Study Of Barium Strontium Titanate Varactor At High Frequency

Abstract

Ferroelectric materials and applications have attracted great research interests in the past few decades.Ba0.5Sr0.5TiO3 (BST) is chosen to fabricate a varactor in a parallel plate structure. Three parallel plate varactors with different electrodes are fabricated by Pulse Laser Deposition (PLD) and ion-sputtering.Dielectric constant and loss versus frequency under different applied bias are characterized. The dielectric dispersion as a function of frequency is attributed to the increase of the effective separation length between top and bottom electrodes which is arising from the voltage drop across the bottom electrode in a varactor. The main source of the varactor loss is due to the resistance of bottom electrode. Varactors using Pt or Au as a bottom electrode have relatively small loss factor and frequency independent dielectric constant, and hence they are suitable to be used in a varactor for high frequency microwave application.