Acoustic Wave Filter Stack With Spinel Layer 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 mitigated by incorporating a polycrystalline spinel layer.
Innovation Solution
Incorporating a polycrystalline spinel layer in acoustic wave devices, which suppresses higher-order modes by altering the propagation velocity of transverse-wave bulk waves, and adding a temperature compensating layer like silicon dioxide to stabilize frequency response across temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a multi-layer substrate with silicon-based materials is used, then the acoustic wave filter can be manufactured with standard materials and processes, but higher-order spurious modes occur that deteriorate out-of-band attenuation characteristics
Solution Approach 1:
The patent employs a composite substrate structure consisting of a silicon-based substrate layer combined with a spinel layer (MgAl2O4, MgGa2O4, or MgIn2O4). This composite material approach allows the device to maintain the manufacturability benefits of silicon-based materials while the spinel layer suppresses higher-order spurious modes through its specific acoustic properties, thereby improving out-of-band attenuation characteristics without sacrificing ease of manufacture
Solution Approach 2:
The spinel layer is strategically positioned between the piezoelectric layer and the silicon substrate, creating a localized region with different acoustic properties. This local modification targets specifically the spurious mode generation at the interface region while leaving the rest of the silicon-based manufacturing structure intact, thus resolving the contradiction between manufacturability and filter performance
2Length of moving object
If the piezoelectric layer thickness is reduced to less than λ, then the device can operate at higher frequencies with smaller dimensions, but the quality factor and frequency stability become more sensitive to temperature variations
Solution Approach 1:
The patent introduces a temperature compensating layer (silicon dioxide, silicon nitride, or aluminum oxide) with specific thermal expansion properties to counteract the temperature-induced frequency drift. This layer modifies the overall thermal response of the device structure, enabling frequency stability to be maintained even when the piezoelectric layer is thin and the device operates at higher frequencies with smaller dimensions
Solution Approach 2:
By combining the thin piezoelectric layer with the temperature compensating layer and the spinel layer, the patent creates a multi-layer composite structure where each layer contributes specific properties: the thin piezoelectric layer enables high-frequency operation with small size, while the compensating and spinel layers collectively provide temperature stability and spurious mode suppression
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 polycrystalline spinel layer enhances the quality factor and out-of-band attenuation characteristics, while the temperature compensating layer reduces frequency variation with temperature, improving the overall performance of acoustic wave filters.
Implementation Method 1
the polycrystalline spinel layer, which suppresses higher-order modes by altering the propagation velocity of transverse-wave bulk waves
Implementation Method 2
adding a temperature compensating layer like silicon dioxide to stabilize frequency response across temperature variations
Implementation Method 3
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
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.