Improvement in tunability and dielectric loss of (Ba 0.5 Sr 0.5 )TiO 3 capacitors using seed layers on Pt/Ti/SiO 2 /Si substrates

• Published in: Journal of materials research 2002-11, Vol.17 (11), p.2831-2836
• Main Authors: Jeon, Young-Ah, Shin, Woong-Chul, Seo, Tae-Suck, Yoon, Soon-Gil
• Format: Article
• Language: English
• ISSN: 0884-2914; 2044-5326
• DOI: 10.1557/JMR.2002.0411

The absence of a low dielectric constant layer at the barium strontium titanate (BST)/Pt interface and a decreased roughness are critical issues in the production of (Ba 0.5 Sr 0.5 )TiO 3 thin films with high tunabilities and low losses. An improvement in dielectric properties was achieved by the insertion of seed layers at the BST/Pt interface by pulsed laser deposition. The higher tunability can be attributed to (100) texturing of the BST films, which is independent of grain size and grain morphologies, thus leading to a variation in seed layer thicknesses. The tunability and dielectric constant of 1600-Å-thick BST films showed a maximum of 53% and 720, respectively, at a seed layer thickness of 100 Å. Dielectric loss is dependent on the roughness of BST films and reached a minimum of 0.8% at a root mean square roughness of 28 Å. The maximum figures of merit, defined as the ratio of tunability to dielectric loss, of approximately 58 at 100 kHz and 198 kV/cm were obtained at a seed layer thickness of 70 Å. The optimized seed layer thickness for BST deposition onto Pt/Ti/SiO 2 /Si substrates plays an important role in maintaining the high tunabilities and low loss, which are suitable for microwave device applications.