Piezoelectric Element Orientation Control Layer

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Solution Overview

Problem

Existing methods for forming piezoelectric thin films on silicon substrates face challenges such as low crystallinity, cracking, and high production costs, particularly when using sol-gel methods, which result in unreliable piezoelectric elements with suboptimal piezoelectric characteristics.

Innovation Solution

A piezoelectric element structure is developed, featuring a cubic or tetragonal perovskite oxide orientation control layer and a lead zirconate titanate piezoelectric layer with a Pb-containing complex perovskite compound, where the crystal grains extend thickness-wise, enhancing orientation control and reliability, and allowing for deposition on inexpensive substrates without the need for expensive MgO single-crystal substrates.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If sol-gel method is used to form piezoelectric thin films on silicon substrates, then production cost is reduced, but crystallinity and reliability deteriorate

Engineering Contradiction:

Improveproduction costVSAvoidcrystallinity

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

An orientation control layer is formed on the silicon substrate before forming the piezoelectric thin film. This preliminary layer controls the crystal orientation of the subsequent piezoelectric film, ensuring high crystallinity and reliability while maintaining compatibility with low-cost silicon substrates and sol-gel processing methods.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The orientation control layer acts as an intermediary between the silicon substrate and the piezoelectric thin film. It mediates the crystal growth process, providing a template that guides the formation of highly crystalline piezoelectric structures without requiring expensive single-crystal substrates.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If MgO single-crystal substrates are used, then piezoelectric characteristics are improved, but production cost increases

Engineering Contradiction:

Improvepiezoelectric characteristicsVSAvoidproduction cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The invention replaces expensive MgO single-crystal substrates with inexpensive silicon substrates. The orientation control layer compensates for the lower inherent quality of silicon, enabling high-performance piezoelectric films to be formed on cost-effective substrates suitable for mass production.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The invention changes the substrate material parameter from MgO single-crystal to silicon, and compensates for the difference by controlling crystal orientation through the orientation control layer. This parameter change enables cost reduction while maintaining piezoelectric performance through process control.

Inventive Principle:

Principle #35Parameter changes

3Volume of moving object

If piezoelectric thin film thickness is reduced, then device size is downsized, but crystallinity and performance deteriorate

Engineering Contradiction:

Improvedevice sizeVSAvoidcrystallinity

Core Design Contradiction:

Volume of moving objectVSManufacturing precision

Solution Approach 1:

The orientation control layer is formed in advance to establish a crystal orientation template before depositing the piezoelectric thin film. This preliminary structure enables even ultrathin films to maintain high crystallinity by guiding crystal growth from the outset, rather than relying on post-processing.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention successfully forms high-quality piezoelectric thin films with thickness of 0.1 μm or less. The orientation control layer enables ultrathin film formation while maintaining crystallinity, allowing significant device downsizing without sacrificing performance.

Inventive Principle:

Principle #30Flexible shells and thin films

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 approach results in piezoelectric elements with improved crystallinity, orientation, and reliability, reducing production costs and increasing the piezoelectric constant, while minimizing cracking and maintaining consistent performance under continuous operation.

Implementation Method 1

a piezoelectric layer having a rhombohedral or tetragonal crystalline structure and made of lead zirconate titanate

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS7312558B2Piezoelectric element, ink jet head, angular velocity sensor, and ink jet recording apparatus

Publication Date: 2007.12.25 PANASONIC HOLDINGS CORP

AI summary

In a piezoelectric element, a cubic or tetragonal orientation control layer (15) is provided on a first electrode layer (14), and formed on the orientation control layer (15) is a piezoelectric layer (16) having a rhombohedral or tetragonal crystalline structure and made of lead zirconate titanate to which a Pb-containing complex perovskite compound expressed by the chemical formula Pb(AaBb)O3 has been added in an amount that is from 1 mol % to 50 mol %. The piezoelectric layer (16) is formed so that the crystal grains thereof become columnar grains which extend in the thickness direction of the piezoelectric layer (16) and in which the ratio of the average cross-sectional diameter to the length is from 1/50 to 1/14.