Electrical switch of phase change materials: toward the control of crystallinity for multi-level reconfigurable nanophotonics

Phase change materials (PCM) have gained a considerable interest in the photonics community as active materials in reconfigurable devices. Their significant change of optical properties upon the amorphous to crystalline reversible phase transition enables a large and dynamical tuning of devices’ response. Among the various PCM, Ge₂Sb₂Te₅ (GST) is the most widely used thanks to its fast phase change as well as the large modulation of its refractive index (Δn > 1). Although this PCM has been mainly exploited for simple binary on-off functions, it presents an additional degree of freedom: the multi-level partial change of state. Indeed, we show in this paper multi-level continuously tunable reflectivity allowed by the electrically-controlled partial crystallization of GST. This is achieved via the Joule effect, by injecting short voltage pulses (few tens of μs) through platinum microheaters underneath GST patches. This electrically-induced phase transition is the most promising strategy for PCM integration in industrial foundries and shows promises for individual pixel addressing in multi-level applications such as neuromorphic computing or grayscale displays.