CMOS monolithic metal-oxide gas sensor microsystems

Abstract

This paper presents two mixed-signal monolithic gas sensor microsystems fabricated in standard 0.8-μm CMOS technology combined with post-CMOS micromachining to form the microhotplates. The on-chip microhotplates provide very high temperatures (between 200°C and 400°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 μm) and a digital proportional-integral-derivative (PID) microhotplate temperature controller. The second microsystem has a fully-differential architecture comprising an array of three microhotplates (diameter of 100 μm) and three digital PID microhotplate temperature controllers (one controller per microhotplate). The on-chip digital PID temperature controllers can accurately adjust the microhotplate temperatures up to 400°C with a resolution of 2°C. Further, both microsystems feature on-chip logarithmic converters for the readout of the metal-oxide resistors (which cover a measurement range between 1 kΩO and 10 MΩ ), 10-bit A/D converters, anti-aliasing filters, 10-bit D/A converters, I 2C serial interfaces, and bulk-chip temperature sensors. Carbon monoxide (CO) concentrations in the sub-parts-per-million (ppm) range are detectable, and a resolution of 0.2 ppm CO has been achieved. © 2006 IEEE.