Lead-Free KNN Piezoelectric Thin Film with Columnar Structure
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Solution Overview
Problem
Conventional piezoelectric thin films, particularly those made from potassium sodium niobate, face challenges in achieving high piezoelectric constants due to small crystal grain sizes and thickness limitations, leading to variations and deteriorations in properties, and they contain lead, which is environmentally undesirable.
Innovation Solution
A piezoelectric thin film element with a potassium sodium niobate-based perovskite structure, specifically (K1-xNax)NbO3, is developed, featuring a columnar structure with crystal grains larger than 0.1 μm but less than 1.0 μm in size and a thickness between 1 μm and 10 μm, optimized through sputtering methods to enhance piezoelectric constants while being lead-free.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If sintering method is used to manufacture piezoelectric materials, then piezoelectric properties can be achieved, but as thickness becomes thinner (close to 10 μm), crystal grain size influence cannot be ignored, causing variation and deterioration of properties
Solution Approach 1:
The patent changes the manufacturing method from sintering to sputtering, and optimizes parameters including film thickness (1-10 μm), crystal grain size (0.1-1.0 μm), and columnar structure formation to achieve reliable piezoelectric properties in thin films without the deterioration seen in conventional sintered materials
Solution Approach 2:
The patent creates a columnar structure with specific crystal grain orientation where crystal grains are elongated in the thickness direction, providing locally optimized properties that maintain piezoelectric performance despite reduced overall thickness
2Reliability
If PZT material is used for piezoelectric elements, then excellent piezoelectric properties are achieved, but the material contains 60-70 weight % lead oxide, which is environmentally undesirable
Solution Approach 1:
The patent uses composite material strategy by combining potassium sodium niobate (KNN) with barium titanate (BT) in specific ratios to achieve high piezoelectric properties without lead, replacing the lead-based PZT material while maintaining or improving performance
Solution Approach 2:
The patent adopts lead-free KNN-based materials as an environmentally friendly alternative to lead-containing PZT, sacrificing some historical performance advantage but gaining ecological sustainability and compliance with environmental regulations
3Volume of moving object
If potassium sodium niobate thin film is used instead of sintered body, then downsizing is achieved, but piezoelectric constant is less than half that of sintered body
Solution Approach 1:
The patent optimizes multiple parameters including film thickness (1-10 μm), crystal grain size (0.1-1.0 μm), deposition conditions, and material composition to achieve high piezoelectric constant in thin film form, overcoming the inherent limitation of thin film technology
Solution Approach 2:
The patent creates a columnar structure with vertically oriented crystal grains that provides locally optimized piezoelectric properties, enabling the thin film to achieve performance comparable to or exceeding conventional sintered materials despite reduced dimensions
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 achieves a significantly higher piezoelectric constant d31 of not less than −100 pm/V, improving the material's performance and environmental sustainability by maintaining excellent piezoelectric properties while avoiding lead usage.
Implementation Method 1
a piezoelectric thin film element that uses a piezoelectric thin film having an alkali niobium oxide based perovskite structure
Implementation Method 2
a method of forming the piezoelectric substance to which a thin film technology and the like to take place of the sintering method is applied has been investigated
Data Source
AI summary
A piezoelectric thin film element includes a substrate, a lower electrode, a piezoelectric thin film, and an upper electrode. The lower electrode, the piezoelectric thin film and the upper electrode are formed on the substrate. The piezoelectric thin film includes a polycrystal thin film including crystal grains, an alkali niobium oxide based perovskite structure represented by a general formula: (K1-xNax)NbO3 (0.4<x<0.7), a film thickness of not less than 1 μm and not more than 10 μm, a columnar structure configured by the crystal grains, a majority of the crystal grains including a shape in a cross-section direction thereof longer than in a plane direction of the substrate, and an average crystal grain size of not less than 0.1 μm and not more than 1.0 μm in the plane direction of the substrate.