Ga19Sb81 film for multi-level phase-change memory

We studied Ga19Sb81 film deposited on SiOx/Si(100) by RF co-sputtering using GaSb and Sb targets aiming for applications in multi-level phase-change memory. Crystallization temperature (Tx) is 228 °C-235 °C determined by electrical resistance versus temperature measurements at various heating rates. The dramatic resistance drop is attributed to increased carrier concentration based on Hall measurements. The films show p-type conduction behavior at all temperature regimes. The temperature for ten-year failure-time (T10y) and the activation energy of crystallization (Ea) is 156 °C and 4.2 eV, respectively, as deduced using Arrhenius plots from as-deposited films. The two-step drop in resistance is attributed to the two-step phase formation as depicted by X-ray diffractometry. Density changes before and after crystallization is 5.3% (Ge2Sb2Te5: 9.5%) as analyzed by the X-ray reflectivity method. Memory switching is carried out by using test cells with a via hole size of 600 nm. Set and reset processes can be achieved by using pulse widths of 20-100 ns. The cycling test showed performance at least 104 set-reset times. Furthermore, two stable set states are routinely achieved by controlling set voltages. The two states can be operated at least 102 cycles steadily with resistance ratios ~ 5 and ~ 22 times, respectively. The two set states arise from the formation of two phases (Sb then GaSb) during set operations.