Multiphysics simulation of optical gate switch operation using a chalcogenide phase-change material

To gain a complete understanding of the optical switch that uses phase-change material, Ge₂Sb₂Te₅ (GST), we conducted a simulation considering various physical phenomena related to the switch, such as electrical conduction, Joule heating, heat diffusion, phase change of GST, and light propagation. It was found that the phase state (amorphous and crystalline) of the GST film can be controlled by applying an appropriate pulse voltage to the indium tin oxide (ITO) heater layer, thereby changing the transmittance of the optical switch. Calculations showed that during cooling in the amorphization process, part of the GST film was recrystallized, reducing the transmittance of the optical switch in the ON state. Moreover, the large temperature difference in the GST film during heating was caused by a substantial amount of Joule heat generated in the region distant from the GST film. This difference in distance from the heat-generating region resulted in a considerable temperature difference in the GST film. Thus, herein, we have proposed modified model structures to reduce this temperature difference in the GST film, which can recrystallize during the amorphization process. Calculation using the modified model structures revealed that increasing the thickness of the ITO heater layer, over which the GST film was not placed, can effectively reduce the temperature difference and eventually suppress recrystallization.