Hysteretic melting and freezing of nanoscale indium islands using local thermal cycling for phase-change memory nodes

Using a transmission electron microscope (TEM) operating in dark-field mode, the melting and freezing transition in nanoscale (approximately 20-200nm diameter) metal islands can be imaged at video rates (33ms/frame). The metal, typically indium, islands are thermally evaporated on one side of a 100nm thick SiN membrane. Local thermal gradients produced by Joule heating of lithographically defined electrodes on the opposite side of the membrane show a hysteretic effect in the melting/freezing of the metal islands. Read and write cycles are accomplished with 5-10 microW power, while a quiescent power of 80-100 microW is required to keep an island near its melting point. The hysteresis indicates a finite nucleation energy during freezing of individual islands. While TEM is not a practical readout mechanism, the behavior suggests a type of phase-change memory node on an inherently nanometer scale. Results for all the aforementioned will be shown, including micrographs, video, and related discussion.