Josephson Junction | Thin Film Deposition for Superconducting circuits
The Josephson effect is observed in a Josephson junction, and describes the flow of a supercurrent between two superconducting electrodes across a non-superconducting gap. These devices are used by researchers to utilize quantum control towards progress in quantum computing, novel sensing devices, as well as fundamental physics.
Josephson junctions form the heart of the superconducting qubit, a leading candidate for the creation of fault-tolerant quantum computation. The non-linear inductance of the Josephson Junction creates an anharmonicity in its energy level spectrum. This allows a quantum mechanical basis (1 or 0) to be established between discrete energy levels, which is essential for forming a quantum bit, or qubit. Josephson Junctions can also be used as a means to detect extremely small magnetic fields, up to 1016 times less than that generated from a refrigerator magnet. These superconducting quantum interference devices, or SQUIDS, have applications in the detection of neural activity in the brain, scientific characterization of materials, and next-generation ultra-low field MRI scanners.
Let’s create a Josephson Junction
This device can be created with a wide range of superconducting materials, but aluminum is a common choice among researchers due to the relative ease of creating a high quality oxide with it, as well as its relatively low melting point (660 °C), making it versatile. What follows are key considerations for the equipment that will build your Josephson junctions.
A Clean Process
Josephson circuits are extremely sensitive to contaminants. For this reason, evaporation and oxidization occur in independently sealed chambers, one for evaporation, and one for oxidization. Perfect isolation is achieved between the oxidization chamber and the deposition chamber using load-locks and programmable, recipe driven automation through Aeres, our advanced process control software. Both chambers are constructed from electro-polished stainless steel to minimize offgasing, and transfer between chambers occurs in situ to minimize venting.
Unprecedented Pressure Control
The most important parameter of a Josephson Junction in certain applications is its critical current density, which is determined by the thickness of the insulating oxide layer between the two aluminum layers. That insulating layer must be as thin as possible, which makes the control of how the film is oxidized of utmost importance. The mass flow controller (which is user regulated from Aeres, Angstrom’s own process control software) allows for exact and precisely repeatable control of this variable.
Electron Beam Source
An e-beam source provides the best versatility for evaporating aluminum intended for superconducting circuits. It allows for a higher volume of material, reduces the need to vent the chamber, further ensuring clean, contaminant free films. Finally, the vapor flux created by e-beam evaporation is ideal for patterning the fine features that Josephson circuits require.
Ion Beam Source
An ion source prepares the substrate for deposition with gentle cleaning or precision etching.
Some materials used to create Josephson Junctions (such as Niobium) require the use of magnetron sputtering. A sputtering source can be seamlessly integrated into your thin film deposition platform.
Connected Deposition Chambers
We create Josephson platforms that support multiple connected (though isolated) chambers for alternate deposition methods as well as analytical tools, all integrated into the overall process automation. This results in platforms of varying configurations, from dual chamber (deposition/load lock) to in-line systems, all the way to robotic radial cluster arrays incorporating deposition, oxidization, and analytical stations.
Variable Angle Stage
Precisely angling the substrate in relation to the deposition plume is essential in the creation of Josephson Junctions. The figure below illustrates one method of creating the devices. The tilt angle on Angstrom’s variable angle stage has better than 0.1° angular repeatability. Substrate heating and cooling can both be integrated into the stage functionality. Angle, stage rotation, and stage temperature are controlled via recipe based user inputs from our Aeres software package. Simply enter desired values, press start, and return to find your completed Josephson Junctions.
Your Josephson Junction System
Your system will be based on the type of junctions you plan to create as well as your specific throughput, material, and infrastructure requirements. Our partners are creating Josephson Junctions on systems of different sizes and designs, but all have a few things in common: at least one load lock for isolated oxidization, a deposition chamber, a variable angle stage, e-beam or sputter sources specific to their needs, and all the thin film experience and service support that Angstrom Engineering brings to bear.
Aeres Control Software
Each variable in the creation of Josephson Junctions is critical to the success of the device. For this reason we have integrated the control of each step into Aeres, our advanced process control software. You decide on each variable, create and edit recipes, and then relax, knowing that each variable will be repeatedly and precisely executed.
Our proprietary Auto Tune PID detection algorithm automatically calculates and utilizes process control variables specific to the material, rate, pressure, and stability required for the given evaporation.
Stage Angle, Rotation, and Temperature Control
Precisely repeatable angles, rotation, and temperature values.
GAS CONTROL & OXIDATION PROCESSING
Fast pumpdowns, precise pressure measurement, and complete control over oxygen gas flow for the oxidization step. You input values into your recipes, and Aeres takes care of the logistics.
Every step of the Josephson Junction creation is precisely executed, is repeatable, and is then documented for review.
The ease of Aeres:
create your recipe by entering each variable value.
Press start. Walk away.
We are exceptionally pleased with the two systems we bought from Angstrom and, based on our experience and what I hear from the community, we have made precisely the best decision.
Dr. Luke Brzozowski – University of Toronto
WE WANT TO HEAR ABOUT YOUR PROJECTS!
Please get in touch and we can collaborate on your Josephson Junction work.
When we work together, amazing things can happen. Your brilliant ideas with our innovative team will create the tool that will bring your research or production to the next level. We’re looking forward to hearing from you: