BAW Filter Layout Using Mutual Inductance to Shrink Inductors
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Solution Overview
Problem
Current filters, such as film bulk acoustic resonators (FBARs), face challenges in miniaturization and cost reduction due to unintended mutual inductance between wiring lines and bonding lines, which affects their inductance and filtering characteristics.
Innovation Solution
The implementation of a multilayer structure with bulk acoustic wave resonators, where the mutual inductance between wiring lines and bonding lines is intentionally designed to adjust the filtering characteristics, including the placement of series and shunt resonators, and inductors, to optimize frequency bands and reduce manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If wiring lines and bonding lines are placed close together to reduce device area, then area is reduced, but unintended mutual inductance increases affecting filtering characteristics
Solution Approach 1:
The patent converts the harmful unintended mutual inductance into a beneficial designed mutual inductance by intentionally placing wiring lines adjacent to bonding lines. The mutual inductance between these lines is calculated and designed to provide the required inductor value, thereby eliminating the need for separate inductor components while improving filtering characteristics.
Solution Approach 2:
The patent merges the function of separate inductors with the bonding lines by utilizing the mutual inductance between wiring lines and bonding lines. This integration eliminates discrete inductor components and reduces the overall filter area while maintaining or improving filtering performance.
2Manufacturing precision
If separate inductors are added to improve filtering characteristics, then filtering performance is improved, but device area and manufacturing cost increase
Solution Approach 1:
The bonding lines serve dual functions: providing electrical connection and acting as inductors through mutual inductance with adjacent wiring lines. This multi-functionality eliminates the need for separate inductor components, reducing device area and manufacturing cost while maintaining filtering characteristics.
Solution Approach 2:
The bonding lines and wiring lines provide their own inductance through mutual inductance, eliminating the need for external inductor components. The filter structure serves itself by utilizing the inherent electromagnetic properties of its existing components.
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 allows for the reduction of inductor volumes and manufacturing costs while adjusting the frequency band positions, resulting in improved filtering performance and miniaturization of filters.
Implementation Method 1
when electrical energy is applied to the first and second electrodes to induce an electric field in a piezoelectric layer, the electric field generates a piezoelectric phenomenon in the piezoelectric layer to allow the resonant part to vibrate in a predetermined direction
Implementation Method 2
the filtering characteristics of the filter being configured through a mutual inductance between the wiring line and the bonding line
Data Source
AI summary
A filter includes a multilayer structure having films configured as bulk acoustic wave resonators; a wiring line connected to the bulk acoustic wave resonators; a cap coupled to the multilayer structure on a bonding line; and the filtering characteristics of the filter being configured through a mutual inductance between the wiring line and the bonding line.