Multilevel Switching in Phase-Change Photonic Memory Devices

Multilevel storage in chalcogenide-based phase-change materials is one of the desired characteristics to design neuromorphic and in-memory computing applications. However, precisely controlling the crystalline and amorphous fraction to achieve reliable multilevel states is one of the key challenges in multilevel switching. Herein, multilevel switching is focused on the aspect of optical domain, where it enjoys the benefits of higher bandwidth with low delay connectivity suitable for non-von Neumann architecture. The essential requirements for multilevel optical switching are discussed in terms of programming techniques, novel device structures, and emerging materials for its better optimization. Furthermore, the impact of nature of crystallization mechanism on the multilevel switching for different families of phase-change materials is reviewed. In addition, the multilevel switching for neuromorphic engineering and in-memory computation based on the integrated photonic memory devices are assessed. Finally, several challenges and different strategies to improve the performance of multilevel switching in phase-change materials are discussed and thereby signify its importance for the design of future on-chip phase-change photonic memory devices.