Nanogranular Al2O3 proton conducting films for low-voltage oxide-based homojunction thin-film transistors

Nanogranular Al2O3 films were deposited by the plasma-enhanced chemical vapor deposition (PECVD) method using gas sources of trimethylaluminum and oxygen at 100 °C. Structural characterizations indicate that the as-deposited nanogranular Al2O3 film has an amorphous structure with excess oxygen due to ambient humidity and residual hydroxyl. As-deposited Al2O3 films show a mean pore size of 7.4 nm, and a high proton conductivity of 1.2 × 10−4 S cm−1 at room temperature with a 30% relative humidity. Low-voltage (1.5 V) indium-tin-oxide (ITO) thin-film transistors gated by such nanogranular Al2O3-based proton conductors exhibit a large current on/off ratio of 2.1 × 107 and a high field-effect mobility of 29 cm2 V−1 s−1. Our results demonstrate that nanogranular Al2O3-based films are promising gate dielectric candidates for portable biosensors.