Nanomechanical and microwave dielectric properties of SrBi 4 Ti 4 O 15 thin films sputtered on amorphous substrates by rf sputtering A. Rambabu • S. Bashaiah • K. C. James Raju Received: 21 November 2013 / Accepted: 2 January 2014 / Published online: 9 January 2014 Ó Springer Science+Business Media New York 2014 Abstract SBTi (SrBi 4 Ti 4 O 15 ) thin films were prepared on amorphous fused silica substrates by rf magnetron sputtering technique and crystallized in a microwave oven and conventional furnace. The difference in crystalline perfection was observed for both conventional and micro- wave annealed films. Nanoindentation and nanoscratch test were preformed to extract the mechanical properties of the films. Microwave annealed films exhibited higher hardness (6.2 GPa), Young’s modulus (103 GPa) and low friction coefficient than conventional annealed films. Microwave dielectric properties are measured at 10 and 20 GHz using spilt post dielectric resonator technique. Microwave annealed films have shown good microwave dielectric properties even at high temperatures by controlling the Bi volatization. 1 Introduction Thin films of bismuth based layered ferroelectrics from the Aurivillius family have been extensively investigated due to their higher fatigue endurance and larger dielectric constant which are crucial for the memory applications [1– 3]. Bi 4 Ti 3 O 12 (BIT) is a promising candidate which is being used from this class of materials in ferroelectric memories because of its large spontaneous polarization. The higher order structures from this family such as SrBi 4 Ti 4 O 15 (SBTi) have larger remnant polarization, due to the increased number of perovskite units generating ferroelectric properties. SBTi, which has a crystalline structure similar to BIT, is another typical layer structured ferroelectric with m = 4 (where m indicates the number of perovskite layers existed between the two bismuth oxide layers) [4]. It’s high Curie temperature (T c = 520 °C) makes it useful over a wide temperature range [5]. The SBTi material consists of four TiO 6 octahedra in the perovskite blocks sandwiched by two neighboring (Bi 2 O 2 ) 2 layers along the c-axis in a unit cell. The ferroelectric properties of SBTi materials can be affected by the crys- tallographic orientation due to their anisotropic crystal structure [6]. However the dielectric properties of these materials are found to be highly dependent on the crystal orientation because the spontaneous polarization in these layered perovskite material lies in the a–b plane alone. It is well known that piezoelectric coefficients depend on the mechanical coefficients which are related to the mechanical state of the materials [7]. Moreover, the mechanical behavior plays a crucial role in the delamina- tion, cracking or fracture, and polarization fatigue of the multilayer thin film structures [8–10]. Consequently, the investigation on the mechanical properties of the bismuth layered-structure ferroelectric thin films is of practical importance in various situations and particularly for the design of piezoelectric devices. The importance of such films have now increased with their potential for applica- tion in MEMS devices where they can be used not only for sensing and actuation but also for energy harvesting even at elevated temperatures. These applications require a closer study of the mechanical properties of the deposited thin films. On the other hand, it is a challenging issue to obtain excellent microwave dielectric properties combined with excellent mechanical properties, especially the enhanced A. Rambabu (&)  K. C. James Raju School of Physics, University of Hyderabad, Hyderabad, India e-mail: rambabuhcu@gmail.com S. Bashaiah ACRHEM, University of Hyderabad, Hyderabad, India 123 J Mater Sci: Mater Electron (2014) 25:1172–1179 DOI 10.1007/s10854-014-1705-9