Surface Acoustic Wave Filter Layer Stack for Leakage Suppression
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Solution Overview
Problem
Conventional surface acoustic wave filters face challenges in achieving high frequencies due to low acoustic velocity in monocrystalline piezoelectric substrates, leading to energy leakage and increased spurious modes, which hinder their application in high-bandwidth communication technologies like 5G.
Innovation Solution
A surface acoustic wave filter with a multi-layer structure is proposed, featuring a support substrate with high acoustic velocity, a low acoustic velocity layer made of silicon dioxide, and a piezoelectric layer with specific Euler angles. This configuration creates a large acoustic velocity difference to reflect acoustic wave energy and reduce spurious modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If monocrystalline piezoelectric substrates are used, then the filter structure is simple, but the acoustic velocity is low leading to energy leakage and inability to achieve high frequencies
Solution Approach 1:
The patent uses a composite structure combining monocrystalline piezoelectric substrate with an acoustic velocity adjustment layer made of polycrystalline materials (such as aluminum nitride or silicon nitride). This composite approach allows the device to achieve high acoustic velocity (over 8000 m/s) while maintaining structural feasibility and manufacturability.
2Reliability
If high acoustic velocity mode is used, then operating frequency can be increased, but acoustic wave energy leaks to the piezoelectric substrate causing quality factor to decrease
Solution Approach 1:
The patent converts the potential harm of acoustic wave energy leakage into a beneficial effect by designing an acoustic velocity adjustment layer that creates an acoustic impedance mismatch. This mismatch reflects the acoustic wave energy back into the piezoelectric substrate, preventing leakage and actually improving the quality factor while maintaining high operating frequencies.
3Productivity
If conventional monocrystalline substrates are used, then manufacturing process is simple, but electrode width required for high frequency is close to theoretical limit of process line width
Solution Approach 1:
The patent changes the acoustic velocity parameter by introducing an acoustic velocity adjustment layer with different material properties. This allows the device to achieve high operating frequencies without requiring extremely narrow electrode widths, thus staying within the theoretical limits of process line width and maintaining manufacturability.
4Reliability
If layered structure is used to suppress energy leakage, then quality factor improves, but spurious modes increase requiring complex suppression means
Solution Approach 1:
The patent applies local quality by creating a specific layered structure with an acoustic velocity adjustment layer positioned at a particular location beneath the piezoelectric substrate. This localized structural modification effectively suppresses spurious modes while maintaining simplicity, avoiding the need for complex suppression means across the entire device.
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 proposed filter effectively suppresses energy leakage and reduces spurious modes, enabling the achievement of high operating frequencies and improving the quality factor of the device, thus enhancing its applicability in advanced communication technologies.
Implementation Method 1
the first acoustic velocity layer with a low acoustic velocity is disposed on the support substrate with a high acoustic velocity, so that a large acoustic velocity difference can be formed below the piezoelectric layer, that is, between the support substrate and the first acoustic velocity layer, so as to reflect acoustic wave energy that is propagated downward, thereby suppressing leakage of acoustic wave energy
Implementation Method 2
a piezoelectric layer, where the piezoelectric layer is disposed on the first acoustic velocity layer, Euler angles of a cut of the piezoelectric layer are (−5° to 5°, 81° to 83°, 85° to 95°), and a longitudinal wave acoustic velocity in the piezoelectric layer is higher than a longitudinal wave acoustic velocity in the first acoustic velocity layer
Data Source
AI summary
A surface acoustic wave filter includes a support substrate with a first acoustic velocity layer disposed above. The first acoustic velocity layer is silicon dioxide with a piezoelectric layer above. Euler angles of a cut of the piezoelectric layer are (−5° to 5°, 81° to 83°, 85° to 95°), and an interdigital electrode is disposed above the piezoelectric layer. A second acoustic velocity layer included between the first acoustic velocity layer and the support substrate; and a material of the second acoustic velocity layer is aluminum nitride or silicon nitride, where a longitudinal wave acoustic velocity in the first acoustic velocity layer is lower than a longitudinal wave acoustic velocity in the piezoelectric layer, and a longitudinal wave acoustic velocity in the second acoustic velocity layer is higher than the longitudinal wave acoustic velocity in the piezoelectric layer.