Elastic Wave Duplexer Ground Via Layout for Better Isolation

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Solution Overview

Problem

Conventional elastic wave filter devices with a WLP structure face challenges in achieving sufficient isolation characteristics due to high inductance between ground terminals and ground potential, particularly in unbalanced input-unbalanced output configurations.

Innovation Solution

A duplexer design incorporating a piezoelectric substrate with an elastic wave filter electrode portion, a support layer, and via hole electrodes, where the ground terminals are commonly connected and bonded with bumps to reduce inductance, enhancing isolation characteristics by configuring the longitudinally coupled resonator elastic wave filter with unbalanced input and output terminals and parallel arm resonators.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If via hole electrodes are used to connect ground terminals to ground potential, then electrical connection is achieved, but large inductance is present between ground terminals and ground potential

Engineering Contradiction:

Improveisolation characteristicsVSAvoidinductance between ground terminals and ground potential

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

Multiple ground terminals are commonly connected on the piezoelectric substrate to form a unified ground connection system. This merging of ground terminals reduces the overall inductance by providing multiple parallel paths for ground current, thereby improving isolation characteristics between transmission and reception filters.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The ground connection is extended into the thickness dimension by using via hole electrodes that penetrate the support layer and cover. This three-dimensional ground connection structure reduces inductance by providing shorter current paths and multiple connection points in the vertical dimension, effectively lowering the harmful inductive effect.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Reliability

If conventional WLP structure is used for elastic wave filter device, then manufacturing is simplified, but isolation characteristics cannot be enhanced to sufficient level

Engineering Contradiction:

Improveisolation characteristicsVSAvoidWLP structure simplicity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The invention maintains the integrated WLP structure while merging multiple ground terminals into a common connection. This approach preserves the manufacturing simplicity of WLP technology while enhancing isolation characteristics through the combined ground connection that reduces inductance.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The invention changes the electrical parameters of the ground connection by creating multiple parallel via hole electrode paths. This parameter change reduces the equivalent inductance of the ground connection while maintaining the physical compactness and manufacturability of the WLP structure.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If unbalanced input-unbalanced output configuration is used, then device complexity is reduced, but isolation characteristics cannot be enhanced to sufficient level

Engineering Contradiction:

Improveisolation characteristicsVSAvoidconfiguration complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The invention applies common ground terminal connection to the unbalanced input-unbalanced output configuration, merging the ground paths to reduce inductance. This enhances isolation characteristics without increasing configuration complexity, as the merging is achieved through the existing WLP structure layers.

Inventive Principle:

Principle #5Merging (Combining)

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 duplexer achieves improved isolation characteristics by reducing the sum of inductances connected to the ground potential, effectively enhancing attenuation between input and output terminals, particularly in unbalanced input-unbalanced output configurations.

Implementation Method 1

an elastic wave filter electrode portion provided on the piezoelectric substrate so as to define an elastic wave filter

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

a plurality of via hole electrodes that penetrate the support layer and the cover and including first and second ends. The plurality of ground terminals are electrically connected to the respective first ends of the plurality of via hole electrodes

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS10270426B2Duplexer

Publication Date: 2019.04.23 MURATA MFG CO LTD

AI summary

At least one of a transmission filter and a reception filter of a duplexer includes a piezoelectric substrate, an elastic wave filter electrode portion on the piezoelectric substrate and including ground terminals to be connected to a ground potential, a support layer provided on the piezoelectric substrate, a cover provided on the support layer to seal a cavity in the support layer, and via hole electrodes penetrating the support layer and the cover and including first and second ends. The ground terminals are commonly connected on the piezoelectric substrate, and the ground terminals are electrically connected to the respective first ends of the plurality of via hole electrodes. The second ends of the via hole electrodes are connected to the ground potential outside of the at least one of the transmission filter and the reception filter.