Qiaozhen Zhang

SAW Characteristics of AlN/SiO 2 /3C-SiC Layered Structure With Embedded Electrodes

A layered structure of aluminum nitride (AlN)/ silicon dioxide (SiO2)/cubic silicon carbide with embedded electrodes, which enables the growth of high-quality AlN thin films, is proposed and studied. The phase velocity, coupling factor, and temperature coefficient of frequency (TCF) of surface acoustic waves in the proposed structure have been investigated using the finite-element method. The simulation results show that a high velocity of 5485 m/s and a large effective coupling factor (K2 ) of 1.45% can be simultaneously obtained for the first mode. The dramatic enhanced K2 of 10.5% is also obtainable on the proposed structure employing Sc0.4Al0.6N thin film. Besides, the excellent zero TCF is also achieved without deteriorating the coupling factor by adding an amorphous SiO2 overlay.

Theoretical analysis of surface acoustic wave propagating properties of Y-cut nano lithium niobate film on silicon dioxide

The surface acoustic wave (SAW) propagating characteristics of Y-cut nano LiNbO3 (LN) film on SiO2/LN substrate have been theoretically calculated. The simulated results showed a shear horizontal (SH) SAW with enhanced electromechanical coupling factor K2 owing to a dimensional effect of the nanoscale LN film. However, a Rayleigh SAW and two other resonances related to thickness vibrations caused spurious responses for wideband SAW devices. These spurious waves could be fully suppressed by properly controlling structural parameters including the electrode layer height, thickness, and the Euler angle (θ) of the LN thin film. Finally, a pure SH SAW was obtained with a wide θ range, from 0° to 5° and 165° to 180°. The largest K2 achieved for the pure SH SAW was about 35.1%. The calculated results demonstrate the promising application of nano LN film to the realization of ultra-wideband SAW devices.

Frequency domain FEM analysis of reflector scattering characteristics for SAW tags

This paper proposes a frequency domain analysis (FDA) based on the finite element method (FEM) for calculating reflector scattering characteristics of SAW tags. This method is applicable not only to devices employing conventional single-crystal substrates but also multi-layered ones. First, reflection characteristics are calculated for a short reflector on 128°YX-LiNbO3 and compared with the result previously reported. Then the method is applied to short reflectors on the AlN/Si layered structure, and their applicability to SAW tags is discussed.

Modeling of lateral SAW propagation including coupling between different SAW modes

This paper describes lateral propagation of surface acoustic waves (SAWs) when two types of SAWs are coupled. For the analysis, the thin plate model proposed by the authors is extended to include interaction between two SAW modes. Firstly, lateral wave propagation in an infinitely long periodic grating is modelled and discussed, it is found that SAW slowness curves can be changed by mode coupling. Then, the model is applied to the analysis of two-dimensional SAW propagation on the Al grating on the 42°YX-LiTaO3 (42-LT) substrate structure to investigate how the lateral SAW propagation changes with the Al grating thickness. Finally, SAW resonators on 42-LT substrate with Cu electrodes are fabricated and the results confirm the feasibility of the model.

Influence of coupling with shear horizontal surface acoustic wave on lateral propagation of Rayleigh surface acoustic wave on 128°YX-LiNbO3

In this paper, we investigate the impact of the coupling with shear horizontal (SH) surface acoustic wave (SAW) on the propagation of Rayleigh SAW in periodic grating structures on 128°YX-LiNbO3. First, the frequency dispersion behavior with longitudinal and lateral wavenumbers of Rayleigh SAW is calculated using the finite element method (FEM) software COMSOL. It is shown that the coupling causes (1) the satellite stopband and (2) variation of the anisotropy factor. It is also shown these phenomena remain even when the electromechanical coupling factor of SH SAW is zero. Then, the extended thin plate model which can take coupling between two SAWs into account, is applied to simulate the result of FEM. Good agreement between these results indicated that the mechanical coupling is responsible for these two phenomena. Finally, including electrical excitation and detection, the model is applied to the infinitely long interdigital transducer (IDT) structure and the calculated result is compared with that obtained by the three-dimensional FEM. The excellent agreement of both results confirms the effectiveness of the extended thin plate model.

SAW/BAW band reject filters embedded in impedance converter

This paper discusses SAW-BAW-based band reject filters. They are composed of the impedance converters, where capacitive elements are replaced with SAW/BAW resonators. First, basic properties of the unit cell are studied. It is shown how basic properties of a unit cell change with the design. It is also shown that when two notches caused by the resonators are placed in proximity, two synergy effects occur: (i) an extra matching point appears on one side of the transition band. This make the insertion loss at the point smaller and the transition band steeper, and (ii) the dip level becomes deeper, and the total rejection level becomes better. Then, the wide rejection band filter is designed by cascading multi-stages, and effectiveness of the device configurations is demonstrated.

Validity evaluation of Sc x Al1−x N material constants based on SAW characteristics

This paper is aimed at examining the validity of material constants reported for use in surface acoustic wave (SAW) device simulations. First, based on the full set of material constants calculated by first principle, bulk acoustic wave velocities are calculated for Sc x Al1−x N and compared with published experimental results. Then, the effects of the Sc x Al1−x N material constants with different Sc content on acoustic characteristics are calculated and the influence of shear vibrations on SAW characteristics are recognized. Then, a series of SAW devices are fabricated on Sc x Al1−x N film/Si substrate structure with various Cu and ScAlN thicknesses h Cu and h ScAlN, respectively, and measured variations of phase velocity V and effective electromechanical coupling factor with these parameters are compared with the calculation. The fairly well-agreed results indicate a reliable set of Sc x Al1−x N material constants for SAW device simulations.

SAW characteristics of AlN/SiO 2 /3C-SiC layered structure with embedded electrodes

A novel sandwich structure of AlN/SiO 2 /3C-SiC with embedded electrodes, which enables the growth of highly quality AlN thin films, is proposed and studied. The phase velocity, coupling factor, and temperature coefficient of frequency (TCF) of SAWs in the proposed structure have been investigated using the finite element method (FEM). The simulation results show that high velocity of 5,485m/s and large effective coupling factor of 1.45% can be simultaneously obtained, which is about 3.4 times larger than the value previously reported. The excellent zero TCF is also achieved without deteriorating the coupling factor by adding the SiO 2 overlay.

Wavenumber Domain Analysis of Surface Acoustic Wave Scattering from Localized Gratings on Layered Piezoelectric Substrate

This paper proposes a general finite element method (FEM)-based wavenumber domain analysis (WDA) to calculate scattering characteristics of surface acoustic wave (SAW) on arbitrary piezoelectric substrates. We add a damping loss mechanism (DLM) to the SAW injection port to avoid interferences from the incident and backscattered modes. After checking the validity of the proposed method, we calculate and study Sezawa mode scattering using a small number of electrodes on the ScAlN/3CSiC structure for demonstration. The frequency dependences of reflection and transmission coefficients and that of the power dissipation ratio for different termination conditions and electrode thicknesses are calculated. Also, the influence of base substrate materials and that of gratings on scattering parameters are explored. Investigation results demonstrate that high reflectivity with suppressed mode conversion can be obtained for the ScAlN-based layer structure if a base substrate with an extremely large velocity is used and if proper grating design is applied.

Modeling and Analysis of Lateral Propagation of Surface Acoustic Waves Including Coupling Between Different Waves

This paper discusses lateral propagation of surface acoustic waves (SAWs) in periodic grating structures when two types of SAWs exist simultaneously and are coupled. The thin plate model proposed by the authors is extended to include the coupling between two different SAW modes. First, lateral SAW propagation in an infinitely long periodic grating is modeled and discussed. Then, the model is applied to the Al-grating/42° YX-LiTaO3 (42-LT) substrate structure, and it is shown that the slowness curve shape changes from concave to convex with the Al grating thickness. The transverse responses are also analyzed on an infinitely long interdigital transducer on the structure, and good agreement is achieved between the present and the finite-element method analyses. Finally, SAW resonators are fabricated on the Cu grating/42-LT substrate structure, and it is experimentally verified that the slowness curve shape of the shear horizontal SAW changes with the Cu thickness.