Novel high density, stacked capacitor MOS RAM

Abstract

A novel one transistor type MOS RAM cell is successfully developed and achieves a higher degree of integration than realized to date with conventional RAM's. This cell provides remarkable area reduction and/or an increase in storage capacitance by stacking the main portion of the storage capacitor on the address transistor. It is called a stacked capacitor RAM (STC RAM) cell. This new cell has a triple level poly-Si structure of poly-Si word lines and Al bit lines. The stacked capacitor is composed of a poly-Si - Si <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> - poly-Si structure. A 256 bit STC MOS RAM is fabricated with 3 µm technology and operates successfully. The STC RAM cell area, 52.5 µm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , is remarkably smaller than the cell area of conventional RAM's with double level poly-Si gate structure, 160 µm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .