2.1 W/mm Output Power Density at 10 GHz for H-Terminated Diamond MOSFETs With (111)-Oriented Surface
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-12-25 |
| Journal | IEEE Journal of the Electron Devices Society |
| Authors | Bing Qiao, Pengfei Dai, Xinxin Yu, Zhonghui Li, Ran Tao |
| Institutions | Nanjing Institute of Technology |
| Citations | 3 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research presents a significant advancement in hydrogen-terminated diamond (H-diamond) MOSFET technology by utilizing a (111)-oriented substrate, leading to record high-frequency power performance.
- Record Power Density: Achieved a record high output power density of 2.1 W/mm at 10 GHz, operating at a relatively low drain bias of -30 V. This significantly surpasses previous results on (001)-oriented diamond (1.26 W/mm).
- Enhanced 2DHG Channel: The use of the (111) orientation resulted in a maximum two-dimensional hole gas (2DHG) sheet density of 1.0 x 1013 cm-2 with a corresponding mobility of 104 cm2/V·s.
- Low Resistance Metrics: The high-quality channel enabled a low Ohmic contact resistance (Rc) of 0.5 Ω·mm and a low on-resistance (Ron) of 24 Ω·mm.
- High Reliability: The fabricated MOSFET (LG = 0.5 ”m) demonstrated a high maximum current density of 750 mA/mm and a robust off-state breakdown voltage of 117 V.
- Passivation Scheme: A high-quality Al2O3/Si3N4 bilayer passivation stack was employed to stabilize the 2DHG channel, contributing to the improved performance.
- High Frequency Operation: The device achieved a maximum oscillation frequency (fmax) of 28 GHz.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Orientation | (111) | N/A | Single-crystal diamond |
| Maximum Output Power Density (Pout) | 2.1 | W/mm | At 10 GHz, VDS = -30 V |
| Maximum Current Density (ID,max) | 750 | mA/mm | LG = 0.5 ”m |
| On-Resistance (Ron) | 24 | Ω·mm | LG = 0.5 ”m |
| Off-State Breakdown Voltage (VBD) | 117 | V | N/A |
| Maximum Oscillation Frequency (fmax) | 28 | GHz | N/A |
| Ohmic Contact Resistance (Rc) | 0.5 | Ω·mm | TLM measurement |
| Specific Contact Resistance (Ïc) | 3.23 x 10-7 | Ω·cm2 | Dramatically reduced compared to previous work |
| 2DHG Sheet Density (ps, max) | 1.0 x 1013 | cm-2 | At VGS = -8 V |
| 2DHG Mobility (”ch, max) | 104 | cm2/V·s | At VGS = -8 V |
| Ungated Channel Sheet Resistance (Rsh) | 7.6 | kΩ/sq | N/A |
| Gate Length (LG) | 0.5 | ”m | Fabricated MOSFET |
| Power Added Efficiency (PAE) | 6.5 | % | At 10 GHz |
| Gain | 4.6 | dB | At 10 GHz |
| Surface Roughness (RMS) | ~1 | nm | 5 ”m x 5 ”m area |
Key Methodologies
Section titled âKey MethodologiesâThe H-diamond MOSFETs were fabricated using a precise sequence of deposition, lithography, and etching steps on a (111)-oriented single-crystal diamond substrate.
- Hydrogen Termination:
- Process: Microwave Plasma Chemical Vapor Deposition (MPCVD).
- Parameters: 700 °C, 2.2 kW power, 10 minutes duration, followed by cooling in H2 atmosphere.
- Ohmic Contact Formation:
- Material: 50 nm thick Au film deposited by Electron Beam Evaporation (EBE).
- Note: The diamond was exposed to air for more than 24 hours prior to Au deposition.
- Device Isolation:
- Process: Oxygen plasma treatment (300 W, 5 minutes) used to convert C-H bonds to C-O bonds in unmasked regions.
- Gate Dielectric Deposition (Al2O3):
- Process: Atomic Layer Deposition (ALD).
- Parameters: 50 nm thickness, 350 °C.
- Pre-treatment: Diamond was annealed in situ at 350 °C for 15 minutes before ALD to remove surface absorbates.
- Secondary Passivation Layer (Si3N4):
- Process: Plasma Enhanced Chemical Vapor Deposition (PECVD).
- Parameters: 100 nm thickness, 250 °C.
- T-Shaped Gate Fabrication:
- Process: Two-step Electron Beam Lithography (EBL) and Inductively Coupled Plasma (ICP) etching for Si3N4 removal.
- Gate Metal Stack: 20/500 nm Ti/Au.
- Pad Metallization:
- Process: ICP etching for Al2O3/Si3N4 contact windows, followed by 20/500 nm Ti/Au evaporation for source, drain, and gate pads.
Commercial Applications
Section titled âCommercial ApplicationsâThe exceptional performance metrics achieved by the (111)-oriented H-diamond MOSFETs position them as critical components for next-generation high-power and high-frequency systems.
- High-Power RF Amplification:
- The record 2.1 W/mm output power density at 10 GHz is highly competitive for X-band applications, including satellite communications and military radar systems.
- 5G/6G Wireless Infrastructure:
- Diamondâs superior thermal conductivity (22 W/cm·K) combined with high current density enables highly integrated, thermally stable power amplifiers necessary for dense, high-frequency telecommunication base stations.
- Power Electronics and Switching:
- The combination of high breakdown voltage (117 V) and low on-resistance (24 Ω·mm) makes these devices excellent candidates for high-speed, high-efficiency power switching applications where minimizing conduction loss is paramount.
- Extreme Environment Sensing/Control:
- Diamond is chemically inert and thermally robust, allowing these devices to be deployed in harsh environments (e.g., aerospace, industrial monitoring) where conventional semiconductors degrade.
View Original Abstract
This paper presents high performance hydrogen-terminated diamond MOSFETs fabricated on a (111)-oriented single-crystal diamond substrate. The diamond surface was passivated by a high-quality Al2O3 grown by ALD at 350°C as well as a secondary passivation layer Si3N4 deposited by PECVD. After passivation, a low ohmic contact resistance <inline-formula> <tex-math notation=âLaTeXâ>$R_{c}$ </tex-math></inline-formula> of <inline-formula> <tex-math notation=âLaTeXâ>$0.5 \Omega \cdot $ </tex-math></inline-formula>mm was obtained and the 2DHG sheet density was as high as <inline-formula> <tex-math notation=âLaTeXâ>$1.0\times 10,,^{\mathrm{ 13}},,{\mathrm{ cm}}^{-2}$ </tex-math></inline-formula> with a corresponding mobility of <inline-formula> <tex-math notation=âLaTeXâ>$104 {\mathrm{ cm}}^{2} /\text{V}\cdot \text{s}$ </tex-math></inline-formula>. The fabricated diamond MOSFET with gate length of <inline-formula> <tex-math notation=âLaTeXâ>$0.5 ~\mu \text{m}$ </tex-math></inline-formula> showcased a high current density of 750 mA/mm, a low on-resistance of <inline-formula> <tex-math notation=âLaTeXâ>$24 \Omega \cdot $ </tex-math></inline-formula>mm, and a high off-state breakdown voltage of 117 V. Thanks to the high current density and low on-resistance, a record high output power density of 2.1 W/mm was achieved at 10 GHz with drain biased at a low voltage of −30 V. These results demonstrate that the output current and output power can be improved by using a (111)-oriented diamond, which is benefit for high-frequency and high-power RF devices.