Direct Inkjet Printing of Composite Thin Barium Strontium Titanate Films

Composite Ba_0.6Sr_0.4TiO₃/MgO thin films with 60% tuning and tan δ of 0.007 at 2 GHz were deposited using metal organic decomposition inks by spin coating on single crystal MgO substrates. The films with approximately 1 mol% MgO in Ba_0.6Sr _0.4TiO₃ had a better tuning/loss ratio than either the 0 or the 10 mol% MgO substituted films. Crystalline Ba_0.5Sr _0.5TiO₃ films were produced on both MgO and alumina substrates by inkjet printing of metalorganic precursors with subsequent thermal decomposition followed by annealing at 900°C. Barium strontium titanate lines as narrow as 100 μm were printed on the alumina substrates. The inkjet-printed films were predominantly (100) oriented on MgO and (110) oriented on alumina. The crystalline quality of the inkjet-printed films was improved by annealing at 1100°C for 3 h in oxygen. Both the printed and the spin-coated films had smooth surfaces (300 Å root-mean-square roughness) as required for subsequent deposition of high-resolution metal electrodes. An inkjet-printed Ba_0.5Sr_0.5TiO₃ film (3500 Å) on MgO annealed at 1100°C had 20% tunability of the dielectric constant (ε) at 9.1 V/μm direct current bias and tan δ < 0.002 at 1 MHz.