A pressure sensitive ionic gel FET for tactile sensing

Field-effect-transistor (FET) is combined with an ionic gel to realize a pressure sensitive ionic-gel field-effect-transistor (PSG-FET) of high sensitivity and low operational voltage. The ionic gels form a layer of charge accumulation in a nanometric scale called the electrical double layer (EDL) on each electrode upon voltage application and exhibit quite high capacitance. The source-drain current through the ZnO channel increases from the initial 44 nA (without pressure) to 783 μA (with pressure, 7 kPa), yielding an ON/OFF contrast as large as 1.7 × 10⁴, due to EDLs, which is interpreted as a pressure sensitivity of 2.2 × 10³ kPa^-1. Judging from the drain current and the gate voltage properties, the threshold voltage is calculated to be 2.8 V owing the large capacitance created by the ionic gel.