A Study of the Radiation Tolerance of CVD Diamond to 70 MeV Protons, Fast Neutrons and 200 MeV Pions

At a Glance

Metadata	Details
Publication Date	2020-11-20
Journal	Sensors
Authors	L. Bäni, Andreas V. Alexopoulos, M. Artuso, Felix Bachmair, M. Bartosik
Institutions	Syracuse University, Istituto Nazionale di Fisica Nucleare, Sezione di Perugia
Citations	13
Analysis	Full AI Review Included

Technical Documentation & Analysis: Radiation Tolerance of CVD Diamond

Executive Summary

This study rigorously quantifies the radiation tolerance of Chemical Vapor Deposition (CVD) diamond, confirming its critical role in high-energy physics (HEP) applications requiring extreme radiation hardness.

Superior Radiation Hardness: CVD diamond (both Single Crystal, SCD, and Polycrystalline, PCD) demonstrates significantly higher radiation tolerance (greater than a factor of two) compared to silicon when exposed to high-energy protons and pions.
Quantified Damage Constants: Precise damage constants (k) were derived for 70 MeV protons, fast reactor neutrons (> 0.1 MeV), and 200 MeV pions, enabling accurate lifetime predictions for diamond detectors.
Neutron Sensitivity: Fast reactor neutrons were identified as the most damaging species tested, exhibiting a relative damage constant (κ) of 4.3 ± 0.4 compared to 24 GeV protons.
Universal Damage Model: A universal damage curve was established, allowing engineers to predict the charge collection distance (ccd) and mean drift path (λ) of any CVD diamond sample based on a single equivalent fluence parameter (24 GeV proton equivalent fluence).
PCD Uniformity Improvement: A key finding is that the spatial uniformity of charge collection in polycrystalline CVD (pCVD) diamond increases with radiation fluence, approaching the uniformity of single-crystal diamond (scCVD).
Material Validation: The research validates the use of high-purity, electronic-grade MPCVD diamond—a core product of 6CCVD—for critical radiation monitoring and tracking applications in future high-fluence accelerator facilities (e.g., HL-LHC).

Technical Specifications

The following table summarizes the critical material properties, processing parameters, and quantified radiation damage constants extracted from the research.

Parameter	Value	Unit	Context
Diamond Material Type	SCD and PCD	-	High-purity Electronic Grade CVD
Nominal Thickness	~500	µm	Samples used in irradiation study
Detector Geometry	Strip Detector	-	50 µm pitch, 25 µm wide strips
Metalization Stack	500 Å Cr / 2000 Å Au	-	Bias and readout electrodes
Post-Processing Annealing	400	°C	4 min in N₂ atmosphere
70 MeV Proton Damage Constant (k)	1.62 ± 0.16	10^-18 cm²/(pµm)	Polycrystalline CVD (pCVD)
Fast Neutron Damage Constant (k)	2.65 ± 0.18	10^-18 cm²/(nµm)	Polycrystalline CVD (pCVD)
200 MeV Pion Damage Constant (k)	2.0 ± 0.5	10^-18 cm²/(πµm)	Combined SCD/PCD fit
Relative Damage (Fast Neutrons)	4.3 ± 0.4	κ	Relative to 24 GeV protons (κ=1.0)
Relative Damage (70 MeV Protons)	2.60 ± 0.29	κ	Relative to 24 GeV protons (κ=1.0)
Relative Damage (200 MeV Pions)	3.2 ± 0.8	κ	Relative to 24 GeV protons (κ=1.0)
Charge Generation Constant	36.0 ± 0.8	e/µm	Electron-hole pairs per micron (MIP)
Minimum Noise Observed	~100	e	Total noise per channel

Key Methodologies

The radiation tolerance study relied on precise material preparation, controlled irradiation, and high-resolution charge collection measurements.

Material Preparation: High-purity scCVD and pCVD diamond samples (approx. 500 µm thick) were subjected to a multi-step hot acid clean and oxygen plasma etch.
Electrode Fabrication: A dual-layer metalization stack (500 Å Cr for adhesion, 2000 Å Au for conductivity) was deposited. A 50 µm pitch strip detector pattern was defined via photolithography.
Thermal Annealing: Devices were annealed at 400 °C for 4 minutes in an N₂ atmosphere to stabilize electrical contacts.
Initial Characterization: Unirradiated Charge Collection Distance (ccd) was measured using a calibrated ⁹⁰Sr β-source setup.
Irradiation Campaigns: Samples were exposed to three distinct particle beams in incremental fluence steps:
- 70 MeV Protons (CYRIC facility).
- Fast Reactor Neutrons (> 0.1 MeV) (JSI TRIGA reactor).
- 200 MeV Positive Pions (PSI facility, via CERN IRRAD).
Post-Irradiation Testing: After each step, the charge collection efficiency was measured using a 120 GeV hadron test beam at CERN, utilizing an eight-plane silicon strip telescope for precise particle tracking (1.3 µm resolution).
Damage Modeling: The inverse mean drift path (1/λ) was fitted linearly against fluence (φ) using the first-order damage model (1/λ = 1/λ₀ + kφ) to determine the damage constant (k).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-quality MPCVD diamond materials and custom fabrication services required to replicate, extend, and deploy the radiation-hard detectors described in this research.

Applicable Materials

To replicate or extend this high-energy physics research, the following 6CCVD materials are explicitly recommended:

Electronic Grade PCD (Polycrystalline CVD): Ideal for large-area detectors (up to 125 mm diameter) where high radiation tolerance and cost-effectiveness are paramount. The study confirms that pCVD uniformity improves under high fluence, making it a robust choice for HL-LHC environments.
Optical Grade SCD (Single Crystal CVD): Recommended for applications requiring the highest initial charge collection distance (ccd) and uniformity (Ra < 1 nm), particularly for small-area, high-precision tracking sensors.
Custom Thickness: We can supply both SCD and PCD wafers at the required ~500 µm thickness (within the 0.1 µm to 500 µm range) or provide thicker substrates up to 10 mm for specialized applications.

Customization Potential

The success of the detectors in this study relied on precise dimensions and specific metal contacts. 6CCVD offers comprehensive in-house customization capabilities:

Required Specification from Paper	6CCVD Customization Service	Technical Advantage
Specific Metalization Stack (Cr/Au)	Custom Metalization: We offer precise deposition of Au, Pt, Pd, Ti, W, and Cu. We can replicate the required 500 Å Cr / 2000 Å Au stack or optimize adhesion layers (e.g., Ti/Pt/Au) for specific operating temperatures and environments.	Ensures robust, low-noise electrical contacts essential for high-resolution strip detectors (50 µm pitch).
Large Area Scaling (Beyond 10x10 mm²)	Large-Format PCD Wafers: We provide PCD plates/wafers up to 125 mm in diameter, enabling the scaling of radiation monitors and trackers for next-generation accelerator experiments.	Supports the development of large-area diamond tracking layers, overcoming the size limitations of scCVD.
High-Precision Surface Finish	Ultra-Low Roughness Polishing: SCD polished to Ra < 1 nm and inch-size PCD polished to Ra < 5 nm.	Critical for minimizing surface leakage currents and ensuring high yield during photolithographic fabrication of fine-pitch electrode structures (e.g., 50 µm strips).
Custom Device Dimensions	Laser Cutting and Shaping: We provide custom laser cutting services to achieve precise sample dimensions (e.g., 5x5 mm² or 10x10 mm²) and complex geometries required for detector integration.	Rapid delivery of application-specific geometries ready for immediate device fabrication.

Engineering Support

6CCVD’s in-house PhD team specializes in optimizing MPCVD growth parameters to control defect density and charge carrier trapping times—factors directly related to the damage constant (k) measured in this research. We can assist with material selection for similar Radiation Monitoring and High-Fluence Tracking projects, ensuring the chosen diamond grade meets the specific fluence and particle requirements derived from the universal damage curve.

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

View Original Abstract

We measured the radiation tolerance of commercially available diamonds grown by the Chemical Vapor Deposition process by measuring the charge created by a 120 GeV hadron beam in a 50 μm pitch strip detector fabricated on each diamond sample before and after irradiation. We irradiated one group of samples with 70 MeV protons, a second group of samples with fast reactor neutrons (defined as energy greater than 0.1 MeV), and a third group of samples with 200 MeV pions, in steps, to (8.8±0.9) × 1015 protons/cm2, (1.43±0.14) × 1016 neutrons/cm2, and (6.5±1.4) × 1014 pions/cm2, respectively. By observing the charge induced due to the separation of electron-hole pairs created by the passage of the hadron beam through each sample, on an event-by-event basis, as a function of irradiation fluence, we conclude all datasets can be described by a first-order damage equation and independently calculate the damage constant for 70 MeV protons, fast reactor neutrons, and 200 MeV pions. We find the damage constant for diamond irradiated with 70 MeV protons to be 1.62±0.07(stat)±0.16(syst)× 10−18 cm2/(p μm), the damage constant for diamond irradiated with fast reactor neutrons to be 2.65±0.13(stat)±0.18(syst)× 10−18 cm2/(n μm), and the damage constant for diamond irradiated with 200 MeV pions to be 2.0±0.2(stat)±0.5(syst)× 10−18 cm2/(π μm). The damage constants from this measurement were analyzed together with our previously published 24 GeV proton irradiation and 800 MeV proton irradiation damage constant data to derive the first comprehensive set of relative damage constants for Chemical Vapor Deposition diamond. We find 70 MeV protons are 2.60 ± 0.29 times more damaging than 24 GeV protons, fast reactor neutrons are 4.3 ± 0.4 times more damaging than 24 GeV protons, and 200 MeV pions are 3.2 ± 0.8 more damaging than 24 GeV protons. We also observe the measured data can be described by a universal damage curve for all proton, neutron, and pion irradiations we performed of Chemical Vapor Deposition diamond. Finally, we confirm the spatial uniformity of the collected charge increases with fluence for polycrystalline Chemical Vapor Deposition diamond, and this effect can also be described by a universal curve.

Tech Support

Original Source

DOI: https://doi.org/10.3390/s20226648

References

2019 - A study of the radiation tolerance of poly-crystalline and single-crystalline CVD diamond to 800 MeV and 24 GeV protons [Crossref]