Study on the Preparation of Diamond Film Substrates on AlN Ceramic and Their Performance in LED Packaging

At a Glance

Metadata	Details
Publication Date	2025-09-08
Journal	Micromachines
Authors	Shasha Wei, Yingrui Sui, Yunlong Shi, Junrong Chen, Tungalag Dong
Institutions	Jimei University
Analysis	Full AI Review Included

Executive Summary

This study successfully developed high-quality diamond thin films on Aluminum Nitride (AlN) ceramic substrates using Microwave Plasma Chemical Vapor Deposition (MPCVD) to significantly enhance heat dissipation for high-power LED packaging.

Core Achievement: The AlN ceramic-diamond composite substrate achieved a total thermal resistance (R_th) of 3.9 K/W (chip-to-substrate) at 3 W power, representing a 50% reduction compared to the bare AlN substrate (7.8 K/W).
Thermal Performance: Under a 1.2 A driving current, the LED junction temperature was reduced by 29.4% compared to the bare AlN substrate (from 99.4 °C to 70.0 °C).
Optimal Recipe: High-quality, dense diamond films were achieved using optimized MPCVD parameters: 4% methane concentration, 900 °C deposition temperature, and 0.5 sccm oxygen flow rate.
Crystallinity: The optimal film exhibited high crystallinity, low impurity content, and a strong (111) preferential growth orientation, confirmed by XRD and Raman spectroscopy (FWHM of 7.3 cm^-1).
Role of Oxygen: Introducing 0.5 sccm oxygen slightly increased the deposition rate (4.1 µm/h to 4.3 µm/h) while effectively suppressing non-diamond carbon phases, improving overall film quality.

Technical Specifications

Parameter	Value	Unit	Context
Substrate Material	AlN Ceramic	N/A	Ø20 mm x 0.8 mm
Diamond Film Thickness	531	µm	After 150 h growth
Optimal Deposition Temperature	900	°C	MPCVD process
Optimal Methane Concentration	4	%	Of total gas flow
Optimal Oxygen Flow Rate	0.5	sccm	Enhances quality, suppresses sp² carbon
Microwave Power	4600	W	MPCVD source frequency 2.45 GHz
Deposition Pressure	155	Torr	MPCVD chamber pressure
Optimal Growth Rate (4% CH₄, 900 °C)	4.6	µm/h	Highest quality/rate balance
Diamond Raman Peak FWHM (Optimal)	7.3	cm^-1	Indicates high crystallinity
LED Test Power	3	W	1 A current, 3 V voltage
AlN/Diamond R_th (Chip-to-Substrate)	3.9	K/W	Lowest thermal resistance achieved
Bare AlN R_th (Chip-to-Substrate)	7.8	K/W	Control group performance
Traditional Al R_th (Chip-to-Substrate)	14.1	K/W	Control group performance (highest R_th due to resin layer)
AlN/Diamond T_junction (1.2 A)	70.0	°C	Stabilized junction temperature
Bare AlN T_junction (1.2 A)	99.4	°C	Stabilized junction temperature
T_junction Reduction (vs AlN, 1.2 A)	29.4	%	Improvement in heat dissipation

Key Methodologies

The study focused on optimizing MPCVD parameters to achieve high-quality diamond films on AlN ceramic substrates, followed by thermal performance testing in packaged LED devices.

1. Substrate Preparation and Seeding

Cleaning: AlN substrates (Ø20 mm x 0.8 mm) were ultrasonically cleaned sequentially in hydrofluoric acid (5 min), acetone, anhydrous ethanol, and deionized water.
Seeding: Substrates were immersed in a W0.25 diamond powder suspension and ultrasonically treated for 30 min to promote nucleation.

2. MPCVD Diamond Film Growth Optimization

Base Parameters: Hydrogen flow rate was fixed at 500 sccm. Microwave power and pressure were adjusted to control deposition temperature.
Methane Concentration Study: Investigated 2%, 3%, 4%, and 5% CH₄ concentrations (at 900 °C, 0.5 sccm O₂).
- Result: 4% CH₄ yielded the best balance of high growth rate (4.1 µm/h), uniform grain size (10 µm), and high crystallinity (low non-diamond carbon).
Deposition Temperature Study: Investigated 700 °C, 800 °C, 900 °C, and 950 °C (at 4% CH₄, 0.5 sccm O₂).
- Result: 900 °C provided the strongest preferential (111) orientation, clear grain boundaries, and optimal quality; 950 °C led to increased graphitization and degraded quality.
Oxygen Flow Rate Study: Investigated 0 sccm, 0.5 sccm, 1.0 sccm, and 1.5 sccm (at 900 °C, 4% CH₄).
- Result: 0.5 sccm O₂ was optimal, promoting CH₄ dissociation via OH radicals, slightly increasing growth rate, and significantly suppressing non-diamond carbon formation. Higher O₂ rates (1.0-1.5 sccm) caused excessive etching and reduced deposition rate.

3. Composite Substrate Fabrication and Packaging

Metallization: The diamond film surface was metallized using photolithography and magnetron sputtering to form a conductive layer.
Control Groups: Traditional aluminum substrates and bare AlN ceramic substrates (both metallized) were used for comparison.
LED Packaging: 3 W cool white LED lamp beads were packaged onto the three substrate types using the same welding process.

4. Thermal Performance Testing

Measurements: LED junction temperature (T_junction) was measured under varying electric currents (0.2 A to 1.2 A) using infrared imaging.
Thermal Resistance Calculation: R_th was calculated using the temperature difference between the LED chip (T_junction) and the substrate bottom surface, referenced to 80% of the input electrical power (P = 3 W).

Commercial Applications

The development of high-thermal-conductivity AlN/diamond composite substrates is critical for industries requiring advanced thermal management solutions in power electronics.

High-Power LED Lighting: Essential for next-generation automotive headlights, high-density display backlighting, and industrial lighting, where heat accumulation limits lifespan and luminous efficiency.
Power Electronics Modules: Used as substrates for high-frequency, high-power devices (e.g., IGBTs, MOSFETs) in electric vehicles, renewable energy inverters, and industrial motor drives.
RF and Microwave Devices: Substrates for Gallium Nitride (GaN) and Silicon Carbide (SiC) devices used in 5G/6G infrastructure and radar systems, where localized heat flux is extremely high.
Advanced Thermal Management: Applicable in any system requiring superior heat spreading and dissipation, leveraging diamond’s thermal conductivity (>2000 W/mK) to overcome the limitations of traditional ceramics (AlN: 180-230 W/mK).
CVD Diamond Substrates: This technology directly supports the manufacturing of high-quality, thick polycrystalline diamond films for use as heat sinks and thermal spreaders in demanding electronic applications.

View Original Abstract

Aluminum nitride (AlN) ceramic materials have relatively low thermal conductivity and poor heat dissipation performance, and are increasingly unsuitable for high-power LED packaging. In this study, diamond films were deposited on AlN ceramic substrates by microwave plasma chemical vapor deposition (MPCVD). The effects of different process parameters on the crystal quality, surface morphology and crystal orientation of diamond films were studied, and the high thermal conductivity of diamond was used to enhance the heat dissipation ability of AlN ceramic substrates. Finally, the junction temperature and thermal resistance of LED devices packaged on AlN ceramic-diamond composite substrate, AlN ceramic substrate and aluminum substrate were tested. The experimental results show that compared with the traditional aluminum and AlN ceramic substrates, AlN ceramic-diamond composite substrates show excellent heat dissipation performance, especially under high-power conditions.

Tech Support

Original Source

DOI: https://doi.org/10.3390/mi16091029

References

2024 - Synthesis and characterization of a high-strength alumina ceramic reinforced by AlN-Al2O3 coating [Crossref]
2024 - Limiting the lattice oxygen impurities to obtain high thermal conductivity aluminum nitride ceramics [Crossref]
2024 - Effects of grain boundary phase distributions on mechanical characteristics of the high thermal conductivity AlN ceramics [Crossref]
2024 - Effect of AlN content on microstructure and properties of SiAlON ceramics prepared via vat photopolymerization [Crossref]
2022 - Monometallic and bimetallic SiC(O) ceramic with Ni, Co and/or Fe nanoparticles for catalytic applications [Crossref]
2022 - Addition Effects of MgO on Structure and Physical Properties in Bi-2212 Ceramics [Crossref]