Reliable Ohmic Contact Properties for Ni/Hydrogen-Terminated Diamond at Annealing Temperature up to 900 °C
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2021-04-17 |
| Journal | Coatings |
| Authors | Xiaolu Yuan, Jiangwei Liu, Jinlong Liu, Junjun Wei, Bo Da |
| Institutions | National Institute for Materials Science, University of Science and Technology Beijing |
| Citations | 2 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research investigates the thermal stability and electrical characteristics of Nickel (Ni) contacts on Hydrogen-Terminated Diamond (H-diamond) for high-temperature electronic applications.
- Core Achievement: Demonstrated highly reliable, thermally stable Ohmic contacts using Ni on H-diamond, maintaining performance after annealing up to 900 °C.
- Performance Metric: The specific contact resistance (ρc) was drastically reduced to 6.0 x 10-5 Ω·cm2 after 900 °C annealing, comparable to state-of-the-art contacts.
- Contact Transition: Contacts were initially Schottky (as-received and 300 °C annealed), transitioning to good Ohmic behavior at 500 °C (ρc = 1.5 x 10-3 Ω·cm2).
- Mechanism: The formation of electrically conductive Ni-related carbides at the Ni/H-diamond interface, confirmed by TEM and EDS analysis, is credited with promoting the significant decrease in contact resistance (Rc).
- Value Proposition: Ni is confirmed as an extremely promising electrode material for H-diamond-based electronic devices requiring operation in high-temperature environments (up to 900 °C).
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Maximum Annealing Temperature | 900 | °C | Rapid Thermal Annealing (RTA) in Ar atmosphere |
| Lowest Specific Contact Resistance (ρc) | 6.0 x 10-5 | Ω·cm2 | Achieved after 900 °C annealing |
| Contact Resistance (Rc) at 900 °C | 19.0 | Ω | Deduced from TLM measurements |
| Surface Sheet Resistance (Rs) at 900 °C | 60.6 | kΩ | Increased Rs attributed to C-H bond damage |
| Ohmic Transition Temperature | 500 | °C | Contacts transition from Schottky to Ohmic |
| Specific Contact Resistance (ρc) at 500 °C | 1.5 x 10-3 | Ω·cm2 | Initial Ohmic performance |
| H-Diamond Epitaxial Layer Thickness | 150 | nm | Grown via Microwave PECVD |
| Ni Electrode Thickness | 100 | nm | Deposited via e-beam evaporation |
| H-Diamond Hole Carrier Concentration | ~1014 | cm-2 | Surface conductivity |
| Diamond Bandgap | 5.5 | eV | Ultrawide energy bandgap |
Key Methodologies
Section titled “Key Methodologies”The study utilized the Transmission Line Model (TLM) structure and high-temperature annealing to characterize the Ni/H-diamond contacts.
- Substrate Preparation: Ib-type (100) single-crystalline diamond was cleaned by boiling in mixed H2SO4 and HNO3 solutions at 300 °C for 3 hours.
- H-Diamond Epitaxy: A 150 nm H-diamond epitaxial layer was grown using Microwave Plasma-Enhanced Chemical Vapor Deposition (PECVD) with the following parameters:
- Deposition Temperature: 900-940 °C
- Chamber Pressure: 80 Torr
- Gas Flow Rates: CH4 (0.5 sccm), H2 (500 sccm)
- TLM Patterning: Five-group TLM electrode patterns were defined using mask-less lithography (250 mJ·cm-2 dose) and LOR5A/AZ5214E photoresists.
- Mesa Etching: Mesa structures were formed using Capacitively Coupled Plasma Reactive-Ion Etching (RIE) with O2 plasma (50 W power, 100 sccm flow, 90 s duration).
- Ni Deposition: 100 nm thick Ni metal was deposited onto the H-diamond via an e-beam evaporation system under a vacuum of approximately 10-5 Pa.
- Annealing Process: Rapid Thermal Annealing (RTA) was performed in an Ar atmosphere at 300, 500, 700, and 900 °C, with a fixed annealing time of 10 minutes for each temperature.
- Characterization: Electrical properties (Current-Voltage curves) were measured at room temperature. Interface analysis was conducted using Transmission Electron Microscopy (TEM) and Energy Dispersive Spectrometer (EDS) after 900 °C annealing to confirm carbide formation.
Commercial Applications
Section titled “Commercial Applications”The demonstrated thermal stability and low contact resistance of Ni/H-diamond contacts enable the use of H-diamond devices in demanding high-temperature and high-power environments.
- High-Temperature Power Electronics: Essential for devices (like MOSFETs and Diodes) operating in environments exceeding 500 °C, such as automotive engines, aerospace systems, and industrial heating controls.
- High-Power RF Amplifiers: Utilizing diamond’s high breakdown field and carrier mobility for high-frequency, high-power density applications (e.g., 3.8 W·mm-1 output power density demonstrated in related H-diamond devices).
- Extreme Environment Sensing: Applications requiring robust electronics, such as neutron generator output monitoring in well logging, or sensors in nuclear reactors.
- Thermal Management Systems: Integration of electronics with diamond’s superior thermal conductivity (22 W·cm-1·K-1) requires thermally stable contacts to maintain performance under high heat flux.
- Next-Generation Wide Bandgap Devices: Promoting the commercial viability of H-diamond field-effect transistors (FETs) by solving the critical issue of contact degradation at elevated temperatures.
View Original Abstract
Ohmic contact with high thermal stability is essential to promote hydrogen-terminated diamond (H-diamond) electronic devices for high-temperature applications. Here, the ohmic contact characteristics of Ni/H-diamond at annealing temperatures up to 900 °C are investigated. The measured current-voltage curves and deduced specific contact resistance (ρC) are used to evaluate the quality of the contact properties. Schottky contacts are formed for the as-received and 300 °C-annealed Ni/H-diamonds. When the annealing temperature is increased to 500 °C, the ohmic contact properties are formed with the ρC of 1.5 × 10−3 Ω·cm2 for the Ni/H-diamond. As the annealing temperature rises to 900 °C, the ρC is determined to be as low as 6.0 × 10−5 Ω·cm2. It is believed that the formation of Ni-related carbides at the Ni/H-diamond interface promotes the decrease in ρC. The Ni metal is extremely promising to be used as the ohmic contact electrode for the H-diamond-based electronic devices at temperature up to 900 °C.
Tech Support
Section titled “Tech Support”Original Source
Section titled “Original Source”References
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