High density 5 Volt-only compatible non-volatile RAM cell

A high density, non-volatile RAM cell composed of a volatile RAM component, merged with a non-volatile element which "shadows" the RAM component, is described. Unlike earlier low density Shadow RAM approaches, small cell size is achieved here by utilizing a vertically integrated 1T-1C DRAM element merged with a highly compact, vertically integrated, triple-level poly-silicon floating gate structure. Non-volatile operations on the floating gate stack are performed by Fowler-Nordheim electron injection through both a tunnel oxide, and through a first level to third level poly-silicon sidewall which has proven successful in earlier E²PROMs. The non-volatile approach lends itself readily to 5 Volt-only implementation, using on-chip voltage multiplication techniques, by virtue of the miniscule Fowler-Nordheim charging currents needed, combined with a single high voltage STORE implementation scheme using a common third level poly-Si line. Cell operation for the non-volatile BULK STORE and BULK RECALL functions as well as volatile bit operations are described. Also shown is the cell layout, which consumes 1.5 mil²area, based on 3µ design rules, making it readily compatible with 16K NOVRAM density levels.