RD42 - Radiation hard diamond sensors

At a Glance

Metadata	Details
Publication Date	2015-12-30
Authors	G. Kasieczka
Citations	2
Analysis	Full AI Review Included

Technical Documentation & Analysis: Radiation Hard Diamond Sensors

Reference Paper: RD42: Radiation hard diamond sensors (Kasieczka, G. et al., CERN RD42 Collaboration) Application Focus: High-Energy Physics (HEP) Tracking Detectors, CERN LHC (CMS, ATLAS) 6CCVD Material Focus: Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) for extreme radiation environments.

Executive Summary

The RD42 collaboration confirms Chemical Vapor Deposition (CVD) diamond as the superior radiation-tolerant material for next-generation tracking detectors in high-luminosity environments like the CERN LHC.

Radiation Hardness Verified: SCD and PCD sensors were successfully tested up to fluences of 1.8 x 10¹⁶ protons/cm², validating diamond’s intrinsic material advantages (large band gap, high displacement energy).
Operational Success: PCD sensors (18 x 21 mm²) are currently deployed in the ATLAS Diamond Beam Monitor (DBM), demonstrating reliability in harsh conditions.
Flux Dependence Analysis: Systematic studies showed that neutron-irradiated SCD pixel sensors exhibited a significant pulse height drop (up to a factor of two) at high particle flux, primarily attributed to the pixel readout threshold and charge sharing effects.
PCD Stability: Neutron-irradiated PCD pad sensors showed no pulse-height dependence up to 300 kHz/cm², highlighting the robust performance of polycrystalline material in certain geometries.
Future Geometry: The development of 3D diamond detectors (470 µm thick, 150 x 150 µm² cells) successfully reduced the charge drift path, enabling low-voltage operation (25 V bias) and promising increased charge yield in highly irradiated materials.
6CCVD Value Proposition: 6CCVD provides the high-purity, large-area SCD and PCD substrates (up to 125mm) required for replicating and advancing these critical radiation-hard sensor designs, including custom metalization and precise thickness control.

Technical Specifications

The following hard data points were extracted from the RD42 collaboration’s beam test results and device specifications:

Parameter	Value	Unit	Context
Maximum Fluence Tested	1.8 x 10¹⁶	protons/cm²	Upper limit of radiation hardness testing
Neutron Fluence (Test Samples)	5.0 ± 0.5 x 10¹³	n/cm²	Dose comparable to CMS PLT pilot run
Particle Flux Range (Beam Test)	1 to 20	MHz/cm²	Pions (250 MeV/c) used for flux dependence study
SCD/PCD Sensor Thickness	≈ 500	µm	Standard pad and pixel test geometry
3D Detector Thickness	470	µm	Prototype sample for bulk electrode structuring
ATLAS DBM Active Area (PCD)	18 x 21	mm²	Installed LHC luminosity monitor
CMS PLT Active Area (SCD)	4.5 x 4.5	mm²	Pilot run tracking sensor
Pixel Electrode Size	75 x 125	µm	Standard pixel geometry tested
3D Detector Cell Size	150 x 150	µm²	Electrode pitch created by femto-second laser
3D Sensor Bias Voltage	25	V	Low-voltage operation enabled by 3D geometry
Planar Strip Bias Voltage	500	V	Comparison voltage for standard planar geometry
Pixel Readout Threshold	≈ 3000	e	Implicated in pulse height drop at high flux

Key Methodologies

The RD42 collaboration employed rigorous methods to test the performance and radiation tolerance of CVD diamond sensors:

Material Selection and Preparation: Single-crystal (SCD) and polycrystalline (PCD) CVD diamond wafers were manufactured and prepared, typically to a thickness of approximately 500 µm.
Irradiation: Samples were subjected to high-dose irradiation, including neutron fluences up to 5.0 x 10¹³ n/cm² and proton fluences up to 1.8 x 10¹⁶ protons/cm², simulating LHC conditions.
Detector Geometry Testing: Two primary planar geometries were tested:
- Pad Geometry: Used for general pulse height measurements. Read out via Ortec 142A preamplifier and 450 amplifier.
- Pixel Geometry: Electrode size 75 µm x 125 µm, read out using the standard CMS PSI46v2 pixel readout chip (ROC).
3D Detector Prototyping: A 470 µm thick SCD sample was structured using a femto-second laser to create 3D electrodes (diamond-like carbon/graphitic material) with a 150 x 150 µm² cell size, enabling reduced drift paths.
Beam Testing: Sensors were tested in beams of 250 MeV/c pions and 120 GeV protons (CERN-SPS). Particle flux was systematically varied between 1 kHz/cm² and 20 MHz/cm².
Signal Analysis: Pulse height was extracted using a 70 ns integration window (pad detectors) or cluster charge summation (pixel detectors). Results were re-scaled to the lowest flux measurement for comparison.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-specification CVD diamond materials and processing services necessary to replicate and advance the RD42 collaboration’s work on radiation-hard sensors for high-energy physics.

Applicable Materials

To meet the demanding requirements of high-radiation tracking and luminosity monitoring, 6CCVD recommends the following materials:

Optical Grade Single Crystal Diamond (SCD): Required for high-precision tracking detectors (like the CMS PLT). Our SCD offers the highest purity and lowest defect density, ensuring optimal charge collection efficiency (CCE) and minimizing leakage current, even after extreme irradiation.
- Relevance: Essential for replicating the high-performance SCD pixel sensors studied.
High-Quality Polycrystalline Diamond (PCD): Ideal for large-area luminosity monitors (like the ATLAS DBM). Our PCD offers excellent uniformity and radiation hardness across large areas.
- Relevance: We offer PCD plates up to 125mm in diameter, significantly exceeding the 18 x 21 mm² plates currently deployed.

Customization Potential

The RD42 research relies heavily on precise geometry, thickness control, and electrode integration. 6CCVD’s in-house capabilities directly address these needs:

Custom Dimensions and Thickness:
- The paper utilized sensors approximately 500 µm thick. 6CCVD routinely supplies both SCD and PCD wafers with precise thickness control from 0.1 µm up to 500 µm, and substrates up to 10mm thick for specialized applications.
- We provide custom plates and wafers up to 125mm (PCD) and custom laser cutting services to match the exact 4.5 x 4.5 mm² or 18 x 21 mm² active areas required.
High-Precision Polishing:
- The creation of fine-pitch pixel and 3D electrode structures requires extremely flat and smooth surfaces for subsequent lithography and laser processing.
- 6CCVD guarantees surface roughness (Ra) < 1nm for SCD and < 5nm for inch-size PCD, ensuring optimal substrate quality for micro-patterning.
Custom Metalization Services:
- The planar and 3D detectors require robust, low-resistance electrodes (e.g., Ti/Pt/Au).
- 6CCVD offers internal metalization capabilities, including deposition of Au, Pt, Pd, Ti, W, and Cu, allowing researchers to specify custom electrode layouts and contact layers necessary for pad, strip, and pixel geometries.

Engineering Support

The observed flux dependence in irradiated SCD pixel sensors highlights the complex interplay between material quality, geometry (pad vs. pixel), and readout electronics (thresholds).

6CCVD’s in-house PhD team specializes in CVD diamond material science and device physics. We can assist engineers and scientists in selecting the optimal SCD or PCD grade to minimize defects that contribute to charge trapping and pulse height degradation under high flux.
We offer consultation on material specifications for similar High-Energy Particle Tracking projects, ensuring the chosen substrate maximizes Charge Collection Efficiency (CCE) and minimizes the impact of radiation-induced defects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We offer global shipping (DDU default, DDP available) to facilitate international research collaborations like RD42.

View Original Abstract

The RD42 Collaboration at CERN is investigating chemical vapor deposition diamond as a material for tracking detectors operating in extreme radiation environments. We present an overview of the latest developments from RD42. The status of diamond based luminosity monitors for the upcoming CERN Large Hadron Collider (LHC) run is described followed by a discussion of recent beam test measurements of the pulse height dependence on the incoming charged particle flux for single-crystal and poly-crystalline diamond sensors. Finally the use of 3D geometries for CVD diamond sensors is reviewed.

Tech Support

Original Source

DOI: https://doi.org/10.22323/1.254.0033