Highly textured chemical solution deposited Ba0.5Sr0.5Ti1-xMnxO3 (x ∼ 0 to 5 at%) thin films for microwave dielectric applications

We have optimized the process methodology to grow highly (100) oriented barium strontium titanate (BaxSr1-xTiO3) (x = 0.5 and 0.6) thin films on lattice-matched (100) lanthanum aluminate (LAO) substrates by sol-gel technique. These films exhibited excellent phase shift and insertion loss characteristics at microwave frequencies. The work has been extended to study the effect of manganese (Mn) doping on the nature of epitaxial growth and electrical behavior of (100) oriented Ba0.5Sr0.5TiO3 (BST) thin films. The degree of texturing and quality of the in-plane epitaxy of BST thin films on lanthanum aluminate (LAO) was found to be improved for upto 3 at% Mn doping. These films were characterized in terms of their electrical properties and dielectric behavior at low (1kHz-1MHz) and microwave frequencies. We have fabricated eight-element coupled microstrip phase shifters (CMPS) and tested them in terms of their degree of phase shift and insertion loss characteristics. The phase shift increases from 239 degrees (undoped) to 337 degrees with 3 at% Mn doping. However, the insertion loss also increases (5.4 to 9.9 dB respectively) with the increase in dopant concentration so that effective kappa factor (defined as phase shift/insertion loss) does not improve significantly and remains in the range of 33-44 degrees/dB. The observed electrical properties are correlated with the structure and microstructure of the Mn doped BST films.