Advanced chemical microsensor systems in CMOS technology [gas sensors]

We report on results achieved with three different chemical microsensor systems featuring three different types of transducers, all of which are monolithically integrated with associated driving and readout circuitry. The capacitive sensor which is sensitive to changes in dielectric properties of the polymer layer upon analyte absorption, and the cantilever which is sensitive to predominantly mass changes, are two polymer-based gas sensors. An on-chip integrated ΣΔ-converter is used to detect the minute capacitance changes of the capacitive sensor. The cantilever is magnetically excited and its vibration is detected using a piezoresistive Wheatstone bridge. Self-oscillation of the cantilever is achieved through monolithic integration of the feedback circuitry. The third transducer is a microhotplate-based gas sensor which relies on the resistance changes of a metal oxide upon gas exposure at an operation temperature of 300-400°C. The ultimate goal is the monolithic integration of all the different transducers with driving and signal-processing electronics and a digital communication interface on the same single chip.