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6CCVD Research

Hydrogen-Terminated Single Crystal Diamond MOSFET with a Bilayer Dielectric of Gd2O3/Al2O3

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2023-05-08
JournalCrystals
AuthorsXiaoyong Lv, Wei Wang, Yanfeng Wang, Genqiang Chen, Shi He
InstitutionsXi’an Jiaotong University
Citations3
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This research successfully demonstrates a high-performance hydrogen-terminated single-crystal diamond (H-diamond) MOSFET utilizing a novel bilayer gate dielectric structure.

  • Novel Dielectric Stack: A Gd2O3/Al2O3 bilayer was employed, marking the first reported use of this stack in an H-diamond MOSFET, leveraging the high dielectric constant (high-k) properties of Gadolinium Oxide.
  • High Dielectric Constant: The magnetron sputtering (SD) deposited Gd2O3 layer achieved an exceptionally high dielectric constant (k = 24.8), significantly exceeding typical literature values (9-14).
  • Excellent Current Performance: The device exhibited typical p-type characteristics with a maximum drain current (IDmax) of 15.3 mA/mm.
  • High Mobility and Switching: An effective carrier mobility (”eff) of 182.1 cm2/Vs was achieved, alongside a high ON/OFF ratio of approximately 5 x 108.
  • Low Leakage: The stable properties of the Gd2O3/Al2O3 stack resulted in a very low gate leakage current density, measured at less than 1 x 10-7 A/cm2.
  • Buffer Layer Function: Atomic Layer Deposition (ALD) Al2O3 served as a critical buffer layer to protect the sensitive H-diamond surface during subsequent high-energy deposition processes.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Substrate Type(001) Single-Crystal DiamondN/AHPHT synthesized
Channel Type2DHG (p-type)N/AHydrogen-terminated
Maximum Drain Current (IDmax)15.3mA/mmAt VDS = -20 V, VGS = -10 V
Effective Carrier Mobility (”eff)182.1cm2/VsAt VGS = 1.0 V
ON/OFF Ratio~5 x 108N/ASwitching performance
Subthreshold Swing (SS)315mV/decSwitching performance
Maximum Transconductance (gm,max)2.01mS/mmAt VGS = -10.63 V
Threshold Voltage (VTH)1.12VExtracted from linear plot
Gd2O3 Dielectric Constant (k)24.8N/ACalculated value (SD layer)
Al2O3 Dielectric Constant (k)4.9N/ACalculated value (ALD layer)
Total Gate Capacitance (Cox)0.146”F/cm2Maximum value
Trapped Charge Density (Qt)1.08 x 1011cm-2In bilayer dielectric
Gate Leakage Current Density (J)<1 x 10-7A/cm2Operating range
Al2O3 Thickness20nmALD deposition
Gd2O3 Thickness52.3nmSD deposition
Gate Length (LG) / Width (WG)20 / 100”mDevice dimensions

Key Methodologies

Section titled “Key Methodologies”

The MOSFET fabrication utilized a combination of CVD, ALD, and magnetron sputtering deposition (SD) techniques:

  1. Substrate Preparation: A 3 x 3 x 0.5 mm3 HPHT (001) single-crystal diamond substrate was cleaned via hot acid treatment (H2SO4:HNO3 = 31.2:36) at 250 °C.
  2. Epitaxial Growth and H-Termination: A 200 nm undoped single-crystal diamond layer was grown via Microwave Plasma CVD (MPCVD), followed by hydrogen treatment to form the 2DHG channel (H-diamond).
  3. Source/Drain (S/D) Electrodes: Traditional photolithography and Electron Beam (EB) deposition were used to plate a 150 nm Au film, defining S/D electrodes with a 20 ”m separation (Lsp).
  4. Device Isolation: UV/Ozone treatment was applied to isolate the active device area.
  5. Al2O3 Buffer Layer (ALD): A 20 nm Al2O3 layer was deposited using Atomic Layer Deposition (ALD) with water vapor and TMA precursors. The process was split into 5 nm at 80 °C and 15 nm at 250 °C.
  6. Gd2O3 High-k Layer (SD): A 52.3 nm Gd2O3 layer was deposited via magnetron sputtering (SD) at Room Temperature (RT). Deposition parameters were 0.5 Pa pressure, 75 W power, and 30 minutes duration.
  7. Gate Metallization: A 150 nm Al electrode was deposited via EB deposition to complete the MOSFET structure (LG = 20 ”m, WG = 100 ”m).

Commercial Applications

Section titled “Commercial Applications”

The demonstrated H-diamond MOSFET technology, leveraging diamond’s intrinsic properties and the high-k Gd2O3 dielectric, is highly relevant for applications requiring extreme performance characteristics.

  • High-Power Switching: Diamond’s ultra-wide band gap (5.45 eV) and high breakdown voltage (>10 MV/cm) make these devices ideal for next-generation power electronics, including power converters and inverters.
  • High-Frequency RF Devices: The high carrier mobility (”eff = 182.1 cm2/Vs) and low parasitic parameters support applications in 5G, WiMAX, and WLAN communications, enabling high-speed RF power amplifiers.
  • Harsh Environment Electronics: Diamond’s superior thermal conductivity (22 W/K cm) and stability allow operation in high-temperature (HT) environments (e.g., automotive, aerospace, deep-well drilling) where silicon devices fail.
  • Radiation-Hardened Systems: Diamond is inherently radiation-hard, making these MOSFETs suitable for use in space, nuclear facilities, and medical imaging equipment.
  • Advanced Memory Integration: The use of Gd2O3, a material commonly utilized in Dynamic Random Access Memory (DRAM), suggests potential for integrating diamond channels into high-density, stable memory architectures.
View Original Abstract

In this paper, two dielectric layers of Al2O3 and Gd2O3 were prepared by an atomic layer deposition (ALD) and magnetron sputtering deposition (SD), respectively. Based on this, a metal-oxide-semiconductor field-effect transistor (MOSFET) was successfully prepared on a hydrogen-terminated single-crystal diamond (H-diamond), and its related properties were studied. The results showed that this device had typical p-type channel MOSFET output and transfer characteristics. In addition, the maximum current was 15.3 mA/mm, and the dielectric constant of Gd2O3 was 24.8. The effective mobility of MOSFET with Gd2O3/Al2O3 was evaluated to be 182.1 cm2/Vs. To the best of our knowledge, the bilayer dielectric of Gd2O3/Al2O3 was first used in a hydrogen-terminated diamond MOSFET and had the potential for application.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2021 - 345-MW/cm2 2608-V NO2 p-type Doped Diamond MOSFETs with an Al2O3 Passivation Overlayer on Heteroepitaxial Diamond [Crossref]
  2. 2018 - 3.8 W/mm RF Power Density for ALD Al2O3-Based Two-Dimensional Hole Gas Diamond MOSFET Operating at Saturation Velocity [Crossref]
  3. 2020 - Normally off hydrogen-terminated diamond field-effect transistor with Ti/TiOx gate materials [Crossref]
  4. 2022 - Leakage current reduction of normally off hydrogen-terminated diamond field effect transistor utilizing dual-barrier Schottky gate [Crossref]
  5. 2022 - Large VTH of Normally-off Field Effect Transistor with Yttrium Gate Material Directly Deposited on Hydrogen-Terminated Diamond [Crossref]
  6. 1988 - Critical evaluation of the status of the areas for future research regarding the wide band gap semiconductors diamond, gallium nitride and silicon carbide [Crossref]
  7. 2020 - Oxidized Si terminated diamond and its MOSFET operation with SiO2 gate insulator [Crossref]
  8. 2016 - Diamond based field-effect transistors with SiNx and ZrO2 double dielectric layers [Crossref]
  9. 2023 - High Performance of Normally-on and Normally-off Devices with Highly Boron-Doped Source and Drain on H-Terminated Polycrystalline Diamond [Crossref]
  10. 2012 - Development of AlN/diamond heterojunction field effect transistors [Crossref]

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