Bulk Acoustic Wave Resonator Devices Research Articles

Nitrogen [N]-incorporated ZnO piezoelectric thin films and their application for ultra-small film bulk acoustic wave resonator device fabrication

Nitrogen [N]-incorporated ZnO films with columnar grains of a preferred c-axis orientation were deposited on p-Si (100) wafers, using an RF magnetron sputter deposition technique. For the N incorporation into the ZnO films, an N2O gas was used as a doping source and also various process conditions such as N2O gas fraction and RF power were applied. Besides, some of the ZnO films were treated with the post annealing process. And then, the micro-structural characteristics of the N-incorporated ZnO films were investigated by a scanning electron microscope, an X-ray diffractometer, and an atomic force microscope techniques. Finally, employing the N-incorporated ZnO films, the solidly mounted resonator-type film bulk acoustic wave resonator devices were fabricated and their resonance characteristics were extracted. As a result, an excellent return loss (S11) of− 63 dB was observed at∼ 0.6 GHz, better than ever reported.

Structural and mechanical characteristics of (1 0 3) AlN thin films prepared by radio frequency magnetron sputtering

The (1 0 3)-oriented aluminum nitride (AlN) thin film is an attractive piezoelectric material for the applications in surface acoustic wave and film bulk acoustic wave resonator devices. In this work, we repot structural and mechanical characteristics of (1 0 3) AlN thin films deposited onto (1 0 0) Si substrates with radio frequency magnetron sputtering at different sputtering powers at 150, 250, and 350 W. Comparisons were made on their crystalline structures with X-ray diffraction, surface morphologies with atomic force microscopy, mechanical properties with nanoindentation, and tribological responses with nanoscratch. Results indicate that for the sputtering power of 350 W, a high-quality (1 0 3) AlN thin film, whose hardness is 18.91 ± 1.03 GPa and Young's modulus is 242.26 ± 8.92 GPa, was obtained with the most compact surface condition.

Bulk acoustic wave analysis of crystalline plane oriented ZnO films

Bulk acoustic wave (BAW) properties of piezoelectric layer are very important design parameters for film bulk acoustic wave resonator devices. In this research, BAW properties of all crystalline plane oriented sputtered and epitaxial ZnO films were analyzed theoretically. The (002), (004), and (006) oriented ZnO films provided a pure longitudinal mode. The (100), (110), (200), (210), (300), and (220) oriented ZnO films provided a pure fast shear mode. The (101), (102), (103), (112), (201), (202), (104), (203), (211), (114), (212), (105), (204), (213), (302), (205), (106), and (214) oriented ZnO films provided a quasilongitudinal mode and a quasishear mode. Those bulk acoustic wave properties can be used for further device design and application.

Improved Resonance Characteristics by Thermal Annealing of W/SiO2 Multi-Layers in Film Bulk Acoustic Wave Resonator Devices

In this paper, we, for the first time, present the effects of the thermal annealing of the W/SiO2 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 multi-layer Bragg reflectors.

Influence of electrode configurations on the quality factor and piezoelectric coupling constant of solidly mounted bulk acoustic wave resonators

This article presents an electrode effect on the quality factor and effective coupling coefficient empirically and theoretically. The possible quality factor detractors in film bulk acoustic wave resonator devices are the acoustic wave attenuation in the metal and piezoelectric films, the wave scattering loss due to the surface roughness, and the electrode electrical loss. Due to the small acoustic wave attenuation of the Mo electrode, the composite Mo–AlN–Mo resonator with the thick electrode provides higher Q values than the resonator with the good quality AlN film and the thin Mo electrode. In such Mo electroded resonators, the effective coupling coefficient is kept relatively high. It is found that the Q value of solidly mounted resonators (SMRs) is not determined by only the piezoelectric film quality, but by a weighted average of the electrode and piezoelectric film quality. Of Q value detractors, the scattering loss originating from surface roughness is thought to be very important factor in SMR quality value.