Piezoelectric Multilayer Component Passivation
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Solution Overview
Problem
Piezoelectric multilayer components face challenges in maintaining passivation integrity under mechanical stress and external influences due to cracking and insufficient protection, especially when the passivation material is the same as the ceramic layers, leading to inadequate dielectric strength and protection.
Innovation Solution
Using a piezoelectric ceramic material for the passivation with a lower electrical coercive field strength than the ceramic layers, allowing for a thicker passivation that can be polarized further from the internal electrodes, reducing tensile stress and enhancing mechanical robustness by introducing compressive stress through firm connection to the piezo stack.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the passivation is made from the same ceramic material as the piezo stack, then the polarization process stretches the passivation to reduce tensile stress, but the passivation thickness must be limited to about one ceramic layer thickness to be sufficiently polarized, which reduces protection capability
Solution Approach 1:
The patent changes the material parameter of the passivation by selecting a piezoelectric ceramic with lower electrical coercivity than the piezo stack ceramic. This parameter change allows the passivation to be polarized more effectively at greater distances from the internal electrodes, enabling increased thickness while maintaining adequate polarization and protection capability.
Solution Approach 2:
The patent employs a composite structure where the passivation is made from a different piezoelectric ceramic material than the piezo stack. This material differentiation creates a composite system where each layer has optimized properties: the piezo stack ceramic provides actuation functionality while the passivation ceramic provides enhanced protective coverage with improved polarizability.
2Reliability
If the passivation is made thicker to improve protection, then the protection against external influences is enhanced, but the electrical stray fields from internal electrodes cannot sufficiently polarize the entire passivation thickness, leading to inadequate stress compensation
Solution Approach 1:
By selecting a piezoelectric ceramic material with lower electrical coercivity for the passivation, the patent changes the material's polarizability parameter. This allows the electrical stray fields from the internal electrodes to effectively polarize thicker passivation layers, ensuring uniform polarization and adequate stress compensation throughout the entire passivation thickness.
3Strength
If the passivation is firmly connected to the piezo stack to transfer expansions, then tensile stress is built up during operation causing cracks, but without firm connection the stress transfer and protection mechanism fails
Solution Approach 1:
The patent changes the material parameter of the passivation to a piezoelectric ceramic with lower electrical coercivity and different expansion characteristics. This parameter change allows the passivation to be pre-compressed during polarization while maintaining firm connection to the piezo stack, creating a stress state that compensates for operational tensile stresses and prevents cracking.
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 increases the thickness and durability of the passivation, providing better protection against mechanical stress and external influences while maintaining dielectric strength, thus extending the component's service life and improving resilience.
Implementation Method 1
The piezo stack is polarized during manufacture of the component in order to impress a remanent polarization on it. This results in an expansion of the piezo stack.
Implementation Method 2
The material of the passivation is a piezoelectric ceramic and is different from the material of the ceramic layers of the piezo stack. In exemplary embodiments of the component, the ceramic of the passivation has a lower electrical coercive field strength than the ceramic layers of the piezo stack.
Implementation Method 3
Due to the fixed connection between the passivation and the piezo stack, the expansions of the piezo stack are transferred to the passivation, so that a tensile stress is built up in it.
Data Source
Figure 1~2
AI summary
The piezoelectric multilayer component comprises a piezo stack (1) having an alternating sequence of piezoelectric ceramic layers (2) and inner electrodes (5, 6), and a passivation (7) on an outer side. The passivation is produced from a piezoelectric ceramic material which is different from the material of the ceramic layers. In the production method, the passivation is polarized together with the ceramic layers.