The integration of phase change materials (PCMs) with photonic devices creates a unique opportunity for realizing application-specific, reconfigurable, and energy-efficient photonic components with zero static power consumption and low thermal crosstalk. In particular, photonic waveguides based on silicon or silicon nitride can be integrated with PCMs to realize nonvolatile photonic memory cells, which are able to store data in the phase state of the PCMs. We delve into the performance comparison of PCM-based programmable photonic memory cells based on silicon photonic and silicon nitride platforms using known PCMs (GST and GSST) for photonic memory applications while showcasing the fundamental limitations related to each design in terms of the maximum number of bits that they can store as well as their optical insertion loss. Moreover, we present comprehensive design-space exploration for analyzing the energy efficiency and cooling time of the photonic memory cells depending on the structure of the heat source. The results show that the silicon-based strip waveguide integrated with GST is the best option to realize a photonic memory cell with the highest bit density (up to 4-bits per cell given 6% spacing between the optical transmission levels). In addition, considering a microheater integration on top of a waveguide on which PCM is deposited, multi-physics simulation results show that as the heat source is placed above the PCM with a gap of 200 nm, the photonic memory cell tends to become more energy-efficient, and the cooling time of the PCM (for set and reset) becomes significantly shorter than the case where the heat source is placed further from the PCM.
