Micro-Acoustic Stack With Aerogel Decoupling for 6 GHz Q Factor
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Solution Overview
Problem
Conventional SAW devices based on lithium tantalate (LiTaO3), lithium niobate (LiNbO3), or quartz bulk substrates fail to support frequencies up to 6 GHz due to poor quality factor and leakage of wave energy into the substrate, which is not suitable for 5G applications.
Innovation Solution
A micro-acoustic device with a stacked material system using a high coupling piezoelectric thin film and a decoupling layer made of low-density aerogel, such as silica, to confine acoustic energy and improve the quality factor, allowing operation up to 6 GHz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional SAW devices based on lithium tantalate, lithium niobate or quartz bulk substrates are used, then the devices can be manufactured with established processes, but the quality factor is poor and wave energy leaks into the substrate, making them unsuitable for frequencies up to 6 GHz
Solution Approach 1:
The patent introduces a decoupling layer as an intermediary between the piezoelectric thin film and the carrier substrate. This layer acts as a mediator that prevents wave energy from leaking into the substrate while maintaining the functionality of the device. The decoupling layer with low acoustic impedance specifically targets and resolves the energy leakage problem that conventional SAW devices suffer from.
Solution Approach 2:
The patent employs a composite material structure consisting of multiple layers: carrier substrate, decoupling layer, and piezoelectric thin film. Each layer is selected for its specific properties - the carrier substrate provides mechanical support, the decoupling layer prevents energy leakage, and the piezoelectric thin film generates and confines the acoustic waves. This composite approach enables the device to achieve high quality factor and support frequencies up to 6 GHz.
2Speed
If longitudinal surface acoustic waves are used to achieve high sound velocity for 5G frequency bands, then the wave velocity is outstandingly high, but the waves are not bounded to the surface and tend to leak wave energy to the substrate, resulting in poor quality factor
Solution Approach 1:
The decoupling layer serves as an intermediary that specifically addresses the energy leakage issue of longitudinal waves. By positioning this layer between the piezoelectric film and substrate, it mediates the interaction and prevents energy from escaping into the substrate, thereby maintaining high quality factor while preserving the high sound velocity advantage of longitudinal waves.
Solution Approach 2:
The patent applies local quality by creating a specific region (decoupling layer) with tailored acoustic properties at the interface where energy leakage occurs. This localized intervention with low acoustic impedance material specifically targets the problem area without affecting the overall wave propagation characteristics, allowing longitudinal waves to maintain their high velocity while preventing energy loss.
3Power
If a piezoelectric thin film is stacked on a carrier substrate to achieve high coupling, then electromechanical coupling is improved, but wave energy couples into the bulk carrier, reducing quality factor
Solution Approach 1:
The decoupling layer acts as an intermediary that separates the piezoelectric thin film from the carrier substrate. This intermediary structure allows the piezoelectric film to maintain strong coupling with the electrodes for high electromechanical coupling, while simultaneously preventing energy from coupling into the bulk carrier substrate, thus resolving the contradiction between coupling strength and energy loss.
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
The device achieves an outstanding high Q factor and low losses, enabling efficient wave confinement and performance in ultra-high frequency regimes, suitable for 5G mobile communication.
Implementation Method 1
The piezoelectric thin film comprises e.g. LiTaO3 or LiNbO3 with varying cut angles. The cut angle is chosen, that the main mode is a longitudinal wave due to its high sound velocity.
Implementation Method 2
The coupling of wave energy into the bulk carrier is reduced by means of a decoupling layer arranged between the piezoelectric thin film and the carrier. The decoupling properties can be achieved with a material having a low density and a low Young's modulus.
Implementation Method 3
Silica aerogel can be manufactured with a porosity of 80 to 99.8%. Hence they possess a respective density of 0.16 to 500 Kg/m3. Such a low density material perfectly hinders acoustic waves from passing a respective decoupling layer.
Data Source
AI summary
A micro-acoustic wave device is proposed for application in ultrahigh frequency range. The device uses a thin film piezoelectric material stacked on a carrier substrate. Additionally, a material is embedded between carrier substrate and piezoelectric thin film that decouples the acoustic of these layers. With this approach it is possible to achieve very high Q factor even for longitudinal waves, which are required for high frequency applications.