Enhanced Interface Stability of Multilayer Bi₂Te₃/Ti/Cu Films after Heat Treatment via the Insertion of a Ti Layer

The interface stability is of great significance for maintaining the high output performance of thin-film thermoelectric devices. Here, it is demonstrated that by introducing a Ti layer and controlling its thickness, the interface stability relating to element diffusion, contact resistance, and mechanical strength can be regulated at Bi₂Te₃/Cu interfaces. After heat treatment, the multilayer interface with a thickness of 270 nm for the Ti layer has a stable structure that can suppress element diffusion, maintain a low specific contact resistivity (7.49 × 10⁻⁶ Ω cm²) and obtain an excellent critical load (58.1 mN). These characteristics are achieved because the Ti film with a thickness of 270 nm can keep multilayer interface stable, maintain the interface as effective junctions, and alleviate stress release. Due to the diffusion of Cu, the Cu-Te compounds are formatted and Cu diffusion into Bi₂Te₃ is generated in the interfaces. Meanwhile, the results show that the Cu diffusion into Bi₂Te₃ has a greater impact on contact resistance than p-CuTe in the interface. The work provides a general method for maintaining the reliability and stability of multilayer interfaces in thin-film thermoelectric devices.