Reversible Crystalline-Crystalline Transitions in Chalcogenide Phase-Change Materials

Phase-change random access memory (PCRAM) is one of the most technologically mature candidates for next-generation non-volatile memory and is currently at the forefront of artificial intelligence and neuromorphic computing. Traditional PCRAM exploits the typical phase transition and electrical/optical contrast between non-crystalline and crystalline states of chalcogenide phase-change materials (PCMs). Currently, traditional PCRAM faces challenges that vastly hinder further memory optimization, for example, the high-power consumption, significant resistance drift, and the contradictory nature between crystallization speed and thermal stability, nearly all of them are related to the non-crystalline state of PCMs. In this respect, a reversible crystalline-to-crystalline phase transition can solve the above problems. This review delves into the atomic structures and switching mechanisms of the emerging atypical crystalline-to-crystalline transitions, and the understanding of the thermodynamic and kinetic features. Ultimately, an outlook is provided on the future opportunities that atypical all-crystalline phase transitions offer for the development of a novel PCRAM, along with the key challenges that remain to be addressed.