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6CCVD Research

Three-dimensional diamond planar spiral detectors

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2025-03-12
JournalScientific Reports
AuthorsRebecca J. Watkins, Patrick S. Salter, Ralph J. Moors, Richard B. Jackman
InstitutionsLondon Centre for Nanotechnology, University College London
Citations2
AnalysisFull AI Review Included

Technical Documentation & Analysis: Three-Dimensional Diamond Planar Spiral Detectors

Section titled “Technical Documentation & Analysis: Three-Dimensional Diamond Planar Spiral Detectors”

Executive Summary

Section titled “Executive Summary”

This research successfully demonstrates a novel approach to fabricating highly resilient and efficient diamond radiation detectors by integrating internal, three-dimensional (3D) electrodes into thick substrates.

  • Core Innovation: Fabrication of planar diamond detectors utilizing femtosecond (fs) laser-written Nano-carbon Network (NCN) “wall” electrodes extending 20 ”m below the surface of a 300 ”m thick Single Crystal Diamond (SCD) substrate.
  • Performance Achievement: The NCN integration achieved “thin” detector performance (20 ”m effective thickness) within a structurally robust, thick substrate, demonstrating Charge Collection Efficiency (CCE) approaching 100% (94% ± 6%).
  • Efficiency Gain: NCN-spiral detectors showed a significant improvement in charge collection, increasing CCE by 25-30% compared to control spiral detectors lacking the internal NCN walls.
  • Speed and Response: Demonstrated fast response times, with a rise time measured at < 1.35 ns, suitable for high-speed particle tracking and spectroscopy.
  • Radiation Resilience: The small internal electrode spacing (50 ”m) is designed to maintain high CCE even after exposure to extreme radiation fluences (e.g., > 1016 particles cm-2), addressing a critical need in fusion and high-energy physics.
  • Material Requirement: The study utilized optical-grade SCD, but noted that performance was limited by significant nitrogen defects, suggesting that Electronic Grade SCD is necessary for optimal, priming-free operation.

Technical Specifications

Section titled “Technical Specifications”

The following hard data points were extracted from the characterization of the NCN-spiral detectors (CMO13/CME05) compared to the reference CIVIDEC MIM detector.

ParameterValueUnitContext
Substrate MaterialSC Diamond (Optical Grade)N/AUsed for fabrication
Substrate Thickness300”mHighly resilient structural thickness
NCN Wall Depth20”mEffective detector thickness for alpha particles
NCN Wall Separation (L)50”mInternal electrode spacing
Surface Contact Separation35”mTi/Pt/Au spiral contacts
Maximum CCE (NCN-Spiral)94 ± 6%Alpha spectroscopy (100V bias)
Maximum Collected Charge54.4 ± 0.9fCTransient Current Measurement (100V bias)
Rise Time (NCN-Spiral)1.22 ± 0.01nsFast response time
Operating Bias (NCN-Spiral)100VApplied bias for maximum charge collection
Operating Field (NCN-Spiral)2.0V ”m-1Calculated using 50 ”m spacing
Dark Current (All Devices)< 2nAMeasured at 100 V bias
Metalization StackTi(50)/Pt(20)/Au(150)nmSurface contacts

Key Methodologies

Section titled “Key Methodologies”

The fabrication relies on advanced MPCVD diamond substrates combined with precision femtosecond laser processing and cleanroom metalization techniques.

  1. Substrate Procurement: Use of 4 x 4 x 0.3 mm Single Crystal Diamond (SCD) substrates, characterized by Raman spectroscopy confirming the presence of Nitrogen-Vacancy (NV) defects (indicating optical grade material).
  2. NCN Fabrication (fs Laser Writing): Internal spiral NCN “wall” electrodes were fabricated using a pulsed Ti:Sapphire femtosecond (fs) laser:
    • Wavelength: λ = 790 nm
    • Pulse Energy: 70 nJ
    • Repetition Rate: 1 kHz
    • Write Speed: 0.2 mms-1
  3. 3D Structure Definition: The laser focus was initiated 20 ”m below the diamond surface and raised layer-by-layer to create 20 ”m high NCN walls, defining the active volume.
  4. Surface Cleaning and Termination: Samples were immersed in an acid etching solution (H2SO4 : (NH4)2S2O8 at 200 °C) followed by an alkaline solution (H2O2 : NH4OH) to achieve an oxygen-terminated surface, critical for reliable metal contact adhesion.
  5. Surface Metalization: Ti(50 nm)/Pt(20 nm)/Au(150 nm) spiral contacts were deposited via electron beam evaporation and patterned using photolithography, resulting in a 35 ”m surface contact separation.
  6. Detector Priming: Detectors required extensive “priming” (> 13 hours) using a 241Am alpha source to fill deep traps caused by nitrogen defects before reaching maximum CCE.

6CCVD Solutions & Capabilities

Section titled “6CCVD Solutions & Capabilities”

6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials and custom fabrication services required to replicate, optimize, and scale this innovative 3D detector technology for high-radiation environments.

Applicable Materials for Replication and Optimization

Section titled “Applicable Materials for Replication and Optimization”

The research noted that performance was limited by the use of optical-grade diamond containing significant nitrogen defects, necessitating lengthy priming. 6CCVD offers materials that directly address this limitation:

  • Electronic Grade Single Crystal Diamond (SCD):
    • Recommendation: For maximum CCE, fastest response times, and elimination of the > 13 hour “priming” requirement, 6CCVD recommends our ultra-high purity SCD (Nitrogen content < 5 ppb). This material ensures minimal charge trapping and maximum carrier mean free path, ideal for high-resolution alpha spectroscopy.
    • Thickness Match: We supply SCD wafers in the required thickness range (0.1 ”m up to 500 ”m), including the 300 ”m substrate used in this study.
  • Polycrystalline Diamond (PCD):
    • Recommendation: For large-area detector arrays or applications where cost-efficiency is paramount, 6CCVD can supply high-quality PCD plates up to 125 mm in diameter. While the paper focuses on SCD, our PCD offers excellent radiation hardness for neutron detection and large-scale monitoring systems.

Customization Potential for 3D Detector Scaling

Section titled “Customization Potential for 3D Detector Scaling”

The 3D NCN fabrication technique requires precise material dimensions and specialized metal contacts. 6CCVD provides comprehensive in-house services to support this complexity:

Requirement from Paper6CCVD CapabilityBenefit to Researcher
Substrate DimensionsCustom Plates/Wafers up to 125 mm (PCD) and custom SCD sizes.Enables scaling of spiral detectors far beyond the 4x4 mm size used in the study.
Thickness ControlSCD and PCD thickness control from 0.1 ”m to 500 ”m.Allows researchers to optimize the structural thickness (e.g., 1 mm or 10 mm substrates for packaging) while maintaining the active layer thickness (e.g., 20 ”m) via NCN walls.
Metalization StackIn-house deposition of Au, Pt, Pd, Ti, W, Cu.We can precisely replicate the required Ti(50 nm)/Pt(20 nm)/Au(150 nm) stack or engineer alternative stacks (e.g., using W or Pt) for enhanced robustness in corrosive or high-temperature environments, as suggested by the authors.
Surface QualitySCD polishing to Ra < 1 nm; Inch-size PCD polishing to Ra < 5 nm.Essential for high-resolution photolithography used to define the 35 ”m surface contact separation and ensure reliable electrical contact to the internal NCN walls.

Engineering Support & Logistics

Section titled “Engineering Support & Logistics”

6CCVD’s in-house PhD team specializes in diamond material science and detector physics and can assist with material selection for similar High-Fluence Alpha/Neutron Detection projects. We offer consultation on:

  • Optimizing SCD purity to eliminate the need for detector “priming.”
  • Designing substrates with integrated NCN vias for back-contacting, removing surface metal contacts and improving robustness against gamma radiation failure points.
  • Selecting appropriate metalization schemes for specific operating environments (e.g., fusion reactors, nuclear liquid monitoring).

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2004 - Semiconductors and Semimetals

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