Acoustic Wave Stack With Spinel Layer for Spurious Wave Suppression
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Solution Overview
Problem
Existing acoustic wave devices face challenges in achieving high temperature characteristics and suppressing spurious waves, particularly at high frequencies, due to limitations in support substrates such as sapphire and polycrystalline materials.
Innovation Solution
The acoustic wave device incorporates a high acoustic velocity substrate with a medium acoustic velocity layer and a piezoelectric substrate, where the acoustic velocity is gradually slowed down from the high acoustic velocity substrate to the medium acoustic velocity layer, utilizing materials like spinel to enhance temperature stability and suppress spurious waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a sapphire substrate is used as support substrate to improve temperature characteristics, then temperature characteristics are improved, but spurious wave occurs particularly on the high-frequency side
Solution Approach 1:
The patent introduces a spinel layer as an intermediary between the sapphire substrate and the piezoelectric substrate. This spinel layer acts as a mediator that maintains the temperature stability provided by sapphire while suppressing the generation of spurious waves, particularly at high frequencies. The spinel layer has acoustic impedance characteristics that are intermediate between sapphire and the piezoelectric substrate, thereby reducing acoustic reflections that cause spurious waves.
Solution Approach 2:
The patent employs a composite structure consisting of multiple layers: sapphire substrate, spinel layer, and piezoelectric substrate. This composite material approach combines the advantages of different materials - sapphire provides temperature stability, spinel provides acoustic impedance matching to suppress spurious waves, and the piezoelectric substrate provides the necessary piezoelectric effect for acoustic wave generation and detection.
2Object-generated harmful factors
If a polycrystalline substrate such as spinel is used as support substrate to suppress spurious wave, then spurious wave is suppressed, but temperature characteristics cannot be realized
Solution Approach 1:
The patent creates a composite structure where a polycrystalline spinel layer is placed between a sapphire substrate and a piezoelectric substrate. The sapphire substrate provides the temperature characteristics (low thermal expansion coefficient, high Young's modulus) while the spinel layer suppresses spurious waves. This composite approach allows both functions to coexist without compromising either temperature stability or spurious wave suppression.
Solution Approach 2:
The spinel layer serves as an intermediary that enables the combination of sapphire's temperature stability with spurious wave suppression. Without this intermediary layer, directly bonding polycrystalline spinel to the piezoelectric substrate would suppress spurious waves but lose the temperature characteristics. The spinel intermediary maintains thermal stability while providing acoustic impedance matching.
3Reliability
If a support substrate with low linear expansion coefficient is bonded to piezoelectric substrate to stabilize frequency characteristic, then frequency characteristic is stabilized, but device complexity increases due to multilayer film substrate
Solution Approach 1:
The patent uses a composite substrate structure consisting of sapphire, spinel, and piezoelectric substrate layers. This composite material approach stabilizes frequency characteristics through the low thermal expansion of sapphire while the spinel layer simplifies the overall structure by providing acoustic impedance matching, reducing the need for additional complex frequency-stabilization mechanisms.
Solution Approach 2:
The patent applies different material properties to different layers: sapphire provides thermal stability for frequency characteristic, spinel provides acoustic impedance matching for spurious wave suppression, and the piezoelectric substrate provides piezoelectric effect. This local quality assignment optimizes each layer's function while maintaining overall device simplicity.
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 improved temperature characteristics and reduced spurious properties, achieving better frequency stability and performance in high-frequency applications.
Implementation Method 1
an acoustic velocity is slowed down gradually from the main surface of the sapphire substrate toward the main surface of the spinel layer between the sapphire substrate and the piezoelectric substrate
Implementation Method 2
a piezoelectric substrate formed directly or via another layer on the main surface of the medium acoustic velocity layer
Data Source
AI summary
An acoustic wave device includes a high acoustic velocity substrate, a medium acoustic velocity layer formed on the main surface of the high acoustic velocity substrate, and a piezoelectric substrate formed directly or via another layer on the main surface of the medium acoustic velocity layer, wherein an acoustic velocity is slowed down gradually from the main surface of the high acoustic velocity substrate toward the main surface of the medium acoustic velocity layer between the high acoustic velocity substrate and the medium acoustic velocity layer; and a method for producing the same.