Multi-level dram trench store utilizing two capacitors and two plates

Abstract

A multi-level memory cell capable of storing two or three bits of digital data occupies only four lithographic squares and requires only one or two logic level voltage sources, respectively. High noise immunity derives from integration of the multi-level signal in the memory cell directly from logic level digital signals applied to two capacitors (as well as the bit line for the eight level mode of operation) by using capacitors having different values in order to avoid digital-to-analog conversion during writing. The capacitors can be simultaneously written and read to reduce memory cycle time. Transistor channels and capacitor connections are formed on adjacent semiconductor pillars using plugs of semiconductor material between pillars as common gate structures and connections. Opposite surfaces of the pillars also serve as storage nodes with common capacitor plates formed by conformal deposition between rows of plugs and pillars.