Transverse Spurious Mode Compensation for AlN Lamb Wave Resonators

Abstract

Lamb wave modes with type I dispersion characteristics exhibit strong affinity toward multi transverse modes behavior above resonance frequency (f r) in the AlN Lamb wave resonators (LWRs), especially the high-transduction-efficiency modes: S 0 and S 1 mode. For conventional interdigital transducer (IDT) design, the IDT aperture and IDT gap are the two main factors impacting the transverse mode placements and strengths, according to the wave vector analysis and finite element method (FEM) simulation. Moreover, the convex slowness curve of the Lamb wave modes propagating in AlN platelets allows the waveguiding and weak lateral leakage into busbars by the high-velocity IDT gap region. Apodization, the standard technique to suppress the transverse modes for IDT-excited resonators, suffers from drawbacks, such as additional loss and reduction of the effective coupling coefficient (k 2 eff). Type I Lamb wave modes in AlN show positive slope in the dispersion branch so that a border region of lower Eigen-resonance frequency is required to form piston mode structure for transverse spurious mode suppression and lateral leakage reduction. Based on dispersion calculations and 2.5D FEM simulations, we demonstrate that by designing the low-velocity border region, such as simply changing the IDT layout, the guiding can be improved and a piston mode can be obtained for the type I Lamb wave modes. INDEX TERMS Aluminum nitride, dispersion, lamb wave, S 0 mode, S 1 mode, transverse modes, piston mode structure.

Metrological Performance of Hybrid Measurement Technique Applied for the Lamb Waves Phase Velocity Dispersion Evaluation

“…a multi-mode character and conversion to other modes on the boundaries of non-uniformities [14], [16]- [20]. The dispersion phenomenon leads to presence of two types of interrelated velocities -phase and group, both frequencies dependent and characterized by dispersion curves [21]- [22]. As the different frequency components propagate with different velocities after some distance they are concentrated in different UGW signal parts in the time domain [23].…”

Dissipation Analysis Methods and Q-Enhancement Strategies in Piezoelectric MEMS Laterally Vibrating Resonators: A Review

“…There are some other design strategies, which are based on more abrupt geometric modifications, proposed to reduce anchor loss, such as using beveled, rounded or chamfered corners at the ends of the resonator bodies [ 115 , 116 , 117 ] and introducing etched slots or holes [ 118 , 119 ], but the broad applicability of these methods to different operating frequencies has not been investigated to date. Another strategy to enhance Q involves designing the electrical excitation configuration to suppress spurious modes which could carry the acoustic energy away from the resonator body [ 120 , 121 ]. This Q-enhancement strategy is attractive for LVRs using more anisotropic piezoelectric materials as the resonator body.…”

“…Some design strategies based on local etching were also proposed to reduce anchor loss such as introducing etched slots [ 118 ] or etched holes [ 119 ] as shown in Figure 8 g,h. Apart from the strategies mentioned above, making modification to IDT electrodes were also proposed as an effective means to suppress spurious resonances and thus enhance Q [ 120 , 121 ]. Giovannini et al [ 120 ] demonstrated a 1.2× enhancement of Q in a 889-MHz AlN LVR using apodized electrode configuration as shown in Figure 8 i.…”

“…However, the apodized electrode configuration usually suffers from reduction of k eff 2 . To boost Q without degrading k eff 2 , Zhou et al [ 121 ] recently proposed a spurious resonance suppression technique for AlN LVR using IDT electrodes with hammerhead structure at the end. This idea borrows from the design of a Piston mode structure, which has been widely used to suppress transverse modes in SAW and FBAR devices [ 122 , 123 ].…”

3D Layout of Interdigital Transducers for High Frequency Surface Acoustic Wave Devices

“…[10][11][12][13][14][15] But in order to achieve a high quality (Q) factor, the piezoelectric layer cannot be too thin and the fabrication techniques are elaborate, resulting in the limited frequency and high cost. Lamb wave devices which combine the strengths of SAW devices and BAW devices have been the hot area of research in recent years [16][17][18][19][20][21], but the process flow of fabrication is even more complicated than that of BAW devices. Aiming at lowering the cost, many researchers are committed to the study of high frequency SAW devices.…”