Surface Acoustic Wave Propagation Properties Research Articles

Giant Reflection Coefficient on Sc0.26Al0.74N Polycrystalline Diamond Surface Acoustic Wave Resonators

Since the commercialization of surface acoustic wave (SAW) devices, the technology is steadily increasing the device performances without compromising their power handling, size and price. Herein, one‐port SAW resonators are fabricated on scandium aluminum nitride (Sc0.26Al0.74N)/polycrystalline diamond heterostructures. SAW propagation properties are studied using three different piezoelectric thin‐film thicknesses within the heterostructure. The Rayleigh and Sezawa resonance frequencies are above 1.5 and 2.5 GHz, respectively, achieving Sezawa mode reflection coefficients below −50 dB. The polycrystalline diamond substrate is synthesized by microwave plasma chemical vapor deposition (MPCVD) on top of a 500 μm‐thick Si (001) substrate. The Sc0.26Al0.74N thin films are synthesized by reactive sputtering at nominally room temperature. The thin film's composition is analyzed by Rutherford backscattering spectrometry (RBS). The full width at half maximum (FWHM) of the X‐ray diffraction (XRD) ω scans below 3° indicates that the synthesized Sc0.26Al0.74N thin films are highly c‐axis oriented. The electromechanical coupling coefficient, quality factor, and dielectric loss parameters are computed by curve fitting the device electrical measurements to the simulation results of a modified Butterworth Van Dyke (mBVD) model implemented in the advance design system (ADS) tool.

SAW propagation characteristics of TeO3/3C-SiC/LiNbO3 layered structure

Surface acoustic wave (SAW) devices based on Lithium Niobate (LiNbO3) single crystal are advantageous because of its high SAW phase velocity, electromechanical coupling coefficient and cost effectiveness. In the present work a new multi-layered TeO3/3C-SiC/128° Y-X LiNbO3 SAW device has been proposed. SAW propagation properties such as phase velocity, coupling coefficient and temperature coefficient of delay (TCD) of the TeO3/SiC/128° Y-X LiNbO3 multi layered structure is examined using theoretical calculations. It is found that the integration of 0.09λ thick 3C-SiC over layer on 128° Y-X LiNbO3 increases its electromechanical coupling coefficient from 5.3% to 9.77% and SAW velocity from 3800 ms−1 to 4394 ms−1. The SiC/128° Y-X LiNbO3 bilayer SAW structure exhibits a high positive TCD value. A temperature stable layered SAW device could be obtained with introduction of 0.007λ TeO3 over layer on SiC/128° Y-X LiNbO3 bilayer structure without sacrificing the efficiency of the device. The proposed TeO3/3C-SiC/128° Y-X LiNbO3 multi-layered SAW structure is found to be cost effective, efficient, temperature stable and suitable for high frequency application in harsh environment.

Evaluation of piezoelectric Ta2O5 thin films deposited on SrTiO3 substrates

Tantalum pentoxide (Ta2O5) piezoelectric thin films were deposited on (100) and (110) planes of strontium titanate (SrTiO3) substrates using an RF magnetron sputtering system. The crystallinity and Rayleigh-type surface acoustic wave propagation properties of the thin films were evaluated. The possibility that the Ta2O5 thin films were crystallized to orthorhombic Ta2O5 on SrTiO3 substrates by providing a buffer layer deposited without applying O2 radical power was demonstrated. From measured pole figures, it is considered that the crystalline Ta2O5/SrTiO3(100) sample has two lattice arrangements orthogonal to each other, and the crystalline Ta2O5/SrTiO3(110) sample has a single lattice arrangement. For a normalized film thickness h/λ of 0.45, the propagation loss for the deposition on SrTiO3(110) was 0.02 dB/λ, whereas that for the X-axis-oriented Ta2O5 thin film on SiO2 substrate was 0.21 dB/λ. Unfortunately, the coupling factor of the crystalline thin film was less than 0.3% for h/λ ranging from 0.29 to 0.45.

Surface acoustic wave devices on AlN/3C–SiC/Si multilayer structures

Surface acoustic wave (SAW) propagation characteristics in a multilayer structure including a piezoelectric aluminum nitride (AlN) thin film and an epitaxial cubic silicon carbide (3C–SiC) layer on a silicon (Si) substrate are investigated by theoretical calculation in this work. Alternating current (ac) reactive magnetron sputtering was used to deposit highly c-axis-oriented AlN thin films, showing the full width at half maximum (FWHM) of the rocking curve of 1.36° on epitaxial 3C–SiC layers on Si substrates. In addition, conventional two-port SAW devices were fabricated on the AlN/3C–SiC/Si multilayer structure and SAW propagation properties in the multilayer structure were experimentally investigated. The surface wave in the AlN/3C–SiC/Si multilayer structure exhibits a phase velocity of 5528 m s−1 and an electromechanical coupling coefficient of 0.42%. The results demonstrate the potential of AlN thin films grown on epitaxial 3C–SiC layers to create layered SAW devices with higher phase velocities and larger electromechanical coupling coefficients than SAW devices on an AlN/Si multilayer structure. Moreover, the FWHM values of rocking curves of the AlN thin film and 3C–SiC layer remained constant after annealing for 500 h at 540 °C in air atmosphere. Accordingly, the layered SAW devices based on AlN thin films and 3C–SiC layers are applicable to timing and sensing applications in harsh environments.

Assessment of langatate material constants and temperature coefficients using SAW delay line measurements

This paper reports on the assessment of langatate (LGT) acoustic material constants and temperature coefficients by surface acoustic wave (SAW) delay line measurements up to 130 degrees C. Based upon a full set of material constants recently reported by the authors, 7 orientations in the LGT plane with Euler angles (90 degrees, 23 degrees, Psi) were identified for testing. Each of the 7 selected orientations exhibited calculated coupling coefficients (K(2)) between 0.2% and 0.75% and also showed a large range of predicted temperature coefficient of delay (TCD) values around room temperature. Additionally, methods for estimating the uncertainty in predicted SAW propagation properties were developed and applied to SAW phase velocity and temperature coefficient of delay calculations. Starting from a purchased LGT boule, the SAW wafers used in this work were aligned, cut, ground, and polished at University of Maine facilities, followed by device fabrication and testing. Using repeated measurements of 2 devices on separate wafers for each of the 7 orientations, the room temperature SAW phase velocities were extracted with a precision of 0.1% and found to be in agreement with the predicted values. The normalized frequency change and the temperature coefficient of delay for all 7 orientations agreed with predictions within the uncertainty of the measurement and the predictions over the entire 120 degrees C temperature range measured. Two orientations, with Euler angles (90 degrees, 23 degrees, 123 degrees) and (90 degrees, 23 degrees, 119 degrees), were found to have high predicted coupling for LGT (K(2) > 0.5%) and were shown experimentally to exhibit temperature compensation in the vicinity of room temperature, with turnover temperatures at 50 and 60 degrees C, respectively.

Surface acoustic wave propagation properties in 0.67Pb(Mg(13)Nb(23))O(3)-0.33PbTiO(3) single crystal poled along [111](c).

Surface acoustic wave (SAW) propagation properties in relaxor-based 0.67Pb(Mg(13)Nb(23))O(3)-0.33PbTiO(3) (PMN-33%PT) ferroelectric single crystals poled along [111](c) has been analyzed theoretically. We found that the X-cut PMN-33%PT has lower phase velocity and higher electromechanical coupling coefficient compared to traditional piezoelectric materials. The power flow angle (PFA) can be zero in specific directions, which could drastically improve the performance of SAW devices. Our theoretical results indicate that the direction about 5 degrees canted from [111](c) is the optimum direction for the X-cut [111](c) poled crystals in SAW device applications. Characteristic curves were also obtained for the phase velocity, electromechanical coupling coefficient, and PFA in Z-cut single-domain PMN-33%PT single crystals.

Numerical Calculation of SAW Propagation Properties at the x-Cut of Ferroelectric PMN-33%PT Single Crystals

Surface acoustic wave (SAW) properties at the x-cut of relaxor-based 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 (PMN-33%PT) ferroelectric single crystals are analyzed theoretically when poled along the [001]c cubic direction. It can be found that PMN-33%PT single crystal is a kind of material with a low phase velocity and high electromechanical coupling coefficient, and the single crystal possesses some cuts with zero power flow angle. The results are based on the material parameters at room temperature. The conclusions provide device designers with a few ideal cuts of PMN-33%PT single crystals. Moreover, choosing an optimal cut will dramatically improve the performance of SAW devices, and corresponding results for crystal systems working at other temperatures could also be figured out by employing the method.

Experimental and theoretical characterization of the surface acoustic wave propagation properties of GaN epitaxial layers on c-plane sapphire

Surface acoustic wave (SAW) propagation properties of gallium nitride (GaN) epitaxial layers on sapphire were theoretically and experimentally characterized. GaN thin films were grown on a c-plane sapphire substrate using a metalorganic chemical vapor deposition system. The experimental characterization of SAW propagation properties was performed with a linear array of interdigital transducer structures, while SAW velocities were calculated by matrix methods. Experimentally, we found pseudo-SAW and high-velocity pseudo-SAW modes in the GaN/sapphire structure, which had a good agreement with calculated velocities.

Surface acoustic wave propagation properties of nitrogenated diamond-like carbon films

Nitrogenated diamond-like carbon (a-C:N) thin films on Si(100) were deposited by radio frequency magnetron reactive sputtering. Using ZnO piezoelectric thin films, the surface acoustic wave (SAW) propagation properties of a-C:N thin films on Si(100) have been experimentally investigated using bidirectional interdigital transducers between ZnO and a-C:N/Si(100). A generalized SAW mode with velocities between 5000 and 7000 m/s were observed. A high velocity pseudo-SAW mode was also observed and identified with simulated data, of which the velocity was 13 850 m/s. We calculated the film elastic constants from the phase velocities in the layered structure. The calculated constants for a-C:N thin films on Si were c11=392.1 and c44=185.7 GPa.

The experimental and theoretical characterization of the SAW propagation properties for zinc oxide films on silicon carbide

The surface acoustic wave (SAW) propagation properties of zinc oxide (ZnO) films on silicon carbide (SiC) have been theoretically and experimentally characterized in the film thickness-to-acoustic wavelength ratio range up to 0.12. The experimental characterization of the SAW propagation properties was performed with a linear array of interdigital transducer (IDT) structures. The measurements characterized the velocity and propagation loss of two surface modes, a generalized SAW (GSAW) mode with velocities between 6000 and 7000 m/s, and a high velocity Pseudo-SAW (HVPSAW) mode with velocities between 8500 and 12 500 m/s. The experimentally determined characteristics of the two waves have been compared with the results of calculations based on published data for SiC and ZnO. Simulation of wave characteristics was performed with various values of the elastic constant C(13), which is absent in the published set of material constants for SiC, within the interval permitted by the requirement of positive elastic energy in a hexagonal crystal. The best agreement between the measured and calculated propagation losses of the HVPSAW has been obtained for C(13) near zero. Although for the GSAW mode the calculated velocity dispersion has been found nearly insensitive to the value of C (13) and consistent with the experimental data, for the HVPSAW, some disagreement between measured and calculated velocities, which increased with ZnO film thickness, has been observed for any C(13 ) value. Theoretical analysis of HVPSAW has revealed the existence of a previously unknown high velocity SAW (HVSAW). The displacement components of this wave have been analyzed as functions of depth and confirmed its pure surface, one-partial character.

Recent new experiments in magnetic thin film fabrication: Plasma nitriding and SAW exciting substrate

The physical properties of plasma and their effects on film structure such as phase and morphology are discussed based on the results of plasma diagnosis for plasma evaporation and sputtering, respectively. α″−Fe 16N 2 films, as an example, are systematically synthesized by using the above two independent methods and the degree of nitriding process of Fe atoms is discussed in connection with the results of plasma diagnosis. A new thin film fabrication technique which uses a substrate excited by surface acoustic wave (SAW) is proposed. The structural and magnetic behaviours of ultrathin metallic films are discussed in connection with the intrinsic film growth mode evaluated from the propagation properties of SAW during the film deposition. Metallic multilayers, Co/Cu, are formed as a function of oscillation amplitude of SAW and the GMR effect is discussed in connection with the change of interface conditions.

Propagation of surface acoustic waves in magnetic bubble garnet films

Surface Acoustic Wave (SAW) delay lines have been fabricated on magnetic bubble garnet films. Interdigital transducers on a piezoelectric layer (zinc oxide film sputtered on top of the garnet film) have been used for acoustic wave generation and detection. Amplitude and phase delay variations of the SAW delayed signal were measured as a function of an externally applied dc magnetic field. The maximum change in the SAW propagation properties was observed when the applied field H was parallel to the SAW propagation vector k, and at field strengths of the same order as that required for FMR at the operating frequency. The results are explained qualitatively in terms of an approach which provides an explanation for the dependence of the SAW measurements on the orientation and magnitude of the applied field.