All-Oxide Thin Film Transistors and Rectifiers Enabling On-Chip Capacitive Energy Storage

All-oxide, fully-transparent thin film transistors and rectifiers, processed entirely by atomic layer deposition, have been developed for on-chip capacitive energy storage. Fully depleted thin film transistor (TFT) operation is achieved by optimizing the carrier concentration in the ZnO channels. The TFTs show an average saturation mobility of 10.5 cm2 V−1 s−1, a stable positive turn-on voltage of 0.88 V, a low subthreshold swing of 0.162 V dec−1, and the entire device achieves an overall transmittance of 85%. The field-effect rectifiers (FER) are fabricated based on short-circuiting the gate and drain electrodes of the TFT structure. Rectification ratio of 3.5 × 106 is achieved in DC measurements. Under AC input, the rectifiers can steadily operate at an input frequency up to 10 MHz and amplitude (peak to peak) up to 20 V. The rectifier can be used for signal processing applications with frequency up to 1 MHz. The energy storage utility of the rectifiers is demonstrated by rectifying AC input signals and successfully charging home-made electrochemical on-chip microsupercapacitors. The results demonstrate that integrated, all-oxide thin film rectifiers can be used for on-chip capacitive energy storage.