Toward All‐Carbon Electronics Buried in Diamond
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2025-09-27 |
| Journal | Advanced Electronic Materials |
| Authors | Calum S. Henderson, Patrick S. Salter, Emil T. Jonasson, Richard B. Jackman |
| Institutions | Culham Centre for Fusion Energy, University College London |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: All-Carbon Electronics Buried in Diamond
Section titled “Technical Documentation & Analysis: All-Carbon Electronics Buried in Diamond”Executive Summary
Section titled “Executive Summary”This research demonstrates a paradigm-shifting approach to diamond electronics by fabricating robust, buried nanocarbon networks (NCNs) using femtosecond laser processing, circumventing the limitations of conventional substitutional doping.
- 3D Architecture Fabrication: Successful creation of highly confined, electrically active 3D nanocarbon networks (NCNs) fully encapsulated within ultra-pure CVD diamond substrates.
- Tunable Electrical Behavior: Electrical properties are precisely controlled by varying the laser Pulse Repetition Rate (PRR), achieving a transition from Ohmic conductive (PRR-1k) to semiconductive/ambipolar behavior (PRR-1M and PRR-1k1M).
- High-Stability Diode: The PRR-1k1M overwrite technique yields pseudo-diode characteristics with a rectification ratio exceeding 5500 and proven stability over 120 repeated voltage and temperature cycles.
- Novel Material Phase: The semiconductive behavior is attributed to the formation of a highly strained ‘diaphite’ phase, distinct from bulk sp2 or sp3 carbon, offering a tuneable bandgap.
- Proof-of-Concept FET: A functional, all-carbon Field Effect Transistor (FET) architecture was successfully fabricated entirely within the bulk diamond, demonstrating clear channel current modulation.
- Harsh Environment Potential: This methodology enables the development of robust, all-carbon electronic devices suitable for extreme environments (high temperature, high radiation) by protecting the active regions within the diamond matrix.
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the experimental results and methodology:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Material | CVD Diamond Plate | - | Electronic Grade |
| Substrate Dimensions | 4 x 4 x 0.4 | mm | Used for NCN fabrication |
| Substrate Purity (Boron) | < 1 | ppb | Ultra-low concentration |
| Substrate Purity (Nitrogen) | < 10 | ppb | Ultra-low concentration |
| PRR-1k Resistance (R) | 76 ± 8 | kΩ | Ohmic Conduction |
| PRR-1k Resistivity | 1.4 x 10-3 | Ωm | Calculated for 2 µm column diameter |
| PRR-1k Activation Energy (Ea) | 4.9 ± 0.2 | meV | Semi-metallic (Graphitic) |
| PRR-1M Resistance (R) | > 1 | TΩ | High Resistance |
| PRR-1M Activation Energy (Ea) | 0.54 ± 0.02 | eV | Semiconductive |
| PRR-1k1M Rectification Ratio (Max) | > 5500 | - | Pseudo-diode behavior |
| PRR-1k1M Activation Energy (Ea) | 0.58 ± 0.02 | eV | At 0 V DC bias |
| FET Maximum Current Density (JMax) | 52.5 | µA/µm2 | At VG = -20 V |
| FET Maximum Transconductance (gm) | 39.0(1) | nS | At VD = -20 V |
| Contact Metalization Stack | Ti/Pt/Au (20:5:200) | nm | Ohmic Contacts |
Key Methodologies
Section titled “Key Methodologies”The fabrication of the buried nanocarbon networks (NCNs) relied on precise control of femtosecond laser parameters and subsequent surface preparation.
- Substrate Acquisition: Electronic grade CVD diamond plates (4 x 4 x 0.4 mm) with ultra-low impurity levels (B < 1 ppb, N < 10 ppb) were used.
- NCN Writing (Vertical Columns):
- Laser System: Yb:KGW (Light Conversion Pharos SP-06-1000-pp).
- Wavelength/Pulse: 515 nm wavelength, 170 fs pulse duration, 120 nJ pulse energy.
- PRR Variation: Pulse Repetition Rate (PRR) was varied between 1 kHz (Ohmic, graphitic) and 1 MHz (Semiconductive).
- Writing Path: Laser spot was drawn from the seed side up to the laser side at a speed of 10 µm/s.
- Overwrite Fabrication (PRR-1k1M): Ambipolar devices were created by re-tracing existing PRR-1k channels using the 1 MHz PRR setting.
- 3D Gate Structure Writing (FET):
- Laser System: Ti:Sapphire (SpectraPhysics Solstice).
- Wavelength/Pulse: 790 nm wavelength, 250 fs pulse duration, 110 nJ pulse energy, 1 kHz PRR.
- Focusing: Used a 1.4 NA oil-immersion objective to achieve tighter axial confinement (0.3 µm x 2 µm spot size) for complex 3D gate structures.
- Surface Preparation: Substrates underwent boiling acid cleaning (H2SO4:(NH4)2SO4 at 200 °C) followed by ozone treatment (200 °C, 50 mbar) to oxygen terminate the surface and isolate the devices.
- Contact Fabrication: Ti/Pt/Au (20:5:200 nm thickness) Ohmic contacts were deposited via electron-beam evaporation and annealed at 600 °C in vacuum.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”This research confirms that the future of robust, all-carbon electronics relies on ultra-high purity, low-defect CVD diamond substrates. 6CCVD specializes in providing the foundational materials and advanced processing required to scale and optimize these buried architectures.
Applicable Materials for Replication and Advancement
Section titled “Applicable Materials for Replication and Advancement”The study utilized electronic grade SCD with B < 1 ppb and N < 10 ppb. 6CCVD offers materials that meet or exceed these stringent purity requirements, ensuring minimal background defects that could interfere with the precise femtosecond laser-writing process.
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Optical/Electronic Grade Single Crystal Diamond (SCD):
- Purity: Guaranteed ultra-low nitrogen (< 5 ppb) and boron content, essential for maintaining the intrinsic properties of the bulk diamond surrounding the NCNs.
- Surface Finish: Standard polishing achieves Ra < 1 nm, critical for optimal laser coupling and minimizing spherical aberration during deep internal writing.
- Thickness Control: SCD plates are available from 0.1 µm up to 500 µm, allowing researchers to precisely match the 400 µm thickness used in the paper or explore thinner/thicker substrates for optimized device performance.
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Polycrystalline Diamond (PCD) Substrates:
- For applications where large area coverage is paramount, 6CCVD offers high-quality PCD plates up to 125 mm diameter, suitable for scaling up NCN fabrication techniques.
Customization Potential
Section titled “Customization Potential”6CCVD’s comprehensive in-house capabilities directly support the advanced fabrication steps required to transition this research from proof-of-concept to integrated devices.
| Research Requirement | 6CCVD Capability | Technical Advantage |
|---|---|---|
| Custom Dimensions | Plates/wafers up to 125 mm (PCD) and large-area SCD. | Enables scaling from small 4x4 mm research samples to commercial wafer sizes for integrated circuit development. |
| Metalization Stack | Internal capability for custom Au, Pt, Pd, Ti, W, Cu deposition. | We can replicate the critical Ti/Pt/Au (20:5:200 nm) Ohmic contacts used in the paper, ensuring reliable, low-resistance interfaces for device testing. |
| Substrate Thickness | SCD thickness up to 500 µm (Substrates up to 10 mm). | Allows precise engineering of the vertical channel length and the intrinsic diamond separation layer (5 µm used in the FET gate) for optimized transconductance. |
| Polishing Quality | SCD polishing to Ra < 1 nm; Inch-size PCD to Ra < 5 nm. | Essential for minimizing laser scattering and ensuring the high-quality optical access required for femtosecond laser writing of buried structures. |
Engineering Support
Section titled “Engineering Support”The successful demonstration of the ambipolar ‘diaphite’ phase and the buried FET opens new avenues for robust electronics in extreme environments.
- Expert Consultation: 6CCVD’s in-house PhD team specializes in CVD growth, material characterization, and defect engineering. We offer direct engineering support for projects involving laser-written NCNs, ambipolar diamond devices, and high-power/high-radiation applications.
- Material Optimization: We assist researchers in selecting the optimal SCD grade (e.g., specific nitrogen/boron levels and crystal orientation) to fine-tune the resulting electrical properties of the laser-modified carbon phases (graphite, diaphite) for specific device goals.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract This work investigates the use of femtosecond laser processing to fabricate various nanocarbon structures with distinct electrical behaviors within diamond substrates. Conventional approaches for achieving diamond doping have significant disadvantages, including challenging growth profiles, limited environmental stability, and sub‐optimal psuedo‐vertical structures. Here, it is demonstrated that laser‐written nanocarbon networks (NCNs) directly alleviate these issues, demonstrating the highly repeatable fabrication of robust and precise electrical architectures buried in diamond with proven stability over repeated temperature and voltage cycling. By varying the laser pulse repetition rate (PRR), a transition from Ohmic conductive to semiconductive/ambipolar behavior is achieved in the modified diamond. Furthermore, a proof‐of‐concept, all‐carbon transistor architecture buried within the bulk diamond is presented, showcasing the potential for integrated device fabrication using the laser‐writing process.
Tech Support
Section titled “Tech Support”Original Source
Section titled “Original Source”References
Section titled “References”- 2007 - Physica Status Solidi (A) Applications and Materials Science
- 2018 - Journal of Instrumentation