Tunable Bulk Acoustic Resonator Used In Bst Thin Film Materials Research

Thin film bulk acoustic wave resonators (FBAR) show considerable promise as an integrable solution for RF bandpass filters with center frequencies at GHz. It can replace conventional microwave ceramic filters and surface wave filters (SAW) because it provides several prominent advantages such as small size, high Q, high operating frequency, high power handling capability, good temperature stability. Piezoelectric thin films are an essential component of FBAR. Barium strontium titanate (BaxSr1-xTiO3) thin film is extensively studied as one of the most attractive piezoelectric materials for FBAR application for its low dielectric loss, high electromechanical coupling coefficient. Barium strontium titanate thin film using for film bulk acoustic wave resonators required low dielectric loss, high quality factor and good piezoelectric property.In this thesis, the dielectric properties of barium strontium titanate thin films using for film bulk acoustic wave resonators have been optimized, and micro-fabrication of barium strontium titanate thin film film bulk acoustic wave resonators have been studied. The major conclusions are as follow:1. Mn²⁺-doped barium strontium titanate (BST) thin films have been prepared by RF magnetron sputtering. We have produced good quality BST thin film with dielectric loss less than 1% on Pt/Ti-coated silicon substrate, through optimizing sputtering parameters, such as substrate temperature, sputtering power, sputtering atmosphere and post-annealed condition.2. The electrical characteristics of BST thin films have been improved using oxygen-plasma treatment technique. The plasma treatment can reduce leakage current and dielectric loss. Our experiments have indicated that the treatment condition of 200 W, 400Pa and 5 min was optimized for BST thin films. The loss tangent of the optimized films decreased to 0.7% and leakage current density decreased by two orders of magnitude, as compared with that of the as-deposited films.3. The BST thin film bulk acoustic wave resonators were fabricated using micro-fabricated techniques in this paper. We measured the resonance frequency is 1.69GHz by Agilent vector network analyzer.