Quasi-rapid thermal annealing studies on barium strontium titanate thin films deposited on fused silica substrates

• Nano-crystalline BST films were obtained on amorphous fused silica substrates.
• Crystallization was induced by quasi-RTA, a cost effective approach.
• No evidence of residual strain or surface layer was observed in the annealed films.
• Dielectric properties @10 GHz were measured using split post dielectric resonator.
• Crystallization result in higher density, conductivity, dielectric const. and tan δ.

Thin films of (Ba0.5,Sr0.5)TiO3 (BST5) were deposited at ambient temperature on fused silica substrates by RF magnetron sputtering technique. Nano-crystalline films were obtained upon quasi-rapid thermal annealing (Q-RTA) at temperatures ⩾800 °C for 60 s. The influence of Q-RTA temperature on the structural, morphological, optical and microwave dielectric properties of BST5 thin films have been investigated. The as-deposited and Q-RTA films annealed up to 700 °C were amorphous in nature. On increasing the Q-RTA temperature to 800 °C and above resulted in an amorphous–crystalline phase transition in the films. All the crystalline films show similar full width at half maxima (FWHM) and hence, similar crystallite size of about 12 ± 1 nm. The amorphous–crystalline transition was accompanied by a decrease in the optical band gap from 4.5 to 3.6 and increase in the refractive index from 1.9 to 2.2 as well as in the microwave dielectric constant from 40 to 262. The Root Mean Square roughness (RMSroughness) as measured from AFM show an increase from 0.6 nm to 5.6 nm with an increase in Q-RTA temperature from 400 °C to 1000 °C.

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