SOI-based micro-hotplate microcalorimeter gas sensor with integrated BiCMOS transducer

In this paper we describe the design of a smart calorimetric solid-state gas sensor based on SOI technology and featuring a thin membrane realised through post-process back etching. Micro-heaters are produced from active CMOS elements (i.e. n- or p-channel MOSFETs) and isolated in a thin SOI membrane in order to permit high temperature operation (up to ca. 300 degreesC). Thermodiodes are placed on and off the micro-hotplates to measure operating and ambient temperatures. The device can be operated as a microcalorimeter when one microheater is coated with an active catalytic layer and the other with an inert material. The differential signal is then simply related to the concentration of a combustible gas in air. Full simulations of the I-V device characteristics; temperature of the membrane and transducer circuit have been carried out. The device has been fabricated at IMEC (via Europractice) employing 0.8 mum TEMIC Matra MHS D-MILL BiCMOS technology. These smart sensors feature very low power consumption, high sensitivity and low fabrication cost achieved through full CMOS integration.