Metal-Capped Bilayer Oxide Thin-Film Transistor for Stable Biopotential Sensing

Abstract This work reports oxide thin-film transistors (TFTs) based on a metal-capped (MC) 0.5SZTO/1SIZO bilayer channel for mV-level electrical sensing. The MC layer induces a characteristic ω-shaped current path that redistributes charge transport away from the dielectric/channel interface, thereby reducing carrier interaction with interface trap states. The TFTs exhibit a field-effect mobility of ∼56 cm2V–1s–1, an ION/IOFF ratio on the order of 1010, and a subthreshold swing of ∼290 mV decade–1. Statistical analysis of 20 devices confirms spatial uniformity, and cycle-to-cycle measurements over 80 sweeps show stable operation with minimal hysteresis. Under thermal and bias stress conditions (NBTS/PBTS), the devices exhibit a threshold voltage shift of less than 2 V, indicating suppressed charge trapping. Proof-of-concept biopotential-level electrical sensing is demonstrated by applying mV-level inputs directly to the MC layer, which modulate the channel current through electrostatic modulation and MC-assisted carrier injection. The device exhibits a sensitivity of 86.4% at –60 mV, with a monotonic increase to 335% at –180 mV. These results demonstrate that MC-induced current redistribution in bilayer oxide TFTs enables stable transistor operation and sensitive transduction of mV-level electrical inputs.