Interdigitated Acoustic Wave Electrode Layout for Wider Pass-Bands
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Solution Overview
Problem
Existing acoustic wave devices utilizing bulk waves in thickness shear mode face challenges in achieving desirable filter characteristics, such as increased electrostatic capacitance and pass-band width, without increasing the size of the filter device.
Innovation Solution
The acoustic wave device incorporates a piezoelectric film with a specific configuration of comb-shaped electrodes and a third electrode connected to a reference potential, arranged in a sequence that defines one period, allowing for a reduced size and increased pass-band width.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the electrostatic capacitance of an acoustic wave resonator is increased by enlarging the resonator, then the electrostatic capacitance is improved, but the size of the ladder filter is increased
Solution Approach 1:
The electrode structure is segmented into multiple electrode fingers (first electrode fingers and second electrode fingers) arranged in an interdigitated pattern. This segmentation increases the effective capacitance area without proportionally increasing the overall device footprint, as the electrodes are stacked in a compact interdigitated arrangement rather than spread out linearly
Solution Approach 2:
The patent transitions from a one-dimensional linear arrangement of electrodes to a two-dimensional interdigitated pattern. The electrode fingers are arranged both in the direction of wave propagation and perpendicular to it, creating a compact structure that increases capacitance through vertical stacking and lateral interdigitating, thereby improving capacitance without linearly increasing the filter size
2Device complexity
If a simple configuration with input and output electrodes is used, then the device complexity is reduced, but the pass-band width is insufficient
Solution Approach 1:
The electrode structure is divided into multiple segments (first electrode fingers and second electrode fingers) arranged in an interdigitated pattern. This segmentation creates multiple resonance paths and coupling zones, which broaden the pass-band width while maintaining a relatively simple overall configuration that can be fabricated using standard processes
Solution Approach 2:
Different regions of the electrode structure are given different functions: the first electrode fingers and second electrode fingers are arranged to create specific coupling zones with varying capacitance distributions. This local differentiation of electrode properties enables broadband performance through distributed resonance modes, achieving increased pass-band width without requiring a completely complex multi-resonator structure
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enables a filter device to have a reduced size and an increased pass-band width, effectively addressing the limitations of existing technologies while maintaining desirable filter waveforms.
Implementation Method 1
a piezoelectric layer is disposed on a support. Electrodes defining an electrode pair are disposed on the piezoelectric layer... By application of alternating-current voltage between the electrodes, a bulk wave in thickness shear mode is excited
Data Source
AI summary
An acoustic wave device includes a piezoelectric layer, first and second comb-shaped electrodes, and a third electrode. The first comb-shaped electrode is on the piezoelectric layer, connected to an input potential, and including a first busbar, and first electrode fingers. The second comb-shaped electrode is on the piezoelectric layer, connected to an output potential, and including a second busbar, and second electrode fingers. The third electrode is connected to a potential different from the first and second comb-shaped electrodes, and includes third electrode fingers, and a connection electrode. The connection electrode interconnects adjacent third electrode fingers. The first electrode finger, the third electrode finger, the second electrode finger, and the third electrode finger are arranged in this order. A ratio d/p is greater than or equal to about 0.05.