Improved Thermal Resistance and Electrical Conductivity of a Boron-Doped DLC Film Using RF-PECVD
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-07-07 |
| Journal | Frontiers in Materials |
| Authors | Wanrong Li, Xing Tan, Yeong Min Park, Dong Chul Shin, Dae Weon Kim |
| Institutions | Silla University, Pusan National University |
| Citations | 10 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research successfully developed boron-doped Diamond-like Carbon (B-DLC) films using Radio-Frequency Plasma-Enhanced Chemical Vapor Deposition (RF-PECVD) to significantly enhance thermal resistance and electrical conductivity, addressing limitations of conventional DLC.
- Core Achievement: Boron doping (using B2H6/CH4) dramatically improved the thermal stability of DLC films and enabled high electrical conductivity.
- Thermal Resistance: The thermal decomposition temperature (TGA onset) increased from approximately 300 °C (undoped DLC) to 460 °C for films doped with 30 vol% B2H6/CH4.
- Structural Integrity: 30 vol% B-DLC films remained visually intact (no delamination or cracking via SEM) after heat treatment up to 400 °C, whereas undoped DLC delaminated at 350 °C.
- Electrical Performance: Increasing boron concentration improved electrical conductivity. The 40 vol% B2H6/CH4 film exhibited the lowest sheet resistance, confirming the formation of a p-type semiconducting material.
- Structural Mechanism: Boron doping promotes the formation of sp2 (graphite-like) bonds, which reduces internal compressive stress and facilitates electron tunneling, leading to higher conductivity.
- Trade-off: The improved thermal and electrical properties came at the cost of reduced Vickers hardness (from 1572 HV for undoped to ~1176 HV for doped films).
- Value Proposition: The resulting B-DLC films offer an optimal combination of thermal stability, mechanical robustness, and charge dissipation capability, making them highly suitable for demanding applications.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Material | Si (100) | N/A | Wafers used for deposition |
| Deposition Method | RF-PECVD | N/A | Radio-Frequency Plasma-Enhanced CVD |
| RF Power (Deposition) | 300 | W | Constant power used for all samples |
| Working Pressure | 2.0 x 10-2 | Torr | Pressure during deposition and pretreatment |
| Optimal B2H6/CH4 Ratio (Thermal) | 30 | vol% | Highest TGA stability (460 °C) |
| Optimal B2H6/CH4 Ratio (Electrical) | 40 | vol% | Lowest electrical resistivity |
| Undoped DLC Hardness (Max) | 1572 | HV | Vickers Hardness |
| Doped DLC Hardness (Average) | 1176.3 | HV | Average Vickers Hardness |
| Undoped DLC Thermal Stability (TGA) | ~300 | °C | Onset of weight loss/decomposition |
| Optimal B-DLC Thermal Stability (TGA) | 460 | °C | Onset of weight loss (30 vol% B2H6) |
| B-DLC Film Growth Rate (40 vol% B2H6) | 897.6 | nm/h | Higher than undoped film (799.6 nm/h) |
| Heat Treatment Temperatures | 300, 350, 400 | °C | Used for delamination testing (15 min hold) |
| Undoped DLC Delamination | 350 | °C | Failure point observed via SEM |
| 30 vol% B-DLC Integrity | 400 | °C | Remained intact (highest temperature tested) |
| Boron XPS Peak (B1s) Range | 196.38-199.68 | eV | Confirms boron incorporation |
| Undoped DLC ID/IG Ratio | 0.444 | N/A | Raman analysis (low sp2 content) |
| Doped DLC ID/IG Ratio (Max) | 0.522 | N/A | Raman analysis (30 vol% B2H6, higher sp2 content) |
Key Methodologies
Section titled âKey MethodologiesâThe B-DLC films were fabricated using a controlled RF-PECVD process, followed by rigorous thermal and structural characterization.
- Substrate Cleaning: Si (110) substrates (20 mm x 20 mm) were ultrasonically cleaned sequentially using acetone (C3H6O), ethanol (C2H5OH), and deionized water for 30 minutes each.
- Pretreatment (Plasma Etching): Substrates were pretreated in the chamber using Argon (Ar) plasma to enhance adhesion and ensure thermal stability during subsequent deposition.
- Parameters: 30 sccm Ar flow, 300 W RF power, 30 minutes.
- DLC Deposition: Films were deposited using a mixture of methane (CH4) and diborane (B2H6).
- Doping Ratios: B2H6/CH4 ratios were varied at 0, 10, 20, 30, and 40 vol%.
- Process Parameters: 300 W RF power, 1 hour duration, 2.0 x 10-2 Torr pressure.
- Thermal Resistance Testing (Muffle Furnace): Samples were subjected to heat treatment to evaluate delamination and structural integrity.
- Conditions: Heating rate of 10 °C/min, 15 minutes holding time at target temperatures (300 °C, 350 °C, 400 °C).
- Thermal Gravimetric Analysis (TGA): Used to determine the precise thermal decomposition temperature (onset of weight loss) for undoped and 30 vol% B-DLC films.
- Characterization:
- Structural/Chemical: X-ray Photoelectron Spectroscopy (XPS) confirmed boron incorporation (B1s peak) and Scanning Electron Microscopy (SEM) monitored morphology and delamination post-heating.
- Bonding Analysis: Raman Spectroscopy measured the shift and intensity ratio (ID/IG) of the D and G peaks to quantify the increase in sp2 bonding fraction.
- Mechanical/Electrical: Nano-indenter measured Vickers hardness (HV), and the four-point probe method determined electrical conductivity (sheet resistance).
Commercial Applications
Section titled âCommercial ApplicationsâThe improved thermal resistance and tunable electrical conductivity of B-DLC films make them critical for applications requiring stability under extreme conditions and effective charge management.
- Outer Space Technology:
- Charge Dissipation: High electrical conductivity is essential for dissipating charging electrons in plasma environments on orbit, protecting sensitive components.
- Actuator Components: Used for long-term missions involving solar cell orientation, antenna azimuth, and propulsion gimbal adjustments, where high thermal and tribological stability is required.
- High-Temperature Tribological Coatings: Used in engines, drills, or industrial machinery where conventional DLC fails due to graphitization and performance degradation above 300 °C.
- Semiconductor Devices: The ability to create p-type semiconducting DLC films via boron doping opens avenues for use in thin-film transistors, photovoltaic cells, and advanced microelectronics.
- High-Stress Environment Coatings: Applications requiring low internal stress (a benefit of boron doping) combined with improved thermal stability, such as protective layers in harsh chemical or thermal processing equipment.
View Original Abstract
Diamond-like carbon (DLC) film doped with boron has unique properties and displays higher thermal resistance, lower internal stress, and better electrical conductivity than un-doped DLC film; this makes it is suitable for various applications, especially in outer space. Radio-frequency plasma-enhanced chemical vacuum deposition of boron-doped DLC film was performed to determine the optimal percentage of boron for improving thermal resistance. Additional heat treatment and 40 vol% B2H6/CH4 yielded the best electrical conductivity. X-ray photoelectron spectroscopy, thermal gravimetric analysis, Raman spectroscopy, and the four-point probe method were utilized to analyze the properties of boron-doped DLC film. The boron-doped DLC film displayed outstanding performance in terms of thermal resistance and electrical conductivity.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2007 - Adhesive B-doped DLC films on biomedical alloys used for bone fixation [Crossref]
- 2018 - Pulsed DC plasma CVD system for the deposition of DLC films [Crossref]
- 2007 - Tribology of Diamond-Like Carbon Films: Fundamentals and Applications
- 2002 - Is stress necessary to stabilise sp3 bonding in diamond-like carbon? [Crossref]
- 2002 - Variable range hopping revisited: the case of an exponential distribution of localized states [Crossref]
- 2000 - Property change of diamond-like carbon thin films due to ion implantation. Nuclear Instruments Methods Phys. Res. Section B: Beam Interact [Crossref]
- 1999 - Diamond-like carbonâpresent status [Crossref]
- 2001 - Boron-doped diamond-like amorphous carbon as photovoltaic films in solar cell [Crossref]
- **** - Strange hardness characteristic of hydrogenated diamond-like carbon thin film by plasma enhanced chemical vapor deposition process [Crossref]
- **** - Role of base pressure on the structural and nano-mechanical properties of metal/diamond-like carbon bilayers [Crossref]