul,et al.  Process-dependent thin-film thermal conductivities for thermal CMOS MEMS , 2000, Journal of Microelectromechanical Systems.

[15]  Julian W. Gardner,et al.  Thermal modelling and characterisation of micropower chemoresistive silicon sensors , 1997 .

[16]  Carles Cané,et al.  Detection of low NO2 concentrations with low power micromachined tin oxide gas sensors , 1999 .

[17]  Minho Lee,et al.  Micro gas sensor array with neural network for recognizing combustible leakage gases , 2005 .

[18]  Udo Weimar,et al.  Gas identification by modulating temperatures of SnO2-based thick film sensors , 1997 .

[19]  Hans Strack,et al.  A heated membrane for a capacitive gas sensor , 1992 .

[20]  U. Bonne,et al.  Fabrication and properties of a Si-based high-sensitivity microcalorimetric gas sensor , 1995 .

[21]  P. Chan,et al.  Thermal Analysis And Design Of A Micro-hotplate For Integrated Gas Sensor Applications , 1995, Proceedings of the International Solid-State Sensors and Actuators Conference - TRANSDUCERS '95.

[22]  Theodor Doll,et al.  SnO2:Sb – A new material for high-temperature MEMS heater applications: Performance and limitations , 2007 .

[23]  Three technologies for a smart miniaturized gas-sensor: SOI CMOS, micromachining, and CNTs - challenges and performance , 2007, 2007 IEEE International Electron Devices Meeting.

[24]  Andreas Hierlemann,et al.  Integrated array sensor for detecting organic solvents , 1995 .

[25]  F. Udrea,et al.  High Temperature SQI CMOS Tungsten Micro-Heaters , 2006, 2006 5th IEEE Conference on Sensors.

[26]  Carles Cané,et al.  High-temperature low-power performing micromachined suspended micro-hotplate for gas sensing applications , 2006 .

[27]  Bart van der Schoot,et al.  Thermal optimization of micro-hotplates that have a silicon island , 2002 .

[28]  I. Elmi,et al.  Development of Ultra Low Power Consumption Hotplates for Gas Sensing Applications , 2006, 2006 5th IEEE Conference on Sensors.

[29]  Jérôme Courbat,et al.  Integration of MOX gas sensors on polyimide hotplates , 2008 .

[30]  D. Flandre,et al.  SOI CMOS compatible low-power microheater optimization for the fabrication of smart gas sensors , 2004, IEEE Sensors Journal.

[31]  J. W. Gardner,et al.  Design and optimisation of a high-temperature silicon micro-hotplate for nanoporous palladium pellistors , 2003, Microelectron. J..

[32]  Carles Cané,et al.  Thermal and mechanical aspects for designing micromachined low-power gas sensors , 1997 .

[33]  N. Bârsan,et al.  Micromachined metal oxide gas sensors: opportunities to improve sensor performance , 2001 .

[34]  Andreas Hierlemann,et al.  3D nonlinear modeling of microhotplates in CMOS technology for use as metal-oxide-based gas sensors , 2005 .

[35]  Koji Inoue,et al.  Low-voltage and low-power optimization of micro-heater and its on-chip drive circuitry for gas sensor array , 2002 .

[36]  Wan-Young Chung,et al.  Low Power Micro Gas Sensor , 1995, Proceedings of the International Solid-State Sensors and Actuators Conference - TRANSDUCERS '95.

[37]  Robert Aigner,et al.  Si-planar-pellistor: Designs For Temperature Modulated Operation , 1995, Proceedings of the International Solid-State Sensors and Actuators Conference - TRANSDUCERS '95.

[38]  G. A. Slack,et al.  Thermal Conductivity of Silicon and Germanium from 3°K to the Melting Point , 1964 .

[39]  M. Gaitan,et al.  Tin oxide gas sensor fabricated using CMOS micro-hotplates and in-situ processing , 1993, IEEE Electron Device Letters.

[40]  A. Gué,et al.  Optimization of an integrated SnO2 gas sensor using a FEM simulator , 1998 .

[41]  Mona E. Zaghloul,et al.  A monolithic CMOS microhotplate-based gas sensor system , 2002 .

[42]  U. Smith,et al.  Long-term stability and electrical properties of compensation doped poly-Si IC-resistors , 2000 .