KNN Piezoelectric Stack Sputtering for Uniform Composition Control
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Solution Overview
Problem
Existing piezoelectric stacks with large diameters face issues of non-uniform composition distribution and dielectric breakdown voltage variations due to cracks and abnormal electrical discharge during sputtering, leading to spots with deviating (K+Na)/Nb ratios on the KNN film.
Innovation Solution
A piezoelectric stack with a KNN film having a uniform (K+Na)/Nb ratio of 0.94≤(K+Na)/Nb≤1.03 over its entire inner region, achieved by using a sputtering target material with a Vickers hardness of 150 or more and controlled sintering processes to prevent cracks and ensure uniform composition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a target material with large area (44.2 cm2 or more) is used for mass production, then productivity is improved, but manufacturing precision deteriorates due to non-uniform composition distribution
Solution Approach 1:
The patent applies parameter changes by controlling the Vickers hardness of the target material surface to be 150 or more and adjusting the sintering temperature and time parameters. By optimizing these parameters, the patent achieves both high productivity with large-area targets and high manufacturing precision with uniform composition distribution across the entire target surface.
Solution Approach 2:
The patent applies preliminary action by performing pre-sputtering treatment on the target material before actual film deposition. This preliminary action removes surface contaminants and prepares the target surface, ensuring uniform composition distribution and preventing spots with deviating (K+Na)/Nb ratios in the final KNN film.
2Productivity
If sputtering is performed with high power to increase deposition rate, then productivity is improved, but reliability deteriorates due to cracks and abnormal electrical discharge
Solution Approach 1:
The patent applies parameter changes by optimizing the RF power density to be within 2.7-4.1 W/cm2 and controlling the sputtering pressure and gas flow rates. By carefully adjusting these parameters, the patent achieves high deposition rates while preventing cracks and abnormal electrical discharge, ensuring film quality and reliability.
Solution Approach 2:
The patent applies beforehand cushioning by ensuring the target material has Vickers hardness of 150 or more before sputtering begins. This pre-conditioning of the target material prevents cracks and abnormal electrical discharge during high-power sputtering operations, maintaining both high productivity and film reliability.
3Strength
If the target material thickness is increased to improve hardness, then strength is improved, but device complexity increases due to longer sintering time
Solution Approach 1:
The patent applies parameter changes by optimizing the sintering temperature (900-1200°C) and time (12-24 hours) along with applying controlled pressure during sintering. By adjusting these parameters, the patent achieves the required Vickers hardness of 150 or more while managing the sintering process complexity and production time.
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 ensures uniform dielectric breakdown voltage and improved yield and reliability of piezoelectric devices by maintaining consistent (K+Na)/Nb ratios across the film, reducing variations and enhancing production consistency.
Implementation Method 1
a piezoelectric film (KNN film) deposited by a sputtering method using such a piezoelectric material
Implementation Method 2
heating the mixture while applying a predetermined pressure to the mixture, to obtain sintered ceramics
Data Source
AI summary
Provided is a piezoelectric stack including: a substrate having a main surface with a diameter of 3 inches or more; and a piezoelectric film on the substrate, comprising an alkali niobium oxide containing K, Na, Nb, and O, wherein in the piezoelectric film, a composition of K, Na, and Nb satisfies a relationship of 0.94≤(K+Na)/Nb≤1.03 over an entire inner region of the main surface of the piezoelectric film, excluding its periphery.