Capping Layer for Superconductor Ion Milling Damage Reduction
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Solution Overview
Problem
Ion milling techniques used to remove native oxide from superconductor materials in quantum computing devices often result in damage to the substrate and redeposition of photoresist residues, leading to reduced quality factors and increased energy loss due to the high energy storage capacity of dielectric surfaces compared to metal/superconductor surfaces.
Innovation Solution
A capping layer with a higher ion milling etch rate than the native oxide is applied to prevent reformation of native oxide and minimize damage, formed by materials like silver, gold, titanium nitride, or rhenium, which are in direct contact with the ion milled region, allowing for unimpeded DC current flow and reducing ion-induced damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ion milling is used to remove native oxide from superconductor material, then the electrical contact quality is improved, but substrate damage and photoresist residue redeposition occur
Solution Approach 1:
A capping layer is introduced as an intermediary material between the ion beam and the superconductor base layer. This capping layer has a higher ion milling etch rate than the native oxide, allowing it to be selectively removed while protecting the underlying superconductor material from ion beam damage and preventing photoresist residue redeposition during the oxide removal process
Solution Approach 2:
The capping layer is applied in advance before the ion milling process to protect the superconductor base layer. This preliminary protective action ensures that when ion milling is performed to remove native oxide, the harmful effects are confined to the capping layer which is subsequently removed, rather than damaging the critical superconductor material
2Use of energy by moving object
If ion milling is performed to remove native oxide, then DC current flow is improved, but energy loss increases due to residue redeposition
Solution Approach 1:
The capping layer serves as a protective intermediary that prevents photoresist residue from redepositing on the superconductor base layer during ion milling. By confining the residue to the capping layer which is subsequently removed, the superconductor surface remains clean, maintaining low energy loss and high DC current flow efficiency
Solution Approach 2:
The ion beam, which would normally cause harmful residue redeposition on the superconductor, is redirected to selectively remove the capping layer instead. The capping layer acts as a sacrificial element that absorbs the harmful effects, converting a potentially damaging process into a beneficial one that leaves the superconductor surface clean and ready for optimal DC current flow
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 capping layer effectively prevents native oxide reformation and minimizes ion milling-induced damage, maintaining high quality factors by confining residues and reducing energy storage on the metal/superconductor surface, thus enhancing the performance of quantum circuit elements.
Implementation Method 1
removing the native oxide comprises ion milling the first region of the first layer of superconductor material
Implementation Method 2
The thickness of the metal may be between about 5 nm and about 10 nm. The metal may have a thickness such that the metal behaves as a superconductor material due to the superconductivity proximity effect when the electrical contact junction is cooled below a critical temperature of the superconductor material of the first layer
Data Source
Figure 1A~1D
Figure 2A~2B
Figure 3
AI summary
A method of fabricating an electrical contact junction that allows current to flow includes: providing a substrate including a first layer of superconductor material; removing a native oxide of the superconductor material of the first layer from a first region of the first layer; forming a capping layer in contact with the first region of the first layer, in which the capping layer prevents reformation of the native oxide of the superconductor material in the first region; forming, after forming the capping layer, a second layer of superconductor material that electrically connects to the first region of the first layer of superconductor material to provide the electrical contact junction that allows current to flow.