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Abstract Optical phase shifters constitute the fundamental building blocks that enable programmable photonic integrated circuits (PICs)—the cornerstone of on-chip classical and quantum optical technologies [1, 2]. Thus far, carrier modulation and thermo-optical effect are the chosen phenomena for ultrafast and low-loss phase shifters, respectively; however, the state and information they carry are lost once the power is turned off—they are volatile. The volatility not only compromises energy efficiency due to their demand for constant power supply, but also precludes them from emerging applications such as in-memory computing. To circumvent this limitation, we introduce a phase shifting mechanism that exploits the nonvolatile refractive index modulation upon structural phase transition of Sb2Se3, a bi-state transparent phase change material (PCM). A zero-static power and electrically-driven phase shifter is realized on a CMOS-backend silicon-on-insulator platform, featuring record phase modulation up to 0.09 π/µm and a low insertion loss of 0.3 dB/π, which can be further improved upon streamlined design. Furthermore, we demonstrate phase and extinction ratio trimming of ring resonators and pioneer a one-step partial amorphization scheme to enhance speed and energy efficiency of PCM devices. A diverse cohort of programmable photonic devices is demonstrated based on the ultra-compact PCM phase shifter.

Despite their importance in applications such as nonvolatile memory, integrated photonics, and compact optics, the crystalline‐to‐amorphous transition in chalcogenide phase‐change materials (PCMs) is not understood. Herein, this transition in a technologically relevant infrared (IR) transparent chalcogenide material, Ge2Sb2Se4Te1 (GSST), is examined. Thin films of GSST using fully depleted silicon on insulator (FDSOI) microheaters are discussed and the phase transitions by polarized and unpolarized Raman spectroscopy is studied. It is confirmed that the crystalline‐to‐amorphous transition is driven by conversion of Ge–6Se octahedra to Ge–4Se tetrahedra with the extra Se being incorporated into an Se—Se network. This is similar to the mechanism reported in earlier work for Ge2Sb2Te5 (GST). Recrystallization requires disrupting the Se—Se network and the crystallization activation energy is consistent with the Se—Se bond energy. Across 1000 crystallization–amorphization cycles, GSST exhibits no qualitative change in the Raman spectrum, suggesting limited film oxidation or chemical decomposition. After several hundred cycles, recrystallization is less complete, likely due to dewetting of GSST during the high‐temperature amorphization step leading to compromise of the capping layer and loss of GSST. The utility of GSST as a photonic material through fabrication and testing of a GSST‐coated, integrated silicon photonic Mach–Zender interferometer, is discussed.