Acoustic Wave Filter With Variable Capacitor Tuning
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Solution Overview
Problem
Existing acoustic wave filters face challenges in precisely tuning resonant frequencies due to the need for trimming processes that can lead to undesirable effects like dispersion and yield degradation during manufacturing, particularly when attempting to adjust separate resonators.
Innovation Solution
An acoustic wave filter design incorporating a substrate with voids, first and second resonators, and a variable capacitor with interdigitated electrodes, allowing for frequency tuning by applying voltage without the need for trimming layers on the resonators, thereby simplifying the manufacturing process and improving yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a trimming process is performed to adjust resonant frequency, then the pass band can be tuned, but manufacturing yield degrades due to additional fabrication steps
Solution Approach 1:
The patent implements a variable capacitor with adjustable capacitance that enables dynamic tuning of the pass band frequency without requiring physical trimming of the resonator. The capacitance can be adjusted by changing the overlapping area between movable and fixed electrodes, allowing frequency adaptation while maintaining manufacturing yield.
Solution Approach 2:
The patent changes the electrical parameter (capacitance) rather than the physical dimension (resonator thickness) to achieve frequency tuning. By adjusting the capacitance value of the variable capacitor through electrode displacement, the pass band frequency can be tuned without performing additional etching or trimming processes.
2Manufacturing precision
If etching steps are used to trim the resonator, then resonant frequency can be adjusted, but dispersion occurs due to machining process conditions
Solution Approach 1:
The patent replaces the mechanical etching process with an electrical adjustment mechanism. Instead of physically removing material through etching, the pass band frequency is tuned by electrically adjusting the capacitance of the variable capacitor, which eliminates machining-induced dispersion while maintaining frequency adjustment precision.
3Ease of operation
If photolithography is performed for selective etching, then the resonator can be trimmed, but device complexity increases due to additional fabrication processes
Solution Approach 1:
The variable capacitor structure is pre-integrated into the filter design during the initial fabrication process, eliminating the need for subsequent photolithography and selective etching steps. The frequency tuning capability is built-in from the start, reducing overall fabrication process complexity while maintaining ease of operation.
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 design enables precise tuning of pass band frequencies without additional fabrication steps, reducing defects and improving manufacturing efficiency by eliminating the need for trimming layers and photolithography processes.
Implementation Method 1
The variable capacitor may include a first electrode disposed in the first connector, and a second electrode disposed in the second connector. The variable capacitor is configured to have capacitance dependent on a voltage applied across electrodes of the variable capacitor.
Implementation Method 2
a first piezoelectric body disposed on a top surface of the first lower electrode, and a first upper electrode disposed on a top surface of the first piezoelectric body
Data Source
AI summary
An acoustic wave filter includes a substrate, a first resonator disposed on the substrate, a second resonator disposed on the substrate to be spaced apart from the first resonator, a connector electrically connecting the first and second resonators, and a variable capacitor formed in the connector to tune a pass band frequency of the acoustic wave filter.