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原文
A Smart Single-Chip Micro-Hotplate-Based Gas Sensor System in CMOS-Technology
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℃. The on-chip temperature controller regulates the temperature of the membrane up to 350℃ with a resolution of 0.5℃. A special heater-design was developed in order to achieve membrane temperatures up to 350℃ 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℃ at 350℃ 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 1ppm for carbon monoxide and below 100 ppm for methane.
Key Words: metal-oxide gas sensors； analog IC design；AHDL；CMOS compatible micromachining； microhotplates
1. Introduction
There is a strong interest in CMOS-based microsensors and, in particular, in micro-hotplate-based gas sensors, since miniaturization and the possibility of monolithic integration of transducer and circuitry offer significant advantages such as lowpower consumption, potentiall low costs, and the possibility of applying new dynamic sensor operation modes.
Tin dioxide (SnO2) is a widely used sensitive material for gas sensing in ambient
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