Chemical sensors
Contact: Sadiara FALL
OFETs in configuration bottom contact/bottom gate can be used as chemical sensors when their channel, made of the organic material, is exposed to a gas that has to be analysed. In practice, an element to be sensed (ethanol, acetone, etc.), else called analyte, is introduced mixed to a carrier gas (here N2) on the channel of the transistor. A specially dedicated bench (Fig. 1) allows to measure at the same time the concentration of analyte in the mixture and the output characteristics of the transistor.
At first, output characteristics of the organic transistor are measured for various concentrations of a given analyte (Fig. 2). Repeating these measurements for different analytes allows to establish calibration tables.
Secondly, measuring output characteristics of the organic transistor for an unknown analyte, at a concentration as well unknown, and comparing these characteristics with the calibration table informs about the type of analyte (selectivity) and about its concentration (sensitivity).
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| Fig. 1: Characterisation bench of chemical sensors based on organic field-effect transistors | Fig. 2: Behavior of hole mobility, of hysteresis of the transfer characteristics and of drain current (for fixed drain-source Vds and gate-source Vgs voltages), for different ethanol concentrations, during exposure of a transistor with P3HT (PhD thesis of P. Lienerth) |