Bulk Acoustic Wave Filter Frequency Tuning via Insulating Layer Thickness
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Solution Overview
Problem
The complexity of fabricating bulk acoustic wave filters increases due to the need to adjust resonance frequency differences by varying the thickness of top electrodes, which can affect the performance characteristics of the devices and is economically challenging.
Innovation Solution
A method involving the formation of a sacrificial epitaxial structure mesa on a compound semiconductor substrate, followed by the creation of an insulating layer and polishing to form a polished surface, where bulk acoustic wave resonance structures are built with frequency tuning structures that adjust resonance frequencies by varying the thickness of the insulating layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the thickness of top electrodes is adjusted to tune resonance frequency difference, then the resonance frequency can be tuned, but the fabrication complexity increases and device performance may be affected
Solution Approach 1:
The patent extracts the frequency tuning function from the top electrode thickness adjustment and relocates it to the insulating layer thickness. By removing the tuning requirement from the electrode structure and placing it in the insulating layer, the complexity of electrode fabrication is reduced while maintaining precise frequency control capability.
Solution Approach 2:
The insulating layer serves as an intermediary element that mediates the frequency tuning function. Instead of directly adjusting electrode thickness to control resonance frequency, the patent uses the insulating layer thickness as an intermediate parameter to achieve the same tuning effect with simpler fabrication.
2Adaptability or versatility
If the thickness of top electrodes is varied to achieve resonance frequency tuning, then frequency adjustment is possible, but economic efficiency deteriorates
Solution Approach 1:
The patent changes the parameter used for frequency tuning from electrode thickness to insulating layer thickness. This parameter substitution enables frequency adaptation while using a more economically efficient fabrication approach, as insulating layer deposition and thickness control are typically more cost-effective than precise electrode thickness variation.
3Manufacturing precision
If different thicknesses of top electrodes are used for different resonance structures, then resonance frequency difference is achieved, but the characteristics performance of the structures is affected
Solution Approach 1:
The patent extracts the frequency differentiation function from the electrode thickness variation and transfers it to the insulating layer thickness variation. This allows each resonance structure to have different frequencies through insulating layer thickness while maintaining uniform electrode characteristics, thereby preserving device performance.
Solution Approach 2:
The patent applies local quality by varying the insulating layer thickness locally under different resonance structures to achieve frequency differentiation, while keeping the electrode layers uniform in thickness and composition, thus maintaining consistent material properties and performance characteristics across all devices.
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 method simplifies the frequency tuning process, enhances device performance, and considers economic factors by allowing precise adjustment of resonance frequencies without compromising the characteristics of the bulk acoustic wave resonance structures.
Implementation Method 1
polishing the insulating layer by a chemical-mechanical planarization process to form a polished surface
Implementation Method 2
forming a piezoelectric layer on the bottom electrode layer
Data Source
AI summary
A method for forming cavity of bulk acoustic wave resonator comprising following steps of: forming a sacrificial epitaxial structure mesa on a compound semiconductor substrate; forming an insulating layer on the sacrificial epitaxial structure mesa and the compound semiconductor substrate; polishing the insulating layer by a chemical-mechanical planarization process to form a polished surface; forming a bulk acoustic wave resonance structure on the polished surface, which comprises following steps of: forming a bottom electrode layer on the polished surface; forming a piezoelectric layer on the bottom electrode layer; and forming a top electrode layer on the piezoelectric layer, wherein the bulk acoustic wave resonance structure is located above the sacrificial epitaxial structure mesa; and etching the sacrificial epitaxial structure mesa to form a cavity, wherein the cavity is located under the bulk acoustic wave resonance structure.