Markus Graf

CMOS monolithic metal-oxide sensor system comprising a microhotplate and associated circuitry

A gas sensor system fabricated in industrial CMOS technology is presented, which includes, for the first time, a microhotplate and the necessary driving and control circuitry on a single chip. Post-complementary-metal-oxide-semiconductor (CMOS) fabrication steps, such as micromachining of the membrane structure, the deposition of noble metal on the electrodes, and the processing of the sensitive metal-oxide layer, have been developed to be fully compatible with the industrial CMOS process. Temperatures up to 350/spl deg/C were reached on the hotplates using a low-voltage power supply (5 V). A symmetric hotplate design with a temperature homogeneity of better than 2% in the heated area was realized. The integrated temperature controller regulates the membrane temperature with a resolution of /spl plusmn/0.3/spl deg/C in the tracking mode. The temperature increase on the bulk chip owing to heat transfer through the membrane is less than 2% of the respective membrane operation temperature (6/spl deg/C at 350/spl deg/C membrane temperature). The gas sensing performance of the sensor was assessed by test measurements with carbon monoxide (CO). The gas tests evidenced a limit of detection of less than 5 ppm CO.

A smart single-chip micro-hotplate-based chemical sensor system in CMOS-technology

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.

CMOS Monolithic Metal–Oxide Gas Sensor Microsystems

This paper presents two mixed-signal monolithic gas sensor microsystems fabricated in standard 0.8-

CMOS-Based Monolithic Controllers for Smart Sensors Comprising Micromembranes and Microcantilevers

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Wafer-level flame-spray-pyrolysis deposition of gas-sensitive layers on microsensors

CMOS technology combined with post-CMOS micromachining to form the microhotplates. The on-chip microhotplates provide very high temperatures (between 200

A single-chip CMOS micro-hotplate array for hazardous-gas detection and material characterization

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Connecting heat transfer macromodels for array MEMS structures

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A digital CMOS micro-hotplate array for analysis of environmentally relevant gases

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Smart single-chip CMOS microhotplate array for metal-oxide-based gas sensors

C), which are necessary for the normal operation of metal–oxide sensing layers. The first microsystem has a single-ended architecture comprising a microhotplate (diameter of 300

Digital systems architecture to accommodate wide range resistance changes of metal-oxide sensors

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