Piezoelectric Strain FET (PeFET)-Based Nonvolatile Memories

We propose nonvolatile memory (NVM) designs based on piezoelectric strain FET (PeFET) utilizing piezoelectric/ferroelectric material (PE/FE such as PZT) coupled with 2-D transition metal dichalcogenide (2-D-TMD such as MoS2)-based transistor. The proposed NVMs store bit information in the form of polarization (P) of FE/PE, use electric-field driven P-switching for write, and employ piezoelectricity-induced dynamic bandgap modulation of 2-D-TMD channel for bit sensing. We analyze PeFET with COMSOL-based 3-D modeling, showing that circuit-driven optimization of PeFET geometry is essential to achieve effective strain transduction and adequate bandgap modulation for NVM read. We achieve distinguishability of up to 11x in binary states of PeFETs. We propose various flavors of PeFET NVMs, namely: 1) high-density (HD) NVM featuring a compact access-transistor-less bit-cell; 2) 1T-1PeFET NVM with segmented architecture, targeted for optimized write energy and latency; and 3) cross-coupled (CC) NVM offering a tradeoff between area and latency. PeFET NVMs offer up to 7x smaller cell area, 66% lower write energy, 87% lower read energy, and 44% faster read compared to 2-D-FET static random access memory (SRAM). This comes at the cost of high write latency in PeFET NVMs, which can be minimized by virtue of optimized PE geometry.