HfAlOx/Al2O3 Bilayer Dielectrics for a Field Effect Transistor on a Hydrogen-Terminated Diamond

At a Glance

Metadata	Details
Publication Date	2022-01-07
Journal	Materials
Authors	Minghui Zhang, Fang Lin, Wei Wang, Feng Wen, Genqiang Chen
Institutions	Xi’an Jiaotong University
Analysis	Full AI Review Included

Technical Documentation & Analysis: HfAlOx/Al₂O₃ Bilayer Dielectrics for H-Terminated Diamond FETs

This document analyzes the research detailing the fabrication and characterization of a high-performance hydrogen-terminated (H-terminated) diamond Field Effect Transistor (FET) utilizing HfAlOₓ/Al₂O₃ bilayer dielectrics. The findings directly validate the need for high-quality, custom-engineered MPCVD diamond substrates, a core specialization of 6CCVD.

Executive Summary

The successful fabrication of a high-performance H-terminated diamond FET using an Atomic Layer Deposition (ALD) HfAlOₓ/Al₂O₃ bilayer dielectric demonstrates significant progress toward high-power, high-frequency diamond electronics.

Core Achievement: Successful stabilization and protection of the two-dimensional hole gas (2DHG) channel using a high-k bilayer dielectric stack.
High Current Density: Achieved a maximum drain source current density (I_DSmax) of -6.3 mA/mm, confirming robust p-type channel operation.
Ultra-Low Leakage: Demonstrated exceptionally low gate leakage current density (|I_GS|) of 7.95 x 10^-7 A/cm², significantly lower than comparable reported FETs (MoO₃, Ta₂O₅, ZrO₂ based).
Material Requirement: The device performance relies fundamentally on the quality of the MPCVD-grown homoepitaxial diamond layer on a Single Crystal Diamond (SCD) substrate.
Key Parameters: The device exhibited normally-on characteristics with a threshold voltage (V_TH) of 8.3 V and a high carrier density (p) of 1.50 x 10¹³ cm^-2.
6CCVD Value Proposition: 6CCVD is the ideal supplier for the necessary high-purity SCD substrates and custom MPCVD homoepitaxy required to replicate and scale this advanced device architecture.

Technical Specifications

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

Parameter	Value	Unit	Context
Substrate Material	HPHT SCD	N/A	Starting material for homoepitaxy
Homoepitaxy Thickness	200	nm	Grown by MPCVD
Dielectric Stack	4 nm Al₂O₃ / 30 nm HfAlOₓ	N/A	Deposited via ALD
Maximum Drain Current Density (I_DSmax)	-6.3	mA/mm	At V_GS = -6 V, V_DS = -20 V
Threshold Voltage (V_TH)	8.3	V	Indicating normally-on operation
Maximum Transconductance (G_m)	0.73	mS/mm	Key switching speed metric
Maximum Capacitance (C_ox)	0.22	µF/cm²	Measured at 1 MHz, V_GS = -2 V
Carrier Density (p)	1.50 x 10¹³	cm^-2	Evaluated at V_GS = -2 V
Leakage Current Density (	I_GS	)	7.95 x 10^-7
Dielectric Constant (Calculated)	8.45	N/A	For the HfAlOₓ/Al₂O₃ bilayer
Trapped Charge Density	1.24 x 10¹²	cm^-2	Based on 0.9 V hysteresis

Key Methodologies

The fabrication process relied on precise material engineering and deposition techniques, highlighting the need for high-quality starting materials.

Substrate Preparation: High Temperature High Pressure (HPHT) Single Crystal Diamond (SCD) substrate was chemically cleaned.
MPCVD Homoepitaxy: A 200 nm homoepitaxy layer was grown on the SCD substrate using Microwave Plasma Chemical Vapor Deposition (MPCVD).
H-Termination: The surface was hydrogen-terminated to form the 2DHG channel.
Source/Drain Electrodes: 150 nm Au electrodes were deposited using electron beam evaporation (EB) and lift-off ($L_{SD} = 20$ µm gap).
Isolation: Selective removal of the H-termination via 20 min UV/Ozone treatment.
Dielectric Deposition (ALD): Sequential Atomic Layer Deposition (ALD) of the bilayer stack:
- 4 nm Al₂O₃ (to protect the H-terminated channel).
- 30 nm HfAlOₓ (high-k layer).
Gate Electrode: 150 nm Al gate electrode deposited via EB evaporation and lift-off ($L_G = 4$ µm, $W_G = 100$ µm).

6CCVD Solutions & Capabilities

This research confirms that the performance of advanced diamond FETs is critically dependent on the quality and customization of the diamond material. 6CCVD is uniquely positioned to supply the necessary materials and engineering services to advance this research.

Applicable Materials

To replicate or extend this high-performance H-terminated FET research, 6CCVD recommends the following materials:

6CCVD Material	Specification Relevance	Customization Potential
Electronic Grade SCD Substrates	Provides the high-purity foundation necessary for low defect density and high carrier mobility.	Available in thicknesses from 0.1 µm up to 500 µm.
MPCVD Homoepitaxial Layers	Essential for growing the 200 nm active layer used in the study. 6CCVD guarantees precise thickness control and high crystalline quality.	Custom growth thickness (0.1 µm to 500 µm) and surface termination (H-terminated or O-terminated).
Polycrystalline Diamond (PCD)	For scaling up to larger device arrays or commercial production where cost efficiency is paramount.	Plates/wafers up to 125 mm diameter available.

Customization Potential

The device utilized specific dimensions and metal contacts that fall directly within 6CCVD’s in-house capabilities:

Custom Dimensions: While the paper used small $3 \times 3 \times 0.5$ mm³ substrates, 6CCVD can provide custom SCD plates up to 125 mm (PCD) or large-area SCD for scaling research efforts.
Advanced Polishing: The stability of the H-terminated surface and the quality of the dielectric interface are paramount. 6CCVD offers ultra-smooth polishing services: Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD.
In-House Metalization: The device utilized Au (Source/Drain) and Al (Gate). 6CCVD offers internal metalization services, including:
- Au, Pt, Pd, Ti, W, Cu deposition.
- Custom patterning and layer thickness control for electrodes and contact pads.

Engineering Support

The integration of high-k dielectrics (HfAlOₓ/Al₂O₃) with H-terminated diamond is a complex interface challenge. 6CCVD’s in-house PhD team specializes in diamond surface chemistry and material integration, offering critical support for similar Diamond FET and High-Power Electronics projects. We assist clients in optimizing material selection to ensure thermal stability and maximize 2DHG channel integrity during subsequent processing steps (like ALD).

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

View Original Abstract

In this work, a hydrogen-terminated (H-terminated) diamond field effect transistor (FET) with HfAlOx/Al2O3 bilayer dielectrics is fabricated and characterized. The HfAlOx/Al2O3 bilayer dielectrics are deposited by the atomic layer deposition (ALD) technique, which can protect the H-terminated diamond two-dimensional hole gas (2DHG) channel. The device demonstrates normally-on characteristics, whose threshold voltage (VTH) is 8.3 V. The maximum drain source current density (IDSmax), transconductance (Gm), capacitance (COX) and carrier density (ρ) are −6.3 mA/mm, 0.73 mS/mm, 0.22 μF/cm2 and 1.53 × 1013 cm−2, respectively.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma15020446

References

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