Partial Crystallization of $\hbox{HfO}_{2}$ for Two-Bit/Four-Level SONOS-Type Flash Memory

The nonvolatile memory properties of the partially crystallized HfO
₂
charge storage layer are investigated using short-channel devices of gate length L
_g
down to 80 nm. Highly efficient two-bit and four-level device operation is demonstrated by channel hot electron injection programming and hot hole injection erasing for devices of L
_g
> 170 nm, although the reduction of the memory window is observed for devices of L
_g
< 170 nm. A memory window of 5.5 V, ten-year retention of V
_th
clearance larger than 1.5 V between adjacent levels, endurance for 10
⁵
programming/erasing cycles, and immunity to programming disturbances are demonstrated. Flash memory with partially crystallized HfO
₂
shows a larger memory window than HfO
₂
nanodot memory, assisted by the enhanced electron capture efficiency of an amorphous HfO
₂
matrix, which is lacking in other types of reported nanodot memory. The scalability, programming speed, V
_th
control for two-bit and four-level operation, endurance, and retention are also improved, compared with NROM devices that use a Si
₃
N
₄
trapping layer.