A5078113747- Diamond and Carbon-based Materials Research
- Semiconductor materials and devices
- GaN-based semiconductor devices and materials
- Metal and Thin Film Mechanics
- Silicon Carbide Semiconductor Technologies
- Thermal properties of materials
- Force Microscopy Techniques and Applications
- Electronic and Structural Properties of Oxides
- Mechanical and Optical Resonators
- High-pressure geophysics and materials
- Adhesion, Friction, and Surface Interactions
- Advanced Surface Polishing Techniques
- Advancements in Semiconductor Devices and Circuit Design
- ZnO doping and properties
- Advanced MEMS and NEMS Technologies
- Nanowire Synthesis and Applications
- Heat Transfer and Optimization
- Carbon Nanotubes in Composites
- Photonic Crystals and Applications
- Photocathodes and Microchannel Plates
- Ga2O3 and related materials
- Advanced ceramic materials synthesis
- Photonic and Optical Devices
- Nanofluid Flow and Heat Transfer
- Thin-Film Transistor Technologies
United States Naval Research Laboratory
2015-2024
University of California, Los Angeles
2020
Georgia Institute of Technology
2020
United States Navy
2016-2018
Stanford University
2016
Kyung Hee University
2016
University of Illinois Urbana-Champaign
2016
Science Applications International Corporation (United States)
2006-2013
Northrop Grumman (United States)
2012
Geophysical Center
2006
Nanocrystalline columnar-structured diamond films with column diameters less than 100 nm and thicknesses in the range of 1–5 μm were grown on silicon substrates by chemical vapor deposition (CVD) a microwave plasma reactor purified methane hydrogen used as reactants. Uniform conformal nucleation densities excess 1012 cm−2 accomplished prior to growth seeding explosively formed nanodiamonds, which resulted good optical quality films. The film thickness was measured situ laser reflectometry...
We report the fabrication and operation of nanomechanical resonant structures in nanocrystalline diamond. For this purpose, continuous diamond films as thin 80 nm were grown using microwave plasma enhanced chemical vapor deposition. The lateral dimensions fabricated small 50 measured mechanical frequencies up to 640 MHz. quality factors range 2500–3000 at room temperature. elastic properties these obtained via measurements indicate a Young’s modulus close that single-crystal
Diamond-based photonic devices offer exceptional opportunity to study cavity QED at room temperature. Here we report fabrication and optical characterization of high quality crystal (PC) microcavities based on nanocrystalline diamond. Fundamental modes near the emission wavelength negatively charged nitrogen-vacancy (N-V) centers (637 nm) with factors (Qs) as 585 were observed. Three-dimensional Finite-Difference Time-Domain (FDTD) simulations carried out had excellent agreement experimental...
While there is a great wealth of data for thermal transport in synthetic diamond, remains much to be learned about the impacts grain structure and associated defects impurities within few microns nucleation region films grown using chemical vapor deposition. Measurements inhomogeneous anisotropic conductivity thinner than 10 μm have previously been complicated by presence substrate boundary resistance. Here, we study conduction suspended polycrystalline with thicknesses ranging between 0.5...
The first CVD nanocrystalline diamond micromechanical disk resonator with material-mismatched stem has been demonstrated at a record frequency of 1.51 GHz an impressive Q 11,555, which is more than 7X higher in previous 1.14-GHz polysilicon resonator, and achieves frequency-Q product 1.74/spl times/10/sup 13/ that now exceeds the 1/spl some best quartz crystals. In addition, 1.27-GHz version excess 12,000 exhibits measured motional resistance only 100 k/spl Omega/ dc-bias voltage 20 V, 34X...
The in-plane and cross-plane thermal conductivity of polycrystalline diamond near its nucleation region have been measured by Raman thermography assisted TiO2 nanoparticles picosecond time-domain thermoreflectance (TDTR). This information has combined with a finite element model making use the real grain structure, including on orientation, film extracted transmission electron microscopy (TEM). methodology allows to simultaneously determine resistance between grains lattice sample without...
The development of electronic devices, especially those that involve heterogeneous integration materials, has led to increased challenges in addressing their thermal operational temperature demands. heat flow these systems is significantly influenced or even dominated by boundary resistance at the interface between dissimilar materials. However, controlling and tuning transport across an adjacent materials so far drawn limited attention. In this work, we grow chemical vapor-deposited diamond...
High electron mobility transistors (HEMTs) based on the AlGaN/GaN heterostructure are excellent candidates for power switching applications due to high critical field of wide bandgap III-N materials. However, reduction drain current at bias is a recognized device problem dominated by self-heating processes in regimes [1]. Reducing HEMT channel temperature increases carrier mobility, decreases transition times, reduces losses, and ultimately improves converter efficiency. Despite attractive...
Reduced performance in Gallium Nitride (GaN)-based high electron mobility transistors (HEMTs) as a result of self-heating has been well-documented. To mitigate this effect, the incorporation thermal conductivity diamond heat spreading films or substrates proposed. A mid-process integration scheme, termed "gate-after-diamond," is shown to improve budget for NCD deposition and enables scalable, large-area coating without degrading Schottky gate metal. The optimization process step presented...
A finite-element model coupling 2-D electron gas (2-DEG) density, piezoelectric polarization charge QP, and intrinsic stress induced by a nanocrystalline diamond capping layer, was developed for AlGaN/GaN high mobility transistors. Assuming the surface potential is unchanged an additional from capping, tensile cap leads to in heterostructure and, thus increase 2-DEG under gate. As result, compressive near gate edges would develop lead decreased regions between source drain contacts (SDCs)....
Gallium nitride (GaN) high electron-mobility transistors (HEMTs) offer considerable high-power operation but suffer in reliability due to potentially damaging self-heating. In this study, self-heating AlGaN/GaN HEMTs on conductivity substrates is assessed using a high-resolution thermoreflectance (TR) imaging technique, compare the thermal response between GaN-on-Si, GaNon-Diamond, and GaN-on-4H-SiC. The TR method accuracy at density verified nonlinear coefficient of (CTR) as function...
The low thermal conductivity of β-Ga2O3 is a significant concern for maximizing the potential this ultra-wide bandgap semiconductor as power switching device technology. Here, we report on use nanocrystalline diamond (NCD) deposited via microwave plasma enhanced chemical vapor deposition (MP-CVD) top-side, device-level management solution lateral transistor. NCD was grown MP-CVD β-(AlxGa1−x)2O3/β-Ga2O3 heterostructures prior to gate formation field-effect A reduced growth temperature 400 °C...
We present the first nanomechanical resonators microfabricated in single-crystal diamond. Shell-type only 70 nm thick, thinnest single crystal diamond structures produced to date, demonstrate a high-quality factor (Q ≈ 1000 at room temperature, Q 20 000 10 K) radio frequencies (50-600 MHz). Quality dependence on temperature and frequency suggests an extrinsic origin dominant dissipation mechanism methods further enhance resonator performance.
Thin diamond films of thickness near 1 μm can have highly nonuniform thermal conductivities owing to spatially varying disorder associated with nucleation and grain coalescence. Here, we examine the nonuniformity for nanocrystalline chemical vapor deposited 0.5, 1.0, 5.6 using picosecond thermoreflectance from both top bottom surfaces, enabled by etching a window in silicon substrate. The extracted local vary less than 100 W m−1 K−1 more 1300 suggest that most defective material is confined...
Trace amounts of Mg deposited on a diamond (100) substrate surface facilitate the growth cubic boron nitride (c‐BN) by ion beam‐assisted molecular beam epitaxy. Fourier transform infrared spectroscopy indicates that films grown with are cubic, while those without either hexagonal BN or lacking measurable signatures. Initiating 0.005 monolayer equivalent is sufficient to yield epitaxial >99% c‐BN. Reflection high energy electron diffraction, loss spectroscopy, and X‐Ray photoelectron...
In this work, the transient thermal and electrical characteristics of top-gated (TG), ultrathin, atomic-layer-deposited (ALD), back-end-of-line (BEOL) compatible indium oxide (In2O3) transistors on various thermally conductive substrates are co-optimized by visualization self-heating effect (SHE) utilizing an ultrafast high-resolution (HR) thermo-reflectance (TR) imaging system overcome challenges through substrate management short-pulse measurement. At steady-state, temperature increase (...
In this split-wafer study, we have compared the dc, pulsed, small and large signal RF electrical performance of nanocrystalline diamond (NCD) coated AlGaN/GaN high electron mobility transistors (HEMTs) to reference devices with silicon nitride passivation only. The NCD-coated HEMTs were observed outperform in transconductance, large-signal gain, output power density, power-added efficiency at 4 GHz. measured improvements suspected be related reduced dispersion lower source access resistance...
Top-side integration of nanocrystalline diamond films in the fabrication sequence AlGaN/GaN high electron mobility transistors is demonstrated. Reliable oxygen plasma etching capping layer, required for a diamond-before-gate process, was implemented by using sacrificial SiN "dummy" gate. Hall characterization showed minimal (∼6%) reduction sheet carrier density and commensurate increase resistance, while maintaining on-state drain current density. Off-state threshold voltage were increased,...
Ga2O3 has attracted great attention for electronic device applications due to its ultra-wide bandgap, high breakdown electric field, and large-area affordable substrates grown from the melt. However, thermal conductivity is significantly lower than that of other wide bandgap semiconductors, which will impact ability be used in power density applications. Thermal management electronics key reliability, especially frequency devices. Similar method cooling GaN-based electron mobility...
Nanocrystalline diamond films and e-beam patterning techniques have been used to fabricate visible near-infrared photonic slab crystals (PhCs) with deep submicron feature sizes. Two methods of fabrication, both based on electron-beam lithography, explored are detailed in this Communication. The first method uses direct flowable oxide as a hard mask for subsequent highly anisotropic oxygen plasma reactive ion etching the nanocrystalline film. second involves image inversion employs an...