Laminated Acoustic Wave Resonator for High Q and Low Thickness Sensitivity
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Solution Overview
Problem
Existing acoustic wave devices face challenges in achieving a high Q factor with minimal variation in characteristics due to film thickness variations, particularly with thin piezoelectric films used in previous designs.
Innovation Solution
The acoustic wave device incorporates a piezoelectric film laminated on a low acoustic velocity film, which is itself on a high acoustic velocity support substrate, with a bonding layer at strategic interfaces, and a film thickness of the piezoelectric film set between 1.5λ and 3.5λ, utilizing materials like LiTaO3 and silicon oxide to enhance Q factor and reduce variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thin piezoelectric film (1.5λ or less) is used to increase the Q factor with high acoustic velocity laminate, then the Q factor is improved, but the variation in characteristics caused by film thickness variation is increased
Solution Approach 1:
The patent changes the thickness parameter of the piezoelectric film from the conventional thin film (1.5λ or less) to a thicker range (1.5λ to 3.5λ), which fundamentally alters the device characteristics to simultaneously achieve high Q factor and reduced sensitivity to thickness variations
Solution Approach 2:
The patent employs a composite laminate structure consisting of a high acoustic velocity substrate, a low acoustic velocity film, and a piezoelectric film with specific thickness ratio, creating a composite system that optimizes both Q factor and manufacturing tolerance
2Reliability
If a low acoustic velocity film is laminated on a high acoustic velocity substrate to increase Q factor, then the Q factor is improved, but the device complexity and number of components increase
Solution Approach 1:
The patent optimizes the thickness ratio between the low acoustic velocity film and the piezoelectric film (1:2 to 1:4), which allows achieving high Q factor with a simplified laminate structure rather than adding more layers
Solution Approach 2:
The patent applies the low acoustic velocity film selectively with specific thickness relationship to the piezoelectric film, creating localized acoustic velocity differentiation that enhances Q factor without requiring complex multi-layer structures throughout the entire device
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 increases the Q factor while minimizing variations in characteristics, improving frequency-temperature stability and reducing higher-order modes, leading to more reliable acoustic wave devices for resonators and filters.
Implementation Method 1
a piezoelectric film; an IDT electrode provided on one surface of the piezoelectric film
Implementation Method 2
The acoustic velocity of a bulk wave propagating in the high acoustic velocity support substrate or the high acoustic velocity film is higher than the acoustic velocity of an acoustic wave propagating in the piezoelectric film
Data Source
AI summary
An acoustic wave device includes a high acoustic velocity support substrate defining and functioning as a high acoustic velocity member, a low acoustic velocity film, a piezoelectric film, and an IDT electrode that are laminated in this order. When a wavelength of an acoustic wave determined by an electrode finger cycle of the IDT electrode is represented by λ, a film thickness of the piezoelectric film is about 1.5λ or more and about 3.5λ or less. The acoustic velocity of a bulk wave propagating in the high acoustic velocity support substrate is higher than the acoustic velocity of an acoustic wave propagating in the piezoelectric film. The acoustic velocity of a bulk wave propagating in the low acoustic velocity film is lower than the acoustic velocity of an acoustic wave propagating in the piezoelectric film.