Capacitive sensors in CMOS technology with polymer coating

Abstract

In this paper we report the fabrication of a new integrated capacitive chemical sensor by industrial CMOS technology, followed by a single maskless polymer-coating step. An on-chip sigma-delta modulator measures the difference between the sensing and reference capacitors, performs offset and gain calibration and provides a digital output signal. Experimental data have been obtained in a series of measurements, in which several transducers covered with different polymer films (poly-etherurethane, PUT, polycyanopropylmethylsiloxane, PCM, ethylcellulose, EC, and polyepichlorohydrine, PECH) are exposed to various organic gases at different concentrations. The sensor signals show a clear linearity and low hysteresis for both polar and non-polar gases, thus confirming the feasibility of smart capacitive chemical sensors in IC technology.