Liquid Ejecting Head Electrode Stress Management
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Solution Overview
Problem
Piezoelectric elements in liquid ejecting heads, such as those used in inkjet printers, are prone to cracking due to stress caused by electrode formation and reduced chamber volumes, which compromise their deformation and crack resistance.
Innovation Solution
A method involving the formation of a first layer with a higher thermal expansion rate than the piezoelectric body, a sacrifice layer that oxidizes easily, and a second layer with conductivity, followed by heating and cooling processes to alleviate stress and suppress crack formation, while maintaining deformation capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the piezoelectric body is made thinner to reduce the volume of the pressure generating chamber, then the density and precision of the liquid ejecting head is improved, but the piezoelectric body becomes more susceptible to cracking due to applied stress
Solution Approach 1:
The patent changes the physical and chemical parameters of the electrode materials and their deposition conditions. Specifically, it controls the thickness of the iridium electrode layer to be 1-10 nm, adjusts the sputtering gas pressure to 0.1-10 Pa, and controls the oxygen partial pressure during heating to 10-1000 Pa. These parameter changes optimize the electrode structure to reduce stress on the thin piezoelectric body while maintaining electrical conductivity.
Solution Approach 2:
The patent employs a composite electrode structure consisting of multiple layers: an iridium layer (1-10 nm) deposited on the piezoelectric body, followed by a thicker iridium layer (10-100 nm), and finally a conductive material layer (100-500 nm). This composite structure distributes stress more effectively and provides both adhesion and electrical conductivity, preventing cracks in the thin piezoelectric body.
2Reliability
If the electrode thickness is increased to improve adhesion with the piezoelectric body, then the electrical connection is improved, but the electrode captures sputtered gas and elongates, generating compression stress that applies tension stress to the piezoelectric body
Solution Approach 1:
The patent optimizes the electrode deposition parameters by controlling the sputtering gas pressure (0.1-10 Pa) and limiting the iridium layer thickness to 1-10 nm. This prevents excessive gas capture and elongation during sputtering, reducing compression stress in the electrode that would otherwise transfer as tension stress to the piezoelectric body.
Solution Approach 2:
The patent applies different thicknesses and materials to different layers of the electrode structure. The first iridium layer (1-10 nm) provides optimal adhesion with minimal stress, while the second iridium layer (10-100 nm) and conductive material layer (100-500 nm) provide electrical conductivity. This localized differentiation of layer properties resolves the contradiction between adhesion and stress.
3Manufacturing precision
If the distance between nozzle openings is decreased to increase density, then the printing precision is improved, but the volume of the pressure generating chamber is reduced, requiring increased deformation amount of the piezoelectric body
Solution Approach 1:
The patent modifies the operational parameters of the piezoelectric body by optimizing the voltage application conditions and electrode structure. The multi-layer electrode structure with controlled thicknesses enables more efficient electrical field distribution, allowing the thinner piezoelectric body to achieve sufficient deformation for liquid ejection despite the reduced chamber volume from decreased nozzle spacing.
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 method enhances the crack resistance and deformation capability of piezoelectric elements, ensuring reliable ink ejection with reduced voltage drop and improved durability.
Implementation Method 1
forming a first layer having a greater thermal expansion rate than the piezoelectric body and the same conductivity as the second electrode, on the piezoelectric body
Implementation Method 2
forming a sacrifice layer, which is more easily oxidized than the first layer, on the first layer; heating the vibration plate, the first electrode, the piezoelectric body, the first layer and the sacrifice layer
Data Source
AI summary
A method for manufacturing a liquid ejecting head which includes forming a first electrode on a vibration plate, forming a piezoelectric body on the first electrode, and forming a first layer having a greater thermal expansion rate than the piezoelectric body and the same conductivity as the second electrode, on the piezoelectric body. The method also includes forming a sacrifice layer on the first layer, heating the vibration plate, the first electrode, the piezoelectric body, the first layer, and the sacrifice layer to oxidize the sacrifice layer, and then cooling the vibration plate, the first electrode, the piezoelectric body, the first layer, and the sacrifice layer after the heating. Lastly, a second layer having the same conductivity as the second electrode is formed on the first layer and the sacrifice layer, after the cooling.