Acoustic Wave Dielectric Composition Gradient for Spurious Mode Shift
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Solution Overview
Problem
Conventional acoustic wave devices experience spurious radiation due to high-order modes when the film thickness of the dielectric layer is greater than 0.8 times the wavelength of the main wave, leading to degraded frequency characteristics.
Innovation Solution
A dielectric layer with a composition that continuously increases the propagation velocity of transverse waves from the boundary surface to the upper surface, shifting the high-order mode radiation to higher frequencies and reducing its influence, while also allowing for a simpler manufacturing process with fewer sputtering steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the film thickness of the dielectric layer is made not smaller than 0.8 times as large as a wavelength of a main wave to confine the main wave inside the acoustic wave device, then the energy confinement of the main wave is improved, but a spurious radiation by a high-order mode is generated in the vicinity of a frequency of the main wave
Solution Approach 1:
The dielectric layer is designed with non-uniform composition distribution, where the proportion of SiO2 varies continuously from the lower portion (near piezoelectric body) to the upper portion. This creates local variations in transverse wave propagation velocity, allowing the lower portion to confine the main wave while the upper portion suppresses high-order mode spurious radiation by presenting a higher propagation velocity medium.
Solution Approach 2:
The composition of the dielectric layer is changed continuously in the thickness direction, with the SiO2 proportion decreasing from lower to upper portions. This parameter change results in a corresponding change in transverse wave propagation velocity, enabling different regions of the dielectric layer to perform different functions: main wave confinement near the piezoelectric body and high-order mode suppression at the upper region.
2Reliability
If the dielectric layer is made up of a medium with low transverse wave propagation velocity to confine the main wave, then the main wave energy is confined on the boundary between piezoelectric body and dielectric layer, but the spurious radiation by high-order mode cannot be suppressed
Solution Approach 1:
The dielectric layer is designed with non-uniform composition distribution, where the proportion of SiO2 varies continuously from the lower portion (near piezoelectric body) to the upper portion. This creates local variations in transverse wave propagation velocity, allowing the lower portion to confine the main wave while the upper portion suppresses high-order mode spurious radiation by presenting a higher propagation velocity medium.
Solution Approach 2:
The composition of the dielectric layer is changed continuously in the thickness direction, with the SiO2 proportion decreasing from lower to upper portions. This parameter change results in a corresponding change in transverse wave propagation velocity, enabling different regions of the dielectric layer to perform different functions: main wave confinement near the piezoelectric body and high-order mode suppression at the upper region.
3Object-generated harmful factors
If the dielectric layer composition is clearly separated between upper and lower portions to suppress spurious radiation, then the high-order mode spurious radiation can be reduced, but the number of sputtering steps increases, reducing productivity
Solution Approach 1:
The composition of the dielectric layer is changed continuously in the thickness direction, with the SiO2 proportion decreasing from lower to upper portions. This parameter change results in a corresponding change in transverse wave propagation velocity, enabling different regions of the dielectric layer to perform different functions: main wave confinement near the piezoelectric body and high-order mode suppression at the upper region.
Solution Approach 2:
The dielectric layer is formed as a single continuous layer with composition changing portion, combining the functions of main wave confinement and high-order mode suppression in one structure. This eliminates the need for multiple separate dielectric layers with different compositions, thereby reducing the number of sputtering steps from multiple layers to a single layer formation process.
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 solution effectively suppresses spurious radiation by high-order modes, improves frequency characteristics, and increases the electromechanical coupling factor of the main wave, enhancing energy confinement and productivity.
Implementation Method 1
a medium where propagation velocity of a transverse wave continuously increases in a direction from a boundary surface in contact with the piezoelectric body to an upper surface of the dielectric layer
Implementation Method 2
interdigital electrode that is arranged on the piezoelectric body and excites an acoustic wave
Data Source
AI summary
An acoustic wave device has: a piezoelectric body; an interdigital electrode that is arranged on the piezoelectric body and excites an acoustic wave; and a dielectric layer that is arranged on the piezoelectric body so as to cover the interdigital electrode. The dielectric layer includes a composition changing portion made up of a medium where propagation velocity of a transverse wave continuously increases upward. With this configuration, it is possible to shift a spurious radiation by a high-order mode that propagates inside the dielectric layer to a higher frequency, so as to reduce an influence of the spurious radiation by the high-order mode.