An on-chip embedded NVM (eNVM) enables a zero-standby power system-on-a-chip with a smaller form factor, faster access speed, lower access power, and higher security than an off-chip NVM. Differently from the high density eNVM technologies such as dual-poly eflash, FeRAM, STT-MRAM, and RRAM that typically require process overhead beyond standard logic process, the moderate density eNVM technologies such as e-fuse, anti-fuse, and single-poly embedded flash (eflash) can be fabricated in a standard logic process with no process overhead. Among them, a single-poly eflash is a unique multiple-time programmable moderate density eNVM, while it is expected to play a key role in mitigating variability and reliability issues of the future VLSI technologies; however, the challenges such as a high voltage disturbance, an implementation of logic compatible High Voltage Switch (HVS), and a limited sensing margin are required to be solved for its implementation using a standard I/O device. This thesis focuses on alleviating such challenges of the single-poly eflash memory with three single-poly eflash designs proposed in a generic logic process for moderate density eNVM applications. Firstly, the proposed 5T eflash features a WL-by-WL accessible architecture with no disturbance issue of the unselected WL cells, an overstress-free multi-story HVS expanding the cell sensing margin, and a selective WL refresh scheme for the higher cell endurance. The most favorable eflash cell configuration is also studied when the performance, endurance, retention, and disturbance characteristics are all considered. Secondly, the proposed 6T eflash features the bit-by-bit re-write capability for the higher overall cell endurance, while not disturbing the unselected WL cells. The logic compatible on-chip charge pump to provide the appropriate high voltages for the proposed eflash operations is also discussed. Finally, the proposed 10T eflash features a multi-configurable HVS that does not require the boosted read supplies, and a differential cell architecture with improved retention time. All these proposed eflash memories were implemented in a 65nm standard logic process, and the test chip measurement results confirmed the functionality of the proposed designs with a reasonable retention margin, showing the competitiveness of the proposed eflash memories compared to the other moderate density eNVM candidates.
University of Minnesota Ph.D. dissertation. December 2013. Major: Electrical Engineering. Advisor: Chris H. Kim. 1 computer file (PDF); xx, 129 pages.
Design of Logic-Compatible Embedded Flash Memories for Moderate Density On-Chip Non-Volatile Memory Applications.
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