Cu-Ga Sputtering Target Coexistence Microstructure for Machining
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Solution Overview
Problem
High-Ga-containing Cu--Ga binary alloy sputtering targets with high Ga content face issues of cracking and fracturing during machining due to poor workability and low bending strength, and insufficient sintering density, which affects the efficiency of solar cell power generation.
Innovation Solution
A Cu--Ga binary alloy sputtering target with a coexistence microstructure of low-Ga and high-Ga phases, where the low-Ga phase is surrounded by the high-Ga phase, and the inclusion of sodium (Na) to enhance mechanical workability and bending strength, with specific Ga and Na content ranges to prevent cracking and improve sintering density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high Ga content (exceeds 28 atomic %) is used in Cu-Ga sputtering target, then the light-absorbing layer efficiency is improved, but the target becomes very hard and inductile with poor workability
Solution Approach 1:
The patent applies local quality by creating a non-uniform microstructure where low-Ga phase (15-25 atomic % Ga) and high-Ga phase (30-45 atomic % Ga) coexist in specific spatial arrangements. The low-Ga phase forms continuous networks or surrounds high-Ga phases, providing ductility at critical locations (grain boundaries) while high-Ga phases provide overall Ga content for efficiency. This local differentiation resolves the contradiction between high Ga content requirements and machining workability.
2Strength
If the target is highly densified with high Ga content, then the bending strength is improved, but cracking or fracturing occur during surface machining by cutting
Solution Approach 1:
The patent implements beforehand cushioning by introducing a ductile low-Ga phase network that surrounds and cushions the brittle high-Ga phases before machining occurs. This low-Ga phase acts as a pre-positioned cushion that absorbs stress concentrations and prevents crack propagation during cutting operations, allowing the target to maintain high bending strength while resisting machining-induced cracking.
3Ease of manufacture
If Ga content difference between high-Ga phase and low-Ga phase is large, then the two-phase coexistence microstructure is formed to prevent cracking, but sintering is not proceeded sufficiently and density becomes low
Solution Approach 1:
The patent applies parameter changes by optimizing the Ga content ranges of both phases (low-Ga: 15-25 atomic %, high-Ga: 30-45 atomic %) and controlling their volume fractions and spatial distributions. By adjusting these parameters within specific ranges, the patent achieves sufficient Ga diffusion during sintering while maintaining the two-phase microstructure that prevents cracking. The parameter optimization ensures both adequate sintering density and crack prevention capability.
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 prevents cracking and fracturing during machining, achieves high density and bending strength, and improves the efficiency of electric power generation in solar cells by ensuring easy machining and thermal resistance.
Implementation Method 1
CuGa is sputtered at about 500 nm and an In film is sputtered on the sputtered CuGa
Implementation Method 2
heating a laminated film, in which CuGa is sputtered at about 500 nm and an In film is sputtered on the sputtered CuGa at the thickness of about 500 nm, in H2Se gas at 500° C. to diffuse Se in CuGaIn
Data Source
AI summary
A Cu—Ga binary alloy sputtering target having excellent mechanical workability, high density, and high bending strength, and a method of producing the sputtering target are provided. The sputtering target has a composition including 28 to 35 atomic % of Ga and the balance made of Cu and inevitable impurities. In addition, the sputtering target has a coexistence microstructure in which a low-Ga-containing Cu—Ga binary alloy phase is surrounded by a high-Ga-containing Cu—Ga binary alloy phase. The low-Ga-containing Cu—Ga binary alloy phase includes 26 atomic % or less of Ga and a balance made of Cu. The high-Ga-containing Cu—Ga binary alloy phase includes 28 atomic % or more of Ga.