SAW Filter Capacitive Electrode Layout for Size and Steepness
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current elastic wave apparatuses face challenges in size reduction due to the design of capacitance portions, which lead to degradation in filter characteristics and unnecessary wave excitation, and existing filters struggle to incorporate electrostatic capacitance effectively.
Innovation Solution
The elastic wave apparatus incorporates a capacitive electrode with interdigitating third and fourth electrode fingers, connected via busbars and insulating films, oriented perpendicular to the IDT electrode, allowing for parallel connection and reduced surface acoustic wave interference, thereby enhancing electrostatic capacitance and filter steepness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the capacitance portion uses electrode fingers extending in the same direction as IDT electrode fingers, then the capacitance portion can be simply connected, but unnecessary waves are excited and filter characteristics degrade
Solution Approach 1:
The patent applies asymmetry by orienting the electrode fingers of the capacitance portion perpendicular to the IDT electrode fingers, rather than parallel. This asymmetric arrangement prevents the excitation of unnecessary surface acoustic waves while maintaining the capacitive function, thereby improving filter characteristics without complicating the connection structure
Solution Approach 2:
Instead of extending electrode fingers in the same direction as conventional designs, the patent inverts the approach by extending them perpendicular to the IDT electrode fingers. This inversion eliminates harmful wave excitation while preserving the capacitive coupling function between the IDT electrode and ground
2Reliability
If a capacitance portion is provided in the filter, then electrostatic capacitance can be added, but the size of the filter cannot be reduced
Solution Approach 1:
The patent merges the capacitance portion with the IDT electrode structure by using the IDT electrode fingers themselves as one set of comb-shaped electrodes and positioning the capacitive electrode fingers perpendicular to them. This integration eliminates the need for separate capacitance structures, adding electrostatic capacitance without increasing filter size
Solution Approach 2:
The patent transitions from a one-dimensional arrangement (electrode fingers extending in the same direction) to a two-dimensional arrangement (electrode fingers extending perpendicular to each other). This dimensional change allows the capacitance portion to be formed within the existing footprint of the IDT electrode, achieving size reduction while maintaining electrostatic capacitance
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 enables size reduction of elastic wave apparatuses while improving filter characteristics by effectively adding electrostatic capacitance and reducing unnecessary wave effects, leading to increased steepness around the passband edges.
Implementation Method 1
An electrostatic capacitance is therefore able to be added to the IDT electrode
Implementation Method 2
an IDT electrode that is provided on the piezoelectric substrate and includes a plurality of first electrode fingers and a plurality of second electrode fingers which interdigitate with each other
Data Source
AI summary
An elastic wave apparatus includes a piezoelectric substrate, an IDT electrode on the piezoelectric substrate and includes first electrode fingers, second electrode fingers, a first busbar, and a second busbar, a capacitive electrode including third electrode fingers, fourth electrode fingers, a third busbar, and a fourth busbar, an insulating film laminated on the capacitive electrode, a first wiring line including a first portion facing the capacitive electrode via the insulating film, and a second wiring line that connects the first busbar and the third busbar. The capacitive electrode extends in a lateral direction with respect to the IDT electrode in a surface acoustic wave propagation direction.