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The lithographically tunable and small size features of Lamb wave resonators (LWRs) take a bright future for their use in high frequency narrow band filters. Resonant frequency drift due to temperature variation has a large impact on the narrower passband and a temperature coefficient of frequency (TCF) closer to 0 can broaden the stable temperature range of the resonator. This paper proposes a method of etching grooves in the area of the piezoelectric layer not covered by the Interdigital transducer (IDT) electrodes to improve the temperature stability of the Lamb resonator. Through the finite element method and theoretical analysis, the phase velocity, group velocity, and TCF dispersion curve of different modes of the resonator with groove structure were determined. The reason for the change of TCF under different normalized thicknesses of AlN was explained through the conversion of the LWR from a contour mode resonator (CMR) to a Cross-Sectional Lamé Mode Resonator. Simulation and test have shown that etching grooves have the effect of reducing TCF by adjusting the electromechanical coupling coefficient. The test shows that 205 nm-depth grooves can lower the TCF of the S0 mode IDT-Open LWR from −13.3 to −5.1 ppm/°C and S1 mode from −36.8 to −9.0 ppm/°C, respectively. The TCF of S0 and S1 mode LWRs decreased by 61.7% and 75.5%, respectively, after 205 nm groove etching. The groove etching method greatly raises the temperature stability of the LWR, enabling Lamb wave filters to operate stably over a wider temperature range. [ABSTRACT FROM AUTHOR]

High-performance Lamb wave devices have a vast application prospect in modern wireless communication systems. This paper proposes a method of spurious mode suppression by reducing the overlap length of electrodes according to modal shapes. The AlN/Al0.8Sc0.2N composite film is used to achieve a trade-off between electromechanical coupling coefficient (k t 2) and Q factor. The finite-element analysis (FEA) is employed to study the performance of the lowest-order symmetric mode (S0) Lamb wave resonators (LWRs), and the FEA result shows a spurious mode in the impedance response. According to the results of modal shape analysis, the typical LWR, the LWR with the circle-shaped arrangement of electrodes, the LWR with the circle-shaped apodization, and the LWR with the arc-shaped apodization are fabricated to suppress the spurious mode and investigate the performance of the LWRs. The measurement results show that the spurious mode is effectively suppressed over a wide frequency range (1.9–2.2 GHz) by the three designed electrode configurations. The LWR with the circle-shaped apodization working at 2.023 GHz has a Qp factor of 955, a moderate k t 2 of 2.97%, a figure-of-merit (Q × k t 2) of 28.4, and a large value of f × Q × k t 2 (5.773 × 1010). Utilizing modal shapes to design the electrode configuration of LWRs can suppress spurious modes without significant performance deterioration. [ABSTRACT FROM AUTHOR]

Lamb wave resonators (LWRs) exhibiting high-quality factors and clean spectra demonstrate promising applications in RF communication and sensing. This paper discusses the relationship between the spurious mode, the quality factor, and the effective electromechanical coupling factor of resonators. When the resonant frequency of the spurious mode is slightly below the parallel resonant frequency (fp), the quality factor at fp (Qp) decreases dramatically. To enhance Qp and suppress the spurious mode, the LWRs with busbars including only the top electrode (non-overlap busbars) and the LWRs with busbars incorporating both top and bottom electrodes (overlap busbars) are designed and fabricated. The LWR with 12 μm-wide overlap busbars exhibits a notable enhancement in Qp, elevating it from 553.76 to 1488.17 and suppresses the spurious mode simultaneously. This research introduces a promising approach to suppress the spurious mode and enhance the quality factor of Lamb wave resonators, thereby holding great potential for applications in sensors and mobile communication. [ABSTRACT FROM AUTHOR]

This paper presents a modified Lamé-mode resonator (MLMR) with a high, effective electromechanical coupling coefficient (K e f f 2). With trapezoidal grooves introduced by etching the superficial piezoelectric material between interdigitated electrodes (IDTs), the MLMR can remarkably improve K e f f 2 , eliminate spurious modes, and reduce the internal stress of piezoelectric material. The Lamé mode resonator (LMR) with four different electrode configurations is investigated by using finite element method simulation first; then, the impact of the groove's vertical (h) and horizontal (θ) size on K e f f 2 and spurious modes of MLMRs is theoretically analyzed and optimized. It is noted that all the modified structures can improve K e f f 2 except the IDT-Ground structure. This work demonstrates a simulated K e f f 2 as high as 10.47% in the modified IDT-Floating structure, and 10.73% in the modified IDT-IDT structure, which is the highest ever reported in S0 mode AlN LMR. The MLMR shows great prospect for fabricating broad bandwidth filters. [ABSTRACT FROM AUTHOR]

The thin film bulk acoustic resonator (FBAR) has emerged as a promising choice for liquid sensors because of its high frequency and sensitivity. To investigate the potential of FBAR devices working as the liquid sensors, we study the operating law of FBAR in liquid environments and explore the different loading effects of liquid on the shear mode and longitudinal mode. By analyzing the device and liquid interactions, we modify the Mason model of FBAR in the liquid environment. Subsequently, the influence of the piezoelectric film with different tilt angles and liquids on the characteristics of FBAR is discussed. We also prepared Sc0.2Al0.8N film-based FBAR to confirm the influence of different liquid environments on the resonant performances. The results show that the frequency drift of FBAR in the shear mode is related to density and viscosity of liquid, and the frequency drift of FBAR in the longitudinal mode is related to bulk modulus and density of liquid. The resonant frequency of FBAR in the shear mode is more sensitive with glycerol solution than that of FBAR in the longitudinal mode. This work can provide a research basis for the application of FBAR liquid sensors. [ABSTRACT FROM AUTHOR]