Scanning Probe Microscopy and Microwave Characterization of Nanostructured Ferroelectric Barium Strontium Titanate Thin-Films Fabricated by Pulsed Laser Deposition

A series of nanostructured ferroelectric thin-films of barium strontium titanate were fabricated using a pulsed laser deposition system with real-time in-situ process control. Pulsed laser deposition parameters were optimized for growth of tunable, low-loss nanostructured thin-films for use in the development of high frequency tunable microwave devices. Thin-films were grown at identical temperatures and energy densities as oxygen ambient pressures were varied from 19 mT through 1 T. Structural and electrical characterization were performed using contact-mode AFM and surface potential imaging. Microwave characterization was performed using coplanar waveguide lines and resonators to characterize the frequency dependent dielectric properties ($\varepsilon _{r}$ and tan $\delta )$. Contact-mode AFM showed an increase in grain size with increase in oxygen ambient pressure from 38-75 mT. Surface potential imaging demonstrated that X patterns written by applying a voltage to thin-films with an AFM tip in contact mode are electrically switchable. Microwave characterization showed that thin-films grown at 75mT oxygen partial pressure yielded the most stable films in terms of tunability and loss-tangent over a wide frequency range.