Acoustic Wave Substrate Crystallinity Layout for Low-Ripple Resonance
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Solution Overview
Problem
Acoustic wave devices with lithium niobate or lithium tantalate piezoelectric layers face challenges in reducing ripples in frequency characteristics, which affect their performance and efficiency.
Innovation Solution
The implementation of a support substrate with an attenuation layer of different crystallinity, combined with a piezoelectric layer and electrodes, helps to minimize ripples by controlling wave propagation and reducing reflection, achieved through specific manufacturing methods such as ion implantation or laser irradiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional acoustic wave device structure is used, then the device can operate with basic functionality, but ripples appear in frequency characteristics
Solution Approach 1:
The support substrate is designed with non-uniform crystallinity: a first region with first crystallinity and a second region with second crystallinity. This local quality variation creates different acoustic wave propagation characteristics in different regions, enabling the attenuation of surface acoustic waves in specific areas to reduce frequency ripples while maintaining device functionality.
Solution Approach 2:
The patent changes the crystallinity parameter of the support substrate material in different regions. By controlling the crystallinity (e.g., through monocrystalline vs. polycrystalline structures), the acoustic wave velocity and attenuation characteristics are modified, allowing suppression of spurious modes and reduction of frequency ripples without affecting the overall device operation.
2Productivity
If the device is miniaturized to improve integration, then productivity increases, but maintaining high Q-factor becomes difficult
Solution Approach 1:
The support substrate employs regions with different crystallinity properties to create localized acoustic wave attenuation zones. This allows the device to be miniaturized while the engineered crystallinity distribution maintains proper acoustic wave confinement and resonance characteristics, preserving the Q-factor despite reduced device dimensions.
3Object-generated harmful factors
If reflectors are added to suppress surface acoustic waves, then frequency ripple reduction is achieved, but device complexity increases
Solution Approach 1:
Instead of adding physical reflector structures, the patent modifies the crystallinity parameter of the support substrate material itself. This intrinsic material property change provides acoustic wave attenuation and spurious mode suppression without requiring additional structural components, thereby reducing device complexity while achieving the desired frequency characteristic improvement.
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 acoustic wave device's performance by reducing frequency ripples, improving resonance characteristics, and maintaining a high Q-factor even with miniaturization, while also reducing the need for reflectors and minimizing wave propagation loss.
Implementation Method 1
At least part of the support substrate includes an attenuation layer, the at least part of the support substrate overlapping a region located between the non-overlap portion of the first electrode and the non-overlap portion of the second electrode in plan view, the attenuation layer having a crystallinity different from a crystallinity of the support substrate
Implementation Method 2
the attenuation layer being formed by ion implantation applied to the second surface of the support substrate
Implementation Method 3
the attenuation layer being formed by laser irradiation applied to the second surface of the support substrate
Implementation Method 4
a piezoelectric layer overlapping the support substrate as seen in a first direction
Data Source
AI summary
An acoustic wave device includes a support substrate, a piezoelectric layer, and first and second electrodes. The piezoelectric layer overlaps the support substrate in a first direction. The first and second electrodes extend over at least a first major surface of the piezoelectric layer. The first and second electrodes face each other and are at different potentials. A space between a second major surface of the piezoelectric layer and the support substrate is covered by the piezoelectric layer. The first and second electrodes each include an overlap portion overlapping the space in the first direction and a non-overlap portion not overlapping the space in the first direction. At least part of the support substrate includes an attenuation layer and overlaps a region between the non-overlap portions of the first and second electrodes in plan view. The attenuation layer and the support substrate have different crystallinities.