Acoustic Wave Filter Stack With Spinel Layer for Out-of-Band Attenuation
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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 are generated that deteriorate out-of-band attenuation characteristics
Solution Approach 1:
The patent employs a composite substrate structure consisting of a silicon base layer combined with a spinel layer. This composite material approach leverages the manufacturing advantages of silicon while introducing spinel's acoustic properties to suppress spurious modes, thereby resolving the contradiction between ease of manufacture and out-of-band attenuation performance
Solution Approach 2:
The patent modifies the acoustic impedance parameters of the substrate by introducing a spinel layer with specific acoustic properties. By changing the acoustic impedance profile through this intermediate layer, the generation of higher-order spurious modes is suppressed, improving out-of-band attenuation while maintaining the silicon-based manufacturing process
2Volume of moving object
If the piezoelectric layer thickness is reduced to less than λ, then the device size is minimized, but the quality factor and out-of-band attenuation are affected by spurious modes
Solution Approach 1:
The composite silicon-spinel substrate structure is designed to work synergistically with the thin piezoelectric layer. The spinel layer's acoustic impedance characteristics compensate for the reduced piezoelectric layer thickness, maintaining quality factor and suppressing spurious modes despite the minimized device size
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 and manufacturing process become more complex
Solution Approach 1:
The substrate is segmented into distinct functional layers: a silicon base layer providing mechanical support and manufacturing advantages, and a spinel layer providing acoustic wave filtering properties. This segmentation allows each layer to be optimized independently while working together to suppress spurious modes
4Stability of the object's composition
If a temperature compensating layer is added between the spinel layer and piezoelectric layer, then temperature stability is improved, but the device structure becomes more complex
Solution Approach 1:
The temperature compensating layer acts as an intermediary between the spinel substrate layer and the piezoelectric layer. This intermediate layer provides thermal expansion compensation and stress management, stabilizing the acoustic wave properties across temperature variations while maintaining a modular layered 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
The use of a polycrystalline spinel layer in acoustic wave devices effectively suppresses higher-order spurious modes, enhancing the quality factor and out-of-band attenuation characteristics, leading to improved performance in filtering radio frequency signals.
Implementation Method 1
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
Implementation Method 2
The polycrystalline spinel layer can be in physical contact with the piezoelectric layer... the polycrystalline spinel layer helps in lowering the cutoff frequency without affecting the shear horizontal mode, thereby suppressing higher-order spurious modes
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, a temperature compensating layer between the spinel layer and the 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 that is less than λ. In some embodiments, the spinel layer can be a polycrystalline spinel layer.