SH Acoustic Wave Electrode Structure for Low-Loss Resonators
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Acoustic wave devices using Shear Horizontal (SH) waves face limitations in reducing loss due to the high velocity of SH waves, which leads to bulk wave emission, and existing techniques for reducing loss are not effective when using grating electrodes on piezoelectric substrates.
Innovation Solution
The use of a Y-cut X-propagation lithium tantalate substrate with a grating electrode composed of metal films, where the film thickness ratio (h/λ) multiplied by the density and Poisson's ratio of the metal films exceeds 0.08, reduces the acoustic velocity of SH waves, minimizing bulk wave emission and loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the acoustic velocity of SH wave is reduced by attaching a slow acoustic velocity material, then the emission of bulk wave is reduced and loss is reduced, but the device complexity increases due to additional material layers
Solution Approach 1:
The patent changes the physical parameters of the electrode material itself to achieve the desired effect. By selecting metal films with high density and appropriate Poisson's ratio (such as Cu, Ag, Au, Al, or their alloys), the electrode inherently functions as a slow acoustic velocity material without requiring additional layers. The key parameter is the product (ρi/ρ0)×(Pi/P0) being greater than 0.55, which directly controls the acoustic velocity reduction and bulk wave emission suppression.
Solution Approach 2:
The electrode serves multiple functions simultaneously: it acts as both the electrical conductor for generating the acoustic wave and as the slow acoustic velocity material for reducing bulk wave emission. This multi-functionality eliminates the need for separate loss-reduction layers, thereby reducing device complexity while maintaining energy efficiency.
2Loss of energy
If the film thickness h is increased to reduce loss, then the acoustic velocity of SH wave is reduced, but the manufacturing precision requirements increase
Solution Approach 1:
The patent transforms the single parameter control (h/λ) into a multi-parameter control system where the product (h/λ)×(ρi/ρ0)×(Pi/P0) > 0.08 determines the performance. This allows flexibility in selecting h, λ, ρi, and Pi combinations, enabling manufacturers to choose from various metal materials with different properties while maintaining the required performance threshold.
Solution Approach 2:
The patent employs composite material selection by choosing from various metal films (Cu, Ag, Au, Al, or their alloys) with different density and Poisson's ratio characteristics. This material selection approach provides manufacturing flexibility, as different metals can be used depending on available fabrication capabilities and cost considerations, while all satisfy the performance criterion.
3Reliability
If a grating electrode is used instead of uniform electrode, then the acoustic wave device performance is improved, but the manufacturing complexity increases
Solution Approach 1:
The electrode is segmented into a grating structure with periodic fingers rather than a continuous uniform layer. This segmentation creates the necessary spatial modulation to generate and control surface acoustic waves effectively. The grating structure consists of multiple electrode fingers with specific pitch λ, enabling the device to achieve its intended performance for acoustic wave generation and propagation.
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 a low-loss resonator with improved Q-values and reduced undesired lateral-mode waves, optimizing the acoustic wave device's performance by controlling the film thickness and pitch of the grating electrodes.
Implementation Method 1
a grating electrode that is composed of one or more metal films laminated on the substrate, and excites an acoustic wave
Implementation Method 2
The SH wave is the surface acoustic wave applying a stress to shear the piezoelectric substrate in a direction which is parallel to a surface of the piezoelectric substrate and orthogonal to a propagation direction of the SH wave
Data Source
AI summary
An acoustic wave device includes: a Y-cut X-propagation lithium tantalate substrate having a cut angle of 20° or more and 48° or less; and a grating electrode that is composed of one or more metal films laminated on the substrate, and excites an acoustic wave, wherein when a density of each metal film in the one or more metal films is represented by ρi, a Poisson's ratio of each metal film is represented by Pi, a film thickness of each metal film is represented by hi, a density of Cu is represented by ρ0, a Poisson's ratio of Cu is represented by P0 and a pitch is represented by λ, a total value of “(hi/λ)×(ρi/ρ0)×(Pi/P0)” for each metal film with respect to the one or more metal films is more than 0.08.