Tunable Microwave Device Fabrication on Low‐Temperature Crystallized Ba0.5Sr0.5TiO3 Thin Films by an Alternating Deposition and Laser Annealing Process

This article demonstrates a method to fabricate crystalline Ba0.5Sr0.5TiO3 (BST) thin films at a lower temperature of ≈300 °C using an excimer laser by an alternating depositing and annealing process. Firstly, a BST thin film with a thickness of ≈120 nm is deposited at 300 °C (laser energy of ≈2 J cm−2) and subsequently laser annealed (66 mJ cm−2) at 300 °C. This process is repeated five times to obtain thicker device quality films. XRD patterns, TEM, Raman, and UV–Vis–NIR spectroscopy confirm that phase formation of BST thin films has taken place. The band edge value for BST thin films is observed to decrease systematically from 4.65 eV (amorphous, 300 °C) to 3.56 eV (5‐layers, crystalline, 300 °C). A varactor device with a Circular Patch Capacitor (CPC) structure is patterned on the five‐stage laser annealed BST thin films processed at 300 °C, which shows a microwave tunability of 34% at 1 GHz compared to conventionally deposited BST films (prepared at 700 °C). This study provides a way for fabricating ferroelectric thin film based tunable devices at low temperatures, making the process compatible with low melting substrates in flexible electronics and other situations where there is a temperature constraint. Fabrication of crystalline ferroelectric films of device quality at a lower temperature of 300 °C by a novel approach of sequential layer‐by‐layer deposition and laser annealing to overcome the limited depth of crystallization in laser annealing is reported. A good device (varactor) response from these films demonstrate that this process is useful to fabricate microwave and electro‐acoustic devices on polymer substrates for flexible electronics.