Bulk Acoustic Wave Resonator Thickness Tuning for Frequency Control
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Solution Overview
Problem
Existing bulk acoustic wave filter manufacturing processes face challenges in achieving uniform resonator thickness and high electromechanical coupling coefficients, leading to low yield and inconsistent filter performance due to limitations in film thickness uniformity and etching uniformity.
Innovation Solution
A method involving sequential formation of metal hard mask layers, photolithography, oxidation, and etching of the piezoelectric layer to achieve resonators with varying thicknesses, followed by the deposition of upper electrode layers, allowing for precise control of resonant frequencies and improved electromechanical coupling coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional film deposition and etching processes are used to manufacture bulk acoustic wave resonators, then the manufacturing process is simple, but the film thickness uniformity and etching uniformity are poor, leading to low yield and inconsistent resonator performance
Solution Approach 1:
The patent divides the manufacturing process into multiple sequential stages: forming sacrificial layers at different positions, depositing piezoelectric layers, selectively removing sacrificial layers, and repeating the process. This segmentation allows precise control over piezoelectric layer thickness at different resonator positions, achieving high thickness uniformity (less than 5nm variation) while managing process complexity through systematic step-by-step fabrication
Solution Approach 2:
The patent employs preliminary action by first forming sacrificial layers at specific positions before depositing the piezoelectric layer. These sacrificial layers serve as placeholders that define where the piezoelectric material should be deposited and what thickness it should achieve. This preliminary structuring enables precise thickness control in subsequent processing steps without requiring complex real-time adjustments
2Manufacturing precision
If conventional manufacturing processes are used, then the process is straightforward, but the electromechanical coupling coefficient is insufficient and resonant frequency control is imprecise
Solution Approach 1:
The patent applies local quality by creating resonators with different piezoelectric layer thicknesses at different positions on the substrate. Each resonator's sacrificial layer configuration is locally optimized to achieve the desired resonant frequency. This local customization allows precise control of resonant frequencies across multiple resonators while maintaining a relatively straightforward manufacturing process that can be scaled
Solution Approach 2:
The patent utilizes parameter changes by varying the piezoelectric layer thickness as the key parameter to control resonant frequency. By changing this physical parameter through controlled deposition and selective removal processes, the patent achieves precise frequency tuning. Additionally, the electromechanical coupling coefficient is enhanced by optimizing the piezoelectric layer structure, demonstrating parameter optimization for improved performance
3Adaptability or versatility
If uniform piezoelectric layers are deposited across all resonators, then the deposition process is simple, but it is impossible to achieve different resonant frequencies for different resonators
Solution Approach 1:
The patent segments the substrate into multiple regions, each with its own sacrificial layer configuration. This segmentation allows different piezoelectric layer thicknesses to be achieved at different locations. The process maintains adaptability by allowing custom sacrificial layer patterns for each resonator type while managing complexity through standardized deposition and removal cycles applied across all segments
Solution Approach 2:
The patent uses sacrificial layers as intermediary structures that enable future differentiation. These temporary structures serve as mediators that allow uniform deposition processes to result in non-uniform final products. The sacrificial layers are removed after serving their purpose of defining the piezoelectric layer thickness, leaving the desired resonator structures without requiring complex direct deposition control
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 enables the production of resonators with different resonant frequencies, enhancing the effective electromechanical coupling coefficient and manufacturing yield by directly forming piezoelectric layers with varying thicknesses, improving thickness uniformity and measurement accuracy.
Implementation Method 1
an acoustic transducer converts electrical signals into acoustic signals (acoustic waves) using inverse piezoelectric effect, and converts received acoustic waves into electrical signals via piezoelectric effect
Implementation Method 2
oxidizing the piezoelectric layer outside the effective area of the first resonator to the N-th resonator to form an N-th oxidized part of the piezoelectric layer
Data Source
AI summary
A method of manufacturing a bulk acoustic wave filter is provided, including: forming an acoustic reflection air cavity, a sacrificial layer, a seed layer, a lower electrode layer and a piezoelectric layer of n resonators on a substrate in sequence, wherein n is greater than or equal to 2; taking N from 1 to n for respectively repeating following steps: forming an N-th metal hard mask layer, defining an effective area of a first resonator to an N-th resonator by using a photolithography process, removing the N-th metal hard mask layer outside the effective area of the first resonator to the N-th resonator, oxidizing the piezoelectric layer outside the effective area of the first resonator to the N-th resonator to form an N-th oxidized part of the piezoelectric layer, and etching the N-th oxidized part of the piezoelectric layer; removing the metal hard mask layer of the effective area of the first resonator to the N-th resonator, so as to form the piezoelectric layer having different thicknesses of the first resonator to the N-th resonator; and forming an upper electrode layer on the piezoelectric layer having different thicknesses of the first resonator to the N-th resonator.