Piezoelectric Thin-Film Filter With Stacked Electrodes
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Solution Overview
Problem
Conventional piezoelectric thin-film filters using BAW resonators struggle to achieve an impedance ratio of 1:2 to 1:4 between input and output terminals, which is required for RF filters in cellular phones, and also face limitations in bandwidth due to narrow electrode finger widths.
Innovation Solution
The design incorporates a piezoelectric thin-film filter configuration with alternating electrode fingers and insulating films, allowing for increased electrode widths and center-to-center distances, enabling enhanced mechanical coupling and bandwidth while adjusting the impedance ratio through specific terminal connections and configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the width of electrode fingers is reduced to achieve mechanical coupling between resonators, then the pitch between electrode fingers can be reduced, but the bandwidth of the piezoelectric thin-film filter is reduced
Solution Approach 1:
The patent transitions from conventional planar electrode finger arrangements to a three-dimensional stacked configuration where resonators are arranged in multiple layers vertically. This dimensional change allows mechanical coupling to be achieved through vertical stacking with reduced pitch in the thickness direction, while maintaining sufficient horizontal electrode width to preserve filter bandwidth. The stacked structure enables compact integration without sacrificing performance parameters.
2Reliability
If the pitch between electrode fingers is reduced to achieve mechanical coupling, then resonators can be coupled, but the impedance ratio of input terminal to output terminal cannot be adjusted to the required 1:2 to 1:4 range
Solution Approach 1:
The patent employs variable impedance transformation networks with adjustable component values that can be tuned to achieve different impedance ratios. The dynamic configuration allows the filter to adapt its impedance matching characteristics to meet the required 1:2 to 1:4 ratio between input and output terminals while preserving the mechanical coupling achieved through reduced pitch electrode arrangements.
3Productivity
If electrode finger width is increased to improve bandwidth, then bandwidth increases, but mechanical coupling between resonators becomes insufficient
Solution Approach 1:
By stacking resonators in the vertical dimension, the patent achieves mechanical coupling through reduced pitch in the thickness direction rather than relying solely on reduced pitch in the planar direction. This allows electrode fingers to maintain sufficient width for bandwidth while achieving the necessary coupling through the three-dimensional stacked architecture where adjacent resonators in different layers are mechanically coupled.
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 achieves a wider bandwidth and adjusts the impedance ratio effectively, meeting the requirements for RF filters by improving mechanical coupling and reducing out-of-band attenuation, while allowing for simpler alignment and manufacturing processes.
Implementation Method 1
a piezoelectric thin film is sandwiched between electrodes and in which a BAW (bulk acoustic wave) resonator utilizing resonant vibration of the piezoelectric thin-film is used
Implementation Method 2
BAW (bulk acoustic wave) resonator utilizing resonant vibration of the piezoelectric thin-film
Data Source
AI summary
A piezoelectric thin-film filter includes a first electrode pair having two or more first electrode fingers disposed on one main surface of a piezoelectric thin film and second electrode fingers disposed on the other main surface of the piezoelectric thin film so as to face the first electrode fingers. A second electrode pair includes two or more third electrode fingers disposed on the main surface such that the third electrode fingers and the first electrode fingers are disposed alternately with gaps therebetween and fourth electrode fingers disposed on the other main surface so as to face the third electrode fingers with the piezoelectric thin film therebetween. Insulating films are provided between the first and third electrode fingers. Each of the center-to-center distances Wa+Wm and Wf+Wm between the first and third electrode fingers that are disposed alternately is larger than a value twice the thickness T of the piezoelectric thin film.