Transient Phase-Change Effect in Phase-Change Memory Devices

摘要

Phase-change random access memory (PCRAM) is one of the next-generation memories with the most potential due to its many good characteristics, such as nonvolatility, high endurance and long data retention. PCRAM has the potential to replace flash memory, which has limited durability and speed. PCRAM is based on phase change from a high-resistance amorphous state to a low-resistance crystalline state and vice versa in nanosecond timescale. However, the mechanism by which phase change occurs is still unknown. This work introduces a transient electrical method to relate the phase change phenomenon to the mechanism behind it. In this thesis, PCRAM devices were fabricated with Ge2Sb2Te5 (GST) and AgInSbTe, which are well known nucleation and growth dominated phase change materials. The transient electrical waveform during crystallization was identified as a method to characterize the phase change phenomenon in the device and provide a link to the mechanism behind the phase change effect. Two time periods, delay time and current recovery time, were discovered during this transient electric analysis, which relate to nucleation and growth of the phase change material. This method could potentially be used across different device structures and phase change materials to identify their effect on the phase change mechanism.