Article

A SAW Resonator With Two-Dimensional Reflectors

TriQuint Semiconductor, Apopka, FL, USA.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control (Impact Factor: 1.51). 01/2010; 57(1):30-7. DOI: 10.1109/TUFFC.2010.1375
Source: PubMed

ABSTRACT

It is known that a part of the loss of leaky SAW resonators is due to radiation of acoustic energy in the bus-bars. Many researchers are working on so-called phononic crystals. A 2-D grating of very strong reflectors allows these devices to fully reflect, for a given frequency band, any incoming wave. A new device based on the superposition of a regular SAW resonator and a 2-D periodic grating of reflectors is proposed. Several arrangements and geometries of the reflectors were studied and compared experimentally on 48 degrees rotated Y-cut lithium tantalate. In particular, a very narrow aperture (7.5 lambda) resonator was manufactured in the 900 MHz range. Because of its small size, this resonator has a resonance Q of only 575 when using the standard technology, whereas a resonance Q of 1100 was obtained for the new device without degradation of the other characteristics. Because of the narrow aperture, the admittance of the standard resonator showed a very strong parasitic above the resonance frequency, whereas this effect is drastically reduced for the new device. These results demonstrate the feasibility of the new approach.

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    • "Many researchers are working on the study of using 2D PCs on the SAWs devices. Marc [6] has proposed a SAW resonator with 2D reflectors which improved the Q of SAW resonator a lot. He analyzed the model of SAW resonator based on 2D reflectors with approximating the dots by a uniform metallic layer adopting finite element method (FEM)/boundary element method (BEM) used in 1D IDTs [7]. "
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    ABSTRACT: A three-dimensional (3D) finite element method (FEM) model was proposed to analyze the resonant modal of the transducers based on two-dimensional (2D) phononic crystals (PnCs). Using this model two modals existed with symmetric modal and anti-symmetric modal can be extracted, and then reflectivity of the transducers was derived. An example of transducer based on 2D PnCs composed of IDTs of aluminum strips and tungsten stubs on top of IDTs was analyzed. The calculated reflectivity with different thickness of the stubs shows that a optimal thickness of tungsten stubs exists for a specified IDTs. This modal analysis offer a useful tool for the optimal designing 2D PnCs on the surface acoustic waves devices.
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    • "On the other hand, classical 1D SAW resonators alleviate this problem by using transducers and reflectors of the same topology. As shown earlier by M. Solal [10] this also can be achieved in 2D periodic arrays employing planar technology. Here we further investigate this type of topology in view of both achieving a complete bandgap characteristics as well as design of novel transducer topologies without analog in the 1D design. "
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    ABSTRACT: 2D composite grating building blocks with hexagonal symmetry are proposed and analyzed as efficient reflectors and transducers in the design of low loss surface acoustic wave (SAW) resonators. Eigen-frequency and frequency response finite element analyses (FEA) are used to study the propagation and excitation characteristics of SAWs in the 2D composite structures. The proposed structures have the advantage of being compatible with the planar SAW technology, while exhibiting a complete frequency bandgap. Three distinct types SAW phononic transducers are here invented and their operation confirmed both analytically and experimentally. The proposed research paves the way for subsequent implementation of the phononic bandgap technology in high performance micro-acoustic RF components.
    No preview · Conference Paper · May 2014
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    ABSTRACT: It is well known than transverse effects like radiation in busbars are an important contribution in the loss of Leaky SAW resonators. Due to the complex nature of the wave and to the presence of several modes, scalar models are not sufficient to predict these effects. It is also known that the electrode gap has a strong impact on these effects. A periodic FEM/BEM model is presented and used to simulate the effect of the gap. Test devices are measured and compared with the simulation with a good agreement. The results show that smaller gaps are favorable.
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