Acoustic Wave Electrode Structure for Low-Resistance Compact Filters
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Solution Overview
Problem
Existing acoustic wave devices using bulk waves in a thickness shear mode face challenges in reducing the size of filter devices while maintaining satisfactory filter characteristics, due to high electrical resistance and instability of electrodes connected to reference potentials.
Innovation Solution
The acoustic wave device incorporates a piezoelectric film with a comb-shaped electrode configuration, including a third electrode connected to a reference potential, which is arranged to intersect with other electrodes through an insulator layer, reducing electrical resistance and stabilizing potential.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the size of the acoustic wave resonator is increased to increase electrostatic capacitance, then the electrostatic capacitance is improved, but the size of the filter device increases
Solution Approach 1:
The patent introduces a third electrode connected to reference potential that extends in the direction orthogonal to the signal transmission path, utilizing the vertical dimension (thickness direction of piezoelectric film) to reduce electrical resistance without increasing the planar footprint of the filter device
Solution Approach 2:
The third electrode is divided into multiple third electrode fingers that are arranged side by side and connected by third busbars, segmenting the reference potential connection into multiple parallel paths to reduce overall electrical resistance
2Loss of energy
If the width of the electrode connected to reference potential is increased to reduce electrical resistance, then the electrical resistance is improved, but the layout freedom is reduced
Solution Approach 1:
Instead of increasing electrode width in the planar direction, the patent extends the third electrode in the thickness direction of the piezoelectric film, utilizing the vertical dimension to reduce electrical resistance while maintaining layout freedom in the planar direction
Solution Approach 2:
The third electrode is segmented into multiple thin third electrode fingers connected by third busbars, achieving low electrical resistance through multiple parallel paths without requiring any single electrode to have large width
3Loss of energy
If the length of the electrode connected to reference potential is increased to reduce electrical resistance, then the electrical resistance is improved, but the potential stability deteriorates due to long routing
Solution Approach 1:
The third electrode is divided into multiple short third electrode fingers rather than one long electrode, with each finger connected to third busbars that provide low-inductance connections to the reference potential, reducing both electrical resistance and potential instability
Solution Approach 2:
The third electrode fingers extend in the thickness direction of the piezoelectric film rather than along the signal transmission path, shortening the routing length in the planar direction while maintaining effective reference potential connection
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 reduction in the size of filter devices and decreases the electrical resistance of electrodes connected to reference potentials, thereby improving the stability and filter characteristics of the device.
Implementation Method 1
A piezoelectric layer is provided on a support body. A pair of electrodes are provided on the piezoelectric layer. The pair of electrodes face each other on the piezoelectric layer, and are connected to mutually different potentials. An alternating current (AC) voltage is applied between the electrodes to excite the bulk wave in the thickness shear mode.
Data Source
AI summary
An acoustic wave device includes a piezoelectric film including a piezoelectric layer including a piezoelectric body, one of first and second comb electrodes connected to an input potential and the other of the first and second comb electrodes connected to an output potential. An order in which a first electrode finger, a second electrode finger, and a third electrode finger are arranged side by side is an order in which the first electrode finger, the third electrode finger, the second electrode finger, and the third electrode finger are set as one period when the order is started from the first electrode finger. At least one of a portion of the first comb electrode and a portion of the third electrode, and a portion of the second comb electrode and a portion of the third electrode intersects each other on the piezoelectric layer with the insulator layer interposed therebetween.