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In this Letter, we explore a non-degenerate phase independent parametric quality factor (Q)-enhancement technique for aluminum nitride (AlN) Lamb wave resonators. Unlike other active Q-enhancement techniques which require precise phase control of the electronic feedback loop, this technique is implemented by parametrically pumping AlN material stiffness to realize a negative resistance seen at the signal path. The negative resistance is dependent on the nonlinear material modulation and multi-resonance coupling in the device. A nonlinear circuit model is developed to simulate the parametric coupling of each resonance and extract the nonlinearity of AlN from experimental data. With proper pump frequency and pump power, the device quality factor is boosted in both simulation and experiment. The demonstrated Q-enhancement method is simple to implement and can be applied to other types of resonators that have nonlinear behavior and support multi-resonance operation. [ABSTRACT FROM AUTHOR]

Aluminum scandium nitride (Al1−xScxN/AlScN) (x = 0.32) Lamb wave resonators (LWR) have been fabricated and tested to demonstrate electromechanical coupling coefficients (kt2) in excess of 10%. The resonators exhibited an average kt2 and unloaded quality factor (Qu) of 10.28% and 711, respectively, when calculated from the measured data. Applying the Butterworth Van-Dyke (BVD) model to the measured data enabled the extraction of the resonator's lumped element parameters to calculate the motional quality factor (Qm), which neglects the contributions of the electrical traces. For the best measured resonator response, results from the BVD model showed a Qm of 1184 and a resulting figure-of-merit (FOM = K2 · Qm) of 100. Comparing the response of similar AlScN and AlN resonators shows that the AlScN LWR has a significantly lower motional resistance (Rm), suggesting that AlScN has a strong potential for use in piezoelectric microelectromechanical oscillators. [ABSTRACT FROM AUTHOR]

A concept for the development of spectrum-clean S1 Lamb wave resonator (LWR) utilizing an aluminum nitride (AlN) plate with damped edge reflectors is demonstrated. Numerical analysis is performed on the dispersive characteristics of the Lamb modes propagating in AlN plates, and the design parameters to enable zero group velocity (vg) for the S1 mode are identified. The simulation results based on finite element analysis verify that the use of the damped edge reflectors, instead of the conventional edge reflectors, can efficiently de-couple most of the Lamb waves such as the S0 mode by mode conversion upon edges, but not the S1 mode characterizing zero vg. Specifically, the measured frequency response of a 1.38-GHz AlN S1 LWR with damped edge reflectors yields a clean spectrum up to 6 GHz and excellent resonance passband performance. [ABSTRACT FROM AUTHOR]

The generation of ultrasonic surface waves with a photoacoustic-laser-source has become useful for the noncontact nondestructive testing and evaluation (NDT&E) of materials and structures. In this work, a hybrid ultrasound based NDT&E method is proposed based on the photoacoustic-laser-source as a noncontact Lamb wave generator by incorporating a line-arrayed patterned candle soot nanoparticle-polydimethylsiloxane (CSNPs-PDMS) patch as the signal amplifier and with a narrow bandwidth. The CSNP-PDMS composite has been investigated as the functional patch for its laser energy absorption efficiency, fast thermal diffusion, and large thermoelastic expansion capabilities. The signal amplitude (in mW) from the CSNP-PDMS patch exhibits 2.3 times higher amplitude than the no patch condition and a narrower bandwidth than other conditions. Furthermore, improvement in the sensitivity is also achieved through the selection of the aluminum nitride sensing system. The overall combination of the Lamb wave generation and receiver-sensing system in this study is found to be very promising for a broad range of noncontact NDT&E applications. [ABSTRACT FROM AUTHOR]

This letter reports a spurious mode free GHz aluminum nitride (AlN) lamb wave resonator (LWR) towards high figure of merit (FOM). One dimensional gourd-shape phononic crystal (PnC) tether with large phononic bandgaps is employed to reduce the acoustic energy dissipation into the substrate. The periodic PnC tethers are based on a 1 μm-thick AlN layer with 0.26 μm-thick Mo layer on top. A clean spectrum over a wide frequency range is obtained from the measurement, which indicates a wide-band suppression of spurious modes. Experimental results demonstrate that the fabricated AlN LWR has an insertion loss of 5.2 dB and a loaded quality factor (Q) of 1893 at 1.02 GHz measured in air. An impressive ratio of the resistance at parallel resonance (Rp) to the resistance at series resonance (Rs) of 49.8 dB is obtained, which is an indication of high FOM for LWR. The high Rp to Rs ratio is one of the most important parameters to design a radio frequency filter with steep roll-off. [ABSTRACT FROM AUTHOR]

In this letter, we demonstrate a technique to eliminate the spurious modes in aluminum nitride Lamb wave resonators (LWRs). The transverse acoustic wave characteristics are examined, and a resonance modulation theory on the regulation of mechanical boundary conditions is deducted. As examples of embodiments, vertical and lateral protrusion structures are proposed for the suppression. Finite element analysis verifies that the employment of these structures effectively restrains the transverse modes, and the measured electrical performance of the LWR with protrusions demonstrates an 11 dB reduction in the spurious response. [ABSTRACT FROM AUTHOR]

This letter reports on the design and experimental demonstration of a microscale fractal-like phononic bandgap (PBG) structure in aluminum nitride (AlN). The micro-fabricated fractal phononic crystals (PnCs) exhibit two frequency stop bands for symmetric lamb waves in the Γ-Χ direction centered about 900 MHz (bandwidth of 11.1%) and 1.10 GHz (bandwidth of 9.1%) with maximum acoustic rejection of 40 dB. Differently from the conventional phononic bandgap designs, the unit cell consists of a center air square scatterer with four side air square scatterers repeating at its corners. The presence of these side squares essentially shortens the scattering distance between the unit cells and translates into the suppression of higher frequency vibrational modes. In other words, this design is capable of extending the frequency of operation of the PBGs for a given unit cell and minimum feature size. For the purpose of the demonstration, AlN lamb wave transducers were utilized to launch symmetric lamb waves into the PBG structure. The evidence of direct in-plane integration between the transducers and the PnC structure operating in the ultra high frequency range lays the foundation for the development of ultrasonic devices based on PBGs. [ABSTRACT FROM AUTHOR]

A Lamb wave resonator utilizing an aluminum nitride (AlN) plate with biconvex edges to enhance the quality factor (Q) is demonstrated. The simulation results based on finite element analysis verify that the use of the biconvex edges, instead of the conventional flat edges, can efficiently confine mechanical energy in the AlN Lamb wave resonator. Specifically, the measured frequency response of a 491.8-MHz AlN Lamb wave resonator with biconvex edges yields a Q of 3280 which represents a 2.6× enhancement in Q over a 517.9-MHz Lamb wave resonator on the same AlN plate but with the suspended flat edges. [ABSTRACT FROM AUTHOR]

Cubic silicon carbide (3C-SiC) layer can provide advantages of high frequency and high quality factor for Lamb wave devices due to the superior properties of high acoustic velocity and low acoustic loss. In this study, Lamb wave propagation characteristics in composite membranes consisting of a c-axis oriented aluminum nitride (AlN) film and an epitaxial 3C-SiC (100) layer are investigated by theoretical calculation. The lowest symmetric mode Lamb wave propagating along the [011] direction exhibits a phase velocity higher than 10 000 m/s and an electromechanical coupling coefficient above 2% in the AlN/3C-SiC multilayered membranes. [ABSTRACT FROM AUTHOR]

In this letter, temperature compensation for aluminum nitride (AlN) Lamb wave resonators operating at high temperature is presented. By adding a compensating layer of silicon dioxide (SiO2), the turnover temperature can be designed for high temperature operation by varying the normalized AlN film thickness (hAlN/λ) and the normalized SiO2 film thickness (hSiO2/λ). With different designs of hAlN/λ and hSiO2/λ, the Lamb wave resonators were well temperature-compensated at 214 °C, 430 °C, and 542 °C, respectively. The experimental results demonstrate that the thermally compensated AlN Lamb wave resonators are promising for frequency control and sensing applications at high temperature. [ABSTRACT FROM AUTHOR]

The basic principles and technology for the development of lateral-field-excited Lamb acoustic wave resonators on sputter-deposited c-oriented thin aluminum nitride films are presented. The experimental results demonstrate that Lamb waves can be successfully used as an alternative to high-velocity surface acoustic waves. [ABSTRACT FROM AUTHOR]