Piezoelectric Element Upper Electrode Grain Conformity
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Solution Overview
Problem
Piezoelectric elements used in actuator devices and liquid ejecting heads face issues such as delamination and crack formation due to repeated operations, primarily caused by poor adhesion between the upper electrode film and the piezoelectric layer.
Innovation Solution
The piezoelectric element is designed with a lower electrode film, a piezoelectric layer composed of columnar grains, and an upper electrode film that conforms to the surface shape of the piezoelectric layer, with the upper electrode film having an average grain size of ¼ or less of the piezoelectric layer's average grain size minus two standard deviations, and a thickness of 10 to 200 nm, ensuring improved adhesion and electrical conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional piezoelectric element structure is used with a flat upper electrode film, then the manufacturing process is simple, but the adhesion between the upper electrode film and piezoelectric layer is poor, causing delamination and cracks during repeated operations
Solution Approach 1:
The upper electrode film is designed with varying grain sizes that conform to the surface shape of the columnar piezoelectric grains. The grain size of the upper electrode film is controlled to be 1/4 or less of (m-2σ) where m is the average grain size of the piezoelectric layer and σ is the standard deviation. This local variation in grain size creates better mechanical interlocking and adhesion at the interface between the electrode film and piezoelectric layer, preventing delamination and crack formation during repeated operations.
2Reliability
If the upper electrode film is made thinner to improve flexibility and adhesion, then the electrical conductivity may be compromised, but making it thicker improves conductivity while reducing adhesion
Solution Approach 1:
The thickness of the upper electrode film is precisely controlled within the range of 10 to 200 nm. This parameter optimization ensures that the film is thin enough to maintain flexibility and conform to the piezoelectric layer surface shape for good adhesion, while being thick enough to provide satisfactory electrical conductivity for the piezoelectric element operation.
3Reliability
If the piezoelectric layer uses large grain size for better piezoelectric properties, then the adhesion with upper electrode film improves, but the standard deviation increases making consistent manufacturing difficult
Solution Approach 1:
The average grain size of the piezoelectric layer is controlled within the range of 1 to 10 μm, and the standard deviation is controlled to be 0.2 μm or less. This precise parameter control ensures that the grain size is large enough to provide good piezoelectric properties and adhesion, while maintaining consistency for reliable manufacturing. The upper electrode film grain size is then set to 1/4 or less of (m-2σ) to optimize the interface adhesion.
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 configuration enhances the adhesion between the upper electrode film and the piezoelectric layer, preventing delamination and crack formation, while maintaining satisfactory electrical conductivity and displacement properties, leading to improved durability and reliability of the actuator devices and liquid ejecting heads.
Implementation Method 1
a piezoelectric layer composed of a piezoelectric material, such as a crystallized piezoelectric ceramic material, having the function of electromechanical transduction
Data Source
AI summary
A piezoelectric element includes a lower electrode film disposed on a substrate, a piezoelectric layer 70 disposed on the lower electrode film, a upper electrode film 80 disposed on the piezoelectric layer 70, wherein the piezoelectric layer 70 is formed of a plurality of columnar grains 70a, and the upper electrode film 80 conforms to the surface shape of each of the grains 70a of the piezoelectric layer 70.