Acoustic Wave Filter Trenches for Transverse Mode Suppression
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Solution Overview
Problem
Existing acoustic wave devices face challenges in effectively suppressing transverse modes without increasing device size or reducing electromechanical coupling coefficients, as current methods either decrease static capacitance or damage central regions during fabrication.
Innovation Solution
Incorporating trench portions in the piezoelectric layer overlapping with edge regions of interdigital transducer electrodes, which increase effective thickness and create a piston mode distribution without altering the duty factor in the central region, thus preventing size increase and central region damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hammer head portions are added to electrode fingers in edge regions to suppress transverse modes, then transverse mode suppression is improved, but device size increases due to reduced static capacitance requiring larger IDT
Solution Approach 1:
The patent introduces trench portions only in the edge regions of the piezoelectric layer, creating local structural variations that generate piston mode distribution to suppress transverse modes. This localized approach avoids modifying the entire device structure, thereby preventing overall size increase while achieving the desired mode suppression effect.
Solution Approach 2:
Instead of modifying the electrode finger geometry in the planar dimension (which would increase device area), the patent introduces trenches in the vertical dimension by removing piezoelectric material. This dimensional shift allows transverse mode suppression through acoustic velocity reduction without expanding the device footprint.
2Reliability
If duty factor in central region is reduced below 0.5 to achieve velocity difference for transverse mode suppression, then transverse mode suppression is improved, but static capacitance decreases leading to larger device size
Solution Approach 1:
The patent creates acoustic velocity differences locally in the edge regions through trench portions, rather than globally reducing the duty factor in the central region. This localized modification maintains the central region's duty factor above 0.5, preserving static capacitance while still achieving transverse mode suppression through the piston mode distribution created by the trenches.
3Reliability
If mass loading strips are formed on edge regions to suppress transverse modes, then transverse mode suppression is improved, but central region becomes damaged during fabrication
Solution Approach 1:
Instead of adding mass loading strips that require complex fabrication processes potentially damaging the central region, the patent extracts material by forming trenches in the piezoelectric layer. This removal-based approach uses simpler etching processes that can be precisely controlled to affect only the edge regions, leaving the central region intact and undamaged.
4Reliability
If thicker passivation layer is used in central region to suppress transverse modes, then transverse mode suppression is improved, but electromechanical coupling coefficient is reduced
Solution Approach 1:
The patent achieves transverse mode suppression through localized trench portions in the edge regions rather than using a thicker passivation layer in the central region. This approach creates piston mode distribution where needed without interfering with the electromechanical coupling in the central region, thereby maintaining high coupling coefficients while still suppressing transverse modes.
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
The solution effectively suppresses transverse modes while maintaining high electromechanical coupling coefficients and power durability, and simplifies fabrication by avoiding central region damage during trench formation.
Implementation Method 1
a layer of piezoelectric material 506 disposed on the layer of dielectric material 104
Implementation Method 2
An interdigital transducer electrode (IDT) 108 is disposed on top of the layer of piezoelectric material 106
Data Source
AI summary
An acoustic wave device, a radio frequency filter and an electronics module are provided. The acoustic wave device comprises a layer of piezoelectric material, a pair of interdigital transducer electrodes disposed on an upper surface of the layer of piezoelectric material, each interdigital transducer electrode including a bus bar and a plurality of electrode fingers extending from the bus bar towards an edge region of the interdigital transducer electrode at the distal ends of the electrode fingers, and trench portions located in the upper surface of the layer of piezoelectric material, the trench portions overlapping with the edge regions of the interdigital transducer electrodes. The acoustic wave device provides effective suppression of transverse modes.