Fig. 1. A high-Q ring resonator loaded with 10 μm long 20-nm-thick Sb₂S₃.

a Schematic of the device (the encapsulation ALD Al₂O₃ layer is not shown), b optical, and c Scanning-Electron Microscope (SEM) images of the micro-ring resonator. The Sb₂S₃ thin film, n⁺⁺, and p⁺⁺ doped silicon regions are represented by false colors (blue, orange, and green, respectively). d Measured micro-ring spectra in two phases (SET: three 1.6 V, 200-ms-long, 3.4 mJ pulses to change Sb₂S₃ to the crystalline state; RESET: three 7.5 V, 150-ns-long, 56 nJ pulses to change Sb₂S₃ to the amorphous state). The spectra are averaged over ten cycles of reversible electrical switching, and the shaded area shows the standard deviation. Norm. Trans. stands for normalized transmission, normalized to a reference waveguide on the same chip.