IDT Electrode Layering in Acoustic Wave Devices for Temperature Stability
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Solution Overview
Problem
Acoustic wave devices with a piezoelectric substrate and high-acoustic-velocity film exhibit a large absolute difference in temperature coefficients of acoustic velocity between resonant and anti-resonant points, affecting stability in electrical characteristics.
Innovation Solution
The acoustic wave device incorporates a piezoelectric substrate with a high-acoustic-velocity material layer and a piezoelectric layer, where the thickness of the piezoelectric layer is about 3λ or smaller, and the sum total of the electrode layer thickness, based on a density ratio, is equal to or larger than the piezoelectric layer thickness, reducing the absolute difference in temperature coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a high acoustic velocity film and low acoustic velocity film are interposed between the piezoelectric film and support substrate, then the electromechanical coupling coefficient is improved, but the absolute difference in temperature coefficients of acoustic velocity between resonant and anti-resonant points increases
Solution Approach 1:
The patent changes the physical parameters of the electrode layers by controlling their thickness and material composition. Specifically, the sum of the thicknesses of the first and second electrode layers is set to be 0.05λ to 0.20λ, which optimizes the temperature coefficient characteristics while maintaining the electromechanical coupling coefficient.
Solution Approach 2:
The patent uses composite material structures with multiple layers including the piezoelectric film, high acoustic velocity film, low acoustic velocity film, and electrode layers. This composite structure allows simultaneous optimization of electromechanical coupling and temperature stability by carefully designing the properties of each layer.
2Power
If the piezoelectric film is joined to the support substrate with high and low acoustic velocity films, then the electromechanical coupling coefficient increases, but the temperature coefficient difference ΔTCV becomes large
Solution Approach 1:
The patent optimizes the thickness parameters of the electrode layers to be within the range of 0.05λ to 0.20λ. This parameter optimization reduces the temperature coefficient difference while preserving the high electromechanical coupling coefficient achieved through the multi-layer structure.
Solution Approach 2:
The patent applies different material properties and thicknesses to different local regions (layers) of the device. The electrode layers have specific thickness constraints (0.05λ to 0.20λ) that differ from the other layers, creating local quality variations that reduce temperature coefficient differences while maintaining overall 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 enhances the electrical characteristics and reduces temperature-related differences in acoustic velocity, improving stability and insertion loss in acoustic wave devices.
Implementation Method 1
a piezoelectric substrate including a high-acoustic-velocity material layer 4 and a piezoelectric layer 6
Implementation Method 2
an IDT electrode 7 on the piezoelectric substrate 2
Implementation Method 3
An acoustic velocity of a bulk wave which propagates in the high-acoustic-velocity material layer 4 is higher than an acoustic velocity of an acoustic wave which propagates in the piezoelectric layer 6
Data Source
AI summary
An acoustic wave device includes a piezoelectric substrate including an acoustic reflection layer and a piezoelectric layer on the acoustic reflection layer, and an IDT electrode on the piezoelectric substrate and including electrode fingers. When a wavelength defined by an electrode finger pitch of the IDT electrode is λ, a thickness of the piezoelectric layer is about 3λ or smaller. The electrode fingers include at least one electrode layer. A sum total of a thickness of the at least one electrode layer converted based on a density ratio of the at least one electrode layer and Al assuming that the at least one electrode layer includes Al is a same or larger than the thickness of the piezoelectric layer.