Acoustic Wave Stack with Velocity Regions for Stable High-Frequency Filtering
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Solution Overview
Problem
High-frequency acoustic wave devices with surface acoustic wave elements face challenges in maintaining superior temperature characteristics and suppressing spurious waves, particularly at high frequencies, due to the use of support substrates like sapphire which can introduce inferior filter characteristics.
Innovation Solution
The acoustic wave device incorporates a medium layer with distinct first and second acoustic velocity regions, where the second acoustic velocity region has a different acoustic velocity than the first, and is strategically positioned to enhance the confinement of acoustic waves within the piezoelectric substrate, reducing spurious waves and improving temperature stability by using materials like silicon nitride, silicon oxynitride, and sapphire for the support substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a support substrate such as a sapphire substrate having a high Young's modulus and a low linear expansion coefficient is bonded to a piezoelectric substrate to suppress expansion and contraction due to temperature change, then temperature characteristics are improved, but spurious wave occurs particularly on the high-frequency side and filter characteristics become inferior
Solution Approach 1:
The medium layer is divided into multiple layers with different acoustic velocities (first acoustic velocity region and second acoustic velocity region). This segmentation creates a structured acoustic velocity distribution that suppresses spurious waves while maintaining temperature characteristics, resolving the contradiction between temperature stability and spurious wave suppression.
Solution Approach 2:
Different regions of the medium layer are assigned different acoustic velocity characteristics. The first acoustic velocity region has a specific acoustic velocity while the second acoustic velocity region has a different acoustic velocity, creating local variations that control acoustic wave propagation to suppress spurious waves without compromising overall temperature stability.
2Temperature
If a support substrate such as a sapphire substrate is bonded to a piezoelectric substrate to suppress expansion and contraction due to temperature change, then temperature characteristics are improved, but filter characteristics become inferior
Solution Approach 1:
The medium layer is segmented into multiple layers with different acoustic velocities, creating a controlled acoustic environment that maintains filter characteristics while preserving temperature stability provided by the support substrate structure.
Solution Approach 2:
Local variations in acoustic velocity within the medium layer are designed to optimize filter characteristics by controlling acoustic wave behavior in specific regions, while the overall structure maintains temperature characteristics through the support substrate.
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 results in an acoustic wave device with improved temperature characteristics and reduced spurious properties, effectively addressing the limitations of existing devices by optimizing the acoustic wave propagation and reflection within the device structure.
Implementation Method 1
The medium layer includes an acoustic wave device having a first acoustic velocity region and a second acoustic velocity region penetrating at least one half of the thickness of the medium layer. The second acoustic velocity region has an acoustic velocity different from that of the first acoustic velocity region.
Implementation Method 2
The SAW element is the element that includes IDT (Interdigital Transducer) having a pair of comb-shaped electrodes on a piezoelectric substrate.
Data Source
AI summary
An acoustic wave device includes a support substrate, a medium layer formed on the support substrate, a piezoelectric substrate formed on the medium layer, and a resonator formed on the piezoelectric substrate. The medium layer includes a first acoustic velocity region and second acoustic velocity regions penetrating at least one half of the thickness of the medium layer. The second acoustic velocity region has an acoustic velocity different from that of the first acoustic velocity region.