Hotplate-based monolithic CMOS microsystems for gas detection and material characterization for operating temperatures up to 500○C

Two monolithic CMOS microsystems for gas detection and material characterization fabricated in industrial 0.8-mum CMOS technology combined with post-CMOS micromachining are presented. The first microsystem comprises an array of three microhotplates, and three single-ended proportional temperature controllers (one controller per microhotplate), which regulate the microhotplate temperature up to 350degreesC using a polysilicon resistor as a temperature sensor on the, microhotplate. The second microsystem comprises one microhotplate, and a fully differential proportional temperature controller, which regulates the microhotplate temperature up to 500degreesC using a platinum (Pt) resistor as a temperature sensor on the microhotplate. For gas sensing applications, the microhotplates were covered with tin dioxide.(SnO2), which changes its conductivity upon exposure to gaseous analytes. Gas tests evidenced a detection limit of 0.2 ppm for carbon monoxide (CO). For material characterization, the microhotplates were covered with ammonium nitrate (NH4NO3), which exhibits a melting point of 169.6degreesC according to the CRC Handbook of Chemistry and Physics. The measured melting point was 168 +/- 2degreesC. Temperature sensors, on- and off-membrane (near the circuitry), showed excellent thermal isolation between the heated membrane area and the circuitry area on the bulk chip (overall chip temperature rose by max. 3degreesC at 500degreesC microhotplate temperature).