KNN Thin Film Piezoelectric Element Grain Size Gradient
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Solution Overview
Problem
Thin film piezoelectric elements using potassium sodium niobate (KNN) face challenges with high leakage current due to large crystal grain sizes, which impede their practical application, as crystal grain boundaries act as pathways for electrical current, and conventional annealing methods are insufficient in eliminating oxygen vacancies in dielectric thin films formed by sputtering methods.
Innovation Solution
A thin film piezoelectric element structure is developed where the KNN thin film is divided into three regions of equal thickness, with a specific ratio of smallest to largest average crystal grain sizes (10% to 80%), and the region with the smallest grain size is positioned next to the electrode films, incorporating additives like Mn, Li, Sr, Ba, Zr, and Ta to reduce leakage current while maintaining high piezoelectric properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the crystal grain size is increased to improve piezoelectric properties, then the piezoelectric performance is enhanced, but the leakage current increases due to crystal grain boundaries acting as current passages
Solution Approach 1:
The patent applies local quality by creating a gradient crystal grain size distribution within the thin film, where crystal grains near the electrode interfaces are smaller (reducing leakage current pathways) while crystal grains in the bulk remain larger (maintaining piezoelectric properties). This spatial variation in crystal grain size allows simultaneous optimization of both leakage current resistance and piezoelectric performance.
Solution Approach 2:
The patent employs parameter changes by controlling the average crystal grain size to be within a specific range (0.1 μm to 1 μm) and maintaining the c-axis orientation perpendicular to the substrate surface. These parameter optimizations enable the material to achieve both low leakage current and high piezoelectric coefficients, resolving the contradiction between the two performance aspects.
2Reliability
If conventional annealing methods are used to eliminate oxygen vacancies, then some defect reduction is achieved, but leakage current remains high due to insufficient elimination of oxygen vacancies in sputtered dielectric thin films
Solution Approach 1:
The patent applies parameter changes by optimizing the annealing temperature and atmosphere parameters to effectively reduce oxygen vacancies in the sputtered dielectric thin film without causing excessive crystal grain growth or material degradation, thereby achieving low leakage current while maintaining manufacturing feasibility.
Solution Approach 2:
The patent uses composite materials by combining the potassium sodium niobate piezoelectric thin film with a sputtered dielectric thin film layer. This composite structure allows the dielectric layer to provide additional insulation and defect passivation, complementing the annealing treatment and further reducing leakage current beyond what annealing alone can achieve.
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 structure effectively decreases leakage current and enhances the piezoelectric properties, enabling the production of high-performance thin film piezoelectric elements suitable for applications in hard disk drives and ink jet printers.
Implementation Method 1
piezoelectric sensors, such as gyro sensors, pressure sensors, pulse wave sensors, shock sensors, and microphones, that use the piezoelectric effect of converting a force applied to a piezoelectric thin film into a voltage
Implementation Method 2
piezoelectric actuators, such as hard disk drive head assemblies and ink jet print heads, that use the inverse piezoelectric effect of a piezoelectric thin film deforming when a voltage is applied to the piezoelectric thin film
Data Source
AI summary
A thin film piezoelectric element according to the present invention includes a potassium sodium niobate thin film having a structure in which a plurality of crystal grains are present in a film thickness direction; and a pair of electrode films sandwiching the potassium sodium niobate thin film. When the potassium sodium niobate thin film is divided into three regions of the same thickness in the film thickness direction and average crystal grain sizes A1, A2, and A3 of the respective regions are determined, a ratio m/M of the smallest average crystal grain size m among A1, A2, and A3 to the largest average crystal grain size M among A1, A2, and A3 is 10% to 80%. The region having the smallest average crystal grain size m lies next to one of the pair of electrode films.