Electrical properties of WSi2 nanocrystal memory with SiO2/Si3N4/SiO2 tunnel barriers

Nonvolatile memory devices using the WSi2 nanocrystals on variable oxide thickness tunnel barrier composed of SiO2/Si3N4/SiO2 (ONO) layers were fabricated and their electrical properties were evaluated. The WSi2 nanocrystals with diameter of 2.5 nm and density of 3.6 × 1012 cm−2 were formed by using radio-frequency magnetron sputtering in the argon ambient and post-annealing process. In the device with 7-nm-thick ONO tunnel barrier, the threshold voltage shifts due to the memory effect of nanocrystals were observed about 1.6 V under +8 V/−10 V program/erase (P/E) voltages for 500 ms and maintained about 1.0 V after 106 s. The P/E speeds of this device were 100 ms with 1.0 V memory window. These results indicate that the ONO tunnel barrier with 7-nm-thickness provides an effective tunneling thickness for the fast P/E speeds and comparative physical thickness for long charge retention characteristic in nonvolatile memory devices.