Elastic Wave Ladder Filter Electrode Layout for Ripple and Passband Loss

Solution Overview

Problem

Elastic wave filter devices face challenges in achieving both increased steepness in filter characteristics and lower loss in the passband while effectively reducing or preventing transverse-mode ripple.

Innovation Solution

The elastic wave filter device incorporates a ladder filter structure with series and parallel arm resonators, featuring piezoelectric bodies, busbars, and electrode fingers with specific width configurations in edge and central areas to control acoustic velocity, thereby reducing transverse modes and optimizing bandwidth ratio.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the film thickness of IDT electrodes or the bandwidth ratio of elastic wave resonators is adjusted to increase steepness in filter characteristics, then the steepness is improved, but the loss in the passband increases and manufacturing precision becomes difficult to control

Engineering Contradiction:

Improvesteepness in filter characteristicsVSAvoidloss in the passband

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent applies local quality by creating edge areas with different electrode finger widths compared to the central area. Specifically, the electrode fingers in the edge areas have widths that are 1.05 to 1.20 times wider than those in the central area, while the acoustic velocity in edge areas is reduced to 0.80 to 0.95 times that of the central area. This localized modification of electrode geometry and acoustic properties enables independent control of filter characteristics without affecting the entire resonator uniformly, thereby achieving steepness improvement without compromising passband loss.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent employs parameter changes by systematically varying the electrode finger width and acoustic velocity in different regions of the resonator. The width ratio between edge area electrodes and central area electrodes is controlled within 1.05 to 1.20 times, and the acoustic velocity ratio is controlled within 0.80 to 0.95 times. These precise parameter adjustments enable optimization of filter steepness while maintaining acceptable passband loss characteristics.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the film thickness of IDT electrodes or the bandwidth ratio of elastic wave resonators is adjusted to increase steepness in filter characteristics, then the steepness is improved, but the manufacturing precision becomes difficult to control with high accuracy

Engineering Contradiction:

Improvesteepness in filter characteristicsVSAvoidcontrol of film thickness and bandwidth ratio

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent applies local quality by creating edge areas with different electrode finger widths compared to the central area. Specifically, the electrode fingers in the edge areas have widths that are 1.05 to 1.20 times wider than those in the central area, while the acoustic velocity in edge areas is reduced to 0.80 to 0.95 times that of the central area. This localized modification of electrode geometry and acoustic properties enables independent control of filter characteristics without affecting the entire resonator uniformly, thereby achieving steepness improvement without compromising passband loss.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent employs parameter changes by systematically varying the electrode finger width and acoustic velocity in different regions of the resonator. The width ratio between edge area electrodes and central area electrodes is controlled within 1.05 to 1.20 times, and the acoustic velocity ratio is controlled within 0.80 to 0.95 times. These precise parameter adjustments enable optimization of filter steepness while maintaining acceptable passband loss characteristics.

Inventive Principle:

Principle #35Parameter changes

3Object-generated harmful factors

If large-width portions are provided in edge areas to form piston mode, then transverse-mode ripple is reduced or prevented, but the bandwidth ratio increases and steepness in the high-frequency range decreases

Engineering Contradiction:

Improvetransverse-mode rippleVSAvoidsteepness in the high-frequency range

Core Design Contradiction:

Object-generated harmful factorsVSReliability

Solution Approach 1:

The patent applies local quality by creating edge areas with different electrode finger widths compared to the central area. Specifically, the electrode fingers in the edge areas have widths that are 1.05 to 1.20 times wider than those in the central area, while the acoustic velocity in edge areas is reduced to 0.80 to 0.95 times that of the central area. This localized modification of electrode geometry and acoustic properties enables independent control of filter characteristics without affecting the entire resonator uniformly, thereby achieving steepness improvement without compromising passband loss.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent employs parameter changes by systematically varying the electrode finger width and acoustic velocity in different regions of the resonator. The width ratio between edge area electrodes and central area electrodes is controlled within 1.05 to 1.20 times, and the acoustic velocity ratio is controlled within 0.80 to 0.95 times. These precise parameter adjustments enable optimization of filter steepness while maintaining acceptable passband loss characteristics.

Inventive Principle:

Principle #35Parameter changes

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 ensures increased steepness in filter characteristics and reduced loss in the passband, effectively preventing transverse-mode ripple and enhancing high-frequency range performance.

Implementation Method 1

each of the elastic wave resonators including a piezoelectric body

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

an elastic wave filter device using a surface acoustic wave or a boundary acoustic wave

Methodology Applied

Scientific EffectSurface acoustic wave: Surface Acoustic Wave

Data Source

PatentUS11843363B2Elastic wave filter device

Publication Date: 2023.12.12 MURATA MFG CO LTD

AI summary

An elastic wave filter device includes a ladder filter that includes series arm resonators and parallel arm resonators. In one series arm resonator in which the acoustic velocity in a first and second edge area is lower than in a central area, each first electrode finger includes a large-width portion having a width larger than in remaining portions in the second edge area, and each second electrode finger includes a large-width portion having a width larger than in remaining portions in the first edge area. In at least one of remaining series arm resonators and the parallel arm resonators, each first and second electrode finger includes a large-width portion having a width larger than in remaining portions in both of the first and second edge areas.