Dual-port ferroelectric NAND flash memory for large memory window, QLC programmable and disturbance-free operations

Abstract

The ferroelectric NAND flash memory devices have garnered interest because of their rapid switching speed, low operating voltage, and superior reliability in comparison to conventional charge-trap flash memory. In particular, hafnia-based ferroelectrics have been intensively studied thanks to their relatively low crystallization temperature, CMOS compatibility, and excellent scaling characteristics. However, when processing the 3D integration, FeNAND devices based on hafnia encounter thermal instability issues due to the high process temperature required for both deposition and annealing of the poly-Si channel. Furthermore, FeNAND devices suffer from the read/pass disturbance and narrow memory window (MW) stems from the sub-loop characteristics and intrinsic small coercive field of hafnia ferroelectrics. To address these issues, we propose oxide channel dual-port FeNAND devices with additional gate dielectric and gate metal on the opposite side of the ferroelectrics from the channel layer. The thermal stability and disturbance issues are resolved with the low-temperature process oxide channel (<300 °C) and an extra gate stack. We experimentally verified that our devices show a broad MW range of 10 V, operate using quad-level-cell technology, and exhibit excellent levels of reliability. In addition, considering the findings from the experiments, we propose a 3D process integration strategy and evaluate the characteristics of dual-port 3D FeNAND devices using TCAD modeling.