SAW Resonator Medium Layer for Temperature Stability and Spurious Suppression
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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 stripe-shaped first and second acoustic impedance regions on a support substrate, improving temperature stability and reducing spurious behavior by altering the acoustic impedance and arrangement of these regions in relation to the IDT electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a support substrate with high Young's modulus and low linear expansion coefficient (e.g., sapphire substrate) is bonded to the piezoelectric substrate to suppress expansion and contraction due to temperature change, then temperature characteristics are improved, but spurious waves occur particularly on the high-frequency side and filter characteristics become inferior
Solution Approach 1:
The medium layer is segmented into multiple acoustic impedance regions with different acoustic impedances arranged in stripes. This segmentation creates a phononic crystal structure that selectively suppresses spurious waves at specific frequency bands while maintaining temperature compensation functionality.
Solution Approach 2:
The medium layer uses composite material structure with multiple acoustic impedance regions having different acoustic properties. This composite structure enables simultaneous achievement of temperature characteristics and spurious wave suppression by creating acoustic bandgaps at harmful frequencies.
2Stability of the object's composition
If a support substrate is bonded to the piezoelectric substrate to stabilize frequency characteristic, then frequency stability is improved, but device complexity increases due to additional layers and manufacturing steps
Solution Approach 1:
The medium layer serves multiple functions simultaneously: it acts as a temperature compensation layer, a phononic crystal structure for spurious wave suppression, and an acoustic impedance matching layer. This multi-functionality reduces the need for separate components and simplifies the overall device structure.
Solution Approach 2:
The patent combines the temperature compensation function and spurious wave suppression function into a single medium layer structure. By integrating these functions, the device complexity is reduced compared to using separate layers for each function.
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 significantly enhances temperature characteristics and suppresses spurious behavior across various resonance modes, leading to improved filter performance by minimizing unwanted resonant peaks.
Implementation Method 1
The medium layer includes stripe-shaped first acoustic impedance regions having longitudinal directions and lateral directions, and stripe-shaped second acoustic impedance regions having longitudinal directions and lateral directions and an acoustic impedance different from that of the first acoustic impedance regions
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 including IDT electrodes formed on the piezoelectric substrate. The medium layer includes stripe-shaped first acoustic impedance regions having a longitudinal direction and a lateral direction, and stripe-shaped second acoustic impedance regions having a longitudinal direction and a lateral direction and an acoustic impedance different from that of the first acoustic impedance regions, which are alternately arranged with the first acoustic impedance region.