Diamond-Like Carbon for the Fast Timing MPGD

At a Glance

Metadata	Details
Publication Date	2020-04-01
Journal	Journal of Physics Conference Series
Authors	A. Colaleo, G. De Robertis, F. Licciulli, M. Maggi, A. Ranieri
Institutions	University of Pavia, Istituto Nazionale di Fisica Nucleare, Sezione di Pavia
Citations	7
Analysis	Full AI Review Included

Diamond-Like Carbon for Fast Timing MPGD: Material Analysis and 6CCVD Solutions

This document analyzes the requirements and findings of the research paper “Diamond-Like Carbon for the Fast Timing MPGD” and outlines how 6CCVD’s expertise in Chemical Vapor Deposition (CVD) diamond, particularly Boron-Doped Diamond (BDD), provides superior, scalable, and stable material solutions for next-generation Micro-Pattern Gaseous Detectors (MPGDs).

Executive Summary

The following points summarize the core technical achievements and material challenges addressed in the research:

Application Focus: Development of the Fast Timing MPGD (FTM) concept to drastically improve time resolution in particle detectors from O(5-10 ns) to a target of ~1 ns, essential for High Luminosity LHC (HL-LHC) and Future Circular Collider (FCC-hh) upgrades.
Material Requirement: The FTM design necessitates highly resistive electrodes, specifically Diamond-Like Carbon (DLC) films (~100 nm thick) deposited on polyimide (PI) foils.
Target Resistivity: A critical surface resistivity of approximately 100 MΩ/□ was targeted to balance high signal transparency with adequate rate capability.
Deposition Success: Both Ion Beam Sputtering (IBS) and Pulsed Laser Deposition (PLD) successfully achieved the target 100 MΩ/□ resistivity on 6x6 cm² and 2x2 cm² substrates.
Key Challenge Identified: Poor adhesion and delamination of the DLC film during the necessary wet-etching process (for GEM-like holes) proved to be the primary obstacle to prototype development.
Stability Improvement: PLD demonstrated superior film stability and uniformity over larger areas (3x3 cm²) compared to IBS samples, which suffered from time-dependent oxidation and resistivity drift.
Future Direction: Continued characterization (Raman, XPS) is required to correlate the sp³/sp² carbon fraction with electrical transport properties to ensure robust, scalable production.

Technical Specifications

The following hard data points were extracted from the experimental results and simulations:

Parameter	Value	Unit	Context
Target Time Resolution	~1	ns	FTM goal, achieved at N=8 layers (250 µm width)
Standard MPGD Resolution	O(5-10)	ns	Limitation due to primary ionization fluctuations
Target Surface Resistivity	100	MΩ/□	Required for resistive DLC electrodes
DLC Film Thickness	~100	nm	Thickness used for resistive layer
Polyimide Substrate Thickness	50	µm	Base material for DLC deposition
Maximum Simulated Gain (G)	10⁴	-	Achieved at 500 V Anode Potential (Ar:CO₂ 70:30)
Drift Velocity (v_d)	70	µm/ns	Calculated at E = 3 kV/cm
PLD Laser Fluence (100 MΩ/□)	5	J/cm²	Optimized parameter for target resistivity
IBS Main Ion Beam Energy	1200	eV	Used for deposition of samples 1819, 1820, 1821
N₂ Doping Resistivity (Sample 1821)	~30	MΩ/□	Result of Nitrogen inclusion in IBS process

Key Methodologies

The research focused on two Physical Vapor Deposition (PVD) techniques to produce DLC films with controlled resistivity and high uniformity:

Substrate Preparation: Polyimide (PI) foils (50 µm thick) were used as the base material. Prior to DLC deposition, an assistance Argon (Ar) ion beam was focused directly onto the PI substrate to remove organic compounds and improve initial adhesion.
Ion Beam Sputtering (IBS):
- A dual Kaufman ion-beam system was utilized.
- The main ion source bombarded a pyrolytic graphite target at a 45° angle.
- An assistance Ar ion source (50-100 eV) was used simultaneously to compactify the deposited carbon ions, aiming to improve film uniformity and quality.
- Nitrogen (N₂) doping was introduced in sample 1821 to further tune the surface resistivity.
Pulsed Laser Deposition (PLD):
- A multi-gas excimer laser (248-193 nm, 20 ns pulses, 10 Hz) was used to ablate a rotating pyrolytic graphite target in a vacuum chamber.
- The laser fluence was identified as the critical parameter for tuning the DLC sp³/sp² ratio and, consequently, the film resistivity.
- Substrate rotation was implemented to homogenize the plasma plume and achieve high uniformity over 3x3 cm² areas.
Electrical Characterization:
- Surface resistivity was measured using thin copper (Cu) bars spaced 5 cm apart, applying voltages between 50 V and 500 V (found to be voltage-independent).
- A custom tool with concentric circular electrodes (1 cm inner radius, 2 cm outer radius) was used to confirm measurements and remove bias.
- The Van Der Pauw method was employed for specific resistivity measurements on PLD samples, yielding sub-% uncertainties on the central value.

6CCVD Solutions & Capabilities

The research highlights the critical need for highly stable, uniform, and tunable resistive films for advanced particle detectors. While the paper focuses on DLC, 6CCVD offers Boron-Doped Diamond (BDD), a superior MPCVD material that inherently solves the stability, adhesion, and uniformity challenges faced by PVD-deposited carbon films.

Applicable Materials: The BDD Advantage

The ideal material for replicating and advancing this FTM research is Boron-Doped Polycrystalline Diamond (BDD).

Requirement	6CCVD BDD Solution	Technical Advantage over DLC
Resistive Electrode	Tunable BDD Films: We engineer BDD films where resistivity can be precisely controlled from metallic (10^-3 Ωcm) to semi-insulating (10¹⁰ Ωcm).	Superior Stability: BDD is chemically inert and thermally stable up to 800 °C, eliminating the time-dependent oxidation and resistivity drift observed in DLC.
High Uniformity	MPCVD Growth: Our proprietary MPCVD process ensures exceptional doping uniformity across large areas.	Intrinsic Quality: Eliminates the non-uniformity and V-shaped plume issues inherent to PLD/IBS methods, guaranteeing consistent electrical performance.
Adhesion & Etching	Robust CVD Structure: Diamond films are grown directly, offering intrinsic adhesion far superior to sputtered or ablated films on polyimide.	Processing Compatibility: BDD is highly compatible with advanced micro-structuring techniques, including dry etching (RIE) and laser cutting, necessary for creating GEM-like patterns without delamination.

Customization Potential for FTM Prototypes

6CCVD’s in-house capabilities directly address the dimensional and integration needs of advanced detector prototypes:

Custom Dimensions & Scale-Up: The paper used 6x6 cm² and 3x3 cm² samples. 6CCVD provides Polycrystalline Diamond (PCD) plates up to 125 mm in diameter, enabling the scale-up required for full-size FTM modules for LHC upgrades.
Thickness Control: We offer precise thickness control for both Single Crystal Diamond (SCD) and PCD from 0.1 µm up to 500 µm, allowing engineers to optimize the resistive layer thickness for specific capacitance and rate requirements.
Advanced Metalization Services: The paper required Cu bars for testing. 6CCVD offers internal deposition of complex metal stacks (e.g., Ti/Pt/Au, W, Cu) with high precision, ready for subsequent photolithography and readout integration.
Polishing Excellence: Our SCD substrates achieve surface roughness Ra < 1 nm, and inch-size PCD achieves Ra < 5 nm, ensuring optimal surface quality for subsequent micro-patterning and electrode deposition.

Engineering Support

6CCVD’s in-house PhD team specializes in the material science of diamond for high-energy physics and sensor applications. We offer comprehensive engineering support to assist researchers in:

Material Selection: Determining the optimal BDD doping level and film thickness to achieve the precise 100 MΩ/□ sheet resistance required for Fast Timing MPGD projects.
Integration Strategy: Consulting on the best practices for integrating BDD films into complex detector architectures, including metalization and micro-structuring techniques.

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

View Original Abstract

Abstract The present generation of Micro-Pattern Gaseous Detectors (MPGDs) are radiation hard detectors, capable of detecting effciently particle rates of several MHz/cm 2 , while exhibiting good spatial resolution (≤ 50 µm) and modest time resolution of 5-10 ns, which satisfies the current generation of experiments (High Luminosity LHC upgrades of CMS and ATLAS) but it is not sufficient for bunch crossing identification of fast timing systems at FCC-hh. Thanks to the application of thin resistive films such as Diamond-Like Carbon (DLC) a new detector concept was conceived: Fast Timing MPGD (FTM). In the FTM the drift volume of the detector has been divided in several layers each with their own amplification structure. The use of resistive electrodes makes the entire structure transparent for electrical signals. After some first initial encouraging results, progress has been slowed down due to problems with the wet-etching of DLC-coated polyimide foils. To solve these problems a more in-depth knowledge of the internal stress of the DLC together with the DLC-polyimide adhesion is required. We will report on the production of DLC films produced in Italy with Ion Beam Sputtering and Pulsed Laser Deposition, where we are searching to improve the adhesion of the thin DLC films, combined with a very high uniformity of the resistivity values.

Tech Support

Original Source

DOI: https://doi.org/10.1088/1742-6596/1498/1/012015

References

**** - A novel fast timing micropattern gaseous detector: FTM
1999 - Diamond-like carbon: state of the art [Crossref]
1999 - Diamond-like carbon — present status [Crossref]
2010 - Penning transfer in argon-based gas mixtures [Crossref]
2011 - Progress on large area GEMs [Crossref]
2009 - Progress on large area GEMs
2015 - The micro-Resistive WELL detector: a compact spark-protected single amplification-stage MPGD [Crossref]
2014 - Carbon Sputtering Technology for MPGD detectors
2019 - Fabrication and performance of a RWELL detector with Diamond-Like Carbon resistive electrode and two-dimensional readout [Crossref]
2005 - Ion-beam sputtering deposition of CsI thin films [Crossref]