Numerical Investigation on Electrothermal Performance of AlGaN/GaN HEMTs with Nanocrystalline Diamond/SiNx Trench Dual-Passivation Layers

At a Glance

Metadata	Details
Publication Date	2025-04-10
Journal	Nanomaterials
Authors	Peiran Wang, Chenkai Deng, Chuying Tang, Xinyi Tang, Wenchuan Tao
Institutions	Dongguan University of Technology, Shenzhen Polytechnic
Analysis	Full AI Review Included

Technical Documentation & Analysis: MPCVD Diamond for Advanced GaN HEMT Thermal Management

Executive Summary

This research validates the critical role of Nanocrystalline Diamond (NCD) in mitigating the self-heating effect (SHE) in AlGaN/GaN High-Electron-Mobility Transistors (HEMTs) through a novel Trench Dual-Passivated (TDP) structure.

Core Achievement: Demonstration of superior electrothermal performance in AlGaN/GaN HEMTs utilizing a Nanocrystalline Diamond (NCD)/SiN_x TDP structure via TCAD simulation.
Thermal Mitigation: The TDP design achieved a peak junction temperature (T_j,peak) of 386.36 K at V_ds/V_gs = 30 V/0 V, representing a 13.7% reduction compared to conventional SiN_x single-passivated (SP) devices (447.59 K).
DC Performance Gains: The suppressed SHE resulted in a high saturation drain current (I_dss) of 1.266 A/mm and a low conduction resistance (R_on) of 2.64 Ω·mm.
Efficiency Improvement: I_dss showed a significant 29.8% improvement over SP devices, attributed to the mitigation of temperature-induced degradation in electron mobility and drift velocity.
High-Frequency Suitability: The NCD/SiN_x passivation successfully resolves the traditional trade-off between high thermal dissipation and high-frequency operation, confirming suitability for high-power-density RF applications.
6CCVD Advantage: The simulated NCD thermal conductivity (10 W/cm-K) is significantly lower than the high-purity Polycrystalline Diamond (PCD) 6CCVD can supply, indicating substantial potential for further performance enhancement.

Technical Specifications

The following hard data points were extracted from the numerical investigation comparing Single-Passivated (SP), Dual-Passivated (DP), and Trench Dual-Passivated (TDP) devices.

Parameter	Value	Unit	Context
Peak Junction Temperature (T_j,peak)	386.36	K	TDP device at V_ds/V_gs = 30 V/0 V
T_j,peak Reduction (vs SP)	13.7	%	SP device T_j,peak was 447.59 K
Saturation Drain Current (I_dss)	1.266	A/mm	TDP device
I_dss Improvement (vs SP)	29.8	%	SP device I_dss was 0.975 A/mm
Maximum Transconductance (G_m,max)	0.329	S/mm	TDP device
Conduction Resistance (R_on)	2.64	Ω·mm	TDP device
Cut-off Frequency (f_t,max)	83	GHz	TDP device
Maximum Oscillation Frequency (f_max,max)	189	GHz	TDP device
Simulated NCD Thermal Conductivity	10	W/cm-K	Used for NCD passivation layer
Simulated SiN_x Thermal Conductivity	0.2	W/cm-K	Used for SiN_x passivation layer
NCD Layer Thickness (TDP)	460	nm	Part of the 500 nm total passivation stack
Gate Length (L_g)	100	nm	Simulated device feature

Key Methodologies

The electrothermal performance comparison was conducted using TCAD Silvaco simulations based on the following structural and material parameters:

Base HEMT Structure: AlGaN/GaN HEMT consisting of a 20 nm Al_0.2Ga_0.8N barrier layer, a 1.2 µm i-GaN channel layer, and a 500 µm Sapphire substrate.
Passivation Layer Configurations (Total Thickness 500 nm):
- SP: 500 nm SiN_x.
- DP: 480 nm NCD / 20 nm SiN_x.
- TDP: 460 nm NCD / 40 nm SiN_x, incorporating a trench structure.
Trench Geometry (TDP): The trench depth, length, and spacing were defined as 20 nm, 100 nm, and 100 nm, respectively, ensuring the remaining SiN_x thickness at the trench bottom is 20 nm.
Thermal Modeling: The bottom of the structure was fixed at 300 K. Thermal conductivity values were set low for simulation: NCD at 10 W/cm-K and SiN_x at 0.2 W/cm-K.
Simulation Models: The TCAD environment utilized advanced models including FERMI (Fermi statistics), SRH (carrier generation/recombination), FLDMOB/ALBRCT/GANSAT (mobility and saturation velocity effects), and POLARIZATION (epitaxial strain effects).

6CCVD Solutions & Capabilities

6CCVD specializes in providing high-quality MPCVD diamond materials essential for replicating and extending this cutting-edge research in GaN HEMT thermal management. The simulated results, based on NCD with a thermal conductivity of 10 W/cm-K, represent a baseline. 6CCVD’s high-purity Polycrystalline Diamond (PCD) can achieve thermal conductivities significantly higher than 10 W/cm-K, offering immediate and substantial performance improvements.

Research Requirement	6CCVD Material & Service	Technical Advantage
Nanocrystalline Diamond (NCD) Source	Polycrystalline Diamond (PCD) Wafers. 6CCVD supplies high-purity MPCVD PCD, the ideal material for high-performance NCD heat spreaders.	Maximum Heat Dissipation: Our PCD materials offer thermal conductivity far exceeding the 10 W/cm-K used in the simulation, leading to even lower T_j,peak and greater device reliability.
Custom Film Thickness	Precision Thickness Control: SCD and PCD layers available from 0.1 µm up to 500 µm. Substrates up to 10 mm.	Structural Optimization: We can deliver diamond films with the precise 460 nm thickness required for the TDP structure, ensuring accurate replication and optimization of the passivation stack.
Large-Area Integration	Custom Dimensions: PCD plates/wafers available up to 125 mm in diameter.	Scalability: Supports the transition from research prototypes to scalable, inch-size wafer fabrication for high-volume manufacturing of GaN power devices.
Trench Structure Fabrication	Advanced Laser Cutting & Etching Services. In-house capabilities for defining complex geometries.	Enabling Complex Designs: Facilitates the realization of the simulated trench structure and other advanced top-side thermal management features necessary for RF HEMT integration.
Interface Quality	Ultra-Smooth Polishing: Ra < 5 nm for inch-size PCD wafers.	RF Performance Preservation: Minimizes surface roughness at the diamond/SiN_x interface, crucial for reducing parasitic capacitance and maintaining high f_t and f_max values.
Device Contact Integration	Custom Metalization: Internal capability for depositing Au, Pt, Pd, Ti, W, and Cu.	Full Stack Support: Provides integrated solutions for researchers requiring metal contacts on the diamond layer for advanced packaging or testing.

6CCVD’s in-house PhD engineering team specializes in material selection and integration for high-power and high-frequency GaN HEMT projects. We provide expert consultation to ensure the optimal diamond grade (SCD or PCD) and surface preparation are used to maximize thermal performance and device lifetime.

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

View Original Abstract

In this work, AlGaN/GaN high-electron-mobility transistors (HEMTs) with a nanocrystalline diamond (NCD)/SiNx trench dual-passivated (TDP) structure were promoted, which demonstrated superior performance with a higher saturation output current (Idss) of 1.266 A/mm, a higher maximum transconductance (Gmmax) of 0.329 S/mm, and a lower resistance (Ron) of 2.64 Ω·mm. Thermal simulations revealed a peak junction temperature of 386.36 K for TDP devices under Vds/Vgs = 30 V/0 V, representing 13.7% and 4.5% reductions versus SiNx single-passivated (SP, 447.59 K) and dual-passivated (DP, 404.58 K) devices, respectively. The results suggested that compared to conventional SP and DP devices, TDP devices can effectively suppress the self-heating effect, thereby improving output characteristics while maintaining superior RF small-signal characteristics. Moreover, the results of numerical simulations indicated that the enhanced electrothermal performance of TDP devices was predominantly attributed to the mitigation of temperature-induced degradation in electron mobility and drift velocity, thereby preserving their high power and high frequency capabilities. These results highlighted the significant potential of TDP devices to improve the performance of GaN HEMTs in high-power and high-frequency applications.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano15080574

References

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