SAW Mode Research Articles

Use of periodic trenches in SMR-type XBAR for suppression of transverse mode resonances and lateral leakage

This paper discusses the use of periodic trenches to the top SiO2 layer of the Bragg reflector in solidly-mounted-resonator type laterally-excited-bulk-wave-resonators for the slowness manipulation to suppress both transverse mode resonances and lateral leakage. First, it is shown that the SAW slowness surface can be flattened by the application of periodic trenches, and this is owing to the coupling of the propagating SAW mode with resonances of periodic trench walls. It is also shown that flattening the SAW slowness surface enables us to suppress transverse mode resonances well. However, its impact on lateral leakage is not obvious. Then, the broadband piston mode design is applied, and its effectiveness is demonstrated for the suppression of both transverse mode resonances and lateral leakage. Deposition of a dielectric layer to the gap regions is also proposed as an alternative for leakage suppression, and it is shown that Si3N4 is appropriate as a dielectric material.

Acoustic wave propagation along AlN on Bi12GeO20 structures

Using Bi12GeO20 plate coated by AlN film, the main characteristics of the A0, S0, A1, and S1 Lamb waves are numerically calculated and compared with those of SAW in the same structure. It is shown that (i) there exist only one SAW mode for this material combination, (ii) the mode exist in a narrow range of AlN thickness, (iii) it can be excited using four different transducer configurations, (iv) the velocity and coupling constants of the mode are, respectively, higher and lower as compared with the values for the uncoated Bi12GeO20 substrate. On the other hand, for Lamb waves (i) there are several modes of different orders, (ii) the modes exist in a wide range of the AlN thickness, (iii) they may be excited using twelve IDT configurations, (iv) the velocities and coupling constants of the waves may be larger and smaller as compared with the values for the uncoated plate, (v) both characteristics of the modes depend on the mode order, film thickness, plate thickness, and transducer configuration, and (vi) the depth profiles of the modes are neither symmetrical nor anti-symmetrical. These properties make Lamb waves more attractive than SAW. Application of the waves and the structure for some applications are suggested.

Study on electromechanical coupling coefficients of surface acoustic waves in layered systems

The aim of this paper is to utilize the effective permittivity approach to calculate the electromechanical coupling coefficients of surface acoustic waves in layered systems. The effective permittivity offers a direct relation to the voltage‐induced charge density at the interface, and can be used to calculate the phase velocity dispersion and the electromechanical coupling coefficients of a layered piezoelectric medium exactly. In this paper, the formulation based on the matrix method for calculating the effective permittivity of a layered piezoelectric medium with three types of electrode arrangements is given first. Then, based on this formulation, we calculated phase velocity dispersions of the generalized SAW mode and the HVPSAW mode in layered systems of ZnO/Diamond and LiNbO3/Diamond. In addition, the electromechanical coupling coefficients of surface acoustic waves in the aforementioned layered systems with three different electrical boundary conditions were analyzed and discussed.

Propagation of a shear-horizontal surface acoustic mode in a periodically grooved AlN/Al2O3 microstructure

We investigate the shear-horizontal surface acoustic waves (SH-SAWs) generated on an AlN/Al2O3 microstructure by laser-micromachined grooves on the AlN film. In the absence of grooves, the AlN/Al2O3 device shows resonance for only a lower velocity SAW mode. However, when grooves of periodicity smaller than half the wavelength of the surface acoustic wave are micromachined, a higher velocity resonance due to a SH-SAW mode is observed in the device. It is found that our SH-SAW mode remains undamped and is able to propagate across the device when loaded with a biofluidic mass. We have also measured the mass sensitivity of the SH-SAW mode under biofludic load in terms of frequency shift. Measurements show that this mode has a very high mass sensitivity of the order 1.35 ng/ml, which suggests that the device can be applied for the detection of a small concentration of antigens in a biofluid. In this article, the fabrication and grooving techniques of the device are also addressed.

Guided propagation of surface acoustic waves in AlN and GaN films grown on4H–SiC(0001)substrates

The propagation modes of surface acoustic waves ~SAW! in AlN and GaN layers are identified for the case of the acoustic wave being confined in the epitaxial layers by the fast-velocity SiC substrate. Higher-order Rayleigh modes emerge when the SAW wavelength is reduced to be below the layer thickness. We also report on the observation of an extremely-high-velocity SAW mode, which exists when the SAW wavelength is about an order of magnitude larger than the layer thickness. These guided modes enable us to utilize SAW velocities which can be even larger than the Rayleigh velocity in the substrate while maintaining the large electromechanical coupling coefficient of the overlayer.

Surface-acoustic-wave directional coupler for apodization of integrated acoustooptic filters

A SAW waveguide directional coupler that was used to provide a raised-cosine apodization of the SAW beam intensity, in order to achieve sidelobe suppression of an integrated acoustooptic filter, is demonstrated. The SAW guide coupler consisted of two closely spaced, evanescently coupled parallel acoustic waveguides. A single guided SAW mode was excited by a miniature transducer imbedded in a 100-mum-wide waveguide, and in excess of 99% of the SAW energy was transferred from the original waveguide to the coupled guide, and back, across a gap of 20 mum. The coupling length (for complete crossover) was 9.8 mm and depended exponentially on gap, as expected. This SAW coupler resulted in 10-dB sidelobe suppression compared to an unapodized acoustooptic filter.

Design of SAW Sensor in Liquid

A SAW sensor in a liquid medium utilizing a leaky SAW mode having a shear horizontal displacement has been studied, and the device sensitivities have been investigated both theoretically and experimentally. Sensors of liquid viscosity and mass loading have been demonstrated utilizing the present mode on 36° rotated Y-cut X-propagation LiTaO3.