Skip to content
6CCVD Research

Contact resistance of various metallisation schemes to superconducting boron doped diamond between 1.9 and 300 K

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2021-02-25
JournalCarbon
AuthorsScott Manifold, Georgina M. Klemencic, Evan L. H. Thomas, Soumen Mandal, Henry A. Bland
InstitutionsEngineering and Physical Sciences Research Council, Cardiff University
Citations8
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”
  • Objective: Verified the stability and performance of five metallization schemes (Ti, Cr, Mo, Ta, Pd) on highly boron-doped nanocrystalline diamond (B-NCD) across a wide temperature range (300 K down to 1.9 K).
  • Ohmic Stability: All tested contact schemes remained ohmic throughout the temperature range, confirming that high boron doping (>2x1021 cm-3) ensures tunneling dominates carrier transport, even at cryogenic temperatures.
  • Superconducting Regime Performance: A significant reduction in contact resistivity was observed below the B-NCD critical temperature (Tc ~2.4 K) for all schemes.
  • Optimal Cryogenic Contacts: Ta/Pt/Au provided the lowest contact resistivity at 1.9 K (8.07 ± 0.62 x 10-6 Ω.cm), followed closely by Mo/Pt/Au (1.3 x 10-5 Ω.cm).
  • Suboptimal Cryogenic Contacts: The Ti/Pt/Au scheme performed the least favorably in the superconducting regime (8.83 ± 0.10 x 10-4 Ω.cm), likely due to the high intrinsic electrical resistivity of Titanium Carbide (TiC) formed at the interface.
  • Methodology: Contact resistance was accurately measured using a modified Transmission Line Model (TLM) approach, which excluded the effective contact length (LT) term to account for variable carbide formation and the non-linear behavior in the superconducting state.
  • Mechanical Stability: All tested carbide-forming and carbon-soluble contacts demonstrated mechanical stability across numerous temperature cycles (300 K to 1.9 K).

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
B-NCD Film Thickness200nmGrown via MW-CVD
Critical Temperature (Tc)~2.4KDetermined via Van Der Pauw pattern
Boron Doping Concentration>2x1021cm-3Assumed based on 12800 ppm gas phase B/C ratio
Contact Resistance (300 K, incl. LT)0.82 to 8.03 x 10-7Ω.cm2Conventional TLM calculation (compares favorably to literature)
Contact Resistance (1.9 K, excl. LT) - Ta/Pt/Au8.07 ± 0.62 x 10-6Ω.cmLowest resistivity in superconducting regime
Contact Resistance (1.9 K, excl. LT) - Mo/Pt/Au1.3 ± 0.01 x 10-5Ω.cmSecond lowest resistivity in superconducting regime
Contact Resistance (1.9 K, excl. LT) - Ti/Pt/Au8.83 ± 0.10 x 10-4Ω.cmHighest resistivity in superconducting regime
Interface Metal Thickness (Ti, Cr, Mo, Ta)50nmCarbide forming layer
Pt Diffusion Barrier Thickness50nmUsed in all carbide schemes
Au Capping Layer Thickness200nmTotal Au thickness (50 nm PVD + 150 nm Thermal Evaporation)
Pd Contact Thickness200nmTotal Pd thickness
Carbide Annealing Parameters600 °C / 10 min-For Ti, Cr, Mo, Ta schemes (in N2 RTA)
Pd Annealing Parameters400 °C / 3 min-For Pd scheme (in N2 RTA)
Titanium Carbide Resistivity (20 °C)3-8 x 10-3Ω.mHigh resistivity justifies poor Ti performance at 1.9 K
Chromium Carbide Resistivity (20 °C)1.47 x 10-8Ω.m-

Key Methodologies

Section titled “Key Methodologies”
  1. Substrate and Seeding: High resistivity silicon wafer buffered with 500 nm of SiO2, seeded using electrostatic self-assembly of ~5 nm diamond nanoparticles.
  2. B-NCD Film Growth: Grown via Microwave Assisted CVD (MW-CVD) using low CH4/H2 chemistry (<3% CH4) and trimethylboron (B/C ratio 12800 ppm) to achieve high boron doping (>2x1021 cm-3).
  3. Mesa Definition: 200 x 1200 µm mesas patterned using photolithography, a nickel mask, and subsequent Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE).
  4. Surface Termination: Oxygen termination achieved by ashing the mesas in an oxygen plasma (1 min at 30 W, 30 SCCM O2, 0.1 mT pressure).
  5. Metallization (PVD/Thermal Evaporation):
    • Carbide Schemes (Ti, Cr, Mo, Ta): Deposited as trilayers (50 nm interface metal / 50 nm Pt diffusion barrier / 50 nm Au cap) via magnetron PVD, followed by 150 nm Au top-up via thermal evaporation (Total 300 nm).
    • Pd Scheme: 200 nm Pd deposited.
  6. Annealing: Rapid Thermal Annealing (RTA) performed in a nitrogen atmosphere:
    • Carbide schemes: 600 °C for 10 minutes.
    • Pd scheme: 400 °C for 3 minutes.
  7. Measurement: Contact resistance measured using a modified linear Transmission Line Model (TLM) pattern (separations 5 µm to 160 µm) in a Quantum Design Physical Properties Measurement System (PPMS) across 1.9 K to 300 K.

Commercial Applications

Section titled “Commercial Applications”
  • Superconducting Nanoelectromechanical Systems (NEMS): The primary application. B-NCD’s high Young’s Modulus combined with superconductivity enables the fabrication of high-quality factor superconducting resonators and sensors (e.g., SQUIDs) that require stable, low-loss contacts below Tc.
  • Cryogenic Quantum Devices: Essential for integrating superconducting diamond components into quantum computing architectures or highly sensitive cryogenic detectors, where local heating from contact resistance must be minimized to preserve critical current density (Jc).
  • High-Power Diamond Electronics: While the focus is cryogenic, the demonstrated low room-temperature contact resistivity (~10-7 Ω.cm2) and thermal stability of these schemes are highly relevant for high-frequency and high-power RF devices operating at elevated temperatures.
  • Extreme Environment Sensors: Diamond’s inherent radiation hardness and thermal conductivity, coupled with reliable metallization, support its use in sensors for harsh environments (e.g., nuclear or space applications).
  • Materials Engineering: Provides validated data for selecting Ta/Pt/Au or Mo/Pt/Au as preferred interfaces for highly doped p-type diamond when designing devices requiring operation in the superconducting state.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 1999 - Diamond MEMS — a new emerging technology [Crossref]
  2. 2010 - Diamond electronic devices [Crossref]
  3. 2014 - Superconducting nano-mechanical diamond resonators [Crossref]
  4. 2007 - Random surface roughness influence on gas damped nanoresonators [Crossref]
  5. 2012 - Influence of surface modification on the quality factor of microresonators [Crossref]
  6. 2018 - Redox agent enhanced chemical mechanical polishing of thin film diamond [Crossref]
  7. 2017 - Superconductivity in planarised nanocrystalline diamond films [Crossref]
  8. 2017 - Fluctuation spectroscopy as a probe of granular superconducting diamond films
  9. 2011 - The diamond superconducting quantum interference device [Crossref]
  10. 2014 - Global and local superconductivity in boron-doped granular diamond [Crossref]

Reads Similar to This

Terahertz emission from diamond nitrogen-vacancy centers Catalytic-enhanced thermal hydrogen-termination of diamond for electronic applications Modelling of Low‐dimensional Functional Nanomaterials