Low energy switching of phase change materials using a 2D thermal boundary layer

TL;DR

This paper demonstrates that inserting 2D materials like MoS2 or WS2 between the substrate and phase change materials significantly reduces the energy required for phase transitions in photonic devices by acting as an effective thermal barrier.

Contribution

The study introduces a novel approach of using 2D materials as thermal boundary layers to enhance energy efficiency in PCM-based photonic devices, without affecting optical performance.

Findings

2D layers reduce laser power for phase change by at least 40%.

Thermal simulations show 2D layers act as effective thermal barriers.

Optical waveguide modes remain unaffected by the 2D layers.

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 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 interfaces. 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.