Threshold voltage instability and charge retention in nonvolatile memory cell with nitride/oxide double-layered inter-poly dielectric

The authors present novel results concerning thin NO (nitride/oxide) double-layered interpoly dielectric in nonvolatile memories. Optimized NO films with thick top-oxide and thin nitride structure offer sufficient charge retention capability in the 10 nm effective oxide thickness region. However, this structure shows an anomalous threshold voltage increase due to the back tunneling of electrons which can be injected into the NO film during programming and baking. The magnitude of this voltage depends on the NO film structure and the electric field during the program or bake procedure. Therefore, these phenomena must be taken into consideration in designing the cell structure and its operating conditions. The results obtained are also effective in considering ONO (oxide/nitride/oxide) scaling in the thin bottom-oxide region.<>