Piezoelectric Actuator Electrode Segmentation for Displacement Uniformity
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Solution Overview
Problem
Variation in displacement characteristics of piezoelectric elements in liquid ejecting heads, particularly due to variations in etching end points during patterning, affects the driving performance of the elements, especially when multiple conductive layers with different Young's moduli are used.
Innovation Solution
A liquid ejecting head design featuring a piezoelectric element with a first electrode composed of a higher Young's modulus material (e.g., iridium) and a second electrode made of a lower Young's modulus material (e.g., platinum), where the second electrode is formed closer to the substrate and thicker, ensuring uniform displacement characteristics by controlling the film thickness precisely during manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If patterning is stopped in the middle of the thickness direction of an electrically-conductive layer having a larger Young's modulus, then manufacturing complexity is reduced, but variation in displacement characteristic of piezoelectric elements increases
Solution Approach 1:
The electrically-conductive layer is divided into multiple layers (first and second electrically-conductive layers) with different Young's moduli. The first layer has a larger Young's modulus and is positioned closer to the piezoelectric body layer, while the second layer has a smaller Young's modulus and is positioned closer to the flow path forming substrate. This segmentation allows the patterning to be stopped after forming the first layer, reducing manufacturing complexity while maintaining displacement characteristic uniformity through the strategic material selection and layer arrangement.
Solution Approach 2:
Different regions of the electrically-conductive structure are assigned different material properties. The first electrically-conductive layer uses a material with larger Young's modulus (e.g., tungsten) to provide structural stability where the piezoelectric body layer is present, while the second layer uses a material with smaller Young's modulus (e.g., molybdenum) in regions where the piezoelectric body layer is not formed. This local quality differentiation ensures uniform displacement characteristics while simplifying the patterning process.
2Device complexity
If a single electrically-conductive layer is used, then device structure is simplified, but variation in displacement characteristic occurs due to etching endpoint variation
Solution Approach 1:
The electrode structure is segmented into multiple electrically-conductive layers with different materials and Young's moduli. This segmentation creates a more robust structure where variation in etching endpoint does not significantly affect the overall displacement characteristic, as the different layers compensate for each other's variations.
Solution Approach 2:
The electrically-conductive structure uses composite materials with different Young's moduli (e.g., tungsten and molybdenum) arranged in specific layers. This composite structure provides better mechanical stability and reduces the impact of etching endpoint variation on displacement characteristics, thereby improving reliability without significantly increasing device complexity.
3Reliability
If the first electrically-conductive layer is made thicker, then electrical conductivity is improved, but displacement characteristic variation increases when close to piezoelectric body layer
Solution Approach 1:
The electrically-conductive layers are designed with local quality differentiation. The first electrically-conductive layer (closer to the piezoelectric body layer) has optimized thickness to ensure good electrical conductivity while maintaining mechanical flexibility. The second electrically-conductive layer (closer to the substrate) has different thickness and material properties to compensate for stress and maintain displacement uniformity. This local optimization resolves the contradiction between conductivity and displacement uniformity.
Solution Approach 2:
The thickness and material parameters of the electrically-conductive layers are carefully adjusted. The first layer uses a material with larger Young's modulus and optimized thickness for conductivity, while the second layer uses a material with smaller Young's modulus and different thickness to balance the mechanical properties. This parameter optimization ensures both good electrical conductivity and uniform displacement characteristics.
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 design improves the displacement characteristics of the piezoelectric elements, reducing variations and enhancing the liquid droplet ejecting performance, leading to improved print quality and reliability of the liquid ejecting head.
Implementation Method 1
a piezoelectric element having a first electrode provided above a flow path forming substrate in which pressure generation chambers are formed, a piezoelectric body layer provided so as to correspond to each pressure generation chamber, and a second electrode provided above the piezoelectric body layer
Data Source
AI summary
A liquid ejecting head includes: a piezoelectric element having a first electrode provided above a flow path forming substrate in which pressure generation chambers are formed, a piezoelectric body layer provided so as to correspond to each pressure generation chamber, and a second electrode provided above the piezoelectric body layer, wherein the first electrode, which is formed in the region facing the region where the piezoelectric body layer is formed, includes a first electrically-conductive layer, and a second electrically-conductive layer, which is made of a material having a smaller Young's modulus than that of the first electrically-conductive layer and is formed closer to the flow path forming substrate than the first electrically-conductive layer; and the first electrode, which is formed in the region facing the region where the piezoelectric body layer is not formed, has a surface constituted of the second electrically-conductive layer.