High Mobility and Drive Current ZnO Thin Film Transistors

Thin film transistors (TFTs) are widely utilized in the display industry as select devices for pixel data and also have potential for 3D ICs and for flexible and large area electronic applications. Recently, oxide semiconductors such as indium gallium zinc oxide (IGZO) and zinc oxide (ZnO) have gained interest because they can provide improved mobility and stability compared to amorphous silicon and reduced manufacturing cost compared to polysilicon. ZnO TFTs with field-effect mobility > 100\mathrm{cm}^{2}/\mathrm{V}\cdot \mathrm{s} have been demonstrated,[1] but these devices were fabricated using pulsed laser deposition (PLD), which may limit large-area and low-cost applications. In contrast to PLD, plasma-enhanced atomic layer deposition (PEALD) is an attractive deposition technique for high-volume manufacturing of oxide semiconductor devices and especially for ZnO. In this work, we have demonstrated a simple process modification using a NO plasma based passivation layer that improves the performance of PEALD ZnO TFTs. ZnO TFTs with 5\ \mu \mathrm{m} channel lengths, PEALD ZnO active layer, and NO plasma-based PEALD AlO passivation layer exhibit drive currents > 250\mathrm{mA}/\mathrm{mm} and field-effect mobilities > 80\ \mathrm{cm}^{2}/\mathrm{V}\cdot\mathrm{s}.