Flip-chip STW filters in the range of 0.4 to 5 GHz

This paper describes surface transverse wave (STW) two-port resonator filters on rotated Y cut quartz substrate which are assembled using flip-chip technology. Those flip-chip STW filters are assembled in 3.2 mm × 2.5 mm or 2.5 mm × 2.0 mm ceramic packages using a gold-gold thermo-sonic face-down-bonding and a gold-tin solder sealing. Frequency characteristics of flip-chip STW filters in the range of 0.4 to 3.5 GHz for commercial telecommunications are shown. Also a demonstrated 5 GHz STW filter for a high-frequency oscillator (OSC) application is presented, which is realized using a conventional i-line stepper and a lift-off process. A narrowband flip-chip STW filter can be suitable for low phase-noise OSC applications. Several OSCs in GHz rage are designed using flip-chip STW filters and those characteristics are presented. In addition, trimming methods using CF₄ chemistry for flip-chip STW filters are described. It is possible to trim the center frequency of flip-chip STW filters while the center frequency is monitoring.