SAW Resonator Bus Bar Structure for Transverse Mode Suppression
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Solution Overview
Problem
Suppression of high-order transverse mode spurious signals and ensuring a satisfactory quality factor (Q) have been challenging in surface acoustic wave (SAW) resonators with heavier electrodes on lower-cut-degree rotated Y-cut LiNbO3 substrates, especially when these electrodes are covered with SiO2 films for temperature compensation.
Innovation Solution
A surface acoustic wave resonator design incorporating a piezoelectric substrate with interdigital transducer electrodes, a first dielectric film of SiO2 for temperature compensation, and a second dielectric film of SiN with trenches and mini bus bar electrodes, which form a piston mode to confine oscillation energy and suppress high-order transverse modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heavier electrodes (Mo) are used to ensure high electromechanical coupling, then electromechanical coupling is improved, but high-order transverse mode spurious signals are generated
Solution Approach 1:
The patent applies local quality by creating a non-uniform dielectric film structure where the thickness varies across different regions. Specifically, the first dielectric film has different thicknesses in the electrode region versus the reflector region, and the second dielectric film has varying thicknesses across its surface. This localized variation in dielectric properties suppresses high-order transverse modes while maintaining the heavy electrode configuration for strong electromechanical coupling.
Solution Approach 2:
The patent employs composite materials by combining multiple dielectric layers (first dielectric film and second dielectric film) with different material properties and thicknesses. This composite dielectric structure works together with the heavy Mo electrodes to achieve both strong electromechanical coupling and suppression of spurious transverse modes through the combined effect of the layered dielectric configuration.
2Stability of the object's composition
If a dielectric film is added for temperature compensation, then temperature stability is improved, but suppression of high-order transverse modes becomes more difficult
Solution Approach 1:
The patent segments the dielectric film into multiple distinct layers: a first dielectric film for temperature compensation and a second dielectric film for transverse mode suppression. Each layer serves a specific function, with the first layer addressing temperature stability and the second layer targeting spurious signal suppression. This segmentation allows both temperature compensation and transverse mode suppression to be achieved simultaneously without compromising either function.
Solution Approach 2:
The patent implements local quality by varying the thickness of dielectric films across different regions. The first dielectric film has different thicknesses in electrode regions versus reflector regions, and the second dielectric film has non-uniform thickness distribution. This localized thickness variation enables the dielectric structure to perform both temperature compensation and transverse mode suppression functions effectively.
3Ease of manufacture
If conventional IDT electrode configurations are used, then manufacturing is simple, but transverse mode suppression is insufficient
Solution Approach 1:
The patent maintains conventional IDT electrode configurations for ease of manufacture while introducing local quality variations through the dielectric film structure. The electrode geometry remains standard and manufacturable, but the underlying and overlying dielectric films have region-specific thickness variations that suppress transverse modes. This approach achieves transverse mode suppression without complicating the electrode fabrication process.
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 design effectively suppresses high-order transverse mode spurious signals while maintaining a certain quality factor, ensuring better operating characteristics by confining energy distribution in a piston-like manner within the resonator.
Implementation Method 1
interdigital transducer electrodes disposed on an upper surface of the piezoelectric substrate... to excite a surface acoustic wave
Implementation Method 2
a first dielectric film for temperature compensation covering the interdigital transducer electrodes and the piezoelectric substrate
Data Source
AI summary
Aspects of this disclosure relate to a surface acoustic wave resonator. The surface acoustic wave resonator includes a piezoelectric substrate, interdigital transducer electrodes disposed on an upper surface of the piezoelectric substrate, a dielectric temperature compensation layer disposed on the piezoelectric substrate to cover the interdigital transducer electrodes, and a dielectric passivation layer over the temperature compensation layer. The passivation layer may include an oxide layer configured to have a sound velocity greater than that of the temperature compensation layer to suppress a transverse signal transmission.