Tuning Sensitivity and Selectivity of Complementary Metal Oxide Semiconductor-Based Capacitive Chemical Microsensors

• Published in: Analytical chemistry (Washington) Vol. 76; no. 9; pp. 2470 - 2477
• Main Authors: Kummer, Adrian M, Hierlemann, Andreas, Baltes, Henry
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01-05-2004
• Subjects: Absorption; Analytical chemistry; Biosensing Techniques - instrumentation; Biosensing Techniques - methods; Biosensing Techniques - trends; Chemistry; Chemistry Techniques, Analytical - instrumentation; Chemistry Techniques, Analytical - methods; Chemistry Techniques, Analytical - trends; Electric Capacitance; Electrolytes; Exact sciences and technology; General, instrumentation; Membranes, Artificial; Metals - chemistry; Polymers - chemistry; Semiconductors; Sensitivity and Specificity; Sensors; Sensitivity; Selectivity; CMOS integrated circuits; Microsensor; Chemical sensor; Capacitive transducer
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac0352272

New details on selectivity and sensitivity of fully integrated CMOS-based capacitive chemical microsensor systems are revealed. These microsystems have been developed to detect volatile organics in ambient air and rely on polymeric sensitive layers. The sensitivity and selectivity changes induced by thickness variation of the sensitive polymer layer allow for tuning of the layer parameters to achieve desired sensor features. Cross-sensitivity to interfering agents can be drastically reduced, as is shown for two important cases:  (a) rendering the capacitive sensor insensitive to a low-dielectric-constant analyte (lower than that of the polymer) and (b) reducing the influence of a high-dielectric-constant analyte, such as water, on the sensor response. The second case is of vital importance for capacitive sensors, since water is omnipresent and evokes large capacitive sensor signals. The thickness-induced selectivity is explained as a combination of dielectric constant change and swelling and has been confirmed by measurements. Experimentally determined sensitivities qualitatively and quantitatively coincide with the calculated values implying understanding of the sensing mechanism.