Crystalline-Crystalline Phase Change

Phase change memories (PCM) based on reversible phase changes between two crystalline states with differing electrical resistivities are expected to have superior writing power and speed as compared to conventional PCM devices which utilize a higher configurational entropy change between a low-resistance crystalline phase and high-resistance amorphous phase. Recent studies have demonstrated crystalline-crystalline (β → γ) phase transformations of In2Se3 can be used in a PCM device so understanding the behavior in In2Se3 phase transformations is critical to developing low energy In2Se3 memory systems.

In In2Se3 PCM devices, the driving force for the phase transformation is Joule heating as thermal energy is converted from the electrical energy supplied [1]. However, it is estimated that the increase in temperature when a voltage is applied between the tip and the surface is not enough to reach the transformation temperature. Identifying the driving force behind the phase transformation will be essential for In2Se3 PCM device design. In single-crystal monolayers of In2Se3 the crystalline-crystalline phase change from α→ β can be explicitly determined by measuring differences in the electrical resistivity before and after a voltage from the STM tip is applied. Extracting information on the phase transformation of In2Se3 in monolayers can be extended to further our knowledge of the scaling behavior of the phase transformations and associated changes of the electrical properties. With this proposal we want to investigate the use an STM tip to drive a solid-solid phase transition in which monolayer α In2Se3 is transformed locally to nanometer-scale domains of β phase In2Se3.The driving force of the phase transitions, and the impact of defects on the transition will be investigated. Locally and selectively engineering phase transitions in these monolayer systems will allow for the improvement of In2Se3 PCM devices.