An Ultralow Subthreshold Swing of 28 mV dec–¹ in Negative-Capacitance Thin-Film Transistors with Ferroelectric Zirconium–Aluminum Oxide Gate Oxide

Subthreshold swing (SS) below the thermionic limit is demonstrated for ZnO thin-film transistors (TFTs) integrated with ferroelectric (FE) zirconium–aluminum oxide (ZAO) gate oxide. The transfer characteristics of FE-ZAO/ZnO TFTs exhibit a substantial memory window of 5.03 ± 0.06 V, a high ION/IOFF ratio of 1.5 × 108, and an ultralow SS of 27.8 ± 2.2 mV dec–1 during the reverse sweep over 4 orders of magnitude of the drain current at a drain voltage (VDS) of 100 mV. An unstable polarization state is observed during the forward sweep, indicating SS below 60 mV dec–1 at an ultralow VDS of 0.1 mV. The negative differential resistance behavior in the output curves further confirms the negative-capacitance effect in FE-ZAO/ZnO TFTs. Finally, a logic inverter is demonstrated with a gain of 37 for cost-effective energy-efficient multistage logic circuits.