Rotated Y-cut LiNbO3 Research Articles

High performance SAW resonator with spurious mode suppression using double-layer electrode transverse modulation

This work aims to solve the problem of tradeoff between various properties and spurious mode suppression in surface acoustic wave (SAW) resonators. A high-angle rotated Y-cut LiNbO3 (LN)/SiO2/Si multilayered structure was proposed to balance the electromechanical coupling coefficient (K 2) and temperature coefficient of frequency (TCF), and the propagation characteristics of Rayleigh mode were simulated by the finite element method. For the widely existing spurious modes, the shear-horizontal wave and longitudinal modes were eliminated by optimizing the cut angle of LN and electrode thickness, and a method of double-layer electrode transverse modulation was proposed to suppress the transverse modes. This method reduces the mass loading effect by replacing the electrode from Cu to Cu/Al. Moreover, the Al thicknesses in different regions are changed to perform the transverse modulation, and thus a widespread suppression of transverse modes is achieved by exciting the piston mode and enhancing the energy constraint, with a significant improvement on quality factor at the resonance frequency. Eventually, the spurious-free SAW resonator has the K 2 of 9.5% and the TCF close to zero. This work provides a feasible scheme for the design of high performance SAW resonators with spurious mode suppression.

Investigations on ion implantation-induced strain in rotated Y-cut LiNbO3 and LiTaO3 * *Project supported by the National Key Research and Development Program of China (Grant No. 2019YFB1803902), the National Natural Science Foundation of China (Grant Nos. 11905282, 61874128, 61851406, 11705262, and 6187407), the Frontier Science Key Program of CAS (Grant Nos. QYZDY-SSWJSC032 and ZDBS-LY-JSC009), Chinese-Austrian Cooperative Research and Development Project

The monocrystalline LiNbO3 (LN) and LiTaO3 (LT) plates have been qualified as a kind of material platform for high performance RF filter that is considerable for the 5G communication. LN and LT thin films are usually transferred on handle wafers by combining ion-slicing and wafer bonding technique to form a piezoelectric on insulator (POI) substrate. The ion implantation is a key process and the implantation-induced strain is essential for the layer transfer. Here, we reported the strain profile of ion implanted rotated Y-cut LN and LT. The ion implantation generates the out-of-plane tensile strain of the sample surface and (006) plane, while both the tensile and compressive strain are observed on the (030) plane. The implanted ions redistributed due to the anisotropy of LN and LT, and induce the main tensile normal to the (006) plane. Meanwhile, the (030) planes are contracted due to the Poisson effect with the interstitial ions disturbing and mainly show a compressive strain profile.

Influence of Coupling Between Rayleigh and SH SAWs on Rotated -Cut LiNbO3 to Their Propagations.

This paper investigates the influence of coupling between Rayleigh and shear-horizontal (SH) surface acoustic waves (SAWs) on rotated Y-cut LiNbO3 to their electromechanical coupling. For the purpose, a coupling-of-mode (COM) model including the coupling between two SAWs is developed, and the coupling influences to their excitation in addition to electromechanical coupling factors are discussed. Then, its validity is confirmed by comparison of its results with the finite-element method analysis. Comparing with the conventional COM shows this extended COM model could fit the complex value area much better in the dispersion curve analysis. After that, variation of COM parameters with the device design is discussed. Then, all COM parameters are fit by polynomial equations and the procedures to find the optimal rotation angle are obtained in terms of the SH mode suppression. It indicates that the optimal angle changes rapidly at certain Cu thickness, which is due to decoupling between two SAW modes. At last, structure based on the low-cut LiNbO3 is discussed and the validity of this COM model is further confirmed.

Applicability of acoustic plate modes with quasi-longitudinal polarization to liquid parameterization

A class of acoustic waves suitable for liquid parameterization is demonstrated not to be restricted to acoustic modes with shear-horizontal polarization. Its substantial extension can be achieved by adding widespread plate modes with quasi-longitudinal (QL) polarization. Their investigation is performed by an example of 128°-rotated Y-cut LiNbO3 plates. The sensitivity of plate modes to the conductivity of liquid adjacent to one of the plate surfaces has been found to depend on a mode number, a plate thickness, and electric conditions on the opposite surface. It is demonstrated that their sensitivity to temperature is affected by the liquid viscosity. One of the QL modes existing in the 128°Y, X + 90° -LiNbO3 plate has been determined numerically. Its applicability for monitoring the electric characteristics of low-viscous liquid media has been examined experimentally.

Monolithically Integrated Tandem Waveguide-Type Acoustooptic Modulator Driven by Surface Acoustic Waves

A waveguide-type acoustooptic modulator (AOM) using coplanar AO coupling due to a surface acoustic wave (SAW), that is, Bragg diffraction, in a tapered crossed-channel proton-exchanged (PE) optical waveguide on a 128°-rotated Y-cut LiNbO3 substrate for an optical wavelength of 1.55 µm has been proposed. In this study, a monolithically integrated tandem waveguide-type AOM driven by SAW was designed and fabricated. The structure considered was a 2×4 optical switch, in which the input ports of two second 1×2 switches were connected to the two output ports of the first 2×2 switch on the same substrate. An interdigital transducer (IDT) with a period length of 32 µm and an overlap length of 2 mm was fabricated in the first and second stages of the AO interaction region. Diffraction efficiency was measured at a driving frequency of approximately 120 MHz. A diffraction efficiency of approximately 90% was obtained for each stage. When both stages were driven at the same frequency, a peak diffraction efficiency of 63% was obtained. Furthermore, the optical frequency shifts for the sum of two driving frequencies and the difference frequency ranging from DC to 5 MHz were observed.

Improvement of Diffraction Properties in Waveguide-Type Acoustooptic Modulator Driven by Surface Acoustic Wave

A waveguide-type acoustooptic modulator (AOM) driven by a surface acoustic wave (SAW) in a tapered crossed-channel waveguide on a 128°-rotated Y-cut LiNbO3 substrate has been proposed for an optical wavelength of 1.55 µm. In this study, to improve the diffraction properties of the waveguide-type AOM, the dependences of the diffraction properties on the relative position of the SAW beam for the diffraction region were simulated using a beam-propagation method (BPM) and measured. By decreasing SAW beam width, although the input voltage needed to obtain the maximum diffraction efficiency increased, diffraction efficiency improved to 84% from the previous value of 65%. Furthermore, to obtain a lower driving voltage, the utilization of a unidirectional transducer was investigated for the AO interaction on a planar optical waveguide at an optical wavelength of 0.633 µm.

Diffraction Properties and Beam-Propagation Analysis of Waveguide-Type Acoustooptic Modulator Driven by Surface Acoustic Wave

A waveguide-type acoustooptic modulator (AOM) driven by a surface acoustic wave (SAW) in a tapered crossed-channel waveguide on a 128°-rotated Y-cut LiNbO3 substrate has been proposed for an optical wavelength of 1.55 µm. In this study, to clarify the conditions for a higher diffraction efficiency and a lower driving power, the diffraction properties of the waveguide-type AOM were measured and simulated. First, an AOM with an AO interaction region length of 3 mm was fabricated and the diffraction efficiency of 65% was obtained. Next, the measured values of the SAW power required for 100% diffraction (P100) for the driving frequencies of 125 MHz and 200 MHz were found to be in agreement with the calculated P100, which shows that there is an optimum driving frequency. Furthermore, optical frequency domain ranging using a frequency-shifted-feedback fiber laser with the waveguide-type AOM was demonstrated. Finally, the diffraction properties of the waveguide-type AOM are simulated using a beam-propagation method (BPM) and compared with the experimental results.

LiNbO3 Ultrasonic Transducers with an Inverted-Domain Layer for Radiation to Solid Media

Heat treatment of lithium niobate (LiNbO3) plates induces domain inversion, thereby yielding a ferroelectric inversion layer. In such a piezoelectric plate with an inversion layer, even-order thickness-extensional modes, as well as odd-order modes, can be excited piezoelectrically. Therefore, ultrasonic transducers using such a piezoelectric plate are expected to operate over a wide frequency range. In this paper, it is shown both theoretically and experimentally that broadband ultrasonic transducers for radiation to solid media can be obtained when the inversion layer is on the side of the acoustic load medium and the inversion layer-to-plate thickness ratio is around 0.3. A 50–110 MHz ultrasonic transducer was fabricated using 36°-rotated Y-cut LiNbO3 plates with an inversion layer. The conversion loss characteristic was evaluated when the transducer was bonded to an acoustic medium of fused silica by a low-temperature Au diffusion bonding technique. The 3 dB specific bandwidth was as large as 74% and the minimum conversion loss was as low as 2 dB.

Half-thickness inversion layer high-frequency ultrasonic transducers using LiNbO/sub 3/ single crystal

Half-thickness inversion layer high-frequency ultrasonic transducers were fabricated using lithium niobate (LiNbO3) single crystal plate. The transducers developed for this study used a 36 degrees rotated Y-cut LiNbO3 thin plate with an active element thickness of 115 microm. The designed center frequency was in the range of 30 to 60 MHz. Half-thickness inversion layer was formed after the sample was annealed at a high temperature, and it is shown that the inversion layer thickness can be controlled by the temperature. Silver powder/epoxy composite and parylene were used as acoustic matching layers. A lossy silver epoxy was used as the backing material. Using an analytical method, the electrical impedance for different inversion layer ratios was determined. The measured resonant frequency was consistent with the modeled data. Even-order higher frequency broadband ultrasonic transducers with a center frequency at 60 MHz was obtained using half-thickness inversion layer of LiNbO3 single crystal.

Broadband ultrasonic transducers using a LiNbO3 plate with a ferroelectric inversion layer.

Some heat treatment of a lithium niobate (LiNbO3) plate induces domain inversion, thereby yielding a ferroelectric inversion layer. In such a piezoelectric plate with an inversion layer, even-order thickness-extensional modes, as well as odd-order modes, can be excited piezoelectrically. Therefore, the ultrasonic transducer using such a piezoelectric plate is expected to operate over a wide frequency range. In this paper, it is shown that broadband ultrasonic transducers can be obtained at a certain thickness ratio of inversion layer to plate, and that the transducer characteristics differ depending on whether the inversion layer is on the front side or on the backside. The broadband characteristics are experimentally demonstrated by fabricating transducers with 9 MHz or 75 MHz center frequency using 36 degrees rotated Y-cut LiNbO3 plates with a ferroelectric inversion layer.

Ultrasonic Focusing Gaussian Source to Receive Nonlinearly Generated Second Harmonic Sound by Itself

A focusing source to concurrently detect the nonlinearly generated second harmonic sound contained in the reflected wave has been produced. A 36° rotated Y-cut LiNbO3 plate of 20 MHz fundamental resonance frequency with a reversed polarization layer formed by heat treatment is bonded to a plane surface of a solid acoustic lens whose thickness is set at a small value so as to avoid the influences of nonlinear distortion and multiple reflection within the lens. One of the electrodes on the piezoelectric plate is fabricated to a 20-point-star shape. The formation of a 20 MHz focused Gaussian beam and the capability of receiving the 40 MHz second harmonic sound are confirmed through experiments.

Diffraction of Guided Optical Waves by Surface Acoustic Waves in Proton-Exchanged 128� Rotated Y-Cut LiNbO3

The acousto-optic diffraction of guided optical modes by surface acoustic waves in the Raman-Nath regime in the single-mode optical waveguide formed by the proton exchange technique in 128° rotated Y-cut lithium niobate has been studied. The experiments have been performed at the optical wavelength 0.6328 μm in a single-TM mode waveguide formed by treatment in pure benzoic acid for 20 min at 230 °C and at the SAW frequency of 78 MHz. The measured dependences of the light intensity diffracted into the zeroth, first and second orders on the driving voltage are in good agreement with the theoretical calculations. The values for the acousto-optic figure of merit M2 = 9.5 × 10—15 s3/kg and the effective photoelastic cefficient peff = 0.14 have been evaluated showing the efficiency of the acousto-optic interaction in proton-exchanged lithium niobate being comparable to that in the pure crystal.

Trapped-Energy Vibratory Gyroscopes Using Rotated Y-cut LiNbO3

In a rotated Y-cut plate of class (3m) crystal such as LiNbO3 and LiTaO3, two orthogonal thickness-shear vibrations can be excited independently, by electric fields perpendicular and parallel to the plate surface. Using the trapped-energy thickness-shear vibrations, vibratory gyroscopes of easy support with no need of trimming are expected to be realized. In this paper, a trapped-energy vibratory gyroscope using a rotated Y-cut of LiNbO3 is proposed. It is shown experimentally that by choosing appropriate electrode dimensions the resonance frequencies of the two orthogonal thickness-shear vibrations almost coincide with each other, and the energy of the thickness-shear vibrations is trapped around the electrodes. The basic characteristics of a vibratory gyroscope using a 163° rotated Y-cut LiNbO3 plate, about 2 mm thick, is presented.

Effects of acoustic waves on activation of thin film Pd and Ni catalysts for ethanol and CO oxidation

The effects of acoustic wave excitation of surface acoustic waves (SAWs) and resonance oscillations (ROs) on catalytic and adsorptive properties of metal thin films have been studied. A 5–200 nm thick Pd thin film was deposited as a catalyst on the Rayleigh SAW propagation path of a 128°-rotated y-cut LiNbO3 single crystal. For ethanol oxidation, the introduction of a 10 MHz SAW increased acetaldehyde production. The activity enhancement varied, depending not only on the surface states (reduced and oxidized Pd surfaces), but also on the thickness of the Pd films: larger activity enhancement occurred for a thick Pd film with an oxidized surface. For CO oxidation, the oxidized Pd had slightly greater effect than reduced Pd, but catalyst activation with SAW-on was small over a whole range of film thickness for both the reduced and the oxidized Pd. The high-resolution IR reflection absorption spectra of CO adsorbed on a 40 nm Pd thin film deposited on the propagation path of a shear horizontal leaky SAW (36°-rotated y-cut LiTaO3) exhibited a large peak, assigned to bridging CO, at 1982 cm-1 and a small on-top CO peak at 2073 cm-1. With SAW-on, the intensity and position of both the peaks remained nearly unchanged, but a shoulder appeared on the bridging CO peak at ca. 1930 cm-1. A laser Doppler measurement showed that a vertical lattice displacement due to the Rayleigh SAW increased with increasing Pd film thickness, up to 50 nm, and was nearly constant over the range 50–200 nm, in which the magnitude of lattice displacement was larger for reduced than for oxidized Pd. SAW-induced catalyst activation is discussed on the basis of reaction mechanisms and the adsorbed states of the reactants. From the dependence of lattice displacement on the thickness and surface states of the Pd films, a model in which the SAW interacts with the charged carriers in the thin films and affects the adsorbed states of the reactants is proposed. Furthermore, it was demonstrated that RO generated on a Pd thin film deposited on z-cut LiNbO3 had a remarkable effect on its catalytic activity for ethanol oxidation.

Velocity and attenuation of surface acoustic waves in proton-exchanged 128 degrees -rotated Y-cut LiNbO3

The velocity and attenuation of surface acoustic waves (SAW) in a 128 degrees -rotated Y-cut lithium niobate crystal with a proton-exchanged optical waveguiding layer on its surface have been studied. The measurements were carried out using the acoustic-optical diffraction method in the SAW frequency range 30-600 MHz. The SAW propagation was mainly along the X axis, though some velocity measurements were carried out for the normal direction. Strong velocity decrease and attenuation increase due to the proton exchange were observed. The acoustic dispersion and losses grow with the waveguide depth and SAW frequency, and are strongly affected by the post-exchange annealing. The results are explained by the formation of a HxLi1-xNbO3 layer on the LiNbO3 with many defects.

Photo-Elastic Constants of Proton-Exchanged LiNbO 3

The acousto optic interaction on proton-exchanged 128°-rotated Y-cut LiNbO3 was investigated to evaluate the photo-elastic constants. The experimental and theoretical analysis using a surface acoustic wave of 200 MHz and a He-Ne laser beam showed that the acoustic power required for 100% diffraction depends on the proton-exchange depth and that the photo-elastic constants of the proton-exchanged layer are 76% of those in unexchanged LiNbO3. The effects of annealing on the photo-elastic constants and the diffraction efficiency were also measured.

Surface Acoustic Wave Properties on Proton-Exchanged 128°-Rotated Y-Cut LiNbO3

The characteristics of surface acoustic waves on proton-exchanged 128°-rotated Y-cut LiNbO3 were investigated at a frequency of 100 MHz. The changes of the phase velocity and the electromechanical coupling coefficient as a function of the proton-exchange depth were measured. From these experiments, the elastic constants and the piezoelectric constants of the proton-exchanged layer were determined. The effects of annealing on the phase velocity and the surface acoustic wave propagation loss were also measured.

Propagation Characteristics of Surface Acoustic Waves in ZnO/LiNbO3 Structures

In this paper, we report that the propagation characteristics of surface acoustic waves (SAWs) in a structure consisting of a piezoelectric layer on a piezoelectric substrate depend on the relationship between the polarities of the two piezoelectric media. The theoretical analysis of the characteristics of the Rayleigh wave in ZnO/128°-rotated Y-cut LiNbO3 structures shows that there is a large difference in values of electromechanical coupling factor K in the two cases where the ZnO layer is deposited on the positive surface and the negative surface of LiNbO3, and that the value of K2 can be as high as 13.3%. The mode coupling phenomenon between the Rayleigh and Love waves is also discussed.

Torsional Actuators Using LiNbO3 Plates with an Inversion Layer

By utilization of a ferroelectric inversion layer formed in a LiNbO3 plate by heat treatment at just below the Curie temperature, a piezoelectric torsional actuator consisting of a single-crystal plate with no bonding layer can be obtained. The optimal cut suitable for generating torsional motion efficiently without causing bending motion is theoretically examined. It is experimentally demonstrated that torsional actuators fabricated using 140°-rotated Y-cut LiNbO3 plates with an inversion layer as thick as half the plate thickness exhibit no hysteresis and little creep. When an actuator with dimensions of 16×7.0×0.1 mm3 is used as a light deflector, a light beam deflection angle as large as 2.08° is obtained at an applied voltage of 220 Vp-p.

Small love-wave SAW resonators with very low capacitance ratio

When a strip grating of periodic strips of Au, Ag, or Pt is produced on a rotated Y-cut LiNbO3, a Love-type surface wave with a high coupling (K2 > 30 percent) is formed and the reflection coefficient per strip is as large as several tens percent. In this paper, a small IDT resonator, with an extremely low capacitance ratio making use of the Love-type surface wave, is studied theoretically and experimentally. First, the admittance characteristics of the IDT are studied by means of the mode-coupling equation, which is determined by the dispersion characteristics derived from the Floquet theorem. It can be shown that the IDT exhibits resonant characteristics and the capacitance ratio is 2.4 – 2.7 if the number of pairs is more than 10. Next, an experiment was carried out by using a combination of the Y-X LiNbO3 substrate and the Au electrodes. It is demonstrated that the resonator with a low-capacitance ratio can be realized, as predicted by the theory. Further, rhombically weighted electrodes are proposed. It is confirmed that the spurious transverse mode and the spurious longitudinal mode can be suppressed simultaneously.