Transfer of High-Temperature-Sputtered BiFeO₃ Thin Films onto Flexible Substrates Using α-MoO₃ Layers

Inducing external strains on highly oriented thin films transferred onto mechanically deformable substrates enables a drastic enhancement of their ferroelectric, magnetic, and electronic performances, which cannot be achieved in films on rigid single crystals. Herein, the growth and diffusion behaviors of BiFeO₃ thin films grown at various temperatures is reported on α-MoO₃ layers of different thicknesses using sputtering. When the BiFeO₃ thin films are deposited at a high temperature, significant diffusion of Fe into α-MoO₃ occurs, producing the Fe_1.89Mo_4.11O₇ phase and suppressing the maintenance of the 2D structure of the α-MoO₃ layers. Although lowering the deposition temperature alleviates the diffusion yielding the survival of the α-MoO₃ layer, enabling exfoliation, the BiFeO₃ is amorphous and the formation of the Fe_1.89Mo_4.11O₇ phase cannot be suppressed at the crystallization temperature. High-temperature-grown BiFeO₃ thin films are successfully transferred onto flexible substrates via mechanical exfoliation by introducing a blocking layer of Au and measured the ferroelectric properties of the transferred films.