Partially Rounded IDT Electrodes for SAW Passband Ripple Control
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Solution Overview
Problem
Surface acoustic wave filters face performance degradation due to transverse leakage, which affects the accuracy and stability of radio frequency signals, particularly in mobile phone front ends, where strong transverse modes cause passband ripples and limited rejection.
Innovation Solution
The implementation of a partially or selectively rounded interdigital transducer electrode with varying corner radii and widths in different regions, along with a support substrate and intermediate layers, to create a piston mode that suppresses transverse waves without additional complex structures like silicon nitride layers or mass loading strips.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional interdigital transducer electrodes with sharp corners are used, then the device structure is simple and easy to manufacture, but transverse modes are not suppressed causing passband ripples and limited rejection
Solution Approach 1:
The electrode fingers are designed with different corner radii in different regions: larger corner radii in border regions and smaller corner radii in center regions. This local variation in geometric properties creates different acoustic impedance characteristics across the electrode surface, which suppresses transverse modes while maintaining the overall simplicity of the interdigital transducer structure.
Solution Approach 2:
The sharp corners of traditional rectangular electrode fingers are replaced with rounded corners having specific radius values. This curvature modification at the finger corners changes the acoustic wave propagation characteristics, effectively suppressing transverse modes and eliminating passband ripples without requiring additional complex structures.
2Reliability
If additional structures like silicon nitride layers or mass loading strips are added to suppress transverse modes, then transverse mode suppression is achieved, but the device complexity and manufacturing process are increased
Solution Approach 1:
Instead of adding physical structures, the invention modifies the geometric parameters of the existing electrode fingers by varying the corner radii across different regions. This parameter change approach achieves transverse mode suppression through acoustic impedance variation created by the rounded corners, eliminating the need for additional layers or mass loading structures.
3Reliability
If uniformly rounded corners are applied to all electrode fingers, then transverse modes are suppressed, but the manufacturing precision requirements increase
Solution Approach 1:
The electrode structure incorporates two distinct types of corners: rounded corners in border regions and sharper corners in center regions. This local differentiation allows each region to contribute differently to transverse mode suppression while providing manufacturing tolerance, as not all corners require the same high-precision rounding.
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 design effectively suppresses transverse modes, maintaining high-quality factor and electromechanical coupling while reducing the complexity of the acoustic wave device, thereby enhancing the accuracy and stability of radio frequency filters.
Implementation Method 1
Each resonator can include a surface acoustic wave device. Example piezoelectric MEMS resonators include surface acoustic (SAW) resonators
Implementation Method 2
a corner between the upper side and the sidewall is more rounded in the second region than in the first region... effectively suppresses transverse modes
Data Source
AI summary
An acoustic wave device is disclosed. The acoustic wave device can include a piezoelectric layer, and an interdigital transducer electrode formed with the piezoelectric layer. The interdigital transducer electrode includes a finger extending from a bus bar. The finger has a first region and a second region between the first region and the bus bar. The finger has a lower side, an upper side opposite the lower side, and a sidewall between the lower side and the upper side. A corner between the upper side and the sidewall is more rounded in the second region than in the first region.