High-contrast and stable operation of a plasmonically-enhanced GSST-based phase-change memory cell using plasmonic chain modes for photonic memory applications

This study focuses on designing a plasmon-enhanced phase change material (PCM) based optical phase change memory with high reading contrast (≈80<i>%</i>, the best recorded so far) and providing operational stability across different design parameters and read wavelength swings. For this, plasmon chain modes are utilized in tandem with a PCM/Ag nano-antenna with a nanometric cross-section, which acts as a memory element. By adjusting the core and cladding of the waveguide and operating in mono-mode conditions, this high contrast is obtained at 1.04~μm. Furthermore, this high contrast is kept stable by using dipolar transverse plasmon chain modes generated by a series of horizontally placed metallic (silver) nanowires along the propagation axis. For the PCM, GSST (<i>Ge</i>₂<i>Sb</i>₂<i>Se</i>₄<i>Te</i>₁) is considered. Having chain modes interact with PCM, instead of the fundamental TE-like or TM-like mode, shifts the peak wavelength of the transmission spectra of the chain mode, differently for amorphous and crystalline states, hence creating a high contrast near the anti-symmetric cut-off wavelength. We also got a good write (11.5 pJ) and erase (41.4 pJ) energy, write (2 ns) and erase (15 ns) latency values, which are an order of magnitude better than contemporary NAND flash, electrical-PCM, and optical-PCM technologies, and comparable with recent advancements in plasmonic PCM memory schemes. This research is an important step towards implementing photonic neuromorphic computing, which promises even THz speeds of operation, at a reduced power consumption, as high contrast directly relates to high packing/crystallization fractions within the PCM cell, which enables multi-level storage within a single cell.