Liquid Ejecting Head Piezoelectric Element Crack Prevention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Piezoelectric elements in liquid ejecting heads, such as ink jet recording heads, are prone to cracking due to tensile stress from substrates during the manufacturing process, particularly due to thermal expansion differences, leading to breakage and reduced durability.
Innovation Solution
A method involving the formation of piezoelectric elements with a longer width in a reference direction on a first substrate, followed by adhering a second substrate with a higher thermal expansion coefficient in the same direction, which applies compression stress to reduce tensile stress and prevent cracking, while also adjusting the thermal expansion coefficients to minimize warpage and correct ejection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the piezoelectric element is formed with a longer width in the reference direction to improve ejection accuracy, then the ejection accuracy is improved, but the tensile stress from the substrate increases causing cracks in the piezoelectric layer
Solution Approach 1:
The patent changes the thermal expansion coefficient parameter of the substrate by selecting a material with a higher thermal expansion coefficient than the piezoelectric element. This parameter change allows the substrate to apply compression stress to the piezoelectric element during temperature changes, counteracting the tensile stress that causes cracks while maintaining the longer width configuration for improved ejection accuracy.
Solution Approach 2:
The patent utilizes thermal expansion differences between the substrate and piezoelectric element. The substrate is designed with a higher thermal expansion coefficient, so when temperature changes occur during operation or manufacturing, the substrate expands or contracts more than the piezoelectric element, generating compression stress that prevents crack formation in the piezoelectric layer.
2Reliability
If the film thickness of the lower electrode is adjusted to relax tensile stress, then the crack resistance is improved, but the manufacturing process becomes troublesome
Solution Approach 1:
Instead of adjusting the film thickness parameter of the lower electrode, the patent changes the material composition parameter of the substrate to achieve the desired stress relaxation. This approach maintains simple manufacturing processes while effectively preventing cracks by selecting a substrate material with appropriate thermal expansion properties.
3Reliability
If the substrate material is changed to have a higher thermal expansion coefficient to apply compression stress, then the crack resistance is improved, but the warpage of the substrate increases
Solution Approach 1:
The patent applies local quality by creating anisotropic thermal expansion properties in the substrate, where the thermal expansion coefficient is higher in the reference direction (longitudinal direction) to provide compression stress to the piezoelectric element, while maintaining controlled expansion in the orthogonal direction to minimize warpage. This directional differentiation allows stress relief without excessive overall warpage.
Solution Approach 2:
The patent introduces asymmetry in the thermal expansion behavior of the substrate by designing it to have different thermal expansion coefficients in different directions. The substrate exhibits higher thermal expansion in the reference direction to generate compression stress, while having controlled expansion in the orthogonal direction, creating an asymmetric thermal response that balances crack prevention with warpage control.
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 breakage of piezoelectric elements, enhances the durability and reliability of liquid ejecting heads, and improves the accuracy of ink droplet ejection by reducing tensile stress and warpage, allowing for easier correction of ejection positions.
Implementation Method 1
a first thermal expansion coefficient in a first direction on an adhesion surface with the first substrate greater than a second thermal expansion coefficient in a second direction orthogonal to the first direction and the first thermal expansion coefficient greater than a thermal expansion coefficient of the first substrate
Data Source
AI summary
Provided is a method of manufacturing a liquid ejecting head, the method including forming a piezoelectric element having a width in a reference direction longer than a width in an orthogonal direction orthogonal to the reference direction on a first substrate, and adhering a second substrate to a surface of the first substrate opposed to the piezoelectric element at a temperature higher than a normal temperature, wherein, in the adhering of the second substrate, the second substrate is adhered such that the first direction of the second substrate is adjusted to the reference direction, using a first thermal expansion coefficient in a first direction on an adhesion surface with the first substrate greater than a second thermal expansion coefficient in a second direction orthogonal to the first direction and the first thermal expansion coefficient greater than a thermal expansion coefficient of the first substrate.