Abstract
Electrode-width-controlled (EWC) single-phase unidirectional transducers (SPUDT) contribute to reduction of insertion loss of surface acoustic wave (SAW) devices due to their strong unidirectional properties. In this work, we propose a method to optimize the unidirectionality of EWC-SPUDT based on our research results that the unidirectionality of the EWC-SPUDT cell is strongly related to its reflectivity and its unidirectional angle. Furthermore, in order to ensure strong unidirectionality to achieve low insertion loss, a simulator based on the finite element method (FEM) is used to study the relationship between geometrical configuration of the EWC-SPUDT cell and its reflection coefficient, as well as its transduction coefficient. Simulation results indicate that the reflection coefficient of the optimized EWC-SPUDT cell composed of 128° YX lithium niobite (LiNbO3) substrate and Al electrodes with thickness of 0.3μm reaches the optimal value of 5.17% when the unidirectional angle is designed to be −90°. A SAW delay line is developed with the optimized EWC-SPUDT cell without weighing, and the simulation results are verified by experiments. The experimental results show that the directivity exceeds 30 dB at the center frequency and the insertion loss is just 6.7 dB.
Highlights
Single-phase unidirectional transducers (SPUDT) are frequently employed in surface acoustic wave (SAW) devices to reduce bidirectional loss and to suppress triple transit echo [1,2,3,4]
In order to describe its performance, the following two parameters are listed: the reflectivity |κ |λ, and the unidirectional angle θ, which is defined as θ = φκ − 2φα, where φκ and φα are the phases of reflection coefficient and transduction, respectively [9]
The results indicate that the simulation results coincide with the experimental results expected at the side-lobes, that is to say, the experiment confirms that our theoretical analysis process is reasonable
Summary
Single-phase unidirectional transducers (SPUDT) are frequently employed in surface acoustic wave (SAW) devices to reduce bidirectional loss and to suppress triple transit echo [1,2,3,4]. DART [5], electrode-width-controlled (EWC) [6], and other SPUDT cells [7,8]. Are the best-known cell types, of which the EWC-SPUDT is the most widely used. A traditional EWC-SPUDT cell consists of three fingers, two narrow electrodes, and one wide electrode, whose widths are λ/8 and λ/4, respectively. In order to describe its performance, the following two parameters are listed: the reflectivity |κ |λ, and the unidirectional angle θ, which is defined as θ = φκ − 2φα , where φκ and φα are the phases of reflection coefficient and transduction, respectively [9]. According to our calculation of a traditional EWC-SPUDT cell, |κ |λ is 1.37% and θ is −83.58◦ , which are very close to the results presented in [10]
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