Improvement of barium strontium titanate solidly mounted resonator quality factor by reduction in electrode surface roughness

Abstract

Two barium strontium titanate solidly mounted resonators with different bottom electrode surface roughnesses were fabricated and tested. The surface roughness of the bottom electrode was reduced by changing the deposition method of the SiO2 layer in the acoustic Bragg reflector in the solidly mounted resonator. The surface roughness was reduced from 2.81 nm RMS to 1.45 nm RMS. This reduction in the surface roughness contributed to a significant increase in the quality factor of the resonator. The quality factor for the device with a smooth platinum bottom electrode was 110 to 87 over a bias range of 5 to 40 V, and for the device with a rough platinum bottom electrode it was 1 to 31 over the same bias range. The effective electromechanical coupling coefficient was 4% at 40 V and 3.4% at 40 V for the smooth and rough platinum bottom electrodes, respectively.