Partial crystallization of HfO2 for Two-Bit/Four-Level SONOS-Type flash memory

Abstract

The nonvolatile memory properties of the partially crystallized HfO2 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 mn, 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 Vth 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 HfO2 shows a larger memory window than HfO2 nanodot memory, assisted by the enhanced electron capture efficiency of an amorphous HfO2 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 Si3N4 trapping layer.