On the Capacitive-to-Resistive Humidity Response of Polyelectrolyte-Gated Metal Oxide Transistors

Abstract

The electrolyte gating of transistors, which directly couples ion transport with electron conduction, is particularly interesting in the field of bio and chemical sensing. When a humidity-sensitive polyelectrolyte is used as the gate dielectric, the resulting ionotronic device becomes a humidity-sensitive transistor providing potential advantages in signal amplification and circuit integration. In this work, a humidity-sensitive polyelectrolyte-gated metal oxide transistor is reported by implementing the capacitive-to-resistive-based sensing mechanism. Due to the correlation between drain current and gate capacitance, the measurement of capacitance or impedance for humidity sensors is converted into the measurement of resistance. Initial sensing studies in the quasi-static DC sensing mode resulted in a limited sensing response. A pulsed sensing mode was proposed to considerably enhance the sensing response I D,80%RH /I D,20%RH to 861. The response in the specific RH range was also found to be tunable with the applied sensing signal. The underlying mechanism is elucidated with frequency-dependent capacitance and impedance analysis of the gate electrolyte using corresponding equivalent circuit model.