Ruyen Ro

Rayleigh surface acoustic wave modes of interdigital transducer/(100) AlN/(111) diamond

In this research, Rayleigh surface acoustic wave (SAW) modes of interdigital transducer (IDT)/(100) AlN/(111) diamond were theoretically analyzed and exhibited some excellent acoustic properties. Those Rayleigh SAW modes have smaller film thickness ratios (h/λ), higher phase velocities, and larger electromechanical coupling coefficients (K2) than the ones of IDT/(002) AlN/(111) diamond. Especially for mode 1, the phase velocity is 10 474 m/s, the K2 is 2.31%, and the film thickness ratio (h/λ) is 0.3. The research results exhibit that IDT/(100) AlN/(111) diamond has some excellent properties and provides a predictable and theoretical basis for further application in high velocity SAW devices.

Rayleigh surface acoustic wave modes of (100) ZnO films on (111) diamond

(100) zinc oxide (ZnO) films were combined with (111) diamond to be a composite high velocity surface acoustic wave (SAW) substrate. Rayleigh SAW modes of (100) ZnO films on (111) diamond were theoretically analyzed. Those Rayleigh SAW modes have smaller films thickness ratios (h/λ), higher phase velocities, and larger electromechanical coupling coefficients (K2) than the ones of (002) ZnO films on (111) diamond. The research results provide a predictable and theoretical basis for further application on the high velocity SAW devices.

Bulk acoustic wave analysis of crystalline plane oriented ZnO films

Bulk acoustic wave (BAW) properties of piezoelectric layer are very important design parameters for film bulk acoustic wave resonator devices. In this research, BAW properties of all crystalline plane oriented sputtered and epitaxial ZnO films were analyzed theoretically. The (002), (004), and (006) oriented ZnO films provided a pure longitudinal mode. The (100), (110), (200), (210), (300), and (220) oriented ZnO films provided a pure fast shear mode. The (101), (102), (103), (112), (201), (202), (104), (203), (211), (114), (212), (105), (204), (213), (302), (205), (106), and (214) oriented ZnO films provided a quasilongitudinal mode and a quasishear mode. Those bulk acoustic wave properties can be used for further device design and application.

Effects of conducting layers on surface acoustic wave in AlN films on diamond

The interdigital transducer (IDT)/AlN/conducting layer/diamond structures are investigated in this study to design surface acoustic wave (SAW) devices in the super high frequency band. Simulation results using the finite element method show that a thin conducting layer can effectively increase the coupling coefficient and, thus, broaden the bandwidth of SAW devices. For the Sezawa mode, it is illustrated that using a Ti layer with a layer thickness-to-wavelength ratio of 0.02 the maximum coupling coefficient is 2.546% and the associated SAW phase velocity is 10657 m/s at the AlN films’ thickness-to-wavelength ratio of 0.14. This coupling coefficient is 105% higher than that in the IDT/AlN/diamond structure. The research results can be applied to design SAW devices using diamond based structures in the super high frequency band.

Bulk Acoustic Wave Analysis of Crystalline-Plane-Oriented Aluminum Nitride Films

Bulk acoustic wave analysis of all crystalline-plane-oriented AlN films were studied in this research. Different crystalline-plane-oriented AlN films will form different vibration modes and acoustic properties. (002)-, (004)-, and (006)-oriented AlN films provided a pure longitudinal mode. (100)-, (110)-, (200)-, (210)-, and (300)-oriented AlN films provided a pure fast shear mode. (101)-, (102)-, (103)-, (112)-, (201)-, (202)-, (104)-, (203)-, (211)-, (114)-, (212)-, (105)-, (204)-, (213)-, (302)-, (205)-, (106)-, and (214)-oriented AlN films provided a quasi-longitudinal mode and a quasi-shear mode. These bulk acoustic wave properties can be used for further device design and application.

High velocity shear horizontal surface acoustic wave modes of interdigital transducer/(100) AlN/(111) diamond

In this research, shear horizontal (SH) surface acoustic wave (SAW) modes of interdigital transducer (IDT)/(100) AlN/(111) diamond propagated along the y-axis were theoretically analyzed and they exhibited excellent SH SAW properties. This is special for mode 0 where the K2 curve shows a maximum value (1.27%) at h/λ=0.28 and the velocity is 7496 m/s. The research results provide a predictable and theoretical basis for further application on high velocity SH SAW devices.

Elastic activity of the chiral medium

Chiral materials are noncentrosymmetric due to handedness in their microstructures. The elastic field behavior in a chiral medium is readily described herein using the governing equations and constitutive relations for noncentrosymmetric, isotropic micropolar materials. Accordingly, linearly polarized longitudinal waves and left and right circularly polarized transverse waves are eigenstates for elastic waves in the chiral medium. Consequently, by using appropriate field representations along with prescribed boundary conditions, scattering characteristics at chiral interfaces can be readily determined. In this paper, transmission characteristics, i.e., magnitudes and rotation angles, of the chiral slab bounded by achiral media for normally incident transverse waves are the focus of this investigation. Simulation results show the Cotton effect in the magnitude and rotation angle curves, verifying theoretically the elastic activity of a chiral medium.

Theoretical analysis of SAW propagation characteristics in (100) oriented AlN/diamond structure

In this study, the finite element method is employed to calculate SAW characteristics in (100) AlN/diamond based structures with different electrical interfaces; i.e., IDT/ AlN/diamond, AlN/IDT/diamond, IDT/AlN/thin metal film/ diamond, and thin metal film/AlN/IDT/diamond. The effects of Cu and Al electrodes as well as the thickness of electrode on phase velocity, coupling coefficient, and reflectivity of SAWs are illustrated. Propagation characteristics of SAWs in (002) AlN/diamond-based structures are also presented for comparison. Simulation results show that to retain a large reflectivity for the design of RF filters and duplexers, the Cu IDT/(100) AlN/diamond structure possesses the highest phase velocity and largest coupling coefficient at the smallest AlN film thickness-to-wavelength ratio.

Design of two-track surface acoustic wave filters with width-controlled reflectors

In this study, the frequency response of two-track surface acoustic wave (SAW) filters with width-controlled reflectors is investigated. The SAW filter consists of two tracks of input and output interdigital transducers (IDTs) and grating reflectors. With proper tailoring, the frequency response of the two-track SAW filter will only be dominated by the reflection characteristics of the reflectors. To achieve optimum performance, the Chebyshev polynomial is employed to calculate the line width distribution of the metal strips of the reflector. The period of the reflector is then adjusted to retain a symmetric response. Different stepwise weighting schemes are applied to recalculate the line width distribution for the realization of the modulated reflector. A novel transmission matrix method is proposed in this study for calculating the frequency responses of these devices. Simulation results show that a filter with high sidelobe suppression, low insertion loss, good shape factor and significantly small ripples in the passband region can be designed by properly tailoring the two-track SAW filter. The results obtained in this study can be employed to design IF filters applicable to the code division multiple access (CDMA) system.

Propagation Characteristics of Surface Acoustic Waves in AlN/128° Y–X LiNbO3 Structures

In this study, propagation characteristics of surface acoustic waves in a layered piezoelectric structure (AlN/128° Y–X LiNbO3) are investigated. The phase velocity and coupling coefficient of the layered structure with interdigital transducers (IDTs) and/or thin metal films deposited at various interfaces are calculated numerically. The effects of the polarity of 128° Y–X LiNbO3 on SAW characteristics are illustrated. The calculated phase velocity and coupling coefficient of SAWs in the IDT/ZnO/128° Y–X LiNbO3 structure are also demonstrated for comparison. The simulation results obtained in this study can be applied to the design of SAW devices using AlN/128° Y–X LiNbO3 structures.