BAW Resonator SiO2 Flap Structure for Higher Q RF Filters
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Solution Overview
Problem
Existing bulk acoustic wave (BAW) resonators in RF filters, used in communication equipment, face challenges in achieving improved quality factor and passband performance, leading to increased attenuation and reduced transmission within the passband region.
Innovation Solution
The introduction of a structured silicon dioxide layer directly deposited on the piezoelectric layer without an intervening seed layer, forming an acoustic mirror structure that enhances energy confinement and increases the quality factor of the electro-acoustic resonator, which is then used in a ladder type RF filter configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional BAW resonator structure is used with a dielectric layer disposed on the piezoelectric layer, then the acoustic energy is confined within the active area, but the quality factor of the resonator is insufficient leading to increased attenuation
Solution Approach 1:
The patent changes the material parameter of the layer disposed on the piezoelectric layer from a generic dielectric material to specifically silicon dioxide (SiO2). This material parameter change results in improved acoustic characteristics and higher quality factor. Additionally, the patent optimizes the thickness parameter of the silicon dioxide layer to be between 50-200 nm, which further enhances the quality factor by optimizing the acoustic confinement without excessive energy loss.
2Ease of manufacture
If the dielectric layer is disposed directly on the piezoelectric layer without an intervening seed layer, then the manufacturing process is simplified, but the acoustic characteristics and quality factor are degraded
Solution Approach 1:
The patent introduces an aluminum oxide (Al2O3) intermediate layer between the piezoelectric layer and the silicon dioxide layer. This intermediary layer serves as a seed layer that improves the deposition quality and adhesion of the silicon dioxide layer on the piezoelectric layer, thereby enhancing the acoustic characteristics and quality factor. The aluminum oxide layer acts as a mediator that facilitates better interface properties without significantly complicating the manufacturing process.
3Reliability
If the silicon dioxide layer is structured to surround the acoustically active area, then the acoustic energy confinement is improved, but the device complexity increases
Solution Approach 1:
The patent segments the silicon dioxide layer into different regions: a first region disposed directly on the piezoelectric layer within or near the acoustically active area, and a second region extending outward to surround the active area. This segmentation allows the layer to perform multiple functions - providing acoustic confinement in the first region and energy containment in the second region - thereby improving energy confinement effectiveness while managing structural complexity through functional zonation.
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 approach results in reduced attenuation and increased transmission within the passband frequency region of the RF filter, improving the overall filter performance by confining acoustic energy and modifying the acoustic characteristics of the resonator.
Implementation Method 1
A bulk acoustic wave (BAW) resonator comprises a piezoelectric layer sandwiched between bottom and top electrodes. An electrical signal applied to the electrodes generates a resonating acoustic wave within the piezoelectric layer
Implementation Method 2
A dielectric layer disposed on the piezoelectric layer surrounding the acoustically active area generates a step feature on the surface of the piezoelectric layer to substantially confine the acoustic energy within the active area
Implementation Method 3
an acoustic mirror disposed thereon
Data Source
AI summary
Electro-acoustic resonator and method for manufacturing the same An electro-acoustic resonator comprises an acoustic mirror (120) disposed on a carrier substrate (110), a bottom electrode (130) and a piezoelectric layer (140). A structured silicon dioxide flap layer (150) is disposed on the piezoelectric layer (140), both layers having a common contact surface. Direct disposal of the silicon dioxide (150) on the piezoelectric layer (140) increases the quality factor of the resonator and leads to enhanced RF filter performance.