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Doubling the capacity of cryochips for quantum computers

Technology News |
By Nick Flaherty


Researchers at Fraunhofer IZM in Germany have developed a high density process for cryogenic electronics for quantum computers.

The team has used indium bumps with a pitch of 7.5um to double the density of the interconnect of qubits cooled to a temperature of a few millikelvins. This is being tested in a dedicated cryometrics lab in Berlin.

Reading and manipulating qubits needs an electronic switch with sufficient port density, and it needs to be thermally decoupled to stop its own heat signal from destroying the quantum entanglement of the qubits.

Current technology to connect up qubit has been stuck at a pitch of 15 micrometres for several years, says Dr Hermann Oppermann of the Fraunhofer Institute for Reliability and Microintegration IZM. His team used galvanic deposition of indium on a pitch of less than 7.5 micrometres.

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As the system needs to be kept at a temperature of 20 milli-Kelvin during operation, its electrical connections can only give off minute amounts of thermal energy. The team managed to deposit and structure superconducting niobium and niobium alloys as vias through several layers of substrates, in interposers. The result is an extremely low-loss circuit carrier that can connect entire qubit arrays in real time and integrate them into highly dense, but scalable systems for quantum computing.

Fraunhofer IZM set up the dedicated cryometric lab in Berlin as the place where this fundamental technology could be developed, suitable materials tested, integration concepts optimized, and superconducting interconnect technologies trialled for cryogenic applications.

The lab lets the researchers test, characterize, and evaluate electrical circuits and make progress with integration technologies for extremely low temperature scenarios. Individual circuit components are cooled down to 3 Kelvin to analyse their resistance properties and draw conclusions about their electrical performance and the reliability of the vias, redistribution layers, and control systems at cryo-temperatures.

Projects are under way to explore new packaging and interconnection technologies for integration under cryogenic conditions.

“As one of our next steps, we will be moving this cryogenic packaging and interconnection technology in the direction of high-frequency, millimetre-wave technology,” said Oppermann.

“We are constantly learning more in this field, which is creating amazing potential in the market for possible applications,” he said. “This is not limited to quantum technology, but also opens up new prospects for conventional applications, like high-performance computing or cryo-sensors. We are always interested in other projects that could benefit from our expertise with packaging technologies for cryogenic applications

https://www.izm.fraunhofer.de/en

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