Acoustic Wave Electrode Layout With Edge-Thinned Piezoelectric Film
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Solution Overview
Problem
Existing acoustic wave devices suffer degradation of electromechanical coupling coefficient and Q characteristics due to the need for increased electrode finger width or mass addition layers to reduce acoustic velocities in specific regions.
Innovation Solution
The acoustic wave device incorporates a piezoelectric film with varying thicknesses in different regions, specifically setting the thickness of the central region and edge regions to achieve lower acoustic velocities without altering electrode finger width or adding mass, by ensuring He < Ht, where λ is the electrode finger pitch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a low-acoustic-velocity region is provided by increasing electrode finger width or adding mass addition layer, then transverse-mode ripples are suppressed, but electromechanical coupling coefficient and Q characteristics degrade
Solution Approach 1:
The invention applies local quality by creating a low-acoustic-velocity region through selective thinning of the piezoelectric film only in the edge regions of the intersecting region, while maintaining the original film thickness in the central region. This localized modification suppresses transverse-mode ripples without affecting the overall electromechanical coupling coefficient and Q characteristics, as the electrode finger width and mass distribution remain unchanged.
Solution Approach 2:
The invention changes the physical parameter of piezoelectric film thickness locally in the edge regions to reduce acoustic velocity. By controlling the film thickness to be thinner in edge regions compared to the central region, the acoustic velocity is reduced without requiring mass addition layers or electrode finger width increases, thereby avoiding degradation of electromechanical coupling coefficient and Q characteristics.
2Object-affected harmful factors
If electrode finger width is increased to reduce acoustic velocity in edge regions, then transverse-mode ripples are suppressed, but device complexity and manufacturing precision requirements increase
Solution Approach 1:
The invention maintains uniform electrode finger width across all regions, applying local quality only to the piezoelectric film thickness in the edge regions. This approach suppresses transverse-mode ripples without complicating the electrode finger structure, keeping the device design simple and manufacturing straightforward.
3Object-affected harmful factors
If mass addition layer is stacked on electrode finger to reduce acoustic velocity, then transverse-mode ripples are suppressed, but electromechanical coupling coefficient degrades
Solution Approach 1:
The invention changes the piezoelectric film thickness parameter instead of adding mass addition layers. By making the piezoelectric film thinner in the edge regions, the acoustic velocity is reduced without adding extra mass that would degrade the electromechanical coupling coefficient. This approach achieves ripple suppression while preserving the coupling between electrical and mechanical energy in the piezoelectric material.
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 effectively reduces or prevents transverse-mode ripples while maintaining electromechanical coupling coefficient and Q characteristics, avoiding degradation commonly seen in previous designs.
Implementation Method 1
a piezoelectric film 4 stacked directly on or indirectly above the support substrate 2
Implementation Method 2
Acoustic velocities of acoustic waves in the first and second edge regions are lower than an acoustic velocity of an acoustic wave in the central region
Data Source
AI summary
An acoustic wave device includes a piezoelectric film stacked directly on or indirectly above a support substrate; and an IDT electrode on the piezoelectric film and including an intersecting region in which first and second electrode fingers overlap with each other in an acoustic wave propagation direction, the intersecting region includes a central region in a direction in which the first and second electrode fingers extend and first and second edge regions on sides outside the central region, acoustic velocities in the first and second edge regions are lower than an acoustic velocity in the central region, a thickness Ht in the central region is different from thicknesses He in the first and second edge regions, and at least either of Ht and He is not more than about 1λ, where λ is a wavelength which is determined by an electrode finger pitch of the IDT electrode.