Rounded IDT Electrode Geometry for SAW Transverse Mode Suppression
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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 oscillators and sensors, and introduces passband ripples and limited rejection in radio frequency applications.
Innovation Solution
The implementation of a partially rounded interdigital transducer electrode with a corner radius in the range of 0.01 to 0.1 times the wavelength, where the corner in the second region is more rounded than in the first region, helps in suppressing transverse modes without additional structural complexities like silicon nitride layers or mass loading strips.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional interdigital transducer electrodes with sharp corners are used, then the device structure is simple, but transverse leakage occurs causing performance degradation
Solution Approach 1:
The patent applies local quality by differentiating the corner radius across different regions of the interdigital transducer electrode. Specifically, fingers in the center region have a first corner radius while fingers in border regions have a second corner radius that is smaller than the first. This localized variation suppresses transverse leakage at the borders while maintaining the electromechanical coupling coefficient in the center region, thereby improving performance stability without requiring entirely new structural approaches.
Solution Approach 2:
The patent changes the geometric parameter of the electrode fingers by introducing different corner radii in different regions. The corner radius is a critical parameter that affects both transverse leakage and electromechanical coupling. By optimizing this parameter locally (larger radius in center, smaller radius at borders), the patent achieves suppression of transverse modes while preserving the desired coupling characteristics, resolving the contradiction between performance and structural simplicity.
2Reliability
If additional structural elements like silicon nitride layers or mass loading strips are added to suppress transverse modes, then transverse leakage is reduced, but device complexity increases
Solution Approach 1:
The patent extracts the transverse mode suppression function from separate structural elements (such as silicon nitride layers or mass loading strips) and integrates it directly into the interdigital transducer electrode geometry itself. By modifying the corner radii of the electrode fingers, the patent achieves transverse mode suppression as an inherent property of the electrode structure, eliminating the need for additional layers or components and thus maintaining device simplicity.
Solution Approach 2:
The patent merges the transverse mode suppression function with the electrode structure by incorporating differentiated corner radii directly into the finger geometry. This consolidation allows the electrode to simultaneously perform its primary function of generating surface acoustic waves and its secondary function of suppressing transverse modes, thereby reducing overall device complexity while achieving the desired performance improvement.
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 approach effectively suppresses transverse modes, maintaining the electromechanical coupling coefficient and quality factor, while reducing structural complexity and enhancing the performance of surface acoustic wave devices in 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
an interdigital transducer electrode formed with the piezoelectric layer
Data Source
AI summary
A method of forming an acoustic wave device is disclosed. The method can include providing a piezoelectric layer, forming an interdigital transducer electrode with the piezoelectric layer, and selectively removing at least a portion of the interdigital transducer electrode. 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, a sidewall between the lower side and the upper side, and a corner between the upper side and the sidewall. Selectively removing at least a portion of the interdigital transducer electrode includes selectively removing at least a portion of the second region of the finger such that the corner in the second region of the finger has a more rounded corner than the corner in the first region.