Tailoring Capping Layers for Phase‐Change Material Photonics

Spatial‐laser programming of low‐loss Sb 2 Se 3 phase‐change materials (PCMs) offers a flexible route toward pixelated and large‐scale nonvolatile reconfigurability in photonic devices. However, complex laser‐induced dynamics often limit precision control and reproducibility. We systematically investigate how encapsulation architectures, a critical yet often overlooked element, govern the phase transition behavior and introduce tailored Al 2 O 3 ‐based hybrid capping solutions for distinct application regimes. For high‐resolution patterning, an additional SiN cap creates vertical heat‐conduction channels that enable subwavelength phase switching. For waveguide‐based low‐power phase tuning, an Al 2 O 3 /SiO 2 hybrid structure provides optimal mechanical confinement and energy efficiency. With this optimized encapsulation, we achieve a minimum nominal feature size of 200 nm (a 100‐nm reduction), 31 resolvable states (3× increase) via monotonic power modulation, and a 15‐mW power window for full amorphization without ablation (7× broader than a conventional 30‐nm Al 2 O 3 encapsulation). Furthermore, we demonstrate significantly enhanced cycling stability in micro‐ring resonator phase‐shifting. Our results position encapsulation engineering as a decisive enabler of high‐performance laser‐manipulated PCM photonics.