Engineering polar nanoclusters for enhanced microwave tunability in ferroelectric thin films

Microwave tunable thin films that can dynamically adjust dielectric properties are essential for next-generation communication and sensing technologies. However, achieving high-tunability often comes at the cost of increased dielectric loss or the need for large bias electric fields. In this study, we address this challenge by engineering nanoclusters in a tin doped barium titanate thin film and systematically investigate their polarization behaviour across the ferroelectric-paraelectric transition. The optimized film exhibits outstanding microwave tunability (~74% at 6 GHz under a low DC bias of 15 V), which are attributed to the presence of polar nanoclusters embedded within a macroscopically non-polar cubic matrix, stabilized by subtle structural features such as twin boundaries, local lattice distortions, and compositional variations. Structural and dielectric analyses confirm that these nanoclusters remain active, enabling strong field-induced permittivity modulation near room temperature. This work demonstrates a promising strategy to achieve high tunability with minimal losses in ferroelectric thin films, thereby addressing a key performance trade-off in the design of advanced microwave tunable devices.