BURIED GRAPHITE PILLARS IN SINGLE CRYSTAL CVD DIAMOND - SENSITIVITY TO ELECTRONS
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2016-01-01 |
| Journal | RAD Association Journal |
| Authors | G. Conte, P. Allegrini, Maurizio Pacilli, S. Salvatori, D.M. Trucchi |
| Institutions | National Research Nuclear University MEPhI, University NiccolĂČ Cusano |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Buried Graphite Pillars in Single Crystal CVD Diamond Detectors
Section titled âTechnical Documentation & Analysis: Buried Graphite Pillars in Single Crystal CVD Diamond DetectorsâThis document analyzes the research detailing the fabrication and performance of a 3D radiation detector utilizing buried graphite pillars within Single Crystal Diamond (SCD). The analysis highlights 6CCVDâs capability to supply the necessary high-purity SCD material and advanced processing services required to replicate and scale this cutting-edge technology for high-energy physics and tracking applications.
Executive Summary
Section titled âExecutive SummaryâThe research successfully demonstrates a high-efficiency 3D radiation detector fabricated using femtosecond laser graphitization within Single Crystal CVD Diamond (SCD).
- Core Achievement: Creation of 212 buried, high aspect ratio graphite pillars (380 ”m deep, 20 ”m diameter) acting as 3D electrodes within a 500 ”m thick SCD slab.
- Fabrication Method: Local graphitization achieved using a 400 fs, 1030 nm IR laser at a 200 kHz repetition rate, enabling precise 3D electrode placement.
- Performance: Demonstrated high charge collection efficiency (CCE) for 90Sr, Y $\beta$-particles (electrons).
- Saturation: Charge collection saturated at 1.40 ± 0.02 fC under a moderate electric field strength of ±0.67 V/”m.
- Architecture Validation: Confirms the viability of all-carbon 3D detector architectures, offering advantages in radiation hardness, low noise (due to low dielectric permittivity $\approx$5.5), and fast transient response.
- Application Potential: Suitable for X-ray and electron spectroscopy, high-luminosity/high-energy physics experiments, and angle-resolved measurements.
Technical Specifications
Section titled âTechnical SpecificationsâThe following table summarizes the critical material and performance parameters extracted from the study:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Base Material | Single Crystal CVD Diamond | N/A | High-purity, low-defect material |
| Slab Dimensions (Used) | 3 x 3 | mm2 | Small scale prototype |
| Slab Thickness | 500 | ”m | Active detector volume |
| Pillar Depth (Electrode Length) | 380 ± 20 | ”m | Buried conductive structure |
| Pillar Diameter | 20 | ”m | Graphitized electrode width |
| Effective Collection Distance (Leff) | 120 ± 5 | ”m | Distance between surface strips |
| Laser Wavelength | 1030 | nm | Femtosecond graphitization source |
| Laser Pulse Duration | 400 | fs | Ultra-short pulse regime |
| Charge Collection Saturation (Negative Bias) | 1.40 ± 0.02 | fC | At -80V bias |
| Electric Field Strength at Saturation | ±0.67 | V/”m | Calculated across Leff |
| Most Probable Value (MPV) | 1.75 ± 0.02 | fC | Orthogonal incidence |
| Estimated Channel Capacitance | 0.03 | pF | Contributes to low electronic noise |
| Diamond Band Gap | 5.47 | eV | Wide band gap insulator |
| Thermal Conductivity (SCD) | 22 | W/cm K | Ensures power dissipation |
Key Methodologies
Section titled âKey MethodologiesâThe fabrication of the 3D diamond detector relied on precise material preparation and advanced laser processing techniques:
- Material Preparation: A 3x3 mm2, 0.5 mm thick Single Crystal CVD diamond slab was used. The four lateral faces were lapped using standard polishing techniques to allow real-time observation of laser graphitization propagation.
- Sample Installation: The diamond was mounted on a computer-controlled XYZ translation stage for precise 3D movement relative to the laser focal point.
- Local Graphitization: A VaryDisc50 laser (1030 nm, 400 fs pulses, 200 kHz repetition rate) was tightly focused inside the diamond bulk. Pulse energy was varied between 0.2-0.8 ”J.
- Electrode Formation: The laser was moved in XYZ directions to form 212 parallel buried graphite pillars (380 ”m deep) and planar graphite back contact strips ($\approx$50 ”m wide, $\approx$10 ”m thick) on the surface.
- Device Assembly: The device was glued with silver paste onto a double-face printed circuit board (PCB).
- Interconnection: The first series of pillars were wire bonded (25 ”m Al/Si wires) directly to the surface graphite strips (powered electrode). The second series (signal electrodes) were wire bonded separately to copper strips on the PCB.
- Pre-Measurement Treatment: The device was heated at 250 °C in air for 300 s to remove adsorbed water and stabilize the I(V) characteristics.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is uniquely positioned to support the replication, optimization, and scaling of this 3D diamond detector technology. Our expertise in high-purity CVD diamond growth and advanced processing meets the stringent requirements of femtosecond laser graphitization research.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate or extend this research, high-purity, low-defect SCD is essential to maximize charge carrier lifetime and mobility.
| 6CCVD Material Recommendation | Specification Rationale |
|---|---|
| Optical Grade Single Crystal Diamond (SCD) | Required for high transparency at 1030 nm (IR laser) and minimal defects (low nitrogen concentration) to ensure long carrier lifetimes (0.321 ”s for electrons, 0.983 ”s for holes). |
| Custom SCD Substrates | We offer SCD plates up to 500 ”m thick, matching the detector volume used in the study, or thicker substrates (up to 10 mm) for high-energy particle applications requiring greater stopping power. |
Customization Potential
Section titled âCustomization PotentialâThe success of 3D graphitization relies heavily on the quality and dimensions of the starting material. 6CCVD offers critical customization capabilities:
- Large Area Scaling: While the paper used a 3x3 mm2 sample, 6CCVD can provide SCD wafers in larger sizes, enabling the fabrication of larger detector arrays for increased coverage in high-energy physics experiments. We offer PCD plates up to 125 mm in diameter.
- Precision Thickness Control: We provide SCD material with thicknesses ranging from 0.1 ”m up to 500 ”m, allowing researchers to precisely tune the active volume for specific particle energy ranges.
- Ultra-Smooth Polishing for Laser Processing: Precise focusing of the femtosecond laser deep into the bulk requires exceptional surface quality. 6CCVD guarantees SCD polishing to Ra < 1 nm, ensuring minimal scattering and optimal focal depth control for 3D graphitization.
- Advanced Metalization Services: The paper used silver paste and Al/Si wire bonding. 6CCVD offers in-house custom metalization stacks (e.g., Ti/Pt/Au, W, Cu), which provide superior adhesion, lower contact resistance, and enhanced stability compared to silver paste, crucial for long-term detector operation and high-vacuum environments.
- Custom Geometry: We offer laser cutting and shaping services to produce custom geometries and precise alignment features required for complex 3D detector assemblies.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in the electronic and structural properties of CVD diamond. We provide consultation services to optimize material selection for similar 3D radiation detection and tracking projects.
- Material Optimization: Assistance in selecting the optimal SCD grade (e.g., specific nitrogen concentration control) to balance carrier lifetime and cost for high-performance detectors.
- Interface Analysis: Support in understanding how surface preparation impacts the graphitization process and the resulting graphite/diamond interface, minimizing active defects that cause charge carrier recombination.
- Global Logistics: We ensure reliable, global delivery of sensitive diamond materials, with DDU (Delivered Duty Unpaid) as default and DDP (Delivered Duty Paid) options available.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
The charge collection performance of a diamond-graphite detector is reported. Buried graphite pillars with high aspect ratio were formed inside a single crystal synthetic diamond slab by using a femtosecond IR laser with 200 kHz of repetition rate. Grouped in two series and connected by graphite strips on the surface, eight independent 3D electrodes were used to collect the charge carriers generated by energy deposited in the detector. Collimated 90Sr,Y ïą -particles were used to test the charge collection in coincidence and self-triggering mode among pillars rows using different irradiation geometries. The charge collected by one pillar row saturates at 1.40±0.02 fC at ±0.67V/ ï m with electrons impinging orthogonally the rows demonstrating a high charge carrier collection efficiency.