Direct Deposition of CVD Diamond Layers on Top of GaN Membranes

At a Glance

Metadata	Details
Publication Date	2020-12-30
Authors	Tibor Izsák, G. Vanko, Milan Držík, Stephan Kasemann, Johann Zehetner
Institutions	Slovak Academy of Sciences, International Laser Center
Citations	2
Analysis	Full AI Review Included

Technical Documentation & Analysis: CVD Diamond on GaN MEMS

Executive Summary

This documentation analyzes the research on the direct deposition of CVD diamond on Gallium Nitride (GaN) membranes, focusing on the technological challenges and proposing specific material solutions available through 6CCVD.

Core Application: Addressing critical thermal management and structural integrity issues in GaN-based Microelectromechanical Systems (MEMS) and high-temperature electronics.
Performance Achievement: Diamond coating dramatically improves structural robustness, enabling GaN membranes to withstand 73 times higher pressure (2.2 MPa) compared to pure GaN membranes (30 kPa).
Key Technological Challenge: Significant intrinsic stress and membrane wrinkling are induced by the 4x mismatch in the Thermal Expansion Coefficient (TEC) between GaN and diamond at room temperature (RT).
Stress Quantification: White light interferometry revealed substantial membrane deflection, reaching approximately 10 µm at 300 °C, necessitating precise control over the deposition temperature (~480 °C).
Material Requirement: The application requires ultra-thin (as low as 1 µm), high-quality CVD diamond films (PCD or SCD) with carefully controlled intrinsic stress profiles.
6CCVD Value Proposition: 6CCVD provides custom, stress-engineered MPCVD diamond films (0.1 µm to 500 µm) and advanced metalization services required to replicate and scale this high-performance GaN/Diamond integration.

Technical Specifications

The following hard data points were extracted from the analysis of the GaN/Diamond MEMS structure:

Parameter	Value	Unit	Context
GaN Membrane Diameter	1	mm	Substrate dimension used in the study
Required Diamond Thickness	1	µm	Minimum thickness required to double the maximum load capacity (FEM simulation)
Max Pressure Withstood (Diamond/GaN)	2.2	MPa	Performance of diamond-coated MEMS
Max Pressure Withstood (Pure GaN)	30	kPa	Baseline performance of pure GaN MEMS
TEC Match Temperature	>500	°C	Temperature where TEC_Diamond ≈ TEC_GaN
TEC Value (Match Point)	4-5 x 10^-6	K^-1	Approximate TEC of both materials above 500 °C
TEC Mismatch (RT)	4x higher	N/A	GaN TEC is 4x higher than Diamond TEC at Room Temperature
Max Membrane Deflection	~10	µm	Measured deflection of pure GaN membrane at 300 °C
Deposition Method	MPCVD	N/A	Ellipsoidal cavity reactor used for growth

Key Methodologies

The experiment focused on front-side diamond deposition on pre-fabricated GaN membranes using Microwave Plasma Chemical Vapor Deposition (MPCVD).

Substrate Preparation: Fabrication of Gallium Nitride (GaN) membranes (1 mm diameter) supported by a Silicon (Si) substrate.
Deposition Technique: Diamond growth performed using an ellipsoidal cavity MPCVD reactor.
Growth Strategy: Focus on front-side deposition (diamond grown directly on top of the GaN membrane), contrasting with previous back-side deposition studies.
Temperature Management: Deposition conducted at elevated temperatures (implied T_dep ~480 °C) to minimize the TEC mismatch during the growth phase.
Nucleation Method: Previous related work highlighted the importance of polymer-based nucleation methods for successful diamond growth on GaN.
Stress and Deflection Analysis: Membrane bending and intrinsic stress were quantified using the bulging method combined with white light interferometry.
Observed Issues: The resulting films exhibited technological issues including wrinkling, thicker diamond layers at the membrane center, and poor quality diamond outside the membrane area, all attributed to TEC mismatch and temperature gradients.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced diamond materials and engineering support necessary to overcome the intrinsic stress and thermal management challenges identified in this research, enabling the successful commercialization of diamond-coated GaN MEMS.

Applicable Materials

To replicate and extend this research, 6CCVD recommends materials optimized for high thermal conductivity and precise thickness control:

Material Recommendation	6CCVD Specification	Application Context
Optical Grade Polycrystalline Diamond (PCD)	High purity, high thermal conductivity (up to 2000 W/mK).	Ideal for thermal spreading layers on GaN devices to suppress self-heating and improve device lifetime.
High Purity Single Crystal Diamond (SCD)	Available in electronic or optical grades.	Recommended if ultra-low defect density or specific electronic properties are required for the GaN interface.
Boron-Doped Diamond (BDD)	Custom doping levels available.	Potential for integrated electrochemical sensors or conductive heating elements within the MEMS structure.

Customization Potential

The success of GaN/Diamond integration hinges on precise material dimensions and interface engineering. 6CCVD’s capabilities directly address the critical requirements of this MEMS application:

Thickness Control: The study requires a critical 1 µm diamond layer. 6CCVD offers SCD and PCD films with thickness precision ranging from 0.1 µm up to 500 µm (wafers) and substrates up to 10 mm.
Scaling and Dimensions: While the paper used 1 mm membranes, 6CCVD can supply custom plates and wafers up to 125 mm (PCD), facilitating seamless transition from R&D prototyping to high-volume manufacturing.
Intrinsic Stress Management: 6CCVD utilizes advanced MPCVD recipes to tailor the intrinsic stress (tensile or compressive) of the diamond film during growth, directly mitigating the TEC mismatch and minimizing the wrinkling and deflection observed in the study.
Interface Engineering (Metalization): Successful integration often requires robust adhesion layers or electrical contacts. 6CCVD offers in-house metalization services, including deposition of Ti, W, Pt, Pd, Au, and Cu stacks, crucial for creating ohmic contacts or robust bonding layers on GaN.
Surface Finish: For optimal interface quality and minimal scattering, 6CCVD provides ultra-smooth polishing: Ra < 1 nm (SCD) and Ra < 5 nm (Inch-size PCD).

Engineering Support

The technological issues related to temperature gradients and thermal expansion mismatch are complex material science problems. 6CCVD’s in-house PhD team specializes in optimizing CVD diamond growth parameters for heterogeneous integration.

Consultation Focus: We provide expert assistance in material selection, nucleation layer optimization (critical for GaN), and recipe tuning to achieve the desired stress state for Diamond-Coated GaN MEMS projects.
Global Logistics: We ensure reliable, global shipping (DDU default, DDP available) of sensitive, high-value diamond materials directly to your research facility.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

We present technological issues in the deposition of diamond films on gallium nitride (GaN) membranes. Many wrinkles and thicker diamond layers were observed at the membrane center and poor quality diamond outside the membrane area. The deflection of the membranes was analyzed by a bulging method using white light interferometry. The membrane bending is discussed in the terms of temperature gradient and mismatch of thermal expansion coefficients of materials.

Tech Support

Original Source

DOI: https://doi.org/10.3390/proceedings2020056035

References

2015 - Diamond-coated three-dimensional GaN micromembranes: Effect of nucleation and deposition techniques [Crossref]