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Discrimination of volatile organic compounds using CMOS capacitive chemical microsensors with thickness-adjusted polymer coating

We present a new method for discriminating organic vapors based on the variation of capacitance changes of an interdigitated CMOS capacitor with the thickness of the sensitive polymer layer. By carefully adjusting the thickness of the polymer layer, discrimination potential in addition to the chemical selectivity of the polymer is provided by the fact that the interdigitated capacitor signals depend on the layer thickness. At polymer thicknesses small compared to the center-to-center spacing of the electrodes, an increase in capacitance is observed for all analytes, whereas for thick layers, the direction of the capacitance changes depends on the dielectric constant of the analyte. Sensors can be designed to be insensitive towards a certain analyte by varying the polymer thickness. Measurements for volatile organic compounds using CMOS capacitors coated with different polymer thicknesses are presented to demonstrate the new way of increasing sensor selectivity.