Multi-level operation of three-dimensionally stacked non-volatile ferroelectric polymer memory with high-performance hole-injection layer

Carrier injection from the source electrode to the semiconducting channel in a field-effect transistor (FET) is efficiently enhanced by inserting an interlayer capable of reducing the injection barrier, yielding a device with a greatly increased ON current. In this study, we demonstrated a non-volatile vertical-channel (VC) ferroelectric field effect transistor (FeFET) memory based on ferroelectric polarization switching of a ferroelectric polymer poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) as a gate insulator with a thin MoO₃ interlayer. Owing to the facile hole injection through the MoO₃ interlayer to a semiconducting channel of the FeFET, the saturated ON current was significantly increased, giving rise to a large ON/OFF memory margin. Optimization of the VC-FeFET thus led to a non-volatile memory operating at a programming voltage of ±25 V with a maximum ON/OFF current margin of 10³, reliable time-dependent data retention for more than 1 year, and write/erase endurance for 10⁵ cycles. Furthermore, by sequentially stacking three arrays of VC-FeFETs with the hole-injection interlayers, we fabricated three-dimensionally (3D) stacked VC-FeFETs. Each device had a sufficient ON/OFF current ratio for multi-level memory operation, in which four distinct states were repetitively programmed and erased with long-term data retention and reliable cycle endurance.