Hybrid Bulk Acoustic Wave Structure for Temperature Stability in LTE Applications

A novel structure of hybrid bulk acoustic wave (BAW) resonator with low temperature coefficient of frequency (TCF) is presented. Implemented with a pair of quarter-wave reflectors on air-cavity reflector, the hybrid BAW resonator exhibits a TCF of as low as -11.5 ppm/°C and an effective electro-mechanical coupling coefficient (kt
²
) of 5.1% at the frequency of 2.5 GHz. The hybrid BAW resonator also shows excellent Q-factors of 1627 and 1842 at resonance and anti-resonance frequency, respectively. RF duplexer configured with the hybrid BAW resonators is provided as well. The fabricated RF duplexer for long term evolution (LTE) band-7, which should be designed to prevent the co-existence problem with WiFi having extremely narrow fractional band-gap of 0.7%, achieves an attenuation of 36.8 dB and an insertion loss of 2.4 dB.