Acoustic Wave Layer Stack for Higher-Order Mode Leakage Control
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Solution Overview
Problem
Acoustic wave devices with silicon support substrates struggle to sufficiently suppress higher-order modes, which are unnecessary waves, due to these modes being easily confined on the piezoelectric layer side.
Innovation Solution
The use of specific support substrates like YAG, rutile, lanthanum aluminate, strontium titanate, or yttrium aluminate, combined with lithium niobate or lithium tantalate as the piezoelectric layer, effectively suppresses higher-order modes by controlling acoustic velocities, allowing the main mode to be confined on the piezoelectric layer while allowing higher-order modes to leak from the support substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon support substrate is used, then the main mode is confined on the piezoelectric layer side, but higher-order modes are also easily confined leading to insufficient suppression
Solution Approach 1:
The invention changes the material parameter of the support substrate from silicon to specific materials (YAG, rutile, lanthanum aluminate, strontium titanate, or yttrium aluminate) that have lower acoustic velocities than the piezoelectric layer. This parameter change in acoustic velocity creates a velocity differential that allows the main mode to remain confined while enabling higher-order modes to leak into the support substrate, thereby resolving the contradiction between mode confinement and higher-order mode suppression.
2Reliability
If the acoustic velocity of support substrate is lower than piezoelectric layer, then higher-order modes can leak from support substrate, but main mode confinement may be affected
Solution Approach 1:
The invention applies local quality by creating different acoustic velocity zones: the piezoelectric layer maintains high acoustic velocity for main mode confinement, while the support substrate uses specific materials with lower acoustic velocities tailored to allow higher-order mode leakage. This localized differentiation of acoustic properties enables simultaneous achievement of main mode stability and higher-order mode suppression without compromising overall system performance.
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 effectively suppresses higher-order modes, improving the admittance-frequency characteristics of the acoustic wave devices by reducing ripples attributed to these modes, thereby enhancing the device's performance.
Implementation Method 1
a piezoelectric layer on the support substrate and an interdigital transducer (IDT) electrode on the piezoelectric layer
Implementation Method 2
a main mode may be confined on a piezoelectric layer side. However, in the acoustic wave device in which the support substrate includes silicon, not only the main mode but also a higher-order mode is easily confined on the piezoelectric layer side
Data Source
AI summary
An acoustic wave device includes a support substrate, a piezoelectric layer on the support substrate, and an IDT electrode on the piezoelectric layer and including electrode fingers. Lithium niobate or lithium tantalate is used as a material of the piezoelectric layer. One of YAG, rutile, lanthanum aluminate, strontium titanate, or yttrium aluminate is used as a material of the support substrate.