IDT Electrode Dielectric Layout for Wider Acoustic Filter Bandwidth
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Solution Overview
Problem
Acoustic wave devices with IDT electrodes directly on piezoelectric bodies face increased capacitance and narrow fractional bandwidth, leading to potential surge breakdown due to high permittivity and concentrated electric fields.
Innovation Solution
Incorporating a dielectric film with lower permittivity than the piezoelectric body between the IDT electrode fingers and busbars, creating gaps that reduce parallel capacitance and prevent surge breakdown, while maintaining a wide fractional bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the IDT electrode is disposed directly on the piezoelectric body, then the device structure is simple, but the capacitance between electrode fingers and busbars increases due to high permittivity of the piezoelectric body
Solution Approach 1:
A dielectric film with lower permittivity than the piezoelectric body is introduced as an intermediary layer between the IDT electrode and the piezoelectric body. This dielectric film acts as a mediator that reduces the parallel capacitance between the electrode fingers and busbars while maintaining the direct contact structure for acoustic wave generation.
Solution Approach 2:
The dielectric film is selectively disposed in specific regions where capacitance reduction is needed, such as between the electrode fingers and busbars, while maintaining direct contact in other regions for effective acoustic wave generation. This local modification optimizes the electrical properties without compromising the overall device function.
2Power
If the IDT electrode is disposed directly on the piezoelectric body, then the electromechanical coupling is strong, but the electric field concentrates between tip ends of electrode fingers and busbars causing surge breakdown
Solution Approach 1:
The dielectric film serves as a protective intermediary layer that distributes the electric field between the IDT electrode and the piezoelectric body. By having lower permittivity than the piezoelectric body, it prevents electric field concentration at critical points such as between tip ends of electrode fingers and busbars, thereby preventing surge breakdown while maintaining strong electromechanical coupling.
Solution Approach 2:
The dielectric film is positioned in advance to cushion and distribute the electric field before it can concentrate and cause surge breakdown. This preventive measure protects the IDT electrode from electrical breakdown under high voltage conditions.
3Device complexity
If the capacitance between electrode fingers and busbars increases, then the device structure remains simple, but the fractional bandwidth becomes narrow and anti-resonant frequency approaches resonant frequency
Solution Approach 1:
The dielectric film with lower permittivity acts as an intermediary that reduces the parallel capacitance between the IDT electrode components. This capacitance reduction widens the fractional bandwidth and separates the anti-resonant frequency from the resonant frequency, improving the device's frequency response characteristics without complicating the overall structure.
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
The solution effectively reduces or prevents surge breakdown and widens the fractional bandwidth of acoustic wave devices by reducing parallel capacitance and enhancing electromechanical coupling, as demonstrated in comparative examples.
Implementation Method 1
permittivity of the first dielectric film is lower than permittivity of the piezoelectric body
Implementation Method 2
an IDT electrode disposed on the piezoelectric body
Data Source
AI summary
An acoustic wave device includes an IDT electrode on a piezoelectric body and the IDT electrode includes first and second busbars, and first and second electrode fingers. A first dielectric film extends from a region between tip end portions of the first electrode fingers and the piezoelectric body to a region between the second busbar and the piezoelectric body with a first gap in between. The second electrode fingers are in direct contact with the piezoelectric body at a center of an overlap width, and a permittivity of the first dielectric film is lower than a permittivity of the piezoelectric body.