Piezoelectric Thin Film with BCC Electrode for Lattice Mismatch

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Solution Overview

Problem

Piezoelectric thin film devices with wurtzite structures face degradation in crystal orientation and piezoelectric characteristics due to lattice mismatch between the piezoelectric thin film and the lower electrode layer, leading to residual stress, cracks, and reduced surface smoothness.

Innovation Solution

A piezoelectric thin film device is developed with a first electrode layer composed of an alloy with a body-centered cubic lattice structure, specifically including elements like Mo, W, V, Cr, Nb, and Ta, which reduces lattice mismatch with the piezoelectric thin film, enhancing crystal orientation and piezoelectric characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a piezoelectric thin film with wurtzite structure is used, then the relative dielectric constant is small and piezoelectric output coefficient is improved, but lattice mismatch with the lower electrode layer occurs causing degradation of crystal orientation

Engineering Contradiction:

Improvepiezoelectric output coefficientVSAvoidcrystal orientation

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

A buffer layer is introduced between the lower electrode layer and the piezoelectric thin film to serve as an intermediary that reduces lattice mismatch. The buffer layer has a lattice constant intermediate between the electrode layer and piezoelectric film, enabling gradual transition and improving crystal orientation while maintaining the beneficial piezoelectric properties of the wurtzite structure film.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The lattice constant of the buffer layer is specifically selected to be intermediate between the lower electrode layer and the piezoelectric thin film. By changing the material parameter (lattice constant) of the intermediate layer, the lattice mismatch is reduced and crystal orientation is improved without sacrificing the piezoelectric output coefficient.

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If the piezoelectric thin film is laminated directly on the lower electrode layer, then device structure is simplified, but residual stress increases causing cracks in the piezoelectric thin film

Engineering Contradiction:

Improvedevice structureVSAvoidcrack resistance

Core Design Contradiction:

Device complexityVSStrength

Solution Approach 1:

The buffer layer acts as a mediator that absorbs residual stress between the lower electrode layer and the piezoelectric thin film. This intermediate layer prevents stress concentration that would otherwise cause cracks, thereby improving crack resistance while adding only one additional layer to the device structure.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of manufacture

If the piezoelectric thin film is laminated directly on the lower electrode layer, then manufacturing process is simplified, but surface smoothness degrades leading to reduced insulation resistance

Engineering Contradiction:

Improvemanufacturing processVSAvoidinsulation resistance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The buffer layer serves as an intermediary that provides a smooth surface for the piezoelectric thin film deposition. Even when laminated directly on the lower electrode layer, the buffer layer maintains surface smoothness, ensuring high insulation resistance while keeping the manufacturing process relatively simple.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 reduces lattice mismatch, improves crystal orientation, decreases residual stress, and increases surface smoothness, leading to enhanced piezoelectric performance and insulation resistance of the piezoelectric thin film device.

Implementation Method 1

the first electrode layer has a body-centered cubic lattice structure, and the piezoelectric thin film has a wurtzite structure

Methodology Applied

Scientific EffectLattice mismatch reduction:

Implementation Method 2

a piezoelectric thin film having a wurtzite structure is used... the piezoelectric output coefficient (g constant=d/ε0εr)

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS11594669B2Piezoelectric thin film element

Publication Date: 2023.02.28 TDK CORP

AI summary

Provided is a piezoelectric thin film device in which lattice mismatch between a piezoelectric thin film and a lower electrode layer (first electrode layer) is reduced. A piezoelectric thin film device 10 comprises a first electrode layer 6a and a piezoelectric thin film 2 laminated directly on the first electrode layer 6a; the first electrode layer 6a includes an alloy composed of two or more metal elements; the first electrode layer 6a has a body-centered cubic lattice structure; and the piezoelectric thin film 2 has a wurtzite structure.