Acoustic wave device and method for producing same
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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 alternating acoustic impedance regions on a support substrate and piezoelectric substrate, where the second acoustic impedance regions are designed to scatter bulk waves and improve temperature stability, using materials like silicon nitride, silicon oxynitride, and sapphire, and employing a multilayer substrate with gold bumps for flip-chip bonding.
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, then temperature characteristics are improved, but spurious waves occur particularly on the high-frequency side and filter characteristics become inferior
Solution Approach 1:
The support substrate is segmented into a first region and a second region with different materials. The first region (under the resonator) uses sapphire or similar material for temperature stability, while the second region (peripheral area) uses a different material to suppress spurious waves. This spatial segmentation allows each region to perform its specific function without interfering with the other.
Solution Approach 2:
Different regions of the support substrate are assigned different material properties tailored to local requirements. The central region requires high stiffness and low thermal expansion for frequency stability, while the peripheral region requires different acoustic properties for spurious wave suppression. This local differentiation of material quality resolves the contradiction between temperature characteristics and spurious wave suppression.
2Stability of the object's composition
If a support substrate is bonded to suppress expansion and contraction due to temperature change, then frequency characteristic stability is improved, but spurious property is not sufficiently suppressed
Solution Approach 1:
The support substrate is divided into functional regions: a first region for frequency stability (under the resonator) and a second region for spurious wave suppression (peripheral area). This segmentation enables simultaneous achievement of frequency stability and spurious wave suppression through region-specific material selection.
Solution Approach 2:
A medium layer with specific acoustic impedance is introduced as an intermediary between the piezoelectric substrate and the support substrate. This intermediate layer helps suppress spurious waves while maintaining the frequency stability provided by the support substrate, acting as a mediator that reconciles the two conflicting requirements.
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 enhances temperature characteristics and suppresses spurious waves effectively, improving the frequency stability and Q value of the acoustic wave device.
Implementation Method 1
The second acoustic impedance regions include a plurality of regions formed in a top view, and the second acoustic impedance regions are formed in three or more regions in where the resonator is formed
Implementation Method 2
The acoustic wave device having a surface acoustic wave (SAW: Surface Acoustic Wave) element is used as a high-frequency filter
Implementation Method 3
The support substrate suppresses the change in the size of the piezoelectric substrate when the temperature changes by using the multilayer film substrate
Implementation Method 4
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 impedance region and second acoustic impedance regions having an acoustic impedance different from the first acoustic impedance region in a top view. The second acoustic impedance regions include a plurality of regions formed in a top view, and the second acoustic impedance regions are formed in three or more regions in where the resonator is formed; and a method for producing the same.