Lead-Free Piezoelectric Layer Crack Suppression
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Solution Overview
Problem
Piezoelectric elements in liquid ejecting heads, such as ink jet recording heads, often experience cracks due to the inherent properties of the piezoelectric materials used, leading to reliability issues and environmental concerns related to lead content in traditional materials like PZT.
Innovation Solution
A piezoelectric element with a piezoelectric layer made of a complex oxide containing bismuth, iron, and titanium, having a perovskite structure, is developed, where the layer is formed to suppress crack formation by controlling the indentation length with a diamond conical indenter, and the material is lead-free to reduce environmental impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional piezoelectric materials like PZT are used, then high piezoelectric properties are achieved, but lead content causes environmental issues
Solution Approach 1:
The invention changes the chemical composition parameters of the piezoelectric material by substituting lead with bismuth, barium, iron, and titanium in specific ratios. The general formula Bi1-aBaaFe1-bTibO3 with controlled stoichiometry achieves high piezoelectric properties without lead, directly resolving the environmental harm while maintaining functional performance
Solution Approach 2:
The invention uses a composite oxide material system combining multiple elements (Bi, Ba, Fe, Ti, and optionally other metals) in a perovskite structure. This composite approach leverages the synergistic effects of different elements to achieve both environmental compatibility and high piezoelectric performance, replacing the simple PZT compound
2Reliability
If various piezoelectric materials are used for the piezoelectric layer, then different piezoelectric properties are achieved, but cracks occur in the piezoelectric layer
Solution Approach 1:
The invention optimizes the compositional parameters within the Bi-Ba-Fe-Ti-O system, specifically controlling the ratios of a, b, and other element contents to achieve the right balance between piezoelectric performance and mechanical integrity. This parameter optimization ensures the material has both high piezoelectric properties and sufficient strength to prevent cracks
Solution Approach 2:
The invention introduces optional local compositional variations by allowing specific metal elements (Mn, Co, Ni, Cu, Zn, Ca, Sr, Pb, Mg, Al) to be incorporated in controlled amounts. These local compositional adjustments can enhance specific properties like crack resistance while maintaining overall piezoelectric performance through controlled heterogeneity in the material structure
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 suppresses crack occurrence in the piezoelectric layer, enhancing the reliability of liquid ejecting heads and reducing environmental load by using a lead-free material with improved piezoelectric properties.
Implementation Method 1
when a diamond conical indenter having an angle of 136° between opposite faces is pressed into the piezoelectric layer at a load of 5 gf for 5 seconds to form cracks extending from an indentation, using a micro Vickers hardness meter
Implementation Method 2
a piezoelectric element deforms a vibration plate to apply a pressure to the ink in the pressure generating chamber, thereby discharging ink droplets through the nozzles
Data Source
AI summary
A liquid ejecting head includes a piezoelectric element including a piezoelectric layer made of a piezoelectric material and an electrode disposed on the piezoelectric layer. The piezoelectric material is such that when a diamond conical indenter having an angle α of 136° between opposite faces is pressed into the piezoelectric layer at a load of 5 gf for 5 seconds to form cracks extending from an indentation, using a micro Vickers hardness meter, the length of the cracks from four corners of the indentation is 15 μm or less.