Compact Ag 5 In 5 Sb 60 Te 30 Phase‐Change Multilayer Film Structures for Ultrabroadband, Omnidirectional, and High‐Efficiency Infrared Absorption

Abstract Achieving ultra‐broadband absorption, high absorption efficiency, and active tunability in the mid‐infrared (MIR) region is essential for advanced applications such as infrared stealth, adaptive thermal control surfaces for spacecraft, and tunable sensing. However, traditional Fabry–Pérot (F–P) absorbers face bandwidth‐efficiency trade‐offs and lack dynamic tunability. To overcome these limitations, a novel dynamically tunable broadband absorber is presented that integrates a high‐loss asymmetric F–P cavity, a periodic asymmetric distributed Bragg reflector (A‐DBR) composed of the phase‐change material Ag 5 In 5 Sb 60 Te 30 (AIST) and TiO 2 , and a top anti‐reflection coating. Through synergistic optimization of multi‐resonant coupling, broadband impedance matching, and reflection suppression, this architecture achieves near‐perfect absorption performance. Across the 1.8–11 µm spectral range, the device exhibits an average absorptance of ≈96.54% (Sim) / ≈83% (Exp) and a relative bandwidth of 143.75%. Moreover, it exhibits ≈30% dynamic tunability near the long‐wave infrared (LWIR) band and maintains high absorption even at oblique incidence angles up to 70°. Importantly, the entire structure is realized using planar thin‐film deposition techniques without the need for nanolithography, ensuring excellent scalability, fabrication simplicity, and compatibility with existing semiconductor processes. This work provides a practical and efficient solution for next‐generation MIR thermal management, infrared stealth technologies, and adaptive photonic sensing platforms.