Piezoelectric Element Exterior Coating for Electrode Migration
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Solution Overview
Problem
Conventional piezoelectric actuators experience a decrease in the degree of polarization due to the pyroelectric effect, especially in smaller devices, and existing solutions fail to prevent migration between internal electrodes effectively without additional components or significant component complexity.
Innovation Solution
A piezoelectric element with a monolithic substrate and internal electrodes, where an exterior portion containing dispersed electroconductive particles is applied to cover exposed internal electrodes, preventing migration and allowing electric charges generated by the pyroelectric effect to flow out, thus maintaining polarization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional insulating layers are used to cover exposed internal electrodes, then migration between electrodes is prevented, but the degree of polarization decreases due to the pyroelectric effect under temperature changes
Solution Approach 1:
The invention changes the material parameter of the exterior coating from conventional insulating materials to a composite material containing electroconductive particles dispersed in an insulating resin. This parameter change allows the coating to simultaneously provide electrical insulation for migration prevention and electrical conductivity for charge dissipation, thereby resolving the contradiction between preventing electrode migration and maintaining polarization stability under temperature changes.
Solution Approach 2:
The invention uses a composite material consisting of an insulating resin matrix with dispersed electroconductive particles. This composite structure combines the insulating properties needed to prevent electrode migration with the conductive properties needed to allow charge dissipation from the pyroelectric effect, thus resolving the contradiction between the two opposing requirements.
2Reliability
If exterior resin coating is applied to cover all side faces, then migration is prevented, but device complexity and manufacturing complexity increase
Solution Approach 1:
The invention applies the electroconductive particle-containing coating selectively only to the side faces where internal electrodes are exposed, rather than coating all surfaces of the piezoelectric element. This localized application approach prevents migration where needed while avoiding unnecessary complexity on other surfaces, thus resolving the contradiction between migration prevention and device complexity.
3Productivity
If smaller piezoelectric elements are manufactured, then productivity is improved, but the pyroelectric effect causes greater polarization loss
Solution Approach 1:
The invention changes the electrical parameter of the exterior coating by incorporating electroconductive particles, which enables the coating to dissipate pyroelectric charges. This parameter change effectively counteracts the enhanced pyroelectric effect in smaller elements, allowing high productivity through miniaturization while maintaining polarization stability.
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 prevents migration and maintains the degree of polarization even under repeated temperature changes, ensuring stable performance and reduced deterioration over time.
Implementation Method 1
an exterior portion for preventing migration is provided which covers exposed portions of the internal electrodes on the side face... The exterior portion contains dispersed electroconductive particles... allowing electric charges generated by the pyroelectric effect to flow out
Data Source
Figure 1A~1C
Figure 2A~2B
Figure 3~4
AI summary
Provided is a piezoelectric element including a monolithic piezoelectric substrate that can prevent not only migration between internal electrodes, but also deterioration resulting from a decrease in the degree of polarization even when temperature changes are repeatedly applied to the piezoelectric element. A piezoelectric element 1, in which a first external electrode 4 and a second external electrode 5 are formed on a first side face 2c and a second side face 2d, respectively, of a monolithic piezoelectric substrate 2 including first internal electrodes 3b and 3d placed at a first electric potential and second internal electrodes 3a, 3c and 3e placed at a second electric potential, which is different from the first electric potential, stacked with piezoelectric layers interposed therebetween, and exterior portions 6 and 7 for preventing migration are provided to cover a third side face 2e and a fourth side face 2f. The exterior portions 6 and 7 contain dispersed electroconductive particles and can prevent not only migration between adjacent internal electrodes, but also a decrease in the degree of polarization resulting from the pyroelectric effect.