Inclined Capacitive Electrode Layout for Compact Elastic Wave Filters
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Solution Overview
Problem
Elastic wave devices with capacitors connected in series to IDT electrodes on piezoelectric substrates face challenges in achieving large electrostatic capacity without increasing size, which can lead to increased resistance loss and degraded performance, particularly in filter devices where insertion loss is a concern.
Innovation Solution
The elastic wave device incorporates a capacitive electrode with a plurality of interdigitated comb-shaped electrode portions connected in parallel, where the intersecting width direction of the capacitive electrode portions is inclined relative to the IDT electrode, allowing for a smaller size and increased electrostatic capacity while minimizing resistance loss by integrating busbars and optimizing electrode finger arrangements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of pairs of electrode fingers of a capacitor-forming comb-shaped electrode pair is increased to obtain a large electrostatic capacity, then the electrostatic capacity is improved, but the capacitor-forming comb-shaped electrode pair becomes long in the intersecting width direction of the IDT electrode, resulting in large unused space on the piezoelectric substrate
Solution Approach 1:
The patent changes the orientation of the capacitor-forming comb-shaped electrode pair from being perpendicular to the IDT electrode's intersecting width direction to being inclined at a specific angle (e.g., 45 degrees). This dimensional change in orientation allows the electrode pair to utilize the substrate area more efficiently, reducing unused space while maintaining the required electrostatic capacity through optimized electrode finger arrangement.
Solution Approach 2:
The patent modifies geometric parameters of the capacitor-forming comb-shaped electrode pair, including the inclination angle relative to the IDT electrode, the number of electrode finger pairs, and the intersecting width. By optimizing these parameters, the design achieves large electrostatic capacity with compact footprint, eliminating the need for excessive unused space on the substrate.
2Quantity of substance
If the intersecting width of a capacitor-forming comb-shaped electrode pair is increased to obtain a large electrostatic capacity, then the electrostatic capacity is improved and unused space is reduced, but the resistance loss of the capacitor-forming comb-shaped electrode pair is increased, degrading the characteristics of the elastic wave device
Solution Approach 1:
The patent introduces an inclination angle parameter for the capacitor-forming comb-shaped electrode pair relative to the IDT electrode. This dimensional change allows the electrode fingers to be arranged in a more efficient pattern that increases the effective facing area for capacitance while minimizing the total length of conductive paths, thereby reducing resistance loss even as electrostatic capacity increases.
Solution Approach 2:
The patent optimizes multiple parameters simultaneously: the inclination angle of the electrode pair, the intersecting width, and the number of electrode finger pairs. By carefully balancing these parameters, the design achieves high electrostatic capacity while controlling resistance loss, preventing degradation of elastic wave device characteristics such as insertion loss.
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 enhances the performance of the elastic wave device by achieving a large electrostatic capacity without increasing insertion loss, allowing for a compact design that maintains good filter characteristics and reduces unused space on the substrate.
Implementation Method 1
a capacitor may be connected in series with the IDT electrode. If the capacitor is provided in the elastic wave device, as described in Japanese Unexamined Patent Application Publication No. 8-65089, it is known that the capacitor is formed on a piezoelectric substrate and a comb-shaped electrode pair, in which electrodes are interdigitated with each other, forms a capacitor
Implementation Method 2
An elastic wave device includes a piezoelectric substrate and an IDT electrode formed on the piezoelectric substrate. The elastic wave device provides, for example, a resonant characteristic and a filter characteristic by using elastic waves excited at the IDT electrode
Data Source
AI summary
An elastic wave device includes a piezoelectric substrate, an IDT electrode located on the piezoelectric substrate, and a capacitive electrode that is located on the piezoelectric substrate and is connected in series with the IDT electrode. The capacitive electrode includes a plurality of capacitive electrode portions, each of which includes a pair of mutually interdigitated comb-shaped electrodes. The plurality of capacitive electrode portions are connected with each other in parallel. The plurality of capacitive electrode portions are arranged such that an intersecting width direction D1 of the capacitive electrode portions is inclined with respect to an intersecting width direction D2 of the IDT electrode. The plurality of capacitive electrode portions are arrayed in an elastic-wave propagating direction D3 of the IDT electrode.