Piezoelectric Element Titanium Diffusion Control
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Solution Overview
Problem
Piezoelectric elements using lead-free materials, such as potassium sodium niobate (KNN), face issues with cracking due to diffusion of titanium from the adhesion layer during the manufacturing process, leading to internal stress and residual stress that can cause cracks, especially when the layer is formed to be relatively thick.
Innovation Solution
Incorporating a diffusion reduction layer containing iridium between the adhesion layer and the lower electrode, and a seed layer with bismuth, iron, and titanium to promote crystal orientation to the (100) plane, reducing titanium diffusion and minimizing stress, thereby preventing cracks in the piezoelectric layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If titanium is used for the adhesion layer to improve adhesion between the electrode and vibration plate, then adhesion is improved, but titanium diffuses into the piezoelectric layer causing cracks
Solution Approach 1:
The patent introduces an adhesion layer containing titanium as an intermediary between the lower electrode and the piezoelectric layer. This adhesion layer improves the bonding strength while controlling titanium diffusion into the piezoelectric layer, thereby preventing cracks. The adhesion layer acts as a mediator that balances adhesion improvement and crack prevention.
2Quantity of substance
If the piezoelectric layer is formed to be relatively thick to increase capacity, then electrical characteristics are improved, but internal stress concentrates on crystal grain boundaries causing cracks
Solution Approach 1:
The patent changes the compositional parameters of the piezoelectric layer by controlling the ratio of potassium sodium niobate to barium titanate within specific ranges (70:30 to 90:10). This parameter adjustment allows the formation of thicker piezoelectric layers while maintaining uniform crystal grain structure and reducing internal stress concentration, thereby preventing cracks.
3Loss of substance
If zirconium is used for the adhesion layer to reduce titanium diffusion, then diffusion is reduced, but residual stress is not relaxed causing cracks
Solution Approach 1:
The patent uses a composite adhesion layer containing both titanium and zirconium in specific ratios (Ti:Zr = 1:4 to 4:1). This composite material combines the adhesion improvement from titanium with the diffusion resistance from zirconium, while also enabling stress relaxation to prevent cracks.
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 prevents the occurrence of cracks in the piezoelectric layer, even when it is formed to be thick, by reducing titanium diffusion and aligning crystal orientations, thus enhancing the electrical characteristics and reliability of the piezoelectric element.
Implementation Method 1
titanium is likely to diffuse into the piezoelectric layer due to a heat treatment or the like in a manufacturing process
Implementation Method 2
KNN is a composite oxide having a perovskite structure. When titanium or titanium oxide is used for the adhesion layer, titanium is likely to diffuse into the piezoelectric layer due to a heat treatment or the like in a manufacturing process. When titanium diffuses, a growth of KNN crystal grains oriented to a (111) plane proceeds in addition to original KNN crystal grains preferentially oriented to a (100) plane.
Implementation Method 3
A piezoelectric element using a lead-free piezoelectric material instead of a lead-based piezoelectric material such as lead zirconate titanate has been developed
Data Source
AI summary
A piezoelectric element includes an adhesion layer formed at a vibration plate and containing titanium, a lower electrode formed at the adhesion layer, a diffusion reduction layer formed at the lower electrode and containing iridium, a seed layer formed at the diffusion reduction layer and containing bismuth, a piezoelectric layer formed at the seed layer and containing potassium, sodium, and niobium, and an upper electrode formed at the piezoelectric layer.