Low-loss tunable capacitors fabricated directly on gold bottom electrodes

Abstract

At microwave frequencies, conductor losses due to the bottom electrode resistance severely limit the performance of metal-insulator-metal capacitors that employ tunable dielectric thin films. Here we demonstrate that a novel tunable dielectric, bismuth zinc niobate (BZN), can be integrated directly with low-resistivity Au bottom electrodes. The favorable crystallization kinetics allowed for a low thermal budget process compatible with Au electrodes. BZN thin films on Au bottom electrodes showed low dielectric loss tangents of ∼0.0005 and high dielectric tunabilities of ∼50%. The Au/BZN interface was abrupt and free of reaction phases. At high frequencies (>1MHz) the total Au/BZN capacitor device loss was reduced compared to capacitors with Pt bottom electrodes. The low device losses of Au/BZN capacitors revealed a device geometry-dependent loss mechanism that contributed significantly to the device loss at high frequencies.