Analysis of ferroelectric thin films deposited by pulsed laser deposition on oxide and fluoride substrates

This work has been carried out as part of an ongoing investigation in which thin film ferroelectric phase shifters are being constructed, tested, and optimized. The phase shifters will be incorporated into multi-element phased array antennas. The beam steering material used here was Ba_0.6Sr_0.4TiO₃ (BSTO) and BSTO with 1 wt% oxide additive. Thin films of BSTO have been deposited by pulsed laser deposition (PLD) onto various oxide and fluoride substrates. These include oxide substrates such as magnesium oxide (MgO), sapphire (Al₂O₃), lanthanum aluminate (LaAlO₃), neodymium gallate (NdGaO₃), and fluoride substrates such as rubidium manganese fluoride (RbMnF₃). These substrates were selected for their relatively low dielectric constants and good lattice matches to the ferroelectric thin film compound (a=3.94 Å). The substrate/film interfaces, areal film thicknesses and compositional variation have been studied using Rutherford backscattering spectroscopy (RBS), and physical thicknesses have been measured using a profilometer. The orientation of the thin films was investigated using glancing angle X-ray diffraction. Various electrodes have been used in order to optimize the electronic properties of the films. These electronic properties were tested at 30 KHz using an HP 4194A impedance analyzer. The measured electronic properties include the dielectric constant, and (change in the dielectric constant with applied electric field). The electronic properties have been correlated to the results derived from RBS and x-ray data and will be discussed in terms of substrate and electroding optimization