In the past the
high voltage needs and
cell leakage currents have limited the
scalability of the
Nitride cell and made the poly
silicon floating gate
cell the primary contender for Non-Volatile memories. As the
process development has matured and technology has scaled to smaller and smaller dimensions, the Poly-
silicon floating gate cell has approached its scaling limitations. This has re-kindled the interest in the
nitride cell. In order to scale the
nitride cell it is necessary to remove the
high voltage requirements that limit scaling of the memory junctions and isolation and the high inherent leakage of unselected cells due to over erase of the cells. It is well known that the
nitride area where the storage happens is only of the order of 300 Angstroms close to the junctions used for generating the energetic carriers by
impact ionization (Channel
Hot Electron Programming). The charges once stored do not move around by conduction in
Nitride and hence can be considered stationary. Hence it is possible to have
Nitride layer covering the areas, where
programming happens, to reduce the over all size of the cell while having a control gate between the Nitride storage areas. This type of Nitride
storage cell can be implemented with a slight increase in
cell size but making the leakage current of non-selected cells a non-issue. A second problem in the prior art is the use of band to band tunneling for erase. This requires high voltages at the drain with
negative voltage on gate. The band to band tunneling is a reliability issue for the junction and need a high degree of tuning. A cell using an erase technology and method called the Tunnel Gun (TG) for achieving the erase of the cells is proposed that eliminate this problem. A combination of TG technology with an added select gate will enable the nitride cells to be much more robust and achieve mainstream status in
high volume manufacturing.