Bulk-Wave Acoustic Element Layout for Low-Loss Miniaturization
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Solution Overview
Problem
Existing acoustic wave devices exhibit significant variations in characteristics, which affect their performance and efficiency, particularly when reduced in size, due to the propagation of Lamb waves that require reflectors on both sides, leading to increased wave propagation loss and decreased Q factor.
Innovation Solution
The design incorporates a piezoelectric layer made of lithium niobate or lithium tantalate with a specific electrode configuration that excites first thickness-shear mode bulk waves, eliminating the need for reflectors and maintaining high Q factor even when reduced in size, by optimizing the thickness and center-to-center distance of electrodes and using a mounting substrate with a metal portion to manage capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the device size is reduced, then the portability and integration are improved, but the propagation loss increases and Q factor decreases
Solution Approach 1:
The patent changes the wave propagation mode from Lamb waves to bulk waves by adjusting the piezoelectric layer thickness to be less than one-tenth of the acoustic wavelength. This parameter change allows the device to maintain high Q factor and low propagation loss even when miniaturized, as bulk waves are less susceptible to boundary effects and energy dissipation in small-scale structures.
Solution Approach 2:
The patent replaces the mechanical reflector system required for Lamb waves with an electrode-based excitation system for bulk waves. By using interdigitated electrodes to directly excite thickness-shear bulk waves in the piezoelectric layer, the design eliminates the need for complex mechanical reflectors, thereby reducing device size while maintaining high resonance efficiency and low energy loss.
2Stability of the object's composition
If reflectors are added to both sides for Lamb wave propagation, then wave confinement is improved, but device complexity and energy loss increase
Solution Approach 1:
The patent extracts and removes the reflector components from the device structure by switching to bulk wave propagation. Bulk waves naturally confine energy within the piezoelectric layer through their propagation characteristics, eliminating the need for external reflectors and thereby simplifying the device structure while maintaining effective wave confinement.
Solution Approach 2:
The patent introduces the piezoelectric layer itself as the medium that provides wave confinement through its material properties and thickness control. By making the piezoelectric layer thickness less than one-tenth of the acoustic wavelength, the layer acts as an inherent waveguide for bulk waves, replacing the need for separate reflector structures and reducing overall device complexity.
3Volume of moving object
If the piezoelectric layer thickness is reduced, then size reduction is achieved, but manufacturing precision requirements increase
Solution Approach 1:
The patent establishes a specific parameter range for the piezoelectric layer thickness (less than one-tenth of the acoustic wavelength) that balances size reduction with manufacturability. This parameter optimization allows sufficient thickness reduction for miniaturization while maintaining a practical lower bound that can be achieved with conventional semiconductor fabrication techniques, thereby managing manufacturing precision requirements.
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 minimizes variations in acoustic wave device characteristics, maintains high Q factor and resonance efficiency, and allows for size reduction without significant propagation loss, achieving good resonance characteristics and fractional bandwidth.
Implementation Method 1
a piezoelectric layer stacked on the support substrate and including an overlap region at least partially overlapping the air gap
Data Source
AI summary
An acoustic wave device includes a mounting substrate; an acoustic wave element on one major surface of the mounting substrate in its thickness direction, and a bump between the acoustic wave element and the mounting substrate. The acoustic wave element includes a support substrate including an air gap, a piezoelectric layer stacked on the support substrate and including an overlap region at least partially overlapping the air gap as viewed in the stacking direction, and a functional electrode located in the overlap region of the piezoelectric layer. The mounting substrate includes a metal portion. A fixed capacitance generated between the acoustic wave element and the mounting substrate is not less than a variable capacitance generated between the acoustic wave element and the mounting substrate.