Elastic Wave Device Acoustic Reflection Layer Spurious Response Reduction
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Solution Overview
Problem
Elastic wave devices experience spurious responses at higher frequencies, affecting communication systems and having inadequate frequency-temperature characteristics, particularly in high-frequency applications like Band 42 and wireless LANs.
Innovation Solution
The elastic wave device incorporates a supporting substrate, an acoustic reflection layer with alternately stacked low and high acoustic impedance layers, where the film thickness of the low acoustic impedance layer closest to the piezoelectric layer is larger than the others, and the high acoustic impedance layers have the same thickness, optimizing reflectance and confining the elastic wave to the piezoelectric layer side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the acoustic reflection layer uses uniformly thick low acoustic impedance layers, then the device structure is simple, but spurious responses occur at higher frequencies affecting communication systems
Solution Approach 1:
The patent applies local quality by making the first low acoustic impedance layer (closest to the piezoelectric layer) have a different thickness than the other low acoustic impedance layers. Specifically, the first layer has a thickness of 0.6-0.9 times the wavelength component in the thickness direction, while other layers have thicknesses of 0.2-0.4 times the wavelength component. This localized variation in thickness optimizes the reflection characteristics and pushes spurious responses to frequencies outside communication bands.
Solution Approach 2:
The patent changes the thickness parameter of the low acoustic impedance layers to control the spurious response frequency. By setting the first low acoustic impedance layer thickness to 0.6-0.9 times the wavelength component and other layers to 0.2-0.4 times, the spurious response frequency is shifted to a frequency ratio of 1.3-1.65 times the fundamental mode, which is outside typical communication bands like Band 42 and wireless LAN bands.
2Ease of manufacture
If the acoustic reflection layer uses uniformly thick layers, then the manufacturing process is simple, but frequency-temperature characteristics are insufficient
Solution Approach 1:
The patent applies local quality by differentiating the thickness of the first low acoustic impedance layer from the other layers. The first layer (adjacent to the piezoelectric layer) has a thickness of 0.6-0.9 times the wavelength component, while subsequent layers have thicknesses of 0.2-0.4 times the wavelength component. This localized thickness variation improves frequency-temperature characteristics while maintaining a relatively simple manufacturing process.
3Reliability
If the first low acoustic impedance layer thickness is increased to improve frequency-temperature characteristics, then frequency-temperature characteristics are improved, but spurious response frequency may move closer to communication bands
Solution Approach 1:
The patent optimizes the thickness parameter of the first low acoustic impedance layer to be 0.6-0.9 times the wavelength component in the thickness direction. This parameter range improves frequency-temperature characteristics while simultaneously positioning the spurious response frequency at 1.3-1.65 times the fundamental mode frequency, which is outside communication bands like Band 42 (3.4-3.6 GHz) and wireless LAN bands (5.15-5.35 GHz).
Solution Approach 2:
The patent applies local quality by making the first low acoustic impedance layer have a specific thickness ratio (0.6-0.9 times wavelength component) compared to other layers (0.2-0.4 times wavelength component). This localized optimization achieves both improved frequency-temperature characteristics and proper spurious response frequency positioning without affecting other layers.
4Object-affected harmful factors
If the acoustic reflection layer uses more layers with varying thicknesses, then spurious responses are reduced, but device complexity increases
Solution Approach 1:
The patent applies local quality by varying the thickness of only the first low acoustic impedance layer (0.6-0.9 times wavelength component) while keeping other low acoustic impedance layers at 0.2-0.4 times the wavelength component. This selective local variation reduces spurious responses without requiring all layers to have different characteristics, thus limiting the increase in device complexity.
Solution Approach 2:
The patent changes the thickness parameter of the first low acoustic impedance layer to a specific range (0.6-0.9 times wavelength component) while maintaining other layers at 0.2-0.4 times. This controlled parameter change effectively reduces spurious responses to frequencies outside communication bands while avoiding excessive structural complexity.
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 spurious responses by distancing them from communication frequency bands and improves frequency-temperature characteristics without degrading reflection characteristics, enhancing the performance of high-frequency front-end circuits and communication apparatuses.
Implementation Method 1
the acoustic reflection layer includes three or more low acoustic impedance layers and two or more high acoustic impedance layers
Implementation Method 2
a piezoelectric layer disposed on the acoustic reflection layer
Data Source
AI summary
An elastic wave device includes a supporting substrate, an acoustic reflection layer disposed on the supporting substrate, a piezoelectric layer disposed on the acoustic reflection layer, and an interdigital transducer electrode disposed on the piezoelectric layer. The acoustic reflection layer includes three or more low acoustic impedance layers and two or more high acoustic impedance layers. A film thickness of the low acoustic impedance layer closest to the piezoelectric layer is larger than a film thickness of the low acoustic impedance layer closest to the low acoustic impedance layer that is closest to the piezoelectric layer.