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The lowest order symmetric Lamb wave propagating in thin aluminum nitride (AIN) film membranes is studied to observe and analyze the resonant structures, which have a great compatibility with the thin film integrated circuits. The application of the specially designed micromachined thin film plate acoustic resonators (FPAR) is shown to be extremely beneficial and efficient, especially when used for structures having low costs and high Qs,

A theoretical approach for the analysis of Lamb waves in grating configurations based on the Floquet-Bloch theorem is developed. The calculations indicate the existence of a frequency stop band exhibiting a complex behavior.

Surface transverse waves (STW) that represent a new generation of the surface acoustic wave (SAW) family offer advantageous properties without the demand for new materials or improved design and technology. The basic achievements of STW in historical and factual order are illustrated.

Highly c-axis oriented aluminum nitride(AIN) thin piezoelectric films are grown on polycrystalline diamond substrates by pulsed direct current(DC) magnetron reactive sputter-deposition. The biggest advantage of the AIN diamond-layered substrate is its very high surface acoustic wave(SAW) velocity.

This study lays a foundation for the design of the SH0 plate acoustic wave (PAW) resonators based on LiNbO3 plate, and are applicable to the ultra-wideband filters and next-generation tunable filters. The coupling coefficient ($k^{2}$) of SH0 mode is optimized to as high as 55% and wideband spurious are well controlled by analyzing the propagation characteristics of plate modes in LiNbO3. The SH0 mode is demonstrated to be slowly dispersive and features the superiority of interdigital transducer (IDT)—defining frequency over most other plate modes. On the device level, the transducer types and electrode materials are investigated and compared. In addition, for edge-reflected SH0 resonators, stopband dispersion analysis is provided and the longitudinal ripples are suppressed. For edge-reflected SH0 resonators, a novel perfect edge reflector is proposed with elimination of longitudinal spurious ripples. [ABSTRACT FROM AUTHOR]

Electro-acoustic sensors proving an adequate operation in liquid media are appropriate candidates for biosensing or liquid monitoring applications. In this context, electro-acoustic devices based on Lamb waves have been widely used for such purpose during the last years. More particularly, S 0 mode Lamb wave resonators (S 0 -LWRs) have shown promising in-liquid performance. However, a theoretical background describing their in-liquid sensing mechanisms has only been published recently. In this work we present the experimental verification of the previously developed theoretical background based on a finite element model. We discuss about similarities and discrepancies between model and experiments, stating a final model correctly describing the in-liquid sensitivity features of S 0 -LWRs. These devices show appreciable different sensitivities of the resonant frequency to liquid viscosity and density, being more sensitive to the latter. Additionally, when they are not electrically isolated, the influence of the liquid electrical properties is superimposed to the mechanical ones and can be correctly extracted. [ABSTRACT FROM AUTHOR]

In a narrowband 2-port resonator on 37?°cut quartz with Al electrodes (hAlu = 100 nm) exploiting surface transverse waves (STW), we have observed parasitic ripples which have been attributed to transverse modes unusually situated on the left side of the main resonance. To suppress these modes, we have used metallization coefficient weighting across the aperture, with more metal in the middle and reduced metallization close to the busbars. The parasitic modes indeed disappeared, but at significantly higher frequency, we have found an additional strong response which does not exist in a resonator with uniform electrode metallization. 3-D simulations showed that the structure has another very different mode, with the wave propagating mainly along the edge of the busbars, but excited with the interdigital electrode system. [ABSTRACT FROM AUTHOR]

Sensors based on thin film electroacoustic (TEA) devices have emerged as a promising alternative to quartz crystal microbalance and surface acoustic wave devices, in view of sensibility, miniaturization and easy integration. TEA devices include quasi-shear film bulk acoustic resonators (QS-FBAR) and S 0 mode Lamb wave resonators (S 0 -LWR) based on AlN films. Despite the work done on the application of TEA devices as in-liquid biological and chemical sensors, a theoretical framework for S 0 -LWRs properly describing their sensing mechanisms is still needed. Here we validate a finite element analysis model on QS-FBARs and study the sensing mechanisms of S 0 -LWRs in liquid media. We show that S 0 -LWRs can sense changes in the dielectric permittivity of the liquid and demonstrate different sensitivities to viscosity and density. A complementary assessment of the S 0 -LWRs losses, dependent in a non-specific manner on the square root of the density viscosity product, provides the ability to discriminate density from viscosity changes on the entire device surface. Finally, with an S 0 -LWR optimization study we show that resolution improves with the decrease of the membrane thickness; however, a trade-off between sensitivity, quality factor and membrane fragility has to be considered. [ABSTRACT FROM AUTHOR]

The characteristics of one-port aluminum nitride (AlN) Lamb wave resonators utilizing the lowest-order symmetric mode with electrically open, grounded, and floating bottom electrode configurations are theoretically and experimentally investigated in this paper. Finite element analysis is performed to take an insight into the static capacitance characteristics of the AlN Lamb wave resonators with various bottom surface conditions. Without sacrificing the transduction efficiency, the floating bottom electrode is capable of reducing the static capacitance in the AlN thin plate and then promotes an efficient improvement in the effective coupling coefficient (k2eff). In addition, in comparison with the grounded bottom electrode, the employment of the floating bottom electrode offers simple fabrication processes for the micromachined Lamb wave resonators. Experimentally, the AlN Lamb wave resonators without the bottom electrode exhibit an average loaded quality factor (Q) as high as 2676 at the series resonance frequency, but a low average k2eff of 0.19%. On the contrary, the Lamb wave resonators with the electrically floating bottom electrode show the largest average k2eff up to 1.13% among the three topologies but a low average loaded Q of 800 at the series resonance frequency. In contrast to the floating bottom electrode, the Lamb wave resonators with the electrically grounded bottom electrode show a smaller average k2eff of 0.78% and a similar average loaded Q of 758 at the series resonance frequency. [ABSTRACT FROM AUTHOR]

This work makes an overview of the progress made during the last decade with regard to a novel class of piezoelectric microwave devices employing acoustic Lamb waves in micromachined thin film membranes. This class of devices is referred to as either thin film Lamb wave resonators or piezoelectric contour-mode resonators both employing thin film aluminum nitride membranes. These devices are of interest for applications in both frequency control and sensing. High quality factor Lamb wave resonators exhibiting low noise, low loss and thermally stable performance are demonstrated and their application in high resolution gravimetric and pressure sensors further discussed. A specific emphasis is put on the ability of these devices to operate in contact with liquids. Future research directions are further outlined. [ABSTRACT FROM AUTHOR]

A novel concept for the development of thin-film micro-acoustic resonators based on the coupling between different plate acoustic modes is demonstrated. The basic principles for the design and fabrication of intermode-coupled plate acoustic wave resonators on c-textured thin aluminum nitride films are presented. More specifically, the lowest order symmetric S0 Lamb wave is excited and then coupled to the fundamental thickness shear bulk resonance by means of a metal strip grating with specific periodicity. The experimental results demonstrate that the grating-assisted intermode coupling can be employed in high-frequency resonators inheriting the low dispersive nature of the S0 mode in combination with the energy localization in the plate bulk typical for the fundamental thickness shear resonance. [ABSTRACT FROM AUTHOR]

The mass sensitivity of thin aluminum nitride (AlN) film S0 Lamb wave resonators is theoretically and experimentally studied. Theoretical predictions based on modal and finite elements method analysis are experimentally verified. Here, two-port 888 MHz synchronous FPARs are micromachined and subsequently coated with hexamethyl-disiloxane(HMDSO)-plasma-polymerized thin films of various thicknesses. Systematic data on frequency shift and insertion loss versus film thickness are presented. FPARs demonstrate high mass-loading sensitivity as well as good tolerance towards the HMDSO viscous losses. Initial measurements in gas phase environment are further presented. [ABSTRACT FROM AUTHOR]

In this work the applicability of the coupling-of-modes (COM) approach to the analysis of thin AlN film plate acoustic resonators (FPAR), utilizing the S0 Lamb wave, is discussed. Analysis based on the Floquet-Bloch theorem as well as COM parameter extraction from a micromachined FPAR test structure are simultaneously used to verify the applicability of the COM approach. Finite element model simulation is used to further study the contribution of the higher order mass loading effects over the Lamb wave propagation under a periodical grating. A possibility to achieve zero sensitivity of the FPAR resonance with respect to the grating strip thickness is identified and physically interpreted for the first time. [ABSTRACT FROM AUTHOR]

Improved performance thin-film plate acoustic wave resonators (FPAR) using the lowest order symmetric Lamb wave (So) propagating in highly textured A1N membranes have been previously demonstrated for the first time. In this work, an experimental study of the resonators' performance vs. a variety of design parameters is performed. Devices operating in the vicinity of the stopband center exhibiting a Q-value of up to 3000 at a frequency of around 875 MHz are demonstrated. Further, low-loss high-Q micromachined 2-port longitudinally coupled thin-film resonators using the SO mode are demonstrated for the first time. For the analysis of the proposed structures, the coupling-of-modes (COM) approach is successfully employed. Initially, the COM model is used for the extraction of physical parameters from one-port FPAR measurements. Subsequently, using the COM model, a satisfactory agreement with the proposed experimental frequency characteristics of SO 2-port FPARs has been achieved, and possibilities for further improvements in the performance discussed. Finally, the frequency spectrum of the one-port devices has been studied and the excited plate modes at different frequencies identified and presented with their Q-factors and temperature coefficients of frequency (TCF). [ABSTRACT FROM AUTHOR]

Presents a study that allowed one to conduct coupling-of-modes (COM) surface transverse wave (STW) loss analysis and estimate the resonator Q from material and layout parameters. COM formalism for analyzing STW; Analysis of extended STW floquet; Design simulation and discussion.

2D composite grating building blocks with hexagonal symmetry are proposed and analyzed as efficient reflectors and transducers in the design of low loss surface acoustic wave (SAW) resonators. Eigen-frequency and frequency response finite element analyses are used to study the propagation and excitation characteristics of SAWs in the 2D composite structures. The proposed structures have the advantage of being compatible with the planar SAW technology, while introducing design principles reminiscent to the semiconductor devices. More specifically, the frequency bandgap characteristics of the various resonator building blocks can be adjusted so that losses related to the SAW diffraction, impedance mismatch, and parasitic SAW radiation from the electrical contacts can be suppressed. Three distinct types SAW resonant topologies employing 2D gratings are deduced from the analytical results. [ABSTRACT FROM AUTHOR]

A concept for the development of thin film micro-acoustic resonators is demonstrated. The basic principles for the design and fabrication of zero-group-velocity Lamb acoustic wave resonators on c-textured thin aluminum nitride films are presented. The experimental results demonstrate that the zero-group-velocity waves can be employed in high frequency resonators with small form factors. [ABSTRACT FROM AUTHOR]

The Green’s function formalism has been applied to the analysis of the fundamental symmetric Lamb mode excited by means of longitudinal wave (LW) transducers. The Lamb wave Green’s function has been related to the properties of the effective permittivity defined as a function of the wave slowness and the relative plate thickness. An electrostatic analysis that neglects the piezoelectric coupling is employed to relate the charge density to the applied voltage. This analysis is subsequently used to calculate the radiation conductance of a LW transducer. The results obtained are consistent with the equivalent circuit approach and define the device coupling as a function of the plate thickness and the intrinsic Lamb wave coupling. [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]

This letter discusses the design of thickness shear mode thin-film bulk acoustic resonator (FBAR) sensor array for in liquid operation with respect to minimizing the observed Q-degradation and crosstalk. [ABSTRACT FROM PUBLISHER]

Abstract: A new design of a solidly mounted resonator (SMR) that utilizes an all-metal Bragg reflector eliminating thus the need for a bottom electrode is proposed. In this configuration, the role of the bottom electrode is taken by the Bragg reflector rendering the resonator “combined electrode-Bragg reflector SMR”. The main advantages of the proposed design are the substantially reduced electrode resistance (and hence higher Q), the utilization of the full piezoelectric coupling at high frequencies as well as expected improvement in power handling capabilities due to lower dissipation and improved heat conductivity. Resonators with the classical and the new design have been fabricated and evaluated. The measurements indicate that indeed the resonators with the new design demonstrate improved performance. [Copyright &y& Elsevier]

Abstract: Piezoelectric c-textured Al(1−x)Sc x N thin films, where the Sc relative concentration, x, varies in the range 0–0.15 have been studied in view of radio frequency (RF) electro-acoustic applications. Thin film bulk acoustic wave resonators (FBARs) employing these films were fabricated and characterized as a function of the Sc concentration for the first time. The measured electromechanical coupling is found to increase by as much as 100% in the above concentration range. The results from this work underline the potential of the c-textured Al(1−x)Sc x N based FBARs for wide band RF applications. [Copyright &y& Elsevier]