High-gain, low-voltage BEOL logic gate inverter built with film profile engineered IGZO transistors

We demonstrate InGaZnO (IGZO) TFTs with channel-length (L) tunable Vth for high-gain BEOL logic gate inverters in a unique film-profile engineering (FPE) approach. In this FPE scheme the thickness and film profile of gate oxide and IGZO active layer are directly tailored by L (0.4–0.8 μm) in a single step, leading to a wide-ranging tunability in Vth of −0.2–+1.6V at no expense of additional masks and process steps. This provides an effective degree of freedom in the layout design for the realization of area-saving, high-gain unipolar logic inverters with load-transistors. Record-high voltage gain of 112 is demonstrated from the unipolar logic inverter with depletion-load 0.4 μm IGZO TFT and 0.7μm IGZO drive-transistor, respectively, at operation voltage (Vdd) of 9V.