Leti proposes FD-SOI spin qubit platform for quantum computing

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www.electronicsweekly.com, Dec. 28, 2021 – 

A paper from CEA-Leti called "A new FD-SOI spin qubit platform with 40nm effective control pitch", notes that operating Si quantum dot (QD) arrays requires homogeneous and ultra-dense structures with aggressive gate pitch.

Such a density is necessary to separately control the quantum dots' chemical potential, i.e. the charge occupation of each dot, from the exchange interaction, or the tunnel barriers between each one.

The research team developed the novel Si quantum-device integration that halves the effective gate pitch and provides full controllability in 1D FD-SOI QD arrays.

The design targets were established thanks to numerical simulations, then the fabricated structure's functionality was validated via 300K statistical electrical characterization, while tunnel-coupling control was demonstrated at cryogenic temperatures.

"This is the first demonstration of electrostatic coupling control over QD systems implemented in CMOS SOI devices by means of back biasing and the use of exchange gates," said Thomas Bédécarrats, a CEA-Leti scientist and lead author of the paper.

"It is a first step towards a successful control of spins for qubit applications. We drew on CEA-Leti's new immersion DUV lithography capability to achieve small features with low variability at throughputs compatible with volume production," Bédécarrats added. "In terms of potential scalability, the process flow used in this research is very similar to standard CMOS technologies. We also added exchange gates that intertwine with the front gates to enable separate control of the tunnel barriers' and quantum dots' chemical potentials."

The resulting CEA-Leti 300 mm FD-SOI spin-qubit platform, which includes two gate layers, is fully compatible with industry processes.

The paper notes that "one of the major advantages Si offers in comparison to other platforms is its scalability." Indeed, error-free quantum computing relies on the use of quantum error correction algorithms, which requires the control of millions of qubits. On silicon spin-qubits platforms, making millions of qubits is similar to making millions of transistors, the paper says. Such a platform will benefit from the semiconductor industry's decades of experience making large volumes of small, dense devices reproducibly.

"The results we present at IEDM 2021 are on par with other research groups' spin qubit demonstrations, and they confirm the advantage of using CMOS-like platforms," Bédécarrats said."However, a high density of qubit devices infers that at least as many ways of control over those qubits are required, which is challenging from an integration perspective."

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