CMOS Monolithic Metal–Oxide Gas Sensor Microsystems

Abstract

This paper presents two mixed-signal monolithic gas sensor microsystems fabricated in standard 0.8-m 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 m) 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 m) 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 k and 10 M ), 10-bit A/D converters, anti-aliasing filters, 10-bit D/A converters, 2 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.Index Terms-CMOS-based microsystem, MEMS, metal-oxide gas sensors, PID control.

CMOS Monolithic Nanoparticle-Coated Chemiresistor Array for Micro-Scale Gas Chromatography

“…Resistanceto-frequency interface circuits [29][30][31] and logarithmic converters [13] are well suited for digitizing a wide range of resistances but have limited resolution because they digitize the large baseline value along with the small sensor response. Higher resolution has been achieved using a passivated (nonsensing) element as a reference for baseline cancellation [32].…”

“…Integrating such a sensor array with CMOS instrumentation electronics monolithically, on a single chip, would significantly enhance GC miniaturization and reduce noise coupled through wiring to maintain high resolution measurements. Several CMOS monolithic chemical sensors have been reported over the last decade [9][10][11][12][13]. However, to date, no such monolithic realization has been reported for low power μGC applications using MPN interfaces.…”

Resistive Sensor Interfacing

“…In addition, a suitable interfacing of the sensitive element with a proper ICs is fundamental, especially when they are fabricated on the same chip. In this sense, CMOS technology is widely used, because it allows to match the reduction of costs of the silicon with the possibility of designing new LV LP interface circuits to be easily dedicated to the portable sensor applications market [21][22][23]36].…”

125ppm resolution and 120dB dynamic range nanoparticle chemiresistor array readout circuit

“…Resistance-to-frequency interface circuits [5][6] and logarithmic converters [7] are well suited for digitizing a wide range of resistances but have limited resolution because they digitize the large baseline value along with the small sensor response. Higher resolution was achieved using a passivated (non-sensing) element as a reference for baseline cancellation [8].…”