Bulk Acoustic Wave Resonator Electrode Step Structure for Spurious Noise
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Bulk acoustic wave resonators face issues with spurious noise and notching due to manufacturing process errors and non-uniform etching, which affect their performance and Q factor.
Innovation Solution
The design includes a second electrode with a protruding portion and an extended portion, along with a lower frame and passivation layer, where the thickness differences and widths of these features are optimized to minimize spurious noise and notching, and the lower frame is formed of an insulating material with lower density than the first electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a frame is formed around the resonator to control resonance waveform, then piston mode operation is improved, but manufacturing precision requirements increase due to strict width and thickness control needs
Solution Approach 1:
The patent applies local quality by creating different thickness regions within the same electrode structure. The second electrode includes a protruding portion with first thickness and an extended portion with second thickness, allowing different regions to serve different functions: the protruding portion maintains piston mode operation while the extended portion provides spacing without requiring precise uniform thickness throughout the entire structure.
Solution Approach 2:
The patent segments the second electrode into distinct portions with different thicknesses. The protruding portion and extended portion are separated by a step, creating discrete functional zones that reduce the need for precise overall dimensional control while maintaining local performance requirements.
2Ease of manufacture
If etching process is used to form cavity and frame, then device structure is created, but spurious noise and notching occur due to non-uniform etching
Solution Approach 1:
The patent changes the geometric parameters of the electrode structure, specifically creating a step between the protruding portion and extended portion of the second electrode. This parameter change modifies how the etching process interacts with the structure, reducing non-uniformity effects and minimizing spurious noise generation while maintaining ease of manufacture through standard etching processes.
3Volume of moving object
If lower frame is positioned close to first electrode for compact design, then device size is reduced, but process errors increase due to tighter tolerances
Solution Approach 1:
The extended portion of the second electrode acts as an intermediary element between the first electrode and the lower frame. This intermediate structure provides a built-in spacing mechanism that maintains appropriate distance between the first electrode and lower frame without requiring tight external tolerances, thus reducing process errors while maintaining compact design.
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 reduces the occurrence of spurious noise and notching, enhancing the performance and Q factor of the bulk acoustic wave resonator by minimizing process errors and improving acoustic impedance and electromechanical coupling coefficients.
Implementation Method 1
a piezoelectric layer disposed on the first electrode and overlapping at least a portion of the first electrode
Data Source
AI summary
A bulk acoustic wave resonator includes a substrate, a first electrode, wherein a cavity is formed between the substrate and the first electrode, a piezoelectric layer disposed on the first electrode and overlapping at least a portion of the first electrode, a second electrode disposed on the piezoelectric layer and overlapping at least a portion of the piezoelectric layer, a passivation layer having at least a portion disposed on the second electrode and overlapping at least a portion of the second electrode, and a lower frame spaced apart from the substrate and having a portion of the cavity disposed therebetween. Any one of the second electrode and the passivation layer includes a protruding portion having a first thickness and an extended portion having a second thickness less than the first thickness, and an inner end of the lower frame and an end of the protruding portion are spaced apart horizontally.