Characterization of phase change memory materials using phase change bridge devices

Abstract

Having become one of the most promising candidates for future nonvolatile memory applications, phase change random access memory is now driving an intensive search for phase change materials with optimized properties. In this paper, phase change bridge devices are utilized as a unique material test vehicle, allowing systematic extraction of crucial material parameters such as resistance contrast, switching speed, threshold voltage, and set and reset power. Bridge devices fabricated from undoped Ge15 Sb85 are presented that reproducibly switch between set and reset states with one decade resistance contrast using current pulses as short as 10 ns. Since devices are fabricated in the amorphous-as-deposited phase, an interesting intermediate device state can be produced, which we attribute to a crystalline center region that fails to completely bridge the amorphous active device volume. The subtle differences between the amorphous-as-melt-quenched and amorphous-as-deposited phases are explored using both bridge devices and optical experiments. It is shown that the large difference in crystallization times between these two amorphous states observed in laser experiments is reflected also in device operation. © 2009 American Institute of Physics.