Overview of the Diamond Detectors

At a Glance

Metadata	Details
Publication Date	2015-05-21
Authors	A. Oh
Institutions	University of Manchester
Analysis	Full AI Review Included

6CCVD Technical Documentation & Analysis

Advanced MPCVD Diamond Detectors for High Energy Physics

Executive Summary

This paper validates the use of CVD diamond for next-generation radiation-hard particle detectors, focusing on the development of 3D detector architectures to significantly enhance performance in extreme environments like the upgraded LHC.

Established Performance: CVD diamond (both SCD and PCD) is proven technology for High Energy Physics (HEP) beam monitoring (ATLAS DBM, CMS BCM) due to its exceptional mechanical and electronic properties.
Radiation Hardness: Diamond detectors are designed to withstand unprecedented radiation fluences, targeting levels of order 10¹⁶ 1 MeV neutron equivalents cm^-2 required for LHC upgrades.
Signal Integrity: Single Crystal Diamond (SCD) achieves full charge collection, while Polycrystalline Diamond (PCD) yields high signal responses (approximately 10,000 electrons for a 500 µm detector).
3D Geometry Innovation: The transition to 3D electrode geometry shortens the charge drift path independently of detector thickness, thereby enhancing radiation tolerance and allowing for reduced operating bias (tested successfully at 25V vs. 500V for planar strips).
Advanced Fabrication: Prototype 3D detectors were successfully fabricated on 500 µm SCD substrates using Cr-Au structured metallization (photolithography) and internal laser graphitization (femto-second pulsing) to create highly conductive bulk columns (1 Ωcm).
6CCVD Advantage: 6CCVD provides the necessary detector-grade SCD and large-area PCD substrates, customizable dimensions, and specialized metalization services required to replicate and scale this crucial detector technology.

Technical Specifications

The following key parameters and performance metrics were established for both planar and prototype 3D diamond detectors:

Parameter	Value	Unit	Context
Target Radiation Tolerance	10¹⁶	1 MeV n_eq cm^-2	Requirement for LHC/FAIR upgrades
PCD Signal Yield (MIP)	~10000	electrons	For 500 µm thick detectors
SCD Signal Yield	Full	Charge Collection	Superior charge transport efficiency
ATLAS DBM PCD Dimensions	18 x 21	mm	Production device size
Prototype SCD Thickness	500	µm	Substrate thickness for 3D fabrication
Prototype SCD Dimensions	4.7 x 4.7	mm	Initial size for 3D feasibility testing
Planar Detector Bias	500	V	Standard operating voltage for strip geometry
3D Detector Bias	25	V	Low operating voltage demonstrates improved charge collection geometry
3D Electrode Diameter	~6	µm	Diameter of laser-graphitized conducting columns
3D Electrode Resistivity	~1	Ωcm	Consistency with nano-crystalline graphite structure
3D Electrode Pitch	100, 150	µm	Lateral spacing between bulk electrodes
Damage Constant k_λ (24 GeV Protons)	0.62 ± 0.07 x 10^-18	µm^-1 cm^-2	Normalized radiation damage parameter

Key Methodologies

The research focused on developing radiation-hard diamond particle sensors, with an emphasis on transitioning from planar structures (used in BCM/DBM) to advanced 3D geometries.

I. Material Selection and Preparation

Material Basis: Both high-quality Polycrystalline CVD Diamond (PCD) and high-purity Single Crystal CVD Diamond (SCD) were utilized. SCD was preferred for 3D prototypes due to its superior charge collection efficiency.
Substrate Dimensions: PCD sheets were used in dimensions up to 18 mm by 21 mm for DBM applications. Prototype 3D devices used SCD substrates of 4.7 mm x 4.7 mm with 500 µm thickness.
Initial Characterization: Samples were exposed to a ⁹⁰Sr source prior to irradiation tests to fill vacant traps and establish a stable baseline condition.

II. Radiation Hardness Testing

Irradiation Sources: Samples were exposed to protons (at 25 MeV, 70 MeV, 300 MeV, 800 MeV, and 24 GeV) and pions (at 300 MeV) across a wide kinetic energy range.
Signal Testing: Signal response (charge collection efficiency) was measured using a strip-detector configuration at an electric field of 2 V µm^-1 with 120 GeV protons.
Damage Parameterization: Radiation damage was quantified using the effective damage constant $k_{\lambda}$ and compared against Norget-Robinson-Torrens displacement per atom (DPA) theory.

III. 3D Detector Fabrication

Metallization: Structured surface electrodes were applied using Cr-Au via a standard photo-lithographic process.
Bulk Electrode Formation: Conducting columns were created by penetrating the full thickness of the diamond (500 µm) using a femtosecond pulsed laser process (laser graphitization).
Electrode Properties: The resulting columns were composed of nano-crystalline graphite, exhibiting a diameter of approximately 6 µm and a targeted resistivity of about 1 Ωcm.
Testing Configuration: The 3D prototype was tested alongside a planar strip detector (50 µm pitch) and a 3D phantom (surface metal only) using a 120 GeV proton beam at CERN SPS, allowing for performance comparison and validation of the bulk electrode approach.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials and custom engineering services necessary to replicate and scale these radiation-hard detector systems for high-energy physics applications.

Applicable Materials

To meet the stringent requirements for high charge collection efficiency and physical size demonstrated in this research, 6CCVD recommends the following materials:

Required Material Grade	6CCVD Catalog Solution	Key Specification Match
Detector-Grade Polycrystalline (PCD)	Electronic Grade PCD Wafers	Used for large-area DBM/BCM applications (e.g., 18 x 21 mm modules). 6CCVD offers sizes up to 125 mm.
Detector-Grade Single Crystal (SCD)	High Purity Optical/Electronic SCD	Required for full charge collection and 3D detector prototyping (500 µm thickness). 6CCVD guarantees SCD up to 500 µm thickness.
Surface Quality	Ultra-Smooth Polishing	Ra < 1 nm (SCD) and Ra < 5 nm (PCD) polishing is essential for high-precision photolithography (Cr-Au patterning) and bonding efficiency (> 99.9% achieved in DBM).

Customization Potential

The successful fabrication of 3D detectors hinges on precise material processing and microstructuring, areas where 6CCVD offers specialized custom engineering:

Custom Dimensions and Substrates: The paper utilized specific PCD module sizes (18x21 mm) and small SCD prototypes (4.7x4.7 mm). 6CCVD offers custom cutting and laser shaping services for any dimension up to 125 mm (PCD) and precise sizes for SCD.
Advanced Metalization Services: The research required a structured Cr-Au layer. 6CCVD offers internal, high-reliability metalization capabilities including Ti, Pt, Au, Pd, W, and Cu, suitable for demanding photolithographic patterning and subsequent bump-bonding processes (as used with the FE-I4 readout chip).
Thickness Control: 6CCVD can consistently supply CVD diamond substrates with precise thickness control, ranging from 0.1 µm to 500 µm for both SCD and PCD, enabling optimal design for charge collection vs. material budget.
Microstructure Feasibility: While the paper used laser graphitization for bulk electrodes, 6CCVD provides engineering support for projects requiring custom laser ablation, trench etching, and precise geometry definition for 3D architectures.

Engineering Support

6CCVD’s in-house PhD team can assist with material selection and design consultation for projects involving Radiation-Hard Particle Detectors and High Energy Physics (HEP) Beam Monitoring. We can optimize substrates based on target operational bias, anticipated radiation flux, and required charge collection distance (CCD).

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

View Original Abstract

Diamond detectors have been used in HEP experiments at the LHC and upgrades are foreseen during the shutdown phase before LHC restarts its operation. CVD diamond has been used extensively in beam condition monitors as the innermost detectors in the highest radiation areas of BaBar, Belle, CDF and all LHC experiments, and is also expected to be used in the experiments at FAIR at the GSI. The lessons learned in constructing the ATLAS Beam Conditions Monitor (BCM), Diamond Beam Monitor (DBM) and the CMS Pixel Luminosity Telescope (PLT) all of which are based on CVD diamond with the goal of elucidating the issues that should be addressed for future diamond based detector systems. The first beam test results of prototype diamond devices with 3D detector geometry should further enhance the radiation tolerance of this material.

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Original Source

DOI: https://doi.org/10.22323/1.227.0024