Junctionless Coplanar-Gate Oxide-Based Thin-Film Transistors Gated by Al₂O₃ Proton Conducting Films on Paper Substrates

Nanogranular Al₂O₃ films deposited by plasma-enhanced chemical vapor deposition show a high proton conductivity of ～1.25 × 10^?4 S/cm and a huge electric-double-layer (EDL) capacitance of ～4.8 μF/cm² at room temperature. Using nanogranular Al₂O₃ proton conducting films as gate dielectrics, junctionless indium-zinc-oxide (IZO) thin-film transistors (TFTs) with a coplanar-gate configuration are fabricated. The unique feature of such junctionless TFTs is that the channel and source/drain electrodes are the same thin IZO film without any source/drain junction. Due to the strong EDL capacitive coupling triggered by mobile protons in nanogranular Al₂O₃, these TFTs show a low-voltage operation of 1.5 V and a high performance with a large field-effect mobility (>18 cm²/V?s), a small subthreshold swing (<130 mV/decade) and a high current on/off ratio (>10⁶). Our results demonstrate that such junctionless TFTs gated by Al₂O₃ proton conducting films have great potential applications in low-power and low-cost electronics.