VHF fundamental AT-cut resonators using flip-chip bonding

We miniaturized a very high frequency (VHF) fundamental AT-cut resonator by flip-chip bonding that joins a turned crystal chip to a ceramic package with gold bumps. The dimensions of the new resonator are 3.8 mm long ×3.8 mm wide ×0.9 mm high. The capacity of the resonator is a quarter of that of a conventional resonator that uses wire bonding. Moreover, we observe high stability in the 155 MHz resonator with a vibrating area of 10 μm thickness. The new resonator is unaffected by stress and contamination due to bonding. Therefore, in the frequency vs. temperature characteristics, hysteresis errors are less than or equal to 1 ppm in the temperature cycle ranging from -40°C to +85°C. In the accelerated aging characteristics at an ambient temperature of +85°C, the frequency shift is less than 1 ppm up to 6,000 hours