Piezoelectric Element Electrode Crystallinity and Open Defect Prevention

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Solution Overview

Problem

Existing piezoelectric devices suffer from open defects due to incomplete electrical coupling at the bond between the electrode layer and the coupling electrode, caused by the depression and through hole formation processes, leading to reduced crystallinity and electrical inefficiencies.

Innovation Solution

A piezoelectric element design featuring a through hole that widens from the first surface to the second surface, with a second electrode layer positioned such that its coupling area meets the through hole with a positional difference of 5 nm or less, and a coupling electrode placed on the coupling area, ensuring minimal disruption during etching and maintaining crystallinity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a through hole is created by etching from the opposite side of the electrode layer, then the piezoelectric layer can be connected through the substrate, but the electrode layer develops a depression and loses crystallinity at the through hole location

Engineering Contradiction:

Improveelectrical coupling completenessVSAvoidelectrode layer crystallinity

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The electrode layer is formed on the piezoelectric layer before the through hole is etched. This preliminary formation allows the electrode layer to be deposited on a flat surface, maintaining its crystallinity, and then the through hole is created without subsequently damaging the electrode layer structure.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Instead of etching the through hole first and then forming the electrode layer (which would cause depression and crystallinity loss), the invention inverts the sequence: the electrode layer is formed first on the intact piezoelectric layer, and then the through hole is etched. This reversal prevents the electrode layer from being damaged by the etching process.

Inventive Principle:

Principle #13The other way round (Inversion)

2Productivity

If the electrode layer is etched simultaneously with the through hole creation, then the processing steps are reduced, but the electrode layer loses crystallinity and creates open defects

Engineering Contradiction:

Improveprocessing efficiencyVSAvoidbond electrical coupling

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The processing steps are segmented into distinct stages: first forming the electrode layer on the piezoelectric layer, then separately etching the through hole in the substrate. This segmentation prevents simultaneous etching of the electrode layer and substrate, avoiding crystallinity loss and ensuring complete electrical coupling without open defects.

Inventive Principle:

Principle #1Segmentation

3Ease of manufacture

If the coupling electrode is placed in a depression of the electrode layer, then the through hole can be filled, but the low-crystallinity portion causes incomplete electrical coupling and open defects

Engineering Contradiction:

Improvethrough hole fillingVSAvoidelectrical coupling completeness

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The electrode layer is formed in advance on a flat piezoelectric layer surface before the through hole is created. This preliminary formation ensures the electrode layer has high crystallinity throughout, including the area that will later be positioned over the through hole, preventing open defects while still allowing the coupling electrode to fill the through hole effectively.

Inventive Principle:

Principle #10Preliminary action

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 design reduces the occurrence of open defects and enhances electrical coupling, improving the piezoelectric element's efficiency and reliability by maintaining the crystallinity of the second electrode layer and reducing contact resistance.

Implementation Method 1

The piezoelectric film is made of a piezoelectric material, such as aluminum nitride (AlN)

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS20220199891A1Piezoelectric element and method for producing the same

Publication Date: 2022.06.23 MURATA MFG CO LTD

AI summary

A piezoelectric element includes a piezoelectric layer, a first electrode layer, a second electrode layer, and a coupling electrode. At least a portion of the second electrode layer faces the first electrode layer with the piezoelectric layer interposed therebetween. The second electrode layer includes a coupling area. The coupling area meets a through hole in a region of the second electrode layer not facing the first electrode layer. The coupling electrode is on the coupling area. Between the coupling area and the surface of the second electrode layer on the piezoelectric layer side excluding the coupling area, the difference in position is about 5 nm or less.