1 W/mm Output Power Density for H-Terminated Diamond MOSFETs With Al2O3/SiO2Bi-Layer Passivation at 2 GHz

At a Glance

Metadata	Details
Publication Date	2020-12-23
Journal	IEEE Journal of the Electron Devices Society
Authors	Xinxin Yu, Wenxiao Hu, Jianjun Zhou, Bin Liu, Tao Tao
Institutions	Nanjing University, Nanjing Institute of Technology
Citations	19
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Power Diamond MOSFETs

This document analyzes the research paper “1 W/mm Output Power Density for H-Terminated Diamond MOSFETs With Al₂O₃/SiO₂ Bi-Layer Passivation at 2 GHz” and outlines how 6CCVD’s advanced MPCVD diamond materials and fabrication capabilities can support and extend this high-performance semiconductor research.

Executive Summary

This study successfully demonstrates a significant breakthrough in diamond RF power electronics by achieving a record output power density using a novel bi-layer passivation scheme.

Record Performance: Achieved a high output power density of 1.04 W/mm at 2 GHz, the highest reported value for a diamond transistor operating at this frequency.
Novel Passivation: Utilized an ALD-Al₂O₃/PECVD-SiO₂ bi-layer dielectric structure to effectively passivate the H-terminated diamond (H-diamond) surface channel.
Enhanced Stability: The bi-layer structure dramatically improved device stability, resulting in current saturation and stable operation over 85 days, overcoming typical instability issues in H-diamond MOSFETs.
Low Contact Resistance: Fabrication yielded an extremely low Ohmic contact resistance of 0.87 Ω·mm, crucial for minimizing parasitic losses in high-power RF devices.
High Frequency Metrics: The device demonstrated strong high-frequency characteristics with an extrinsic cutoff frequency (f_T) of 15 GHz and a maximum oscillation frequency (f_max) of 36 GHz.
Material Foundation: The high performance was enabled by the use of high-quality, (100)-oriented Single Crystal Diamond (SCD) substrates grown via CVD.

Technical Specifications

The following hard data points were extracted from the device characterization results:

Parameter	Value	Unit	Context
Output Power Density (P_out)	1.04	W/mm	Measured at 2 GHz
Maximum Current Density (I_DS,max)	-549	mA/mm	Achieved after surface current saturation (Day 85)
Ohmic Contact Resistance (R_c)	0.87	Ω·mm	Lowest reported value on H-diamond
Sheet Resistance (R_sh)	6.4	kΩ/sq	2DHG channel
Specific Contact Resistance (ρ_c)	1.18 x 10^-6	Ω·cm²	Calculated value
Extrinsic Cutoff Frequency (f_T)	15	GHz	L_G = 0.45 µm
Maximum Oscillation Frequency (f_max)	36	GHz	L_G = 0.45 µm
Power Added Efficiency (PAE)	13.69	%	Measured at 2 GHz
Gate Dielectric Thickness (Al₂O₃)	50	nm	ALD layer
Passivation Thickness (SiO₂)	200	nm	PECVD layer
Substrate Orientation	(100)	N/A	Single Crystal Diamond (SCD)

Key Methodologies

The high-performance H-diamond MOSFET was fabricated using a multi-step process focused on precise surface preparation and bi-layer dielectric deposition.

Substrate Selection: Used 5x5x0.3 mm³ (100)-oriented Single Crystal Diamond (SCD) substrates.
Hydrogen Termination (2DHG Generation): Performed in an MPCVD system (OptoSystem ARDIS-300) at 700 °C, 2.2 kW power, for 10 minutes.
Surface Quality Control: Post-hydrogenation surface roughness was measured to be Ra < 1.0 nm.
Ohmic Contact Formation: 50 nm Au deposited via Electron Beam (EB) evaporation, followed by wet etching (KI solution) to define source/drain regions.
Device Isolation: Achieved by exposing the surface to a low power oxygen plasma for 5 minutes.
Surface Annealing: Substrate annealed in the ALD chamber at 350 °C for 10 minutes to remove adsorbates.
First Passivation/Gate Dielectric (Al₂O₃): 50 nm Al₂O₃ deposited via Atomic Layer Deposition (ALD) at 350 °C using trimethylaluminum (TMA) and deionized water.
Gate Metal Deposition: 20/500 nm Ti/Au stack deposited via EB evaporation.
Second Passivation Layer (SiO₂): 200 nm SiO₂ deposited via Plasma Enhanced Chemical Vapor Deposition (PECVD) at 280 °C.
Test Pad Metalization: Final 20/500 nm Ti/Au stack deposited.

6CCVD Solutions & Capabilities

The successful replication and scaling of this high-power diamond MOSFET technology require ultra-high purity, precisely engineered diamond substrates and advanced metalization capabilities—all core competencies of 6CCVD.

Applicable Materials

To achieve the high mobility and breakdown characteristics necessary for 1 W/mm performance, the following 6CCVD material is required:

Optical Grade Single Crystal Diamond (SCD): High-purity, low-defect, (100)-oriented SCD is essential for maximizing the concentration and stability of the Two-Dimensional Hole Gas (2DHG) channel. 6CCVD provides SCD optimized for electronic applications.

Customization Potential

6CCVD’s in-house manufacturing capabilities directly address the critical material and dimensional requirements of this research:

Research Requirement	6CCVD Capability & Solution	Value Proposition
Substrate Dimensions	Custom plates/wafers up to 125 mm (PCD) and large-area SCD.	We can supply the 5x5 mm² SCD wafers used, or scale up to larger formats for high-volume device runs.
Substrate Thickness	SCD thickness range: 0.1 µm to 500 µm. Substrates up to 10 mm.	We match the 0.3 mm thickness used and offer precise thickness control for thermal management optimization.
Surface Quality (H-Termination)	Guaranteed SCD polishing to Ra < 1 nm.	Ensures the ultra-smooth surface required for stable 2DHG formation and effective, low-damage ALD/PECVD dielectric deposition.
Custom Metal Stacks	In-house deposition of Ti, Au, Pt, Pd, W, and Cu.	We can pre-deposit the required Ti/Au gate and test pad stacks, or the Au ohmic contacts, ensuring high adhesion and minimizing customer fabrication steps.
Patterning & Shaping	High-precision laser cutting and shaping services.	Allows for rapid prototyping of custom device geometries and precise definition of the 5x5 mm² chips from larger wafers.

Engineering Support

The success of this MOSFET relies heavily on the interface quality between the H-diamond and the Al₂O₃/SiO₂ bi-layer.

Interface Optimization: 6CCVD’s in-house PhD team specializes in MPCVD growth and surface preparation techniques. We offer consultation to optimize the hydrogenation recipe (700 °C, 2.2 kW) and subsequent surface cleaning protocols to ensure maximum C-H bond integrity before ALD deposition.
Material Selection for High-Power RF: Our experts can assist researchers in selecting the optimal diamond grade (SCD vs. PCD) and orientation for scaling similar High-Power Diamond MOSFET projects, balancing cost, size, and performance requirements.
Boron Doping (BDD): For applications requiring stable, integrated resistors or alternative contact schemes, 6CCVD offers custom Boron-Doped Diamond (BDD) materials.

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

View Original Abstract

We have demonstrated a novel method of depositing ALD-Al2O3/PECVD-SiO2 bi-layer dielectric to passive the surface channels of the hydrogen-terminated diamond (H-diamond). After Al2O3/SiO2 passivation, the surface current increased with time and then tended to be saturated. Afterwards, it became much more stable and showed a larger current than an unpassivated counterpart. The H-diamond MOSFETs were fabricated by using this bi-layer passivation structure and an extremely low Ohmic contact resistance of <inline-formula> <tex-math notation=“LaTeX”>$0.87~\Omega \cdot $ </tex-math></inline-formula>mm was obtained. The H-diamond RF MOSFET with gate length of <inline-formula> <tex-math notation=“LaTeX”>$0.45~{\mu }\text{m}$ </tex-math></inline-formula> achieved a high current density of −549 mA/mm and an extrinsic <inline-formula> <tex-math notation=“LaTeX”>${f} {\mathrm{ T}}/{f}{\max }$ </tex-math></inline-formula> of 15/36 GHz. By load-pull measurement, a high output power density of 1.04 W/mm was obtained at frequency of 2 GHz. The results reveal that it is a promising solution for high-stable and high-power diamond transistors by using the Al2O3/SiO2 bi-layer passivation.

Tech Support

Original Source

DOI: https://doi.org/10.1109/jeds.2020.3046603

References

2014 - High-reliability passivation of hydrogen-terminated diamond surface by atomic layer deposition of Al2O3 [Crossref]
2015 - Isotope analysis of diamond-surface passivation effect of high-temperature H2O-grown atomic layer deposition-Al2O3 films [Crossref]