Simultaneous determination of the lattice thermal conductivity and grain/grain thermal resistance in polycrystalline diamond
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2017-08-09 |
| Journal | Acta Materialia |
| Authors | J. Anaya, Tingyu Bai, Yekan Wang, C. Li, Mark S. Goorsky |
| Institutions | Georgia Institute of Technology, University of California, Los Angeles |
| Citations | 74 |
| Analysis | Full AI Review Included |
Technical Analysis of Thermal Transport in Near-Nucleation Polycrystalline Diamond
Section titled āTechnical Analysis of Thermal Transport in Near-Nucleation Polycrystalline DiamondāDocumentation based on: Anaya et al. (2017). Simultaneous determination of the lattice thermal conductivity and grain/grain thermal resistance in polycrystalline diamond. Acta Materialia.
Executive Summary
Section titled āExecutive SummaryāThis research utilizes advanced metrology (Raman thermography + picosecond TDTR) combined with real grain structure modeling (TEM + FEM) to precisely characterize the thermal performance of ultra-thin (1 Āµm) polycrystalline diamond (PCD) near the nucleation regionāa critical thermal bottleneck in GaN-on-Diamond High Electron Mobility Transistor (HEMT) applications.
- Precise Quantification: Simultaneous determination of intrinsic lattice thermal conductivity ($\kappa_{in-grain}$) and grain/grain thermal resistance ($R_{GB}$) using a sophisticated, non-adjustable parameter methodology.
- Low Lattice Conductivity: The in-grain lattice thermal conductivity ($\kappa_{in-grain}$) was found to be exceptionally low (250 W/mK), 5-8 times smaller than typical Type IIa single-crystal diamond (SCD), indicating a high density of defects (e.g., Si inclusion, dislocations).
- High Boundary Resistance: Grain boundary resistance ($R_{GB}$) was measured at 0.625 mĀ²K/GW, significantly higher (at least one order of magnitude) than predicted values for clean boundaries, confirming high defect accumulation at grain boundaries.
- Anisotropy Mechanism: The observed thermal anisotropy ($\kappa_{cross-plane}$ is higher than $\kappa_{in-plane}$) naturally emerges from the PCDās characteristic columnar grain structure combined with the high thermal resistance of these boundaries.
- Application Relevance: These findings are crucial for optimizing MPCVD growth recipes to improve thermal management, especially in the demanding near-nucleation layers used for critical electronic integration (e.g., GaN HEMT heat spreaders).
Technical Specifications
Section titled āTechnical SpecificationsāExtracted quantitative parameters derived from the MPCVD diamond film and experimental setup.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Film Thickness | ~1.0 - 1.1 | Āµm | Polycrystalline Diamond (PCD) Film |
| Substrate Thickness | 200 | Āµm | Silicon (Si) Substrate |
| Average In-Plane TC ($\kappa_{in-plane}$) | 95 Ā± 10 | W/mK | Measured experimentally |
| Average Cross-Plane TC ($\kappa_{cross-plane}$) | 175 +65/-42 | W/mK | Measured experimentally via TDTR |
| Fitted In-Grain Lattice TC ($\kappa_{in-grain}$) | 250 (150 to 400) | W/mK | Determined via TEM/FEM model |
| Fitted Grain/Grain Thermal Resistance ($R_{GB}$) | 0.625 (0.26 to 1.06) | mĀ²K/GW | Determined via TEM/FEM model |
| Diamond/Si TBR ($R_{dia-Si}$) | 13.7 +3.8/-3.5 | mĀ²K/GW | Measured via TDTR |
| Al/Diamond TBR ($R_{Al-dia}$) | 5.6 +0.6/-0.5 | mĀ²K/GW | Measured via TDTR |
| Average Grain Size (TEM) | 184 | nm | Determined via Transmission Electron Microscopy |
| Nucleation Seed Density | > 1012 | nuclei/cm2 | Detonation nanodiamond powder |
| TDTR Pump Beam Diameter (1/eĀ²) | 40 | Āµm | Measurement configuration |
| TDTR Probe Beam Diameter (1/eĀ²) | 14 | Āµm | Measurement configuration |
Key Methodologies
Section titled āKey MethodologiesāThe study employed a rigorous, multi-modal approach combining specialized MPCVD synthesis, high-resolution structural analysis, advanced thermal metrology, and sophisticated finite element modeling.
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MPCVD Growth:
- Reactor: IPLAS 5.0 KW CVD reactor.
- Substrate: 200 Āµm thick Silicon (Si).
- Seeding: Ultrasonic treatment using ethanol-based detonation nanodiamond suspension (4 nm average size, > 98% purity).
- Recipe Parameters (Constant): Substrate Temperature 750 Ā°C; Chamber Pressure 7.08 torr.
- Recipe Parameters (Varied): Microwave Power (800 W to 1400 W) and CH4:H2 ratio (0.5% to 0.7%) over the growth duration.
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Structural Characterization:
- TEM/STEM: Transmission Electron Microscopy (TEM) and Scanning Transmission Electron Microscopy (STEM) (Titan S/TEM, 200 kV) were used to extract the real 2D grain structure, grain size distribution (184 nm average), and grain orientation maps (PED).
- Structural Finding: Confirmed well-pronounced columnar grain structure with a preferred out-of-plane (110) orientation.
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Thermal Conductivity Measurements:
- In-Plane TC (Raman Thermography): Diamond membranes (460x1000 Āµm) were fabricated via Si etching. Cr (20 nm)/Au (300 nm) line heaters were patterned. Temperature profiles were measured using Raman spectroscopy assisted by 30 nm TiO2 nanoparticles as nanosensors.
- Cross-Plane TC (Picosecond TDTR): Time Domain Thermoreflectance was used. A 90 nm Al layer was deposited as a transducer on the diamond film/Si substrate stack. Measurements were performed using a Ti:sapphire laser (800 nm, 80 MHz) frequency-doubled to 400 nm, allowing simultaneous fitting of $\kappa_{cross-plane}$ and both interfacial Thermal Boundary Resistances ($R_{dia-Si}$, $R_{Al-dia}$).
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Modeling and Analysis (FEM):
- The experimentally derived real grain structure (from TEM) was imported into a COMSOL Multiphysics Finite Element Model (FEM).
- The model solved the heat equation under equivalent experimental conditions (steady-state for in-plane, transient for cross-plane) for a 2D slab containing >1000 grains and >7500 boundaries.
- This methodology allowed for the simultaneous and unique determination of $\kappa_{in-grain}$ and $R_{GB}$ without relying on arbitrary fitting parameters or bulk-like approximations.
6CCVD Solutions & Capabilities
Section titled ā6CCVD Solutions & CapabilitiesāThis research highlights the critical challenges inherent in the thermal management of diamond nucleation layers, particularly the low in-grain thermal conductivity (250 W/mK) and high grain boundary resistance ($R_{GB}$) found in thin-film PCD. 6CCVD is uniquely positioned to supply the materials required to replicate this research and the high-performance materials necessary to overcome these thermal bottlenecks in advanced applications like GaN HEMT technology.
| Research Requirement | 6CCVD Material Solution | 6CCVD Engineering Capability |
|---|---|---|
| Near-Nucleation PCD Films | Nanocrystalline/Thin-Film PCD | Supply of PCD material up to 500 Āµm thick, mirroring the properties required for advanced thin-film thermal analysis. |
| High TC Heat Spreaders | Optical Grade SCD Wafers | SCD (up to 500 Āµm) offers inherent high $\kappa$ (>2000 W/mK) and eliminates grain boundaries, solving the $R_{GB}$ and low $\kappa_{in-grain}$ problems highlighted in the paper. |
| Custom Dimensions | PCD and SCD Wafers up to 125mm | 6CCVD supplies inch-size wafers for large-area industrial integration, supporting the scale-up from experimental membranes to commercial devices. |
| Experimental Structure Fabrication | Advanced Metalization Services | The paper required Cr/Au and Al deposition. 6CCVD offers in-house custom metalization stacks, including Ti, Pt, Au, Pd, W, and Cu, tailored for heater patterning or high-performance thermal interfaces (e.g., GaN-on-Diamond bonding). |
| Surface Quality | Precision Polishing (Ra < 5 nm) | The structural analysis required high-quality surfaces. 6CCVD offers superior polishing for PCD (Ra < 5 nm) and SCD (Ra < 1 nm), crucial for reliable TDTR measurements and subsequent device integration. |
| Thermal Testing Replication | Engineering Support | Our in-house PhD team provides consultative support for material selection, growth recipe modification assistance, and thermal stack optimization for similar GaN HEMT thermal management projects. |
| Global Logistics | DDU and DDP Shipping | Global delivery services (DDU default, DDP available) ensure researchers receive materials quickly and reliably worldwide. |
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
Tech Support
Section titled āTech SupportāOriginal Source
Section titled āOriginal SourceāReferences
Section titled āReferencesā- 1967 - Continuous operation of GaAs junction lasers on diamond heat sinks at 200Ā Ā°K [Crossref]
- 2008 - Diamond heat spreader layer for high-power thin-GaN light-emitting diodes [Crossref]
- 1992 - On diamond windows for high power synchrotron x-ray beams [Crossref]
- 2014 - Enhancement of hotspot cooling with diamond heat spreader on Cu microchannel heat sink for GaN-on-Si device [Crossref]
- 2001 - Thermal conductivity measurements on CVD diamond [Crossref]
- 2016 - Effect of grain size of polycrystalline diamond on its heat spreading properties [Crossref]
- 1992 - Anisotropic thermal conductivity in chemical vapor deposition diamond [Crossref]
- 2016 - Control of the in-plane thermal conductivity of ultra-thin nanocrystalline diamond films through the grain and grain boundary properties [Crossref]
- 2016 - Thermal management of GaN-on-diamond high electron mobility transistors: effect of the nanostructure in the diamond near nucleation region
- 2007 - Comparison of GaN HEMTs on diamond and SiC substrates [Crossref]