Spinel-Layer Acoustic Wave Filter for Spurious Mode Suppression
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Solution Overview
Problem
Acoustic wave filters in radio frequency systems face challenges with higher-order spurious modes that deteriorate out-of-band attenuation characteristics, particularly in multi-layer substrates with silicon-based materials, which can be addressed by incorporating a polycrystalline spinel layer to suppress these modes.
Innovation Solution
The integration of a polycrystalline spinel layer in acoustic wave devices, which has a lower transverse-wave bulk wave velocity than silicon, helps in lowering the cutoff frequency without affecting the shear horizontal mode, thereby suppressing higher-order spurious modes and improving the quality factor and out-of-band attenuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a silicon-based multi-layer substrate is used in acoustic wave filters, then the device structure is simplified and manufacturing is easier, but higher-order spurious modes occur that deteriorate out-of-band attenuation characteristics
Solution Approach 1:
The patent applies composite materials by combining a silicon-based substrate with a polycrystalline spinel layer to create a multi-layer structure. This composite approach allows the device to maintain the manufacturing advantages of silicon while adding the spinel layer's ability to suppress higher-order spurious modes, thereby improving out-of-band attenuation without sacrificing ease of manufacture.
2Volume of moving object
If the piezoelectric layer thickness is reduced to improve device integration, then the device size is reduced, but the quality factor and out-of-band attenuation may be affected
Solution Approach 1:
The patent uses a composite structure with a polycrystalline spinel layer combined with a thin piezoelectric layer. The spinel layer provides acoustic impedance mismatch that suppresses bulk acoustic wave leakage, allowing the piezoelectric layer to be made thinner for compact device size while maintaining the quality factor through the spinel layer's protective effect.
3Reliability
If a polycrystalline spinel layer is added to suppress higher-order spurious modes, then out-of-band attenuation is improved, but the device structure becomes more complex
Solution Approach 1:
The patent applies segmentation by dividing the substrate structure into distinct functional layers: a silicon-based substrate layer and a polycrystalline spinel layer. This segmentation allows each layer to perform its specific function - the silicon provides mechanical support and ease of manufacture, while the spinel layer specifically targets and suppresses higher-order spurious modes, achieving improved out-of-band attenuation with a relatively simple added structure.
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 quality factor and out-of-band attenuation characteristics by shifting higher-order spurious modes to higher frequencies, effectively filtering radio frequency signals with improved accuracy.
Implementation Method 1
The polycrystalline spinel layer can be in physical contact with the piezoelectric layer. The piezoelectric layer can have a thickness that is less than λ, in which λ is a wavelength of an acoustic wave generated by the acoustic wave device
Implementation Method 2
A surface acoustic wave resonator can include an interdigital transductor electrode on a piezoelectric substrate. The surface acoustic wave resonator can generate a surface acoustic wave on a surface of the piezoelectric layer on which the interdigital transductor electrode is disposed
Implementation Method 3
The acoustic wave device can further include a temperature compensating layer disposed between the polycrystalline spinel layer and the piezoelectric layer
Data Source
AI summary
An acoustic wave device that includes a spinel layer, a piezoelectric layer and an interdigital transducer electrode on the piezoelectric layer is disclosed. The piezoelectric layer is disposed between the interdigital transducer electrode and the spinel layer. The acoustic wave device is configured to generate an acoustic wave having a wavelength of λ. The piezoelectric layer can have a thickness than is less than λ. In some embodiments, the acoustic wave device can include a temperature compensating layer that is disposed between the piezoelectric layer and the spinel layer.