FBAR Mass Load Stack for Flexible Filter Sensitivity Tuning
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Solution Overview
Problem
Conventional methods for fabricating film bulk acoustic resonators (FBARs) on substrates with piezoelectric aluminum nitride (AlN) face limitations due to the inability to form mass loads both on the top electrode and below it, resulting in poor flexibility and sensitivity in FBARs and filters.
Innovation Solution
A method involving the formation of an intermediate metal layer to protect the piezoelectric material layer, allowing for the creation of a mass load layer and top electrode, which includes steps like metal deposition, photoresist coating, lithography patterning, and dry etching, enabling flexible mass load formation and improved process choices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a mass load lift-off process is used to form mass load on the top electrode, then the top electrode mass load can be formed, but it is not possible to form mass load below the top electrode on the piezoelectric material layer
Solution Approach 1:
The patent segments the mass load formation process into two independent stages: first forming a mass load layer on the piezoelectric material layer, then forming another mass load layer on the top electrode. This segmentation allows each layer to be formed using appropriate processes without interfering with each other, enabling both positions to have mass loads simultaneously.
Solution Approach 2:
The patent performs preliminary action by forming the mass load layer on the piezoelectric material layer before forming the top electrode. This preliminary mass load layer is protected by the top electrode during subsequent lift-off processes, allowing it to remain intact while the top electrode mass load is formed through standard lift-off techniques.
2Manufacturing precision
If conventional lift-off process is used, then top electrode mass load can be formed, but the piezoelectric material layer cannot be directly processed due to losses from subsequent processes
Solution Approach 1:
The top electrode serves as an intermediary protective layer between the processing environment and the piezoelectric material layer. During the lift-off process to form the top electrode mass load, the piezoelectric material layer is protected from direct exposure to harsh chemicals and mechanical stresses, preventing damage and maintaining its integrity.
Solution Approach 2:
The patent applies beforehand cushioning by forming a protective layer or using process conditions that cushion the piezoelectric material layer from damage during subsequent lift-off and etching processes. This ensures the piezoelectric layer remains intact while allowing precise mass load formation on the top electrode.
3Device complexity
If mass load is formed only on the top electrode, then the fabrication process is simpler, but the filter sensitivity and flexibility are poor
Solution Approach 1:
The patent applies local quality by forming mass loads at different locations (on the piezoelectric material layer and on the top electrode) with different properties and functions. The mass load on the piezoelectric material layer provides baseline mass loading, while the mass load on the top electrode enables precise frequency tuning, together achieving both simplicity and high sensitivity.
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 enhances the flexibility and accuracy of mass load formation in FBARs and filters by protecting the piezoelectric layer during processing, increasing process choices and sensitivity.
Implementation Method 1
piezoelectric crystal is capable of producing stable resonant frequency signals during operation
Implementation Method 2
performing metal deposition on the surface of the piezoelectric material layer away from the substrate
Implementation Method 3
The metal deposition includes chemical vapor deposition (CVD), physical vapor deposition (PVD) and electroplating
Implementation Method 4
dry etching the top electrode to form a final mass load layer
Data Source
AI summary
The method for fabricating a FBAR provided according to the present invention includes providing a substrate, forming a dielectric material layer on a surface of the substrate away from the substrate, forming a bottom electrode on a surface of the dielectric material layer away from the substrate, forming a piezoelectric material layer on a surface of the bottom electrode away from the substrate, forming an intermediate metal layer on a surface of the piezoelectric material layer away from the substrate, forming a mass load layer on a surface of the intermediate metal layer away from the substrate, and forming a top electrode on a surface of the mass load layer away from the substrate. In this way, process choices are increased, and flexibility in multiple mass load formation of the FBAR below top electrode and in a filter having the FBARs are increased, thereby improving sensitivity in the filter.