Date of Award
Doctor of Philosophy (PhD)
Electrical and Computer Engineering
Aubrey N. Beal
Flash memories (Computers)--Design, Flash memories (Computers)--Reliability
NAND Flash memory is a non-volatile solid-state data storage technology widely used in electronic devices such as smartphones, tablets, laptops, digital cameras, USB drives, solid-state drives (SSDs), autonomous vehicles, space applications, and data centers. NAND Flash memory-based SSDs are increasingly replacing the hard-disk drives (HDD) due to their high-density memory storage, low latency, low power consumption, and light weight. The NAND Flash memory has evolved from its planer 2D architecture to its contemporary 3D vertical layer architecture to meet the exponential storage demand. However, the 3D NAND architecture poses new reliability challenges, such as big block management, poly-Si-related read instability, low cell current, and layer-to-layer variability. In addition, the ever-increasing Flash memory density increases energy consumption and degrades the performance of Flash SSDs. Hence, innovation at the system level is necessary to improve the reliability, energy efficiency, performance, and security of future 3D NAND-based storage systems. The dissertation explores factors affecting 3D NAND Flash memory performance and reliability due to vertical stacking and scaling. First, endurance variability is found iiamong pages due to increasing vertical layers. This causes the under-utilization of the memory blocks leading to lower endurance. An intra-block wear-leveling algorithm based on dynamic, layer-aware logical-down-scaling of Flash memory blocks is proposed to improve overall memory utilization. Second, we identified a disproportionate energy-accuracy trade-off during memory write operation. To address this, the dissertation proposes a technique called EXPRESS, which increases the energy efficiency of Flash memory by up to 50% relative to traditional Flash writes while maintaining data integrity. Third, deleting data instantly from NAND Flash memories incurs hefty overheads and increases wear levels with the risk of data leakage. This work introduces an instant data sanitization method for multi-level-cell Flash memory. The dissertation also proposes a new page-writing technique for hiding secret information using the threshold voltage variation of programmed memory cells. Overall, this dissertation significantly contributes to NAND Flash memory reliability and energy efficiency and proposes several novel techniques and algorithms for improving the performance and endurance of 3D NAND Flash memory-based storage systems.
Raquibuzzaman, Md, "Reliable and energy-efficient 3D NAND flash storage system design using run-time device and system interaction" (2023). Dissertations. 349.