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Project

Alternative Channel Materials for 3-D NAND Memories

Nowadays consumer’ s electronic such as smart phones, tablet, laptops, GPS navigators, health care devices, music players and digital photo/video cameras, is an inextricable part of the modern society and represents one of the fastest growing markets on the earth; the steadily increasing demand for portable devices requiring data storage in huge volume, has triggered an exceptional growth of non-volatile memory market. Non-volatile memories can retain the stored information even when not powered, and there are various solutions available in the market to serve the need of different applications: hard drives, magnetic tapes, compact disks, NAND and NOR flash memories, etc. . Among them, the most popular for mass data storage application are hard drives and NAND flash. Hard drive disks (HDDs) use spinning magnetic platters paired with magnetic head to read and write data. On the other hand NAND flash is a semiconductor memory entirely implemented in solid state circuits, and it does not require moving parts. Even if the cost per bit is relatively higher than HDDs, NAND flash has becoming a new driving force in the semiconductor industry over the last decade, thanks to its proven scalability, low power consumption and robustness, fundamental for portable systems.      

In order to overcome the scaling obstacle in conventional planar NAND Flash, 3D NAND memory technology, has been introduced for mass production for the first time in 2014. The third dimension is exploited by stacking NAND cells on top of each other’s, resulting not only in a significant bit‑density increase but also in a reduced cost-per-bit. The most industrial relevant channel material for 3D NANDs is polycrystalline silicon (poly-Si). However, the conduction in poly‑Si channel is dominated by the grain size distribution and hampered by scattering events at grain boundaries and charged defects. As a consequence, the drive current (ID) required for reading operations, is low, unstable, and decreases as the number of stacked cells increases, rendering poly‑Si unsustainable for long‑term scaling. This thesis is an effort to investigate alternative channel materials with higher electron mobility than poly-Si, as a possible solution to enable further scaling for future 3D NAND generations.

Date:15 Apr 2013 →  4 Sep 2017
Keywords:Flash memories
Disciplines:Nanotechnology, Design theories and methods
Project type:PhD project