Performance of ferroelectric based tunable capacitors as a function of electrode geometry

High quality Ba 0.4 Sr 0.6 TiO 3 and SrTiO 3 films were grown by Pulsed Laser Deposition on single crystal LaAlO 3 and MgO substrates. Temperature dependencies of the dielectric constant and loss tangent of the films were studied using planar interdigitated test capacitors with various electrode geometries. The temperature where the maximum or "peak" capacitance occurs (T p and referred to as the "peak temperature") is found to depend on the electrode geometry in these films. As much as 40 K difference in T p was observed between the STO test capacitors with 5 μm and 40 μm gaps between electrodes. Interface built-in electric field and metal-ferroelectric thermal mismatch strain are considered as possible explanation of the effect of electrode geometry on peak temperature of the capacitors.