This paper compares three different piston mode designs for temperature-compensated surface acoustic wave (TC-SAW) resonators using SiO2/LiNbO3 structure. It was shown that in rough approximation, phase shift given by extra elements for the piston mode operation is determined by their total mass. Thus, the hammer head design without additional metal layers does not work properly when the SiO2 layer is thick due to insufficient mass. On the other hand, piston mode designs using metal dots or stripes is effective to suppress the transverse mode resonances even when the SiO2 layer is thick. Although larger metal thickness is preferable for the wideband operation, it also makes the split of main resonance. Thus, the optimal metal thickness can be found from this trade off, and then the optimal metal width can be found to achieve good transverse mode suppression.
Thin-film piezoelectric-on-silicon (TPoS) microelectromechanical (MEMS) resonators are required to have high Q-factor to offer satisfactory results in their application areas, such as oscillator, filter, and sensors. This paper proposed a phononic crystal (PnC)-reflector composite structure to improve the Q factor of TPoS resonators. A one-dimensional phononic crystal is designed and deployed on the tether aiming to suppress the acoustic leakage loss as the acoustic wave with frequency in the range of the PnC is not able to propagate through it, and a reflector is fixed on the anchoring boundaries to reflect the acoustic wave that lefts from the effect of the PnC. Several 10 MHz TPoS resonators are fabricated and tested from which the Q-factor of the proposed 10 MHz TPoS resonator which has PnC-reflector composite structure on the tether and anchoring boundaries achieved offers a loaded Q-factor of 4682 which is about a threefold improvement compared to that of the conventional resonator which is about 1570.
This paper discusses influence of displacement and patterning of phase shifters for piston mode operation of the temperature compensated (TC) surface acoustic wave (SAW) resonator on SiO2/LiNbO3 structure. As the phase shifters, Cu metals placed on the top surface of SiO2 are considered. First, the conventional Cu stripes are chosen, and their displacement are considered from IDT aperture edges. It is shown that achievable transverse mode suppression is almost identical when the stripe shape is adjusted for each case. Next, Cu dots are considered as patterned phase shifters. It is shown comparable transverse mode suppression is possible also for this case. However, relatively strong SAW lateral leakage occurs when they are placed above IDT fingers. These results indicate that location and pattern can be added as design parameters for the phase shifters on SiO2. It is favorable for further enhancement of total device performances.
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