1-V Full-Swing Depletion-Load a-In–Ga–Zn–O Inverters for Back-End-of-Line Compatible 3D Integration

To enable monolithic three-dimensional integration of the amorphous In–Ga–Zn–O (a-IGZO) and CMOS technologies, the a-IGZO inverters compatible with the low operating voltage ( $\leqq 1$ V) and process temperature of back-end-of-line CMOS have been investigated. We demonstrated a full-swing depletion-load inverter with a voltage gain up to 24 using a CMOS-compatible operating voltage of 1 V. The drive transistor was realized using a low-voltage enhancement-mode a-IGZO thin-film transistor (TFT) with a steep subthreshold swing of 70 mV/decade and a low threshold voltage of 0.5 V. The load transistor was implemented using a bi-layer a-IGZO channel, where the a-IGZO composition was modulated simply by the oxygen flow rate in a depletion-mode TFT.