Acoustic Wave Structure With Rough Silicon Interface for Harmonic Control
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Solution Overview
Problem
Acoustic wave devices with silicon substrates experience harmonic distortion due to a short distance between the silicon substrate and the piezoelectric layer, which affects the propagation of acoustic waves.
Innovation Solution
The acoustic wave device includes a silicon substrate with a rougher first main surface and a piezoelectric layer with a specific thickness, along with an IDT electrode and a dielectric film, where the distance between the silicon substrate and the piezoelectric layer is less than 0.84 times the wavelength of the acoustic wave, and a high acoustic velocity film is used to confine energy and reduce leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the distance between the silicon substrate and the piezoelectric layer is short, then the device structure is compact, but harmonic distortion increases
Solution Approach 1:
A roughness layer is introduced as an intermediary between the silicon substrate and the piezoelectric layer. This roughness layer acts as a mediator that scatters bulk waves and prevents them from reaching the piezoelectric layer, thereby reducing harmonic distortion while maintaining a compact device structure with short distance between the silicon substrate and piezoelectric layer.
Solution Approach 2:
The surface of the silicon substrate is modified to have a specific roughness structure in the region where it contacts the piezoelectric layer. This local quality change creates a roughness layer with specific surface characteristics (average surface roughness of 50 nm to 5 μm) that selectively scatters bulk waves while maintaining overall device compactness.
2Loss of energy
If the silicon substrate has a rough back surface, then bulk wave scattering is improved, but harmonic distortion may increase when the distance to piezoelectric layer is short
Solution Approach 1:
The surface roughness parameters of the silicon substrate are precisely controlled with an average surface roughness between 50 nm and 5 μm. This parameter optimization ensures effective bulk wave scattering while preventing excessive harmonic distortion that would occur with inappropriate roughness values, particularly in compact devices with short substrate-piezoelectric layer distances.
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 effectively reduces or prevents harmonic distortion, improving the Q factor and reducing energy leakage to the silicon substrate, thereby enhancing the acoustic wave device's performance.
Implementation Method 1
The first main surface of the silicon substrate is rougher than the first main surface of the piezoelectric layer
Implementation Method 2
a piezoelectric layer... an IDT electrode is on the first main surface of the piezoelectric layer
Data Source
AI summary
An acoustic wave device includes a silicon substrate, a piezoelectric layer, and an IDT electrode. Each of the silicon substrate and the piezoelectric layer includes first and second opposed main surfaces. The IDT electrode is on the first main surface of the piezoelectric layer, and includes first and second electrode fingers. When a wavelength of an acoustic wave determined by an electrode finger pitch of the IDT electrode is denoted as λ, a distance between the first main surface of the silicon substrate and the second main surface of the piezoelectric layer in a thickness direction of the silicon substrate is less than about 0.84λ. The first main surface of the silicon substrate is rougher than the first main surface of the piezoelectric layer.