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In this paper, we, for the first time, present the effects of the thermal annealing of the W/SiO 2 multi-layer Bragg reflectors on the resonance characteristics of the ZnO-based film bulk acoustic wave resonator (FBAR) devices. In order to improve the resonance characteristics of the FBAR devices, we employed a thermal annealing process after the Bragg reflectors were formed on a silicon substrate using a radio frequency (RF) magnetron sputtering technique. As a result, the resonance characteristics of the FBAR devices were observed to strongly depend on the annealing conditions applied to the Bragg reflectors. The FBAR devices with the Bragg reflectors annealed at 400 C/30 min showed excellent resonance characteristics as compared to those with the non-annealed (as-deposited) Bragg reflectors. The newly proposed simple thermal annealing process will be very useful to more effectively improve the resonance characteristics of the future FBAR devices with multilayer Bragg reflectors.

In this article, we present the thermal annealing effects of the W/SiO2 multilayer reflectors in ZnO-based film bulk acoustic resonator (FBAR) devices with cobalt (Co) electrodes in comparison with those with aluminum (Al) electrodes. Various thermal annealing conditions have been implemented on the W/SiO2 multilayer reflectors formed on p-type (100) silicon substrates. The resonance characteristics could be significantly improved due to the thermal annealing and were observed to depend strongly on the annealing conditions applied to the reflectors. Particularly, the FBAR devices with the W/SiO2 multilayer reflectors annealed at 400 °C/30 min have shown superior resonance characteristics in terms of return loss and quality factor. In addition, the use of Co electrodes has resulted in the further improvement of the resonance characteristics as compared with the Al electrodes. As a result, the combined use of both the thermal annealing and Co electrodes seems very useful to more effectively improve the resonance characteristics of the FBAR devices with the W/SiO2 multilayer reflectors.

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