Diamond lateral FinFET with triode-like behavior
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-02-10 |
| Journal | Scientific Reports |
| Authors | Biqin Huang, Xiwei Bai, Stephen Lam, Samuel J. Kim |
| Institutions | HRL Laboratories (United States) |
| Citations | 6 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research reports the successful fabrication and characterization of a diamond lateral FinFET utilizing a novel ohmic regrowth technique, demonstrating critical performance characteristics for high-power applications.
- Ohmic Regrowth Innovation: A key fabrication step involves ohmic regrowth (P++ diamond) to define the source/drain regions. This technique isolates the channel from the harsh dry etching process, preserving the high quality of the top fin surface and improving ohmic contact resistance.
- Channel Behavior Transition: The device exhibits a transition in its current-voltage (IV) characteristics from pentode-like (typical MOSFET saturation) to triode-like behavior as the channel length is reduced.
- Space Charge Limited (SCL) Transport: For the first time in a diamond FinFET, SCL transport was demonstrated in short-channel devices. This regime, where current is proportional to the square of the voltage (Mott-Gurney Law), is crucial for high-power operation without requiring a fully ionized channel.
- Thermal Stability Analysis: SCL transport was observed at room temperature (RT) but disappeared at 150 °C. This is attributed to the thermal activation of boron dopants, which increases the thermal carrier density by more than 10x, pushing the SCL cross-over voltage out of the tested range.
- High Power Potential: Operating the diamond device in the triode-like, SCL transport regime opens new avenues for diamond electronics, enabling high power capability even with intrinsic or lightly doped channels, provided the ohmic contacts are optimized.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Type | Single Crystalline Diamond | N/A | (100) orientation, undoped |
| Channel Layer Thickness | 500 | nm | Lightly boron-doped (P-) epitaxial layer |
| Nominal Boron Doping (P-) | 5 x 1016 | cm-3 | Channel doping concentration |
| Fin Width | 100 | nm | Fabricated Fin structure |
| Fin Height | 660 | nm | Fabricated Fin structure |
| Channel Length Range Tested | 0.5 to 160 | ”m | Tested for both planar and FinFET devices |
| Gate Dielectric Material | SiO2 | N/A | Deposited via ALD |
| Gate Dielectric Thickness | 45 | nm | Used for channel insulation |
| ALD Deposition Temperature | 200 | °C | SiO2 deposition process |
| Ohmic Contact Metal Stack | Ti/Pt/Au | N/A | Used for source/drain contacts |
| Ohmic Annealing Temperature | 525 | °C | Performed in argon gas |
| Regrowth Height Difference | ~20 | nm | Optimized difference between ohmic region and channel |
| Operating Temperature Range | RT to 150 | °C | Used for IV characteristic analysis |
| SCL Transport Law | I proportional to V2 | N/A | Observed at RT in 0.5 ”m planar MOSFETs |
| Dopant Activation Increase (RT to 150 °C) | >10 | x | Causes transition from SCL to linear ohmic behavior |
Key Methodologies
Section titled âKey MethodologiesâThe diamond FinFET was fabricated using a specialized process flow centered on ohmic regrowth to ensure high channel quality:
- Epitaxial Growth: A 500 nm lightly boron-doped (P-) layer was epitaxially grown on an undoped (100) diamond substrate.
- Fin Patterning and Etch: Fin structures (100 nm wide, 660 nm tall) were defined using dry etching in O2/Ar plasma (40 sccm / 10 sccm).
- Regrowth Masking: A silicon oxide layer was deposited and patterned to expose the source and drain regions for subsequent regrowth.
- Ohmic Regrowth: P++ diamond was regrown via microwave plasma CVD in the exposed source/drain regions. The process was optimized to minimize surface topography, achieving a height difference of approximately 20 nm between the ohmic region and the channel.
- Ohmic Contact Formation: Ti/Pt/Au metal was evaporated onto the regrown P++ regions and annealed at 525 °C in argon gas to form low-resistance ohmic contacts.
- Gate Dielectric Deposition: A 45 nm SiO2 gate dielectric was deposited via Atomic Layer Deposition (ALD) at 200 °C.
- Gate Metallization: Al metal was sputtered and lifted off to form the gate electrode, conformably wrapping the sidewalls of the fins.
Commercial Applications
Section titled âCommercial ApplicationsâThe demonstrated diamond FinFET technology, leveraging high channel quality and SCL transport, is highly relevant for several advanced electronic sectors:
- High-Power Switching: Diamondâs superior thermal conductivity and high breakdown field, combined with the SCL regime (which allows high current density without full ionization), make this device ideal for high-voltage power converters and solid-state circuit breakers.
- Radio Frequency (RF) Electronics: The improved ohmic contacts and preserved channel quality enable high-speed operation, targeting RF amplifiers and switches for 5G/6G infrastructure and radar systems.
- Static Induction Transistors (SITs): The triode-like behavior and SCL transport regime are characteristic of SITs, which are known for high current handling and high-frequency capabilities, offering a robust alternative to traditional MOSFETs in power applications.
- Extreme Environment Sensing/Control: Diamondâs inherent radiation hardness and thermal stability allow these devices to be deployed in harsh environments, such as aerospace, nuclear facilities, or high-temperature industrial processes.
- Fundamental Semiconductor Research: The ability to reliably study SCL transport provides a powerful tool for characterizing defects and charge dynamics within diamond thin films, aiding in the development of future diamond material growth recipes.