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

High quality Ba0.4Sr0.6TiO3 and SrTiO3 films were grown by Pulsed Laser Dep osition on single crystal LaAlO3 and MgO substrates. Temperature dependenci es of the dielectric constant and loss tangent of the films were studied us ing planar interdigitated test capacitors with various electrode geometries . The temperature where the maximum or "peak" capacitance occurs (T-p and r eferred 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 bet ween the STO test capacitors with 5 mum and 40 mum gaps between electrodes. Interface built-in electric field and metal-ferroelectric thermal mismatch strain are considered as possible explanation of the effect of electrode g eometry on peak temperature of the capacitors.