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 exten sively studied transducer is a microcapacitor sensitive to changes in diele ctric properties of the polymer layer upon analyte absorption. An on-chip i ntegrated Sigma Delta -converter allows for detecting the minute capacitanc e changes. The second transducer is a resonant cantilever sensitive to pred ominantly mass changes. The cantilever is electrothermally excited; its vib rations are detected using a piezoresistive Wheatstone bridge. In analogy t o 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 sensin g thermopile and an uncoated reference thermopile each on micromachined mem branes. The measurand is the absorption or desorption heat of organic volat iles in the polymer layer. The difference between the resulting thermovolta ges is processed with an on-chip low-noise differential amplifier. Gas test measurements with all three transducer principles will be presented. The g oal is to combine the three different transducer principles and vary the po lymers in an array type structure to build a new generation of application- specific microsensor systems. (C) 2000 Elsevier Science B.V. All rights res erved.