Nanotechnology and emerging memories

Scaling conventional memories such as SRAM, DRAM and Floating Gate Flash has become difficult in the nanotechnology regions where the properties historically associated with these memories change. Scaled SRAM issues include decreased cell stability, increased sub-threshold leakage and variability. Solutions range from high-k dielectrics to double gate and vertical structures or to added transistors in the cell. Magnetic RAM (MRAM) offers a possible solution for the future. Issues for scaled DRAM include power dissipation and processing of vertical capacitors, and pass transistor engineering. Intermediate solutions include SOI trench and MIM capacitors, and double gate or material engineered transistors. Future DRAMs being investigated include: floating body cells, gain cells and negative differential conductance memories. For non-volatile memory, issues with scaled floating gate flash cells include: capacitive interference between floating gates, loss of coupling between control and floating gate, drain disturbance and charge leakage. Scaling issues differ somewhat for NAND and NOR flash. In the near term, a solution for scaling non-volatile memories is being found by replacing the floating gate with multi-bit trapping site materials such as nitride storage and nanocrystal.allLonger term, various Phase Change RAMs are being investigated for future non-volatile memory. Very low power non-volatile RAM applications are beginning to be served by Ferroelectric memory. Much further out in time, other new memory technologies are being investigated such as MEMs, molecular, and single electron memories.