LiNbO3 Elastic Wave Electrode Stack for Low-Loss Frequency Stability
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Solution Overview
Problem
Existing elastic wave devices face issues with high loss, inadequate frequency temperature characteristics, generation of spurious in higher-order modes, and deterioration in intermodulation distortion (IMD) when using single-layer IDT electrodes or multilayer metal films.
Innovation Solution
The elastic wave device incorporates a piezoelectric substrate made of LiNbO3 with an IDT electrode structure comprising a first electrode layer of high-density metals like Pt, W, Mo, Ta, or Au, and a second electrode layer of Al, along with a silicon oxide film containing hydrogen atoms or hydroxyl groups, optimized in thickness and duty ratio to reduce unwanted waves and improve frequency stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer IDT electrode is used, then device complexity is reduced, but resistance of electrode fingers increases and loss increases
Solution Approach 1:
The IDT electrode uses a composite multilayer metal film structure consisting of a first metal film (high density material such as Pt, W, Mo, Ta, or Au) and a second metal film (Al or Cu). This composite structure combines the advantages of different materials: the high-density first layer provides mechanical stability and appropriate acoustic velocity, while the highly conductive second layer reduces resistance and energy loss.
2Loss of energy
If a multilayer metal film IDT electrode is used, then loss is reduced, but frequency temperature characteristics are insufficient
Solution Approach 1:
A silicon oxide film is deposited on the piezoelectric substrate to compensate for frequency temperature characteristics. The film thickness is specifically controlled (0.01λ ≤ thickness < 0.06λ) to achieve optimal temperature compensation without generating excessive spurious signals. Additionally, the first metal film density is carefully selected to balance acoustic velocity control with temperature stability.
3Temperature
If a silicon oxide film is provided to improve frequency temperature characteristics, then temperature stability is improved, but spurious in higher-order mode is generated
Solution Approach 1:
The silicon oxide film thickness is precisely controlled within the range of 0.01λ ≤ thickness < 0.06λ, where λ is the acoustic wavelength. This specific thickness range provides sufficient temperature compensation while minimizing the generation of spurious signals in higher-order modes. The first metal film density is also optimized to further suppress spurious generation.
4Reliability
If all characteristics (loss, temperature characteristics, spurious reduction) are improved, then device performance is enhanced, but IMD deteriorates
Solution Approach 1:
The first metal film density is specifically selected from high-density materials (Pt, W, Mo, Ta, Au) to optimize the balance between multiple characteristics. This density range provides appropriate acoustic velocity for reducing spurious while maintaining good temperature characteristics and acceptable loss levels, thereby preventing IMD deterioration despite other performance improvements.
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
The solution results in an elastic wave device with low loss, excellent frequency temperature characteristics, reduced spurious in higher-order modes, and improved IMD, making it suitable for high-frequency applications.
Implementation Method 1
an IDT electrode provided on the piezoelectric substrate... the elastic wave device utilizes a Rayleigh wave
Implementation Method 2
the silicon oxide film contains a hydrogen atom, a hydroxyl group, or a silanol group
Data Source
AI summary
An elastic wave device includes a piezoelectric substrate, an IDT electrode on the piezoelectric substrate, and a silicon oxide film arranged on the piezoelectric substrate to cover the IDT electrode. The IDT electrode includes first and second electrode layers laminated on each other, the first electrode layer is made of metal or an alloy with a density higher than a density of metal of the second electrode layer and a density of silicon oxide of the silicon oxide film, the piezoelectric substrate is made of LiNbO3 and θ is in a range of equal to or greater than about 8° and equal to or less than about 32° with Euler Angles (0°±5°, θ, 0°±10°) of the piezoelectric substrate, and the silicon oxide film contains hydrogen atoms, hydroxyl groups, or silanol groups.