Tutorial: 3D Flash Memory from Technology to the System: Past, Present and Future Developments
Violante Moschiano · 2024
Meeting the increasing demand for non-volatile memory in a range of critical applications has required improving memory cost, performance, and power consumption. Moving from 2D to 3D NAND has become critical for meeting these requirements. Substantial density increase is enabled by wafer-level stacking of more than 300 layers and by multi-level cells via threshold-voltage scaling, with up to 5bits/cell. But, such stacking and threshold-voltage control introduce sensitivities to reliability and variations, which impact overall system performance and must be managed with smart circuit design. This tutorial covers the fundamentals of 3D NAND flash, describing the main blocks and major design approaches that have led to the most recent innovations in the field. The tutorial goes on to describe tradeoffs between the components that impact system operation, with intuition on how component-level metrics (tread, tprog, trigger rate) translate to system requirements (MB/s, IOPS, QoS). The tutorial concludes by overviewing and introducing future trends in flash memory to provide perspectives on the evolution of NAND over the next decade.