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	Institute of Microelectronics, Peking University
Analysis	Full AI Review Included

Executive Summary

This numerical investigation promotes a novel Nanocrystalline Diamond (NCD)/SiN_x Trench Dual-Passivated (TDP) structure for AlGaN/GaN High-Electron-Mobility Transistors (HEMTs), demonstrating superior electrothermal performance for high-power applications.

Self-Heating Suppression: The TDP structure achieved the lowest 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).
Thermal Mechanism: The trench design, coupled with high thermal conductivity NCD (10 W/cm-K), enhances horizontal heat dissipation by increasing the thermal interface contact area, effectively reducing thermal resistance.
DC Performance Gain: TDP devices showed a 29.8% improvement in saturation drain current (I_dss = 1.266 A/mm) and the lowest conduction resistance (R_on = 2.64 Ω·mm) compared to SP devices.
Mobility Preservation: The enhanced thermal management mitigates temperature-induced degradation in electron mobility and drift velocity, which directly translates to improved DC characteristics.
RF Capability: The TDP structure maintains high RF performance, achieving a maximum transconductance (G_m,max) of 0.329 S/mm and competitive frequency metrics (f_T,max = 83 GHz, f_max,max = 189 GHz).
Trade-off Resolution: This design successfully resolves the traditional trade-off between maximizing thermal dissipation and maintaining high-frequency operation in GaN HEMTs.

Technical Specifications

Parameter	Value	Unit	Context
Peak Junction Temperature (TDP)	386.36	K	V_ds/V_gs = 30 V/0 V bias
T_j,peak Reduction (TDP vs SP)	13.7	%	Reduction from 447.59 K (SP device)
Saturation Drain Current (I_dss)	1.266	A/mm	TDP device performance
Conduction Resistance (R_on)	2.64	Ω·mm	TDP device performance
Maximum Transconductance (G_m,max)	0.329	S/mm	TDP device performance
Cut-off Frequency (f_T,max)	83	GHz	TDP device performance
Maximum Oscillation Frequency (f_max,max)	189	GHz	TDP device performance
NCD Thermal Conductivity	10	W/cm-K	Heat spreading layer
SiN_x Thermal Conductivity	0.2	W/cm-K	Passivation layer
AlGaN Barrier Composition	Al_0.2Ga_0.8N	-	20 nm thickness
Trench Depth (D_trench)	20	nm	TDP structure geometry
Trench Length/Spacing	100 / 100	nm	TDP structure geometry
Substrate Material	Sapphire	-	Fixed temperature boundary (300 K)

Key Methodologies

The study utilized the TCAD Silvaco simulation tool for a systematic electrothermal comparison of three HEMT passivation structures: SP (Single-Passivated), DP (Dual-Passivated), and TDP (Trench Dual-Passivated).

Device Configuration: All simulated HEMTs featured a 20 nm Al_0.2Ga_0.8N barrier layer, a 1.2 µm i-GaN channel layer, and a 500 µm sapphire substrate. Critical dimensions included a gate length (L_g) of 100 nm, L_gs of 1.6 µm, and L_gd of 2.4 µm.
Passivation Layer Design: The total passivation thickness was fixed at 500 nm for all devices to ensure a fair comparison of thermal management effectiveness.
- SP: 500 nm SiN_x.
- DP: 480 nm NCD / 20 nm SiN_x.
- TDP: 460 nm NCD / 40 nm SiN_x, incorporating trenches (20 nm depth, 100 nm length, 100 nm spacing) to maximize NCD contact area near the hotspot.
Material Parameters: High thermal conductivity NCD (10 W/cm-K) was used as the top-side heat spreader, while SiN_x (0.2 W/cm-K) served as the barrier protection layer to prevent plasma damage during NCD deposition.
Thermal Boundary Conditions: The bottom of the 500 µm sapphire substrate was set to a fixed temperature of 300 K. Thermal conductivity values for AlGaN, GaN, and Sapphire were set at 0.13, 1.8, and 0.35 W/cm-K, respectively.
Physical Models: The simulation incorporated advanced models necessary for GaN HEMT analysis, including the POLARIZATION model (spontaneous and piezoelectric polarization), CALC.STRAIN (epitaxial strain), FERMI statistics, and the GANSAT model for nitride-specific mobility and saturation velocity effects.
Trap Implementation: Interface traps (2 x 10¹²/cm²) and buffer acceptor traps (1 x 10¹⁸/cm²) were included to accurately model static electric characteristics and degradation mechanisms.

Commercial Applications

The enhanced electrothermal performance and reliability offered by the NCD/SiN_x TDP structure are highly valuable for demanding electronic systems.

High-Power Radio Frequency (RF) Systems: Essential for radar, electronic warfare, and 5G/6G base stations, where high power density and high operating frequency must be maintained simultaneously without thermal runaway.
High-Voltage Power Conversion: Suitable for power electronics, including electric vehicle (EV) chargers, industrial motor drives, and solar inverters, benefiting from the low R_on and high current capability under thermal stress.
Aerospace and Defense: Applications requiring extreme reliability and stability under high-power pulsed operation, where junction temperature control is critical for mission success and device lifetime.
mm-Wave Communications: While the TDP structure involves a slight trade-off in parasitic capacitance compared to the DP structure, its superior linearity and thermal stability are crucial for maintaining signal integrity in high-frequency mm-wave front-ends.
Advanced Thermal Management Solutions: This work validates the use of patterned, top-side NCD films as effective heat spreaders, a technology relevant for any semiconductor device facing severe self-heating challenges.

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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