A large cell-ratio and low node leak 16 M-bit SRAM cell using ring-gate transistors

An advanced memory cell for a 16-Mb SRAM (static RAM) has been developed. The cell has ring-shaped gate electrode (ring-gate) driver transistors and PMOS TFT (thin film transistor) loads utilizing steps of underlayers. The ring-gate driver transistors achieve more than 3.2 large cell-ratio ( beta r) which is free from misregistration, and also 2-fA low-leakage current of the memory cell node. The titanium silicided source region (Rs=7 Omega / Square Operator ) of driver transistors is common to both in a cell, so there is little imbalance of the ground line. The 14-fA off-current (Vd=3 V, Vg=0 V) of the TFT makes possible less than 0.3- mu A standby current in a 16-Mb SRAM. It is noted that these device characteristics will certainly make it possible to fabricate a 16-Mb SRAM with this cell.<
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