3,199 research outputs found
Active-matrix GaN micro light-emitting diode display with unprecedented brightness
Displays based on microsized gallium nitride light-emitting diodes possess extraordinary brightness. It is demonstrated here both theoretically and experimentally that the layout of the n-contact in these devices is important for the best device performance. We highlight, in particular, the significance of a nonthermal increase of differential resistance upon multipixel operation. These findings underpin the realization of a blue microdisplay with a luminance of 10⁶ cd/m²
Optimal overlayer inspired by Photuris firefly improves light-extraction efficiency of existing light-emitting diodes
In this paper the design, fabrication and characterization of a bioinspired
overlayer deposited on a GaN LED is described. The purpose of this overlayer is
to improve light extraction into air from the diode's high refractive-index
active material. The layer design is inspired by the microstructure found in
the firefly Photuris sp. The actual dimensions and material composition have
been optimized to take into account the high refractive index of the GaN diode
stack. This two-dimensional pattern contrasts other designs by its unusual
profile, its larger dimensions and the fact that it can be tailored to an
existing diode design rather than requiring a complete redesign of the diode
geometry. The gain of light extraction reaches values up to 55% with respect to
the reference unprocessed LED.Comment: 9 pages, 9 Figures, published in Optics Expres
Fabrication technology for high light-extraction ultraviolet thin-film flip-chip (UV TFFC) LEDs grown on SiC
The light output of deep ultraviolet (UV-C) AlGaN light-emitting diodes
(LEDs) is limited due to their poor light extraction efficiency (LEE). To
improve the LEE of AlGaN LEDs, we developed a fabrication technology to process
AlGaN LEDs grown on SiC into thin-film flip-chip LEDs (TFFC LEDs) with high
LEE. This process transfers the AlGaN LED epi onto a new substrate by
wafer-to-wafer bonding, and by removing the absorbing SiC substrate with a
highly selective SF6 plasma etch that stops at the AlN buffer layer. We
optimized the inductively coupled plasma (ICP) SF6 etch parameters to develop a
substrate-removal process with high reliability and precise epitaxial control,
without creating micromasking defects or degrading the health of the plasma
etching system. The SiC etch rate by SF6 plasma was ~46 \mu m/hr at a high RF
bias (400 W), and ~7 \mu m/hr at a low RF bias (49 W) with very high etch
selectivity between SiC and AlN. The high SF6 etch selectivity between SiC and
AlN was essential for removing the SiC substrate and exposing a pristine,
smooth AlN surface. We demonstrated the epi-transfer process by fabricating
high light extraction TFFC LEDs from AlGaN LEDs grown on SiC. To further
enhance the light extraction, the exposed N-face AlN was anisotropically etched
in dilute KOH. The LEE of the AlGaN LED improved by ~3X after KOH roughening at
room temperature. This AlGaN TFFC LED process establishes a viable path to high
external quantum efficiency (EQE) and power conversion efficiency (PCE) UV-C
LEDs.Comment: 22 pages, 6 figures. (accepted in Semiconductor Science and
Technology, SST-105156.R1 2018
Effective thermal management of multiple electronic components
[[abstract]]The objective of this paper is to provide an effective and accurate analytical solution to compute the spreading thermal resistance of a vapor chamber thermal module, as well as the surface temperatures and the heat flux distributions at the heating surface. The analytical solutions are expressed in a reduced unit system with the governing parameters of the corresponding distance between heat sources, dimensionless plate thickness of the vapor chamber. This paper also presents vapor chamber temperature distribution, and it is correlation to heat source sizes, hence, spreading thermal resistance decreases with the increasing lateral length. There is the obvious difference between spreading thermal and conductive thermal resistance as lateral length is disproportion to heating area. Therefore, spreading thermal resistance is an important factor when design the thermal solution of a high density chipset power, and it caused high temperature in heat sources by embedded a thinner heat sink base. According to Fourier conductivity theorem, spreading thermal resistance is disproportion to sink base, then thermal resistance is not only parameter for vapor chamber module design, it needs to consider spreading resistance of vapor chamber and fin performance for cooling LEDs array, in order to prevent mismatch on numerical analysis and mathematical calculation. Thermal simulation is used as a design tool, and it is close to experimental data. The difference is within 5.9%, and it presents a precise result.[[conferencetype]]國際[[conferencedate]]20101020~20101022[[iscallforpapers]]Y[[conferencelocation]]Taipei, Taiwa
Secure thermal infrared communications using engineered blackbody radiation
The thermal (emitted) infrared frequency bands, from 20–40 THz and 60–100 THz, are best known for applications in thermography. This underused and unregulated part of the spectral range offers opportunities for the development of secure communications. The ‘THz Torch' concept was recently presented by the authors. This technology fundamentally exploits engineered blackbody radiation, by partitioning thermally-generated spectral noise power into pre-defined frequency channels; the energy in each channel is then independently pulsed modulated and multiplexing schemes are introduced to create a robust form of short-range secure communications in the far/mid infrared. To date, octave bandwidth (25–50 THz) single-channel links have been demonstrated with 380 bps speeds. Multi-channel ‘THz Torch' frequency division multiplexing (FDM) and frequency-hopping spread-spectrum (FHSS) schemes have been proposed, but only a slow 40 bps FDM scheme has been demonstrated experimentally. Here, we report a much faster 1,280 bps FDM implementation. In addition, an experimental proof-of-concept FHSS scheme is demonstrated for the first time, having a 320 bps data rate. With both 4-channel multiplexing schemes, measured bit error rates (BERs) of < 10(−6) are achieved over a distance of 2.5 cm. Our approach represents a new paradigm in the way niche secure communications can be established over short links
Flashing LEDs for microalgal production
Flashing lights are next-generation tools to mitigate light attenuation and increase the photosynthetic efficiency of microalgal cultivation systems illuminated by light-emitting diodes (LEDs). Optimal flashing light conditions depend on the reaction kinetics and properties of the linear electron transfer chain, energy dissipation, and storage mechanisms of a phototroph. In particular, extremely short and intense light flashes potentially mitigate light attenuation in photobioreactors without impairing photosynthesis. Intelligently controlling flashing light units and selecting electronic components can maximize light emission and energy efficiency. We discuss the biological, physical, and technical properties of flashing lights for algal production. We combine recent findings about photosynthetic pathways, self-shading in photobioreactors, and developments in solid-state technology towards the biotechnological application of LEDs to microalgal production.Foundation for Science and Technology (FCT, Portugal) [CCMAR/Multi/04326/2013]Nord UniversityNordland County Government (project Bioteknologi en framtidsrettet naering)INTERREG V-A Espana-Portugal project [0055 ALGARED + 5E]Portuguese Foundation for Science and Technology [SFRH/BD/105541/2014, SFRH/BD/115325/2016]info:eu-repo/semantics/publishedVersio
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