A Smart Single-Chip Micro-Hotplate-Based Gas Sensor System in CMOS-Technology

Barrettino, Diego ; Graf, Markus ; Zimmermann, Martin ; Hagleitner, Christoph ; Hierlemann, Andreas ; Baltes, Henry

In: Analog Integrated Circuits and Signal Processing, 2004, vol. 39, no. 3, p. 275-287

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    Summary
    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