ac0352272_si_004.tif (177 kB)
Tuning Sensitivity and Selectivity of Complementary Metal Oxide Semiconductor-Based Capacitive Chemical Microsensors
figure
posted on 2004-05-01, 00:00 authored by Adrian M. Kummer, Andreas Hierlemann, Henry BaltesNew 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.