Pulsed laser fabrication of 3D diamond sensors

At a Glance

Metadata	Details
Publication Date	2015-03-25
Authors	S. Lagomarsino
Institutions	Nello Carrara Institute of Applied Physics, Istituto Nazionale di Fisica Nucleare
Citations	2
Analysis	Full AI Review Included

6CCVD Technical Documentation: Pulsed Laser Fabrication of 3D Diamond Detectors

This document analyzes the research on 3D diamond detectors fabricated using pulsed laser techniques, focusing on the material requirements and performance metrics relevant to high-energy physics (HEP) applications. The analysis highlights how 6CCVD’s advanced MPCVD diamond materials and customization capabilities can support and extend this critical research.

Executive Summary

The following points summarize the core findings and value proposition of the research regarding 3D diamond detectors:

Radiation Hardness Solution: 3D detector architecture successfully implemented in diamond to address charge collection limitations in radiation-harsh environments.
Superior Performance (fs-Laser): Femtosecond (fs) laser fabrication on Single Crystal Diamond (SCD) achieved 100% Charge Collection Efficiency (CCE).
Ultra-Low Bias Voltage: fs-fabricated 3D SCD sensors reached saturation at approximately 3 V, a tenfold reduction compared to the 30 V required by conventional 2D planar reference sensors.
Material Dependence: Nanosecond (ns) laser fabrication resulted in a significant charge loss (up to 30%) due to the formation of a highly resistive, defective sp³-carbon layer surrounding the graphitic electrodes.
Geometry Confirmation: The low saturation voltage confirms that charge collection occurs efficiently along the vertical columnar electrodes, not just the superficial contacts.
Scalability Potential: Projections based on Monte-Carlo simulations indicate that 3D SCD detectors will maintain high CCE (collecting > 7000 electrons) even after extreme proton fluences (up to 2 x 10¹⁶ cm^-2).

Technical Specifications

The following table extracts key quantitative data points from the research paper:

Parameter	Value	Unit	Context
Diamond Thickness	500	µm	SCD and PCD substrates used
3D Electrode Length	500	µm	Columnar electrodes extending through the bulk
Electrode Pitch (Spacing)	80 to 160	µm	Depending on IDC/OSC geometry
fs-Laser Pulse Width	30	fs	Ti:sapphire source (optimal performance)
ns-Laser Pulse Width	8	ns	Nd:YAG source (resulted in 30% CCE loss)
fs-3D SCD Saturation Voltage	~3	V	Voltage required to achieve 90% CCE saturation
2D Planar SCD Saturation Voltage	30	V	Reference sensor saturation voltage
fs-3D SCD Charge Collection Efficiency	100	%	Full collection (equivalent to 18,000 electrons)
ns-3D SCD Charge Loss	~30	%	Attributed to defective surrounding layer
ns-Graphite Resistivity	~60	mΩcm	Lower resistivity, but poor CCE due to defects
fs-Graphite Resistivity	~800	mΩcm	Higher resistivity, but superior CCE
Projected Radiation Fluence	1-2 x 10¹⁶	cm^-2	Expected performance at SLHC vertex (5 years)

Key Methodologies

The fabrication and testing of the 3D diamond detectors involved precise laser processing and specialized characterization:

Substrate Preparation: Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) samples (5x5x0.5 mm³) were sourced for processing.
Superficial Contact Fabrication: Graphitic combs (2D contacts) were engraved onto the diamond surface using the nanosecond (ns) Nd:YAG laser (1064 nm) to ensure optimal geometric characteristics and low resistivity.
3D Columnar Fabrication: Graphitic columns, acting as 3D electrodes, were fabricated in the bulk diamond (500 µm deep) using two distinct laser sources:
- Femtosecond (fs) Laser: Ti:sapphire (800 nm, 30 fs pulse width, ~5 µJ energy).
- Nanosecond (ns) Laser: Nd:YAG (1064 nm, 8 ns pulse width, 10-40 µJ energy).
Sensor Geometry Implementation: Two primary 3D electrode configurations were developed: Interdigitated Combs (IDC) and the more complex Opposite Side Combs (OSC).
Charge Collection Testing: Sensors were tested for CCE using a ⁹⁰Sr beta-particle source. Polycrystalline samples required priming (irradiation) to maximize response.
Signal Analysis: Signals were pre-amplified (1.4 µs peaking time) and calibrated to estimate the number of collected charge carriers (full collection = 18,000 electrons).
Radiation Hardness Projection: The long-term behavior of the 3D sensors under heavy irradiation was simulated using Monte-Carlo methods, based on observed degradation in conventional planar sensors exposed to 24 GeV protons.

6CCVD Solutions & Capabilities

This research confirms the critical role of high-quality diamond substrates and precise fabrication techniques in achieving next-generation radiation detectors. 6CCVD is uniquely positioned to supply the required materials and engineering support to replicate and advance this work.

Research Requirement	6CCVD Applicable Materials & Services	Technical Value Proposition
High-Purity Substrates	Optical Grade Single Crystal Diamond (SCD)	Our SCD material offers the ultra-low defect density essential for achieving the 100% CCE demonstrated by the fs-laser process. We guarantee high-purity material necessary for radiation detection applications.
Custom Thickness (500 µm)	SCD and PCD Thickness Control	6CCVD provides SCD and PCD substrates with precise thickness control ranging from 0.1 µm up to 500 µm (matching the paper’s requirement) and up to 10 mm for specialized substrates.
Large-Area Scaling	Custom Dimensions up to 125 mm	While the prototypes were 5x5 mm², 6CCVD can supply large-area Polycrystalline Diamond (PCD) wafers up to 125 mm diameter, enabling the scale-up required for large-scale HEP experiments.
Electrical Contacts (Combs)	Custom Metalization Services	We offer in-house metalization (Au, Pt, Pd, Ti, W, Cu) for creating robust, low-resistance superficial contacts. We can apply optimized Ti/Pt/Au stacks directly onto laser-graphitized surfaces, ensuring reliable bias and signal readout.
Surface Quality Control	Ultra-Precision Polishing	Our polishing capabilities achieve surface roughness Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD. This minimizes surface leakage currents and erratic discharges, which were noted as a challenge in the polycrystalline samples.
Engineering Support	In-House PhD Material Science Team	6CCVD’s experts can assist researchers in selecting the optimal diamond grade (SCD vs. PCD) and defining specifications (e.g., nitrogen concentration, surface termination) to maximize performance for 3D diamond detector projects.

Call to Action

The successful implementation of 3D electrodes in diamond, particularly the low-voltage operation achieved with SCD, represents a significant step toward future radiation-hard detectors. 6CCVD provides the foundational MPCVD diamond materials necessary for this advancement.

For custom specifications or material consultation regarding 3D diamond detectors or similar radiation hardness projects, visit 6ccvd.com or contact our engineering team directly. We ship globally (DDU default, DDP available).

View Original Abstract

3D detectors, whose electrodes extend perpendicularly to the sensor surface, represent one of the solution proposed for the challenges of radiation-harsh environments in high energy physics [1][2][3][4].We report on the fabrication and characterization of prototypes of 3D diamond detector, which add to the 3D architecture the advantages of diamond as a sensor for tracking purposes.Two different laser sources, a Nd:YAG 1064 Q-switched laser with 8 ns pulse-width and a Ti:sapphire laser source with 30 fs pulse duration have been used to fabricate arrays of graphitic columns in the bulk of a polycrystalline and a single crystal diamond sample.The columns are staggered and connected to graphitic combs which have been fabricated as well by laser irradiation and used as electric contacts.On each sample, an identical pattern of graphitic combs without columns (2D structure) has also been fabricated as a reference.The charge collection efficiency of each 3D sensor has been measured at different voltages and compared with the corresponding 2D structures.The much lower saturation voltages of the 3D sensors compared to those of the planar ones confirm that charge collection takes place at the columnar electrodes.Moreover, an efficiency of 100% is assured by the sensors fabricated with the fslaser source, while a loss in efficiency up to 30% is observed with the sensors fabricated with the ns-laser.The expected behaviour of 3D diamond sensors after strong radiation damage is discussed.

Tech Support

Original Source

DOI: https://doi.org/10.22323/1.189.0010