Self-aligned-gate ZnO TFT circuits

We report combining plasma-enhanced atomic layer deposition (PEALD) ZnO thin-film transistors (TFTs) with a gateself-aligned process to fabricate high-speed circuits. The speed of our previous PEALD circuits (22 ns/stage) was largely limited by the parasitic capacitance between the gate and drain, and a self-aligned-gate process provides higher speed devices and circuits. In this letter, a backside exposure process was used to fabricate gate-self-aligned TFTs with a mobility of 20 cm²/V s. The sevenstage self-aligned-gate PEALD ZnO TFT ring oscillators had a propagation delay of 9.8 ns/stage at a supply voltage of 18 V. These ring oscillators are similar in performance to the best reported saturated-load oxide-semiconductor circuits but with much longer channel length (>5×longer).