Ž . Sensors and Actuators B 70 2000 2–11 www.elsevier.nlrlocatersensorb Application-specific sensor systems based on CMOS chemical microsensors A. Hierlemann ) , D. Lange, C. Hagleitner, N. Kerness, A. Koll, O. Brand, H. Baltes Physical Electronics Laboratory, Institute of Quantum Electronics, ETH Zurich, Honggerberg, HPT H 4.2, CH-8093 Zurich, Switzerland ¨ Abstract 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 SD-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. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Chemical microsensor; Capacitor; Mass-sensitive sensor; Resonator; Calorimetric sensor; Volatile organic compounds; Polymers 1. Introduction Chemical sensors have reached the stage of exploratory use in a variety of industrial and environmental applica- tions, some examples being quality control or on-line process monitoring in the food-industry as well as prelimi- nary tests in the areas of medical practice and personal w x safety. In such contexts, the term Aelectronic noseB 1,2 Ž more recently, even the notion of an Aelectronic tongueB wx. 3 was created, and has grown ever more popular. We believe this term is sometimes misleading and therefore, warrants discussion. wx Following the definition of Gardner and Bartlett 1 , an electronic nose is Aan instrument comprising an array of electronic chemical sensors with partial specificity and an appropriate pattern recognition system, capable of recog- nizing simple or complex odorsB. The majority of cur- ) Corresponding author. Tel.: q 41-1-633-3494; fax: q 41-1-633-1054. Ž . E-mail address: hierlema@iqe.phys.ethz.ch A. Hierlemann . rently available Aelectronic nosesB are capable of differen- tiating between analytes or analyte mixtures from the headspace of different foods or beverages, but in most cases, the sensor response patterns cannot be directly correlated with human olfactory perception. Another more important point concerns the general applicability implied by the term Aelectronic noseB. Most of the sensor systems perform well in certain key applications, but there are few, if any, which exhibit the enormously broad applicability spectrum, at once including the sensitivity and discriminat- ing power of a human or animal nose. In addition, success- ful sensor systems have to be designed and optimized with Ž the key application in mind to guide the selection of . coatings, transduction mechanisms etc. . As yet, however, there is no universally applicable system, that invariably provides satisfactory performance. In the following, we hence prefer the more realistic expression Aapplication- Ž . specific sensor system A triple S B over the notion of an Aelectronic noseB. Industrial CMOS fabrication in combination with post- processing such as micromachining had been used in the 0925-4005r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0925-4005 00 00546-3