Application-specific sensor systems based on CMOS chemical microsensors

We report on results achieved with three different types of polymer-coated chemical microsensors fabricated in industrial CMOS technology followed by post-CMOS anisotropic etching and film deposition. The first and most extensively studied transducer is a microcapacitor sensitive to changes in dielectric properties of the polymer layer upon analyte absorption. An on-chip integrated ΣΔ-converter allows for detecting the minute capacitance changes. The second transducer is a resonant cantilever sensitive to predominantly mass changes. The cantilever is electrothermally excited; its vibrations are detected using a piezoresistive Wheatstone bridge. In analogy to acoustic wave devices, analyte absorption in the polymer causes resonance frequency shifts as a consequence of changes in the oscillating mass. The last transducer is a microcalorimeter consisting of a polymer-coated sensing thermopile and an uncoated reference thermopile each on micromachined membranes. The measurand is the absorption or desorption heat of organic volatiles in the polymer layer. The difference between the resulting thermovoltages is processed with an on-chip low-noise differential amplifier. Gas test measurements with all three transducer principles will be presented. The goal is to combine the three different transducer principles and vary the polymers in an array type structure to build a new generation of application-specific microsensor systems.