Multilayer SAW Structure With Thickness Tuning for Multi-Band Filters
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Solution Overview
Problem
Multilayer piezoelectric substrate (MPS) surface acoustic wave (SAW) devices face challenges in achieving optimal electrical properties, such as coupling factor k2 and temperature coefficient of frequency (TCF), due to the complexity of forming multiple acoustic wave elements in a single die with varying resonant frequencies and thicknesses of piezoelectric layers.
Innovation Solution
The implementation of a surface acoustic wave device with a multilayer piezoelectric structure featuring regions of different thicknesses and a sloped region between them, allowing for the formation of multiple acoustic wave elements with improved electrical properties by adjusting the thicknesses and angles of the piezoelectric layers, and incorporating a trap rich layer and functional layer to enhance energy confinement and mitigate unwanted reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple acoustic wave elements are formed in a single die with varying resonant frequencies, then the device can operate across multiple frequency bands, but the electrical properties (coupling factor k2 and TCF) become difficult to optimize
Solution Approach 1:
The piezoelectric layer is designed with different thicknesses in different regions: a first thickness in a first region for a first resonant frequency, and a second thickness in a second region for a second resonant frequency. This local variation in thickness allows each acoustic wave element to be optimized for its specific frequency band while maintaining optimal electrical properties (coupling factor k2 and TCF) for each region independently.
Solution Approach 2:
The piezoelectric layer is segmented into multiple regions with distinct thicknesses to support multiple acoustic wave elements with different resonant frequencies. The layer is divided such that each region can be independently optimized, with sloped regions separating areas of different thicknesses to enable precise control over acoustic wave propagation and electrical characteristics in each segment.
2Adaptability or versatility
If the piezoelectric layer thickness is varied to achieve different resonant frequencies, then multi-band operation is enabled, but the complexity of forming the structure increases
Solution Approach 1:
Instead of varying resonant frequencies through complex lateral geometry changes or multiple separate layers, the invention utilizes the thickness dimension of the piezoelectric layer. By controlling the thickness profile (with first, second, and sloped regions), the patent enables different resonant frequencies and optimized electrical properties using a single continuous layer, thereby reducing structural complexity compared to multi-layer approaches.
3Reliability
If sloped regions are added between different thickness regions, then acoustic wave reflections are reduced, but the manufacturing process becomes more complex
Solution Approach 1:
The invention introduces sloped regions between areas of different piezoelectric layer thicknesses. These sloped transitions replace abrupt step changes with gradual angular transitions, which reduce acoustic wave reflections and improve device reliability. The sloped regions are integrated into the layer formation process, allowing for controlled manufacturing through standard semiconductor fabrication techniques.
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 configuration enhances the coupling factor k2 and maintains low loss and suitable TCF, enabling the device to operate effectively across multiple frequency bands with reduced size and cost, while preventing damage during processing.
Implementation Method 1
a piezoelectric structure including a first region having a first thickness, a second region having a second thickness different from the first thickness, and a third region sloped between the first region and the second region; a first surface acoustic wave element positioned in the first region
Implementation Method 2
a third region sloped between the first region and the second region; an acoustic obstruction structure positioned at least partially between the first region and the second region
Data Source
AI summary
A surface acoustic wave device is disclosed. The surface acoustic wave device can include a support substrate structure, a first piezoelectric layer over the support substrate structure, a second piezoelectric layer over the first piezoelectric layer, and an interdigital transducer electrode in electrical communication with the second piezoelectric layer.