Diamond lateral FinFET with triode-like behavior

At a Glance

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

6CCVD Technical Documentation: Diamond FinFET Development

Executive Summary

This documentation analyzes the fabrication and electrical characteristics of a diamond lateral FinFET employing an innovative ohmic regrowth technique, demonstrating crucial advancements for high-power and high-frequency diamond electronics.

Technology Breakthrough: Successful implementation of an ohmic regrowth process to form P++ source/drain regions, mitigating surface damage traditionally caused by dry etching and significantly improving ohmic contact resistance.
Novel Transport Mechanism: First observation and analysis of Space Charge Limited (SCL) transport in short-channel diamond FinFET devices, validating a new high-power operating regime where current is proportional to the square of voltage bias (V²).
Enhanced Performance: The high-quality channel, protected by the regrowth process, enables device operation transition from pentode-like saturation to triode-like (SCL) behavior as channel length is reduced.
Material System: The device is built upon high-quality Single Crystal Diamond (SCD) featuring an epitaxially grown, lightly Boron-Doped (P-) channel layer (500 nm thick).
Thermal Stability: SCL transport behavior was confirmed across a wide temperature range, demonstrating consistent operation from room temperature (RT) up to 150 °C.
Application Relevance: The demonstrated triode-like characteristics, enabled by low ohmic contact resistance, pave the way for powerful diamond electronic devices suitable for high-power, low-loss RF applications (e.g., Static Induction Transistors).

Technical Specifications

The following parameters and performance metrics were extracted from the research data:

Parameter	Value	Unit	Context
Substrate Type	Single Crystal Diamond (SCD)	N/A	Nominally undoped, 10 x 10 mm²
Channel Layer Thickness (P-)	500	nm	Epitaxially grown, lightly Boron-Doped
Nominal Boron Doping (P-)	5 x 10¹⁶	cm^-3	Channel concentration
Fin Width	100	nm	Formed via O₂/Ar dry etching
Fin Height	660	nm	Height of the Fin structure
Channel Length (L) Tested	0.5 to 160	µm	Demonstrated SCL in short channels (< 1 µm)
Ohmic Regrowth Height Differential	< 20	nm	Optimized process minimizes topography
Gate Dielectric Material	SiO₂	N/A	Deposited via ALD
Gate Dielectric Thickness	45	nm	Optimized thickness
Gate Dielectric Deposition Temp	200	°C	ALD Process temperature
Ohmic Contact Stack	Ti/Pt/Au	N/A	Evaporated metalization
Ohmic Annealing Parameters	525 °C in Argon	N/A	Optimized contact formation
Operating Temperature Range	RT to 150	°C	Range used to analyze SCL transport
Gate Voltage Sweep Range	5 to -10	V	Applied gate bias during IV tests

Key Methodologies

The Diamond FinFET fabrication relied on highly controlled MPCVD epitaxy and precision dry etching, focusing on preserving the quality of the Fin channel top surface.

Epitaxial Growth: A 500 nm layer of lightly Boron-Doped (P-) diamond was grown epitaxially onto an undoped Single Crystal Diamond (100) substrate.
Fin Definition: Fin structures (100 nm wide, 660 nm tall) were formed using dry etching via O₂/Ar plasma (40 sccm O₂ / 10 sccm Ar).
Regrowth Masking: A silicon oxide (SiO₂) layer was deposited and patterned via dry etching to selectively expose the future source (S) and drain (D) regions for ohmic regrowth.
Ohmic Regrowth: A P++ diamond layer was regrown selectively onto the exposed S/D areas using Microwave Plasma CVD (MPCVD). The process was optimized to limit the height difference between the ohmic region and the channel to < 20 nm.
Gate Dielectric Formation: A 45 nm SiO₂ layer was deposited using Atomic Layer Deposition (ALD) at 200 °C to serve as the gate dielectric.
Gate Metalization: Aluminum (Al) metal was sputtered and patterned via lift-off to form the gate electrode, conformably wrapping around the fin sidewalls.
Ohmic Contact Metalization: The S/D contact pads were opened via wet etching, followed by evaporation of the Ti/Pt/Au stack and subsequent annealing at 525 °C in Argon gas.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced diamond materials required to replicate, scale, and extend the FinFET research detailed in this paper, particularly focusing on the demanding material quality required for ohmic regrowth and SCL transport studies.

Applicable Materials

The successful implementation of this diamond FinFET relies heavily on precise control over doping and crystalline quality, which are core strengths of 6CCVD’s MPCVD process:

Optical Grade Single Crystal Diamond (SCD) Substrates: Essential for the foundational material, ensuring the low defect density and high purity necessary for subsequent epitaxial growth.
Custom Boron-Doped SCD (BDD) Epitaxy:
- P- Channel Layer: We provide lightly boron-doped SCD epitaxy (required nominal concentration of 5 x 10¹⁶ cm^-3) with thicknesses up to 500 µm, offering the high crystalline quality necessary for minimizing scattering and maximizing channel mobility.
- P++ Ohmic Regrowth Material: We supply highly concentrated BDD layers for achieving low-resistance ohmic contacts (P++), critical for the observed triode-like/SCL behavior. Our expertise ensures sharp doping profiles and excellent interface quality required for reliable regrowth.

Customization Potential

Replicating and scaling this device geometry requires highly precise handling and post-processing capabilities, all available in-house at 6CCVD:

Requirement from Paper	6CCVD Custom Capability	Benefit for Researchers
Specific Dimensions (10 x 10 mm²)	Custom Dimensions up to 125 mm	Enables scale-up of device fabrication for large arrays and commercial feasibility testing (PCD).
Fin Height (660 nm)	Custom Thickness Control	We guarantee SCD and PCD thicknesses from 0.1 µm up to 500 µm, ensuring precise material layering for nanoscale architectures.
Ti/Pt/Au Ohmic Contacts	Custom Metalization Services	We offer in-house deposition of metal stacks including Ti, Pt, Au, Pd, W, and Cu, allowing researchers to optimize ohmic contact resistivity post-regrowth.
Precision Patterning	Laser Cutting & Etching Support	Our precision laser cutting services support small feature definition and complex geometry creation, necessary for patterning the S/D and gate regions in future iterations.
High Surface Quality	Ultra-Smooth Polishing	We provide SCD polishing services achieving Ra < 1 nm, which is vital for minimizing surface defects that could degrade channel mobility or interfere with subsequent dry etching steps.

Engineering Support

The transition from Ohmic law transport to Space Charge Limited transport, detailed in this research, is highly sensitive to thermal carrier density and doping concentration. 6CCVD’s in-house team of PhD material scientists specializes in optimizing BDD profiles for specific electronic applications.

We offer expert consultation on:

Optimizing epitaxial recipe parameters to control activated dopant concentration and thermal stability across the critical 20 °C to 150 °C operational range.
Selecting the ideal SCD orientation and crystalline quality for replication or extension of diamond Static Induction Transistor (SIT) projects.

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

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41598-020-59049-5