Acoustic Wave Filter Layout for High-Side Passband Attenuation

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Solution Overview

Problem

Conventional band pass filter devices with acoustic wave resonators made of lithium niobate or lithium tantalate suffer from attenuation deterioration on the higher frequency side of the pass band.

Innovation Solution

Incorporating a first series arm resonator and a first parallel arm resonator with acoustic wave resonators made of lithium niobate or lithium tantalate, along with an inductor connected in series between the resonators, to maintain sufficient attenuation on the higher frequency side of the pass band, utilizing a thickness shear mode for improved resonance characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional acoustic wave resonators with lithium niobate or lithium tantalate are used in filter devices, then the filter can achieve basic pass band functionality, but the attenuation on the higher frequency side than the pass band deteriorates

Engineering Contradiction:

Improveattenuation performance on higher frequency sideVSAvoidfilter structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent changes the physical parameters of the acoustic wave resonator by controlling the thickness of the piezoelectric layer (d) relative to the electrode pitch (p) to satisfy d/p ≤ 0.5. This parameter change modifies the resonance characteristics to improve attenuation on the higher frequency side while maintaining pass band functionality.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent utilizes thickness shear mode vibration in the piezoelectric layer to achieve improved resonance characteristics. By exciting mechanical vibration in the thickness direction of the piezoelectric layer, the resonator achieves better attenuation performance on the higher frequency side.

Inventive Principle:

Principle #18Mechanical vibration

2Reliability

If the piezoelectric layer thickness is increased to improve resonance characteristics, then the Q value increases, but the fractional band width decreases

Engineering Contradiction:

ImproveQ valueVSAvoidfractional band width

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent optimizes the ratio of piezoelectric layer thickness (d) to electrode pitch (p) to satisfy d/p ≤ 0.5. This parameter optimization achieves a balance between Q value and fractional band width, allowing both parameters to be improved simultaneously compared to conventional designs.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses composite structure combining piezoelectric layer with specific electrode patterns and optional buffer layers. This composite approach enables simultaneous improvement of Q value and fractional band width by leveraging the synergistic effects of different material layers and structural configurations.

Inventive Principle:

Principle #40Composite materials

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 increases attenuation on the higher frequency side of the pass band, enhancing the filter's performance by widening the fractional band width and increasing the Q value, thereby improving the filter's ability to maintain attenuation in the N77 and 5 GHz Wi-Fi bands.

Implementation Method 1

an acoustic wave resonator including a piezoelectric layer made of lithium niobate or lithium tantalate and at least one pair of a first electrode and a second electrode on the piezoelectric layer

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

utilizing a thickness shear mode for improved resonance characteristics

Methodology Applied

Scientific EffectThickness shear mode vibration: Vibration

Data Source

PatentUS20230344413A1Filter device

Publication Date: 2023.10.26 MURATA MFG CO LTD

AI summary

A filter device includes a first series arm resonator in a series arm, and a first parallel arm resonator in a parallel arm, each of the first series arm resonator and the first parallel arm resonator is defined by an acoustic wave resonator including a piezoelectric layer made of lithium niobate or lithium tantalate and at least a first electrode and a second electrode on the piezoelectric layer. The acoustic wave resonator satisfies a condition of d/p being equal to or less than about 0.5, when a thickness of the piezoelectric layer is d and a distance between centers of the first and second electrodes adjacent to each other is p. An inductor connected in series to the first series arm resonator is between the first series arm resonator and the first parallel arm resonator.