Elastic Wave Layer Stack for Acoustic Confinement and Low Loss
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Solution Overview
Problem
Existing elastic wave devices suffer from significant propagation loss and inability to effectively confine surface acoustic waves, leading to low Q factors and energy leakage into dielectric substrates, which hinders frequency enhancement.
Innovation Solution
The device incorporates a high-acoustic-velocity supporting substrate with a low-acoustic-velocity film and a piezoelectric film, distributing energy between these layers to enhance confinement and reduce leakage, using materials like silicon oxide and aluminum nitride to adjust acoustic velocities and electromechanical coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a hard dielectric layer is formed between the dielectric substrate and piezoelectric film to increase acoustic velocity, then the frequency of the surface acoustic wave device can be increased, but propagation loss increases and surface acoustic waves cannot be effectively confined within the piezoelectric thin film
Solution Approach 1:
The patent applies local quality by creating distinct acoustic velocity zones: a high acoustic velocity layer adjacent to the piezoelectric film and a low acoustic velocity layer at the substrate interface. This localized variation in acoustic properties confines surface acoustic waves within the piezoelectric film region, preventing energy leakage into the substrate while maintaining high frequency operation.
Solution Approach 2:
The patent uses composite material structure with multiple layers having different acoustic velocities. The combination of high acoustic velocity material (such as aluminum nitride or silicon carbide) and low acoustic velocity material (such as silicon oxide or silicon nitride) creates an acoustic waveguide structure that confines surface acoustic waves, reducing propagation loss while enabling high frequency operation.
2Speed
If a hard dielectric layer is formed to increase acoustic velocity, then frequency can be increased, but surface acoustic waves leak into the dielectric substrate resulting in low Q factor
Solution Approach 1:
The patent implements local quality by positioning a high acoustic velocity layer specifically adjacent to the piezoelectric film where surface acoustic waves propagate, and a low acoustic velocity layer at the substrate interface. This localized acoustic velocity gradient creates an effective waveguide that confines energy within the active region, preventing leakage into the substrate and maintaining high Q factor.
Solution Approach 2:
The patent introduces an intermediary low acoustic velocity layer between the high acoustic velocity layer and the dielectric substrate. This intermediary layer acts as an acoustic barrier that reflects surface acoustic waves back into the piezoelectric film region, preventing energy leakage into the substrate and thereby maintaining high Q factor while still benefiting from the high acoustic velocity layer.
3Speed
If the piezoelectric film thickness is reduced to enable higher frequency operation, then frequency can be increased, but electromechanical coupling coefficient decreases
Solution Approach 1:
The patent applies parameter changes by modifying the acoustic velocity distribution through the introduction of high and low acoustic velocity layers, rather than simply increasing piezoelectric film thickness. This allows the piezoelectric film to remain thin for high frequency operation while the acoustic waveguide structure compensates for the reduced coupling by confining energy more effectively within the active region.
Solution Approach 2:
The patent uses composite material structure with high acoustic velocity layers (such as aluminum nitride or silicon carbide) that provide strong acoustic confinement. This composite structure enables thin piezoelectric films to achieve high frequency operation while maintaining effective electromechanical coupling through the enhanced acoustic energy confinement provided by the high acoustic velocity materials.
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 structure increases the Q factor, enhances electromechanical coupling, and improves frequency stability and bandwidth, allowing for higher frequency operation with reduced propagation loss.
Implementation Method 1
a piezoelectric film stacked on the low-acoustic-velocity film
Implementation Method 2
the acoustic velocity of a bulk wave propagating therein is higher than the acoustic velocity of an elastic wave propagating in the piezoelectric film
Implementation Method 3
surface acoustic waves cannot be effectively confined within the piezoelectric thin film
Data Source
AI summary
An elastic wave device includes a supporting substrate, a high-acoustic-velocity film stacked on the supporting substrate and in which an acoustic velocity of a bulk wave propagating therein is higher than an acoustic velocity of an elastic wave propagating in a piezoelectric film, a low-acoustic-velocity film stacked on the high-acoustic-velocity film and in which an acoustic velocity of a bulk wave propagating therein is lower than an acoustic velocity of a bulk wave propagating in the piezoelectric film, the piezoelectric film is stacked on the low-acoustic-velocity film, and an IDT electrode stacked on a surface of the piezoelectric film.