N. Shibata; H. Maejima; K. Isobe; K. Iwasa; M. Nakagawa; M. Fujiu; T. Shimizu; M. Honma; S. Hoshi; T. Kawaai; K. Kanebako; S. Yoshikawa; H. Tabata; A. Inoue; T. Takahashi; T. Shano; Y. Komatsu; K. Nagaba; M. Kosakai; N. Motohashi; K. Kanazawa; K. Imamiya; H. Nakai, “A 70 nm 16 Gb 16-level-cell NAND Flash Memory,” 2007 Symposium on VLSI Circuits, pp. 190-191, DOI: 10.1109/VLSIC.2007.4342710
Citation:
This paper, presented at the 2007 VLSI Symposium, introduced the first QLC (4 bits per cell) technology with a 16-level threshold distribution, far exceeding the MLC (2 bits per cell) with a 4-level threshold distribution that was being developed at the time. The proposed methodology involved a two-step programming technique: First, memory cells are initially programmed to lower levels than the actual target levels, followed by programming neighboring cells. In the second step, the memory cells are programmed again to achieve the precise 16 levels. This technique effectively eliminates the influence of adjacent cells and results in an extremely narrow threshold distribution, which established QLC as a widely adopted standard in the Flash Memory market supporting both 2-D and 3-D Flash Memory technologies
N. Kimizuka; T. Yamamoto; T. Mogami; K. Yamaguchi; K. Imai; T. Horiuchi, “The impact of bias temperature instability for direct-tunneling ultra-thin gate oxide on MOSFET scaling,” 1999 Symposium on VLSI Technology, pp. 73-74, DOI: 10.1109/VLSIT.1999.799346
Citation:
This 1999 paper showed for the first time that negative bias temperature instability (NBTI) is the rate-limiting factor for reliability in pMOSFETs with ultra-thin SiO2 gate dielectrics. First, it identified that the direct-tunneling electron and/or hole transport does not play a major role in the degradation mechanism. Secondly, it was found that the threshold voltage change caused by BTI for the PMOSFET limits the device lifetime, which is shorter than that defined by hot-carrier induced degradation for the NMOSFET. These results led to the work on nitrided SiO2 and eventually, high-k gate metal stacks. The need to move away from SiO2 was a fundamental pivot that this paper brought into sharp focus and was followed by numerous investigations at various leading-edge companies that confirmed the challenges of using SiO2.
