An Analytical Model for Dual Gate Piezoelectrically Sensitive ZnO Thin Film Transistors

Abstract

Highly sensitive force sensors of piezoelectric zinc oxide (ZnO) dual-gate thin film transistors (TFTs) are reported together with an analytical model that elucidates the physical origins of their response. The dual-gate TFTs are fabricated on a polyimide substrate and exhibited a field effect mobility of ≈5 cm2 V−1 s−1, Imax/Imin ratio of 107, and a subthreshold slope of 700 mV dec−1, and demonstrated static and transient current changes under external forces with varying amplitude and polarity in different gate bias regimes. To understand the current modulation of the dual-gate TFT with independently biased top and bottom gates, an analytical model is developed. The model includes accumulation channels at both surfaces and a bulk channel within the film and accounts for the force-induced piezoelectric charge density. The microscopic piezoelectric response that modulates the energy-band edges and correspondent current–voltage characteristics are accurately portrayed by this model. Finally, the field-tunable force response in single TFT is demonstrated as a function of independent bias for the top and bottom gates with a force response range from −0.29 to 22.7 nA mN−1. This work utilizes intuitive analytical models to shed light on the correlation between the material properties with the force response in piezoelectric TFTs. © 2021 Wiley-VCH GmbH.