Piezoelectric Actuator Electrode with Dual-Melting Diffusion Barrier
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Solution Overview
Problem
The existing methods for producing piezoelectric actuators, such as those used in ink-jet heads, face challenges in maintaining satisfactory piezoelectric characteristics due to the annealing process, which can lead to degradation and exfoliation of layers caused by diffusion of elements and thermal stress.
Innovation Solution
A method involving the formation of a diffusion-preventive layer with multiple stacked layers of different melting-start temperatures is introduced, where the calcination and annealing temperatures are carefully controlled to prevent element diffusion and ensure strong adhesion between layers, thereby maintaining piezoelectric characteristics and mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high temperature annealing is performed to achieve high piezoelectric characteristics, then piezoelectric characteristics are improved, but element diffusion occurs in the piezoelectric film causing degradation of characteristics
Solution Approach 1:
A lower electrode layer is introduced as an intermediary barrier between the substrate and the piezoelectric layer. This layer prevents element diffusion from the substrate to the piezoelectric film during high-temperature annealing, while still allowing the piezoelectric layer to achieve high piezoelectric characteristics through proper annealing treatment.
Solution Approach 2:
The electrode structure is segmented into multiple layers: an upper electrode, a lower electrode layer, and connections to both. This segmentation allows the lower electrode layer to specifically serve as a diffusion barrier while the upper electrode maintains electrical contact, resolving the conflict between high-temperature annealing benefits and element diffusion prevention.
2Reliability
If high temperature annealing is performed to recover piezoelectric characteristics, then piezoelectric characteristics are improved, but thermal stress causes exfoliation of layers
Solution Approach 1:
The annealing temperature is optimized to a specific range (900°C to 1100°C) that balances two competing requirements: high enough to recover piezoelectric characteristics effectively, but controlled to minimize thermal stress that would cause layer exfoliation. This parameter optimization resolves the contradiction between characteristic recovery and layer integrity.
3Object-affected harmful factors
If calcination temperature is lowered to delay sintering and suppress diffusion, then element diffusion is suppressed, but adhesion between lower electrode layer and adjacent layers deteriorates
Solution Approach 1:
The lower electrode layer is formed with specific material composition and structure in advance, before the annealing process. This preliminary preparation ensures that when annealing occurs, the layer can provide effective diffusion protection while maintaining strong adhesion to adjacent layers, resolving the timing conflict between diffusion prevention and adhesion formation.
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 approach effectively suppresses the degradation of piezoelectric characteristics and ensures strong adhesion between layers, preventing exfoliation and maintaining satisfactory piezoelectric performance while minimizing thermal load during production.
Implementation Method 1
an element contained in the substrate is diffused in the piezoelectric film in some cases, thereby degrading the piezoelectric characteristics
Implementation Method 2
a calcination step of calcinating the diffusion-preventive layer
Implementation Method 3
it is necessary to recover the piezoelectric characteristics by performing an annealing process on this piezoelectric layer
Implementation Method 4
a piezoelectric layer is formed on this lower electrode by an aerosol deposition method (AD method). In the aerosol deposition method, a substance in which fine particles of a piezoelectric material such as lead zirconate titanate (PZT) are dispersed in a gas is jetted toward a surface of the substrate
Data Source
AI summary
A lower electrode 3 including a low-temperature melting layer 3A and a high-temperature melting layer 3B having mutually different melting-start temperatures is provided between a vibration plate 2 and a piezoelectric layer 4. In a calcination step of calcinating the lower electrode 3, the calcination is performed at a low temperature at which only the low-temperature melting layer 3A melts, and in an annealing-process step of the piezoelectric layer 4, the annealing process is performed at a high temperature at which the high-temperature melting layer 3B melts. At this time, in the calcination step, the melting of platinum nano-particles occurs in the low-temperature melting layer 3A, rendering the adhesion and diffusion-preventive effect. Further, in the annealing step, in the high-temperature melting layer 3B, platinum particles are melted, rendering the adhesion and diffusion-preventive effect. The degradation of piezoelectric characteristics of the piezoelectric actuator can be suppressed by the annealing process.