Stacked Acoustic Wave Resonators for Compact Filter Waveforms
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Solution Overview
Problem
Existing acoustic wave devices using bulk waves in a thickness shear mode face challenges in achieving satisfactory filter characteristics without increasing the size of the device, as they require larger resonators to enhance electrostatic capacitance, leading to increased filter sizes.
Innovation Solution
The implementation of a configuration featuring a first and second acoustic wave resonator with a piezoelectric layer and a functional electrode, along with an acoustic coupling layer between them, where the thickness of the piezoelectric layer and the center-to-center distance between electrode fingers are optimized to maintain a d/p ratio of 0.5 or smaller, allowing for effective excitation of the thickness shear mode without increasing the device size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the size of the acoustic wave resonator is increased to enhance electrostatic capacitance, then the electrostatic capacitance is improved, but the size of the ladder filter increases
Solution Approach 1:
The patent transitions from a planar configuration to a three-dimensional stacked configuration by placing multiple acoustic wave resonators vertically on the substrate. This vertical stacking enables increased electrostatic capacitance through enhanced coupling in the thickness direction without increasing the planar footprint, thereby resolving the contradiction between capacitance enhancement and filter size reduction
Solution Approach 2:
The patent optimizes the thickness of the piezoelectric layer and the center-to-center distance between electrode fingers (d/p ratio of 0.5 or smaller) to enhance the thickness shear mode excitation efficiency. This parameter optimization increases electrostatic capacitance per unit area, allowing compact filter design with improved capacitance characteristics
2Reliability
If the size of the acoustic wave resonator is increased to obtain satisfactory filter characteristics, then the filter characteristics are improved, but the size of the acoustic wave device increases
Solution Approach 1:
By stacking acoustic wave resonators vertically in the thickness direction, the patent achieves improved filter characteristics through enhanced electrostatic coupling and better resonance control without increasing the planar device footprint, thus resolving the contradiction between filter performance and device compactness
Solution Approach 2:
The patent divides the filter into multiple independent acoustic wave resonator units that are stacked vertically. Each resonator can be independently designed and optimized, allowing satisfactory filter characteristics to be achieved through the collective performance of multiple compact units rather than a single large resonator
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 the attainment of suitable filter waveforms with reduced filter device size by enhancing electrostatic capacitance and coupling strength, while maintaining efficient resonance characteristics and minimizing spurious modes.
Implementation Method 1
a piezoelectric layer provided on a support body. A pair of electrodes are provided on the piezoelectric layer. An alternating current voltage is applied between the electrodes to excite the bulk wave in the thickness shear mode
Implementation Method 2
an acoustic coupling layer laminated between the piezoelectric layer of the first acoustic wave resonator and the piezoelectric layer of the second acoustic wave resonator
Data Source
AI summary
An acoustic wave device includes first and second acoustic wave resonators, each including a piezoelectric layer and a functional electrode, and an acoustic coupling layer laminated between the piezoelectric layer of each of the first and second acoustic wave resonators. Each of the functional electrodes of the first and second acoustic wave resonators includes at least one pair of electrode fingers. In each of the first and second acoustic wave resonators, when a thickness of the piezoelectric layer is defined as d and a center-to-center distance of the electrode fingers adjacent to each other is defined as p, d/p is about 0.5 or smaller. The first and second acoustic wave resonators face each other across the acoustic coupling layer.