Acoustic Multilayer Elastic Wave Structure for 6 GHz Strength
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Solution Overview
Problem
Existing elastic wave devices face challenges in achieving high impedance ratios and maintaining mechanical strength in ultra-high frequency bands above 6 GHz, particularly due to the limitations of piezoelectric thin films becoming extremely thin, which affects their performance and practical usability.
Innovation Solution
The elastic wave device utilizes higher-order modes of resonance characteristics of bulk waves by adjusting the type of piezoelectric substrate and the thickness of each layer of the acoustic multilayer film, allowing for a large impedance ratio without the need for extremely thin substrates or cavities, and incorporates a structure with alternately stacked low and high acoustic impedance films to excite higher-order modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the piezoelectric thin film thickness is reduced to increase excitation frequency in cavity FBARs, then the excitation frequency increases, but the mechanical strength deteriorates and the film becomes difficult to maintain
Solution Approach 1:
The invention changes the vibration mode from fundamental mode to higher-order modes (first overtone, second overtone, etc.), which allows achieving higher excitation frequencies (6 GHz or higher) without reducing the piezoelectric thin film thickness below 0.3 μm, thereby maintaining mechanical strength while increasing frequency
Solution Approach 2:
The invention introduces acoustic multilayer films with alternating high and low acoustic impedance layers, creating a complex layered structure that enables higher-order mode vibrations and achieves ultra-high frequencies without extreme thinning of the piezoelectric layer
2Ease of manufacture
If AlN or ScAlN polycrystalline thin films are used in cavity FBARs, then the device structure is simplified, but attenuation at ultra-high frequencies increases and impedance ratio deteriorates
Solution Approach 1:
The invention uses a composite structure of acoustic multilayer films combining materials with different acoustic impedances (such as AlN/SiN, AlN/SiO2, ScAlN/SiN, ScAlN/SiO2 alternately stacked), which suppresses spurious vibrations and maintains high impedance ratios (60 dB or more) at ultra-high frequencies while keeping the piezoelectric layer as polycrystalline for manufacturing simplicity
3Speed
If the piezoelectric thin film thickness is reduced below 0.3 μm to achieve 6 GHz or higher frequencies, then the excitation frequency increases, but manufacturing precision and quality control become extremely difficult
Solution Approach 1:
The invention changes the vibration mode to higher-order modes, allowing the piezoelectric thin film thickness to be maintained at 0.3 μm or more, which significantly improves manufacturing precision and quality control while achieving 6 GHz or higher excitation frequencies
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 enables good characteristics with a large impedance ratio in the ultra-high frequency band of 6 GHz or higher, maintaining sufficient mechanical strength and improving device performance beyond conventional limitations.
Implementation Method 1
a piezoelectric substrate; an electrode provided in contact with the piezoelectric substrate
Implementation Method 2
the elastic wave device is configured to utilize higher-order modes of resonance characteristics of bulk waves
Data Source
AI summary
An elastic wave device capable of obtaining good characteristics while maintaining sufficient mechanical strength in an ultra-high frequency band of 6 GHz or higher includes: a piezoelectric substrate; an electrode in contact with the piezoelectric substrate; and an acoustic multilayer film in contact with the piezoelectric substrate and/or the electrode. The elastic wave device is configured to utilize higher-order modes of resonance characteristics of bulk waves. The acoustic multilayer film has a low acoustic impedance film and a high acoustic impedance film which are alternately stacked.