Low Energy Switching of Phase Change Materials Using a 2D Thermal Boundary Layer

Abstract

The switchable optical and electrical properties of phase change materials (PCMs) are finding new applications beyond data storage in reconfigurable photonic devices. However, high power heat pulses are needed to melt-quench the material from crystalline to amorphous. This is especially true in silicon photonics, where the high thermal conductivity of the waveguide material makes heating the PCM energy inefficient. Here, we improve the energy efficiency of the laser-induced phase transitions by inserting a layer of two-dimensional (2D) material, either MoS2 or WS2, between the silica or silicon substrate and the PCM. The 2D material reduces the required laser power by at least 40% during the amorphization (RESET) process, depending on the substrate. Thermal simulations confirm that both MoS2 and WS2 2D layers act as a thermal barrier, which efficiently confines energy within the PCM layer. Remarkably, the thermal insulation effect of the 2D layer is equivalent to a ∼100 nm layer of SiO2. The high thermal boundary resistance induced by the van der Waals (vdW)-bonded layers limits the thermal diffusion through the layer interface. Hence, 2D materials with stable vdW interfaces can be used to improve the thermal efficiency of PCM-tuned Si photonic devices. Furthermore, our waveguide simulations show that the 2D layer does not affect the propagating mode in the Si waveguide; thus, this simple additional thin film produces a substantial energy efficiency improvement without degrading the optical performance of the waveguide. Our findings pave the way for energy-efficient laser-induced structural phase transitions in PCM-based reconfigurable photonic devices.

Reconfigurable InP waveguide components using the Sb2S3phase change material

“…If the heat of fusion were considered, we would expect the peak BCB temperature to be even lower when the MoS 2 layer is included because a greater proportion of the available energy is used by the melt-transition. Adding TMDCs at the waveguide-Sb 2 S 3 interface also has the added advantage that the Sb 2 S 3 phase transitions can be induced more efficiently [43]. Indeed, we note that with the MoS 2 layer included in the structure, the laser power required to reach the Sb 2 S 3 melting point was reduced by 23% to 20 mW.…”

“…We suggest a novel solution to overcome the laser-induced damage to the BCB layer during amorphisation. Recently, Ning et al showed that two-dimensional (2D) transition metal dichalcogenides (TMDCs), such as MoS 2 and WS 2 , can be used as thermal barriers during amorphisation of PCMs on silicon waveguides [43]. These TMDCs confine the thermal energy within the PCM layer without significantly influencing the waveguide effective refractive index or the concomitant propagating mode.…”