Authors: Barrettino D.¹; Graf M.²; Zimmermann M.²; Hagleitner C.²; Hierlemann A.²; Baltes H.²

Source: Analog Integrated Circuits and Signal Processing, Volume 39, Number 3, June 2004 , pp. 275-287(13)

Publisher: Springer

Abstract:

This paper presents a monolithic chemical gas sensor system fabricated in industrial CMOS-technology combined with post-CMOS micromachining. The system comprises metal-oxide-covered (SnO₂) micro-hotplates and the necessary driving and signal-conditioning circuitry. The SnO₂ sensitive layer is operated at temperatures between 200 and 350°C. The on-chip temperature controller regulates the temperature of the membrane up to 350°C with a resolution of 0.5°C. A special heater-design was developed in order to achieve membrane temperatures up to 350°C with 5 V supply voltage. The heater design also ensures a homogeneous temperature distribution over the heated area of the hotplate (1–2% maximum temperature fluctuation). Temperature sensors, on- and off-membrane (near the circuitry), show an excellent thermal isolation between the heated membrane area and the circuitry-area on the bulk chip (chip temperature rises by max 6°C at 350°C membrane temperature). A logarithmic converter was included to measuring the SnO₂ resistance variation upon gas exposure over a range of four orders of magnitude. An Analog Hardware Description Language (AHDL) model of the membrane was developed to enable the simulations of the complete microsystem. Gas tests evidenced a detection limit below 1 ppm for carbon monoxide and below 100 ppm for methane.

Keywords: metal-oxide gas sensors; analog IC design; AHDL; CMOS compatible micromachining; micro-hotplates

Document Type: Research article

DOI: http://dx.doi.org/10.1023/B:ALOG.0000029663.89451.a0

Affiliations: 1: Physical Electronics Laboratory, Swiss Federal Institute of Technology, Zurich, ETH Hoenggerberg, HPT H3, 8093 Zurich, Switzerland., Email: barrettino@iqe.phys.ethz.ch 2: Physical Electronics Laboratory, Swiss Federal Institute of Technology, Zurich, ETH Hoenggerberg, HPT H3, 8093 Zurich, Switzerland

Publication date: 2004-06-01

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