Double-Layer SAW Electrode Structure for Higher Coupling
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Solution Overview
Problem
Current ZnO film-based SAW devices have a relatively low electromechanical coupling factor, limiting their application in high-frequency, low-loss, and large-bandwidth SAW filters needed for 5G technology.
Innovation Solution
A SAW device with a double-layer electrode structure comprising a Cu electrode, a piezoelectric film, and an Al electrode on a substrate, where the electrodes are oppositely configured to excite electric fields in specific directions, and a silicon oxide film fills the gap between the substrate and the piezoelectric film, enhancing the electromechanical coupling coefficient.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If ZnO film-based SAW device uses traditional single-layer electrode structure, then preparation is simple and cost is low, but electromechanical coupling coefficient is relatively low
Solution Approach 1:
The single-layer electrode structure is segmented into a double-layer electrode structure consisting of a first electrode layer (Cu) and a second electrode layer (Al). This segmentation allows each layer to contribute different properties: Cu provides high electromechanical coupling while Al provides high conductivity and oxidation resistance, thereby resolving the contradiction between manufacturing simplicity and electromechanical coupling coefficient.
Solution Approach 2:
The patent employs a composite electrode structure combining two different metal materials (Cu and Al) in a double-layer configuration. This composite approach leverages the complementary advantages of each material: Cu's high piezoelectric coupling capability and Al's excellent electrical conductivity and corrosion resistance, thus improving the overall electromechanical coupling coefficient while maintaining preparation feasibility.
2Ease of manufacture
If ZnO film-based SAW device uses Sezawa wave mode, then preparation is easier compared to bulk based devices, but electromechanical coupling factor is relatively low
Solution Approach 1:
The patent changes the structural parameters of the electrode system by introducing a double-layer configuration with specific thickness ratios (first electrode layer 50-150 nm, second electrode layer 50-150 nm). This parameter optimization enhances the electromechanical coupling factor while maintaining the Sezawa wave mode's preparation advantages, resolving the contradiction between ease of manufacture and electromechanical coupling factor.
3Stability of the object's composition
If AlN film is used as piezoelectric material, then temperature coefficient of frequency is stable, but electromechanical coupling coefficient is smaller compared to ZnO
Solution Approach 1:
The patent applies local quality optimization by using ZnO film in the piezoelectric layer where high electromechanical coupling is needed, while accepting that ZnO has higher temperature coefficient than AlN. The double-layer electrode structure compensates for ZnO's temperature instability by enhancing the electromechanical coupling through optimized electrode configuration, thus achieving local optimization of the coupling coefficient where it matters most for filter performance.
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 double-layer electrode structure significantly improves the electromechanical coupling coefficient, enabling the SAW device to meet the requirements for large-bandwidth filters, particularly in 5G applications.
Implementation Method 1
Surface acoustic wave (SAW) devices are electronic devices that transmit information based on the piezoelectric effect
Implementation Method 2
The Cu electrode and the Al electrode are prepared through electron beam evaporation
Implementation Method 3
The silicon oxide film is prepared through radio frequency magnetron sputtering
Data Source
AI summary
Disclosed are methods of preparing a Surface Acoustic Wave (SAW) device, comprising: sequentially depositing a Cu electrode, a silicon oxide film, modifying the surface of the silicon oxide film, and then depositing a piezoelectric film, and an Al electrode on a substrate having an interdigital (IDT) electrode pattern to obtain the SAW device. In some embodiments, the Cu and Al electrodes both have IDT electrode patterns corresponding to the IDT pattern of the substrate. Because the Sezawa wave mode that is adopted is formed by coupling film thickness vibration and transverse vibration, the present invention is characterized in that a longitudinal electric field and a transverse electric field are excited through the double-layer electrodes whereby the electromechanical coupling coefficient of the SAW device can be improved by changing the coupling pattern between the electric fields and the piezoelectric film.