High-tone bulk acoustic resonators on sapphire, crystal quartz, fused silica, and silicon substrates

High-tone bulk acoustic resonators (HBARs) have been fabricated on four types of substrates: c-axis sapphire, AT-cut crystal quartz, fused silica, and ⟨100⟩ single crystal silicon. Quality factors of the HBARs on the four substrates have been compared. Temperature effect on the Q and resonant frequency of the four types of HBARs has been investigated. This paper reports that acoustic absorption in fused silica decreases with increased temperature. Acoustic absorptions in the other three substrates increase with increased temperature. Also, temperature coefficients of frequency of HBARs on sapphire, crystal quartz, fused silica, and silicon have been investigated. Finally, acoustic velocities in the four substrates have been extracted by measuring the frequency difference between two successive resonances of the HBAR on the corresponding substrate, and their dependences on temperature have been investigated.