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Atomic Layer Deposition for Superconducting Qubits

The efficiency of quantum devices is heavily dependant on the choice and quality of the superconducting material used during the operation. Atomic layer deposition (ALD) is an advanced technique that deposits ultra-thin films with atomic-scale precision. 

Our ALD process enables you to produce films with high purity, precise thickness control, conformal coating in high aspect ratio structures and uniformity over large-area substrates.

White Paper

For superconducting single photon detectors it is important that the material of choice exhibits superconducting behaviour at high critical temperatures (Tc) in order to avoid the additional cryocooler techniques that are needed for low Tc material, and that the quantum efficiency (QE) and quantum detection efficiency of these devices is maximised.

Download our White Paper and learn the advantages that our Atomic Layer Deposition process offers for superconducting devices.

ALD for Quantum Devices

Atomic Layer Deposition of Superconducting NbN

Superconducting NbN thin films deposited by plasma ALD with RF substrate bias

Superconducting metal nitrides exhibit superconducting behaviour at high critical temperatures (Tc) and achieve better performance in quantum devices because they have less lossy native oxides than typical sputtered superconducting materials. We've developed a plasma-enhanced ALD process to deposit high quality, high Tc NbN for superconducting devices.

  • RF bias enables stress control to achieve minimal room temperature resistivity
  • Low room temperature resistivity correlates to higher superconducting transition temperature (Tc)
  • The only method for conformal coating of vertical TSVs with superconducting thin films
  • 9 K  Tc measured at Oxford Instruments:
    • For ~45 nm NbN film deposited at 250°C
    • Room temperature ρ = 139 µΩcm; Tc = 12.9 K
  • Higher temperature process possible resulting in higher Tc
Bias RF power chart Tc = 12.9K diagram

Atomic Layer Deposition of Superconducting TiN

Superconducting TiN thin films deposited by plasma ALD with RF substrate bias

We've successfully deposited superconducting TiN by plasma ALD using bias to finely tune film properties such as room temperature resistivity, crystallinity, and stress. Consequently, this has achieved a critical temperature of 3 K for a 90 nm film deposited at 250°C 

  • Tc of ~3 K for 90 nm TiN
  • Qi internal quality factor is a key measure of resonator quality 
  • Successful fabrication of microwave resonators with an internal quality factor of Qi > 106 measured at ~250 mK, based on TiN deposited by plasma ALD in a FlexAL system (Coumou et al, 2013)
  • RF-bias: variable to tune crystallinity, resistivity, film density and stress
  • Further optimisation possible

Atomic Layer Deposition of Tunnel Barriers

Conformal, leak-free & low-pinhole tunnel barriers by plasma-enhanced ALD

Combine the benefits of plasma ALD (PE-ALD) with the capability of clustering systems to other technologies and unlock unique capabilities.

Key advantages of plasma ALD of Al2O3:

  • Higher breakdown voltage
  • Lower leakage current
  • Low pinhole
  • Very smooth films for minimum noise
  • Higher density
  • Atomic thickness precision
  • Faster growth per cycle
  • Low C & H content

Remove amorphous native oxide prior to growing high-quality PE-ALD of Al2O3 by either:

  • Using in-situ pre-clean based on a nitriding/reducing plasma
  • Clustering to an ALE or metal etch module
Tunnel barrier annotated diagram
Lower leakage current plasma ALD diagram and annotation

(Credit: Jinesh et al., 2011)

ALD System for Quantum Applications

The FlexAL atomic layer deposition (ALD) system offers a broad range of optimised high-quality ALD processes for the fabrication of tunnel barriers and passivation layers for a variety of quantum devices, and enables the deposition of superconducting thin films with high critical temperature for TSVs, resonators and single-photon detectors.

Oxford Instruments have a strong history in providing state of the art solutions in this rapidly developing applications are a key enabler of quantum technologies beyond device fabrication solutions.

FlexAL ALD system

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