Piezoelectric Element with Asymmetric Dislocation Density
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Solution Overview
Problem
Existing piezoelectric elements in liquid ejecting heads face challenges in suppressing leak current, which is influenced by the density and position of lattice defects in the piezoelectric layer, particularly edge dislocations, and their relationship with lattice periodicity and stress relief during the film formation process.
Innovation Solution
A piezoelectric element is designed with a higher density of positive edge dislocations in the second portion of the piezoelectric layer compared to the first portion, which is achieved by forming the piezoelectric layer with a sol-gel method and incorporating a heating process to recrystallize the structure, thereby relieving stress and reducing leak current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dislocation layer is formed in the piezoelectric film to relieve inner stress and prevent cracks, then the mechanical reliability is improved, but the leak current increases due to lattice defects
Solution Approach 1:
The patent applies local quality by creating a dislocation layer only in the second portion (bottom part) of the piezoelectric layer, while keeping the first portion (top part) free of dislocations. This localized approach allows stress relief and crack prevention at the electrode interface without introducing harmful lattice defects in the entire piezoelectric layer, thus maintaining low leak current while ensuring mechanical reliability.
2Reliability
If the density of line defects is increased to suppress leak current, then the electrical performance is improved, but the structural integrity may deteriorate
Solution Approach 1:
The patent localizes the high density of line defects (dislocations) to the second portion of the piezoelectric layer adjacent to the second electrode. This localized defect concentration suppresses leak current in the critical region near the electrode while maintaining structural integrity in the first portion where the piezoelectric effect is primarily utilized, thus balancing electrical performance and structural strength.
Solution Approach 2:
The patent converts the harmful effect of lattice defects (which normally increase leak current) into a beneficial localized feature by concentrating dislocations in the second portion. The dislocation layer, which would normally be harmful throughout the structure, is instead used strategically at the electrode interface where it can suppress leak current without compromising the overall structural integrity of the piezoelectric layer.
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 effectively suppresses leak current by generating a higher density of positive edge dislocations in the second portion, leading to improved electromechanical stability and reduced electron conduction, enhancing the efficiency of diaphragm displacement in liquid ejecting heads.
Implementation Method 1
a piezoelectric element which includes a first electrode, a piezoelectric layer including line defects, and a second electrode
Implementation Method 2
incorporating a heating process to recrystallize the structure, thereby relieving stress and reducing leak current
Implementation Method 3
when a sol which is a piezoelectric film precursor is turned into a gel by means of thermal treatment
Data Source
Figure 1~2
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Figure 5
AI summary
Provided is a piezoelectric element (100) including a first electrode (10) provided above a substrate (2), a piezoelectric layer (20) provided above the first electrode, containing potassium, sodium, and niobium, and having a perovskite structure, and a second electrode (30) provided above the piezoelectric layer. In a case where the piezoelectric layer is divided into two portions (26,27) at a center thereof in a thickness direction, the piezoelectric layer includes a first portion (26) on the first electrode side and a second portion (27) on the second electrode side. The piezoelectric layer includes line defects (22). A density of the line defects in the second portion is higher than a density of the line defects in the first portion.