Components Of Light-emitting Diodes Research Articles

Structural and Material-Based Approaches for the Fabrication of Stretchable Light-Emitting Diodes.

Stretchable displays, capable of freely transforming their shapes, have received significant attention as alternatives to conventional rigid displays, and they are anticipated to provide new opportunities in various human-friendly electronics applications. As a core component of stretchable displays, high-performance stretchable light-emitting diodes (LEDs) have recently emerged. The approaches to fabricate stretchable LEDs are broadly categorized into two groups, namely "structural" and "material-based" approaches, based on the mechanisms to tolerate strain. While structural approaches rely on specially designed geometries to dissipate applied strain, material-based approaches mainly focus on replacing conventional rigid components of LEDs to soft and stretchable materials. Here, we review the latest studies on the fabrication of stretchable LEDs, which is accomplished through these distinctive strategies. First, we introduce representative device designs for efficient strain distribution, encompassing island-bridge structures, wavy buckling, and kirigami-/origami-based structures. For the material-based approaches, we discuss the latest studies for intrinsically stretchable (is-) electronic/optoelectronic materials, including the formation of conductive nanocomposite and polymeric blending with various additives. The review also provides examples of is-LEDs, focusing on their luminous performance and stretchability. We conclude this review with a brief outlook on future technologies.

Scalable Bilayer MoS2‐Based Vertically Inverted p–i–n Light‐Emitting Diodes

AbstractHerein, a vertically inverted p–i–n architecture of light‐emitting diodes (LEDs) is designed for manufacturing feasibility and demonstrated scalable bilayer MoS2‐based LEDs. A 4 inch scale bilayer MoS2 is prepared by a two‐step growth method allocating the pre‐deposition of a few‐nm thick metal film and post‐sulfurization. To apply bilayer MoS2 for an active layer in LEDs, the film is transferred over ZnO nanoparticle layers, an electron transfer layer, and then the rest of the LED components are constructed by thermal deposition. This vertically inverted LED architecture allows individual organic or inorganic components to incorporate without degradation during the wet‐transfer process and transfer electron or hole carriers across separate layers, resulting in efficient radiative recombination in the MoS2 emitting layer. MoS2‐based LEDs exhibit electroluminescence of ≈5.41 cd m−2 throughout four active areas of 6.25 mm2 at a driving voltage of 7 V. Therefore, this achievement can overcome the drawbacks of existing transition metal dichalcogenides (TMDs)‐based optoelectrical applications and extend its potential in various fields, such as flexible, ultrathin, or transparent displays.

High-concentration F-incorporated ZnO thin films doped via femtosecond-laser hyperdoping

ZnO is a transparent conductive oxide that has received great attention over the past few decades, as it is a key component in light-emitting diodes, gas sensors, and solar cells. However, the electrical conductivity of intrinsic ZnO is not ideal, and thus, ZnO is often doped with appropriate elements such as fluorine (F). Unfortunately, the lack of adequate precursors in traditional doping methods may increase the difficulty of ZnO doping with F. In this work, we realized, for the first time, high-concentration F-doped ZnO thin films with a high Hall mobility of 20.7 cm2/V/s via femtosecond-laser hyperdoping. The highest atomic percentage of F was determined to be 8.3 at.%, which was over three times larger than that of previously reported F-doped ZnO films. Compared with pristine ZnO, the highest carrier concentration of the F-doped ZnO could be increased by four orders of magnitude, and the resistivity could be reduced by three orders of magnitude. Our results demonstrated that the femtosecond-laser hyperdoping technology could achieve efficient non-metallic hyperdoping of ZnO with high transparency and Hall mobility, thereby reducing the power dissipation and improving the current carrying capacity of ZnO-based devices.

Studying the nomenclature of dioxins using a structure model kit based on electronic components linked with plastic tubes

Abstract Commercially available molecular models are elaborately made but generally expensive, which hinders their distribution to all classroom students. Aiming at developing an affordable molecular model, we developed a structure model kit consisting of inexpensive electronic components including transistors and colored light-emitting diodes (LEDs) with a total cost of ca. 2 USD. The structure model kit was designed for building a family of environmental pollutant molecules known as dioxins, in which transistor, white LED, red LED, and yellow LED components are used to represent sp2 carbon, hydrogen, oxygen, and chlorine atoms, respectively. Herein, we report an activity directed to nonchemistry majors studying environmental science and electronic engineering to help them gain insight into the molecular structure of dioxins using the newly developed structure model kit. The activity was well received by many students, some of whom came to understand the relationship between the structure and nomenclature of dioxins, mainly 2,3,7,8-tetrachlorinated dibenzo-p-dioxin (2,3,7,8-TCDD) and its isomers.

An improved accelerated degradation model for LED reliability assessment with self-heating impacts

Light-emitting diodes (LEDs) are a solid-state light source being used in numerous applications, including display, communications, medical services, etc. However, the reliability assessment of LED components is still challenging due to the growing up of the LED complexity and/or the miniaturization of assembly technologies. To face this challenge, this paper proposes a novel accelerated degradation testing (ADT) model considering the self-heating impact in the degradation process of a LED component. So, the self-heating impact is first analyzed and modeled. In fact, the junction temperature of a LED component depends not only on the heat generation (e.g., drive current, dispersing heat) but also on the current state (degradation level) of the component. Then, a modified stochastic difference equation is developed for modelling the degradation process by considering the self-heating impact. The LED reliability formulation is finally derived. In addition, an estimation method based on the maximum likelihood is developed to estimate the proposed model's parameters from experimental data. To validate our models, a case study for LED light sources is implemented. The obtained results show that, compared to the TM-21 standard and the conventional ADT methods, our proposed approach achieves better results in the LED reliability assessment.

Optical OFDM for SiPM-Based Underwater Optical Wireless Communication Links.

Underwater optical wireless systems have dual requirements of high data rates and long ranges in harsh scattering and attenuation conditions. In this paper, we investigate the advantages and limitations of optical orthogonal frequency-division multiplexing (O-OFDM) signaling when a silicon photo-multiplier (SiPM) is used at the receiver in order to ensure high sensitivity. Considering a light-emitting diode (LED) transmitter and taking into account the limited dynamic range imposed by the transmitter and the SiPM receiver, we study the performance of three popular O-OFDM schemes, i.e., DC-biased, asymmetrically-clipped, and layered asymmetrically-clipped O-OFDM (DCO-, ACO-, and LACO-OFDM, respectively). We consider a constraint on transmit electrical power and take into account the required DC bias for the three considered schemes in practice, showing the undeniable advantage of ACO- and LACO-OFDM in terms of energy efficiency. For instance, for the considered SiPM and LED components, a spectral efficiency of ∼1 bps/Hz with a data rate of 20 Mbps, a link range of 70 m, and a target bit-error-rate (BER) of , ACO and LACO allow a reduction of about 10 and 6 mW, respectively, in the required , compared to DCO-OFDM. Meanwhile, we show that when relaxing the constraint, DCO-OFDM offers the largest operational link range within which a target BER can be achieved. For instance, for a target BER of and a data rate of 20 Mbps, and considering of 185, 80, and 50 mW for DCO-, LACO-, and ACO-OFDM, respectively, the corresponding intervals of operational link range are about 81, , and m. Lastly, we show that LACO-OFDM makes a good compromise between energy efficiency and operational range flexibility, although requiring a higher computational complexity and imposing a longer latency at the receiver.

Cryostat setup for measuring spectral and electrical properties of light-emitting diodes at junction temperatures from 81 K to 297 K.

We introduce a cryostat setup for measuring fundamental optical and electrical properties of light-emitting diodes (LEDs). With the setup, the cryostat pressure and the LED properties of the forward voltage, junction temperature, and electroluminescence spectrum are monitored with temperature steps less than 1.5 K, over the junction temperature range of 81-297 K. We applied the setup to commercial yellow AlGaInP and blue InGaN LEDs. At cryogenic temperatures, the fine structure of the electroluminescence spectra became resolved. For the yellow LED, we observed the phonon replica at 2.094 eV that was located 87 meV below the peak energy at the junction temperature of 81 K. For the blue LED, we observed the cascade phonon replicas at 2.599 eV, 2.510 eV, and 2.422 eV with the energy interval of 89 meV. For both LED types, the forward voltage increased sharply toward the lower temperatures due to the increased resistivity of materials in the LED components. We found significant differences between the temperature dependent behaviors of the forward voltages, spectral peak energies, and bandgap energies of LEDs obtained from the Varshni formula. We also noted a sharp pressure peak at 180-185 K arising from the solid-vapor phase transition of water when the base level of the cryostat pressure was approximately 0.4 mPa.

Automatic System to Fish Feeder and Water Turbidity Detector Using Arduino Mega

This tool system works automatically, which functions to feed the fish and detect the water turbidity. The fish that being feed and the water that is detected are in Aquarium or in Pond. Input for this tool are RTC (real time clock), Turbidity sensor and on/off button. To start or turn off the tool is used on/off button, to feed the fish automatically is used RTC component and to detect water turbidity is used turbidity sensor. Output for this tool is an LCD (liquid crystal display) display, Buzzer, Servo Motor and LED (light emitting diode) component. To display information in writing format is used LCD display, to sounding information in sound format is used buzzer, to move waterways door and foodways door is used servo motor and to indicate the tool is activated and processing is used LED component. The main component of controlling all component and program in this tool is Arduino Mega 2560. To make a tool program that will install in Arduino Mega is used C programming language for Arduino. By using this tool, will make activity in feeding the fish and detect turbidity of water be more effective, more efficient and easier than manually.

Luminescence of red-emitting phosphor Rb5Nb3OF18:Mn4+ for warm white light-emitting diodes

Abstract Red-emitting phosphor Rb5Nb3OF18:Mn4+ was prepared by an ion exchange method and its crystal structure, luminescent properties and application were discussed. Mn4+ in Rb5Nb3OF18 which has appropriate band gap experiences a strong crystal field and emits intense red light around 633 nm with one broad excitation band at ∼470 nm. In addition, the light-emitting diodes (LEDs) coated Rb5Nb3OF18:Mn4+ exhibit excellent luminescent performances, such as the white LED can emit warm white light with high luminous efficiency (113.6 lm/W). Hence, Rb5Nb3OF18:Mn4+ could be a potential red component for white LEDs.

Thermophotonic cooling in GaAs based light emitters

Fundamental thermodynamic considerations reveal that efficient emission from an electrically injected light emitting diode (LED) can lead to the cooling of the device. This effect, known as electroluminescent (EL) cooling, has been identified decades ago, but it has not been experimentally demonstrated in semiconductors at practical operating conditions due to the extreme requirements set for the efficiency of the light emission. To probe the conditions of EL cooling in GaAs based light emitters, we have designed and fabricated LED structures with integrated photodiodes (PDs), where the optically mediated thermal energy transport between the LED and the PD can be easily monitored. This allows characterization of the fundamental properties of the LED and a path for eliminating selected issues encountered in conventional approaches for EL cooling, such as the challenging light extraction. Despite several remaining nonidealities, our setup demonstrates a very high directly measured quantum efficiency of 70%. To characterize the bulk part of the LED, we also employ a model for estimating the power conversion efficiency (PCE) of the LED, without the contribution of non-fundamental nonidealities such as photodetection losses. Our results suggest that the PCE of the LED peaks at around 105–115%, exceeding the 100% barrier required to reach the EL cooling regime by a clear margin. This implies that the LED component in our device is in fact cooling down by transporting thermal energy carried by the emitted photons to the PD. This provides a compelling incentive for further study to confirm the result and to find ways to extend it for practically useful EL cooling.

Single chip design for detection and recovery of series LED open/short fault tolerance circuit

Light emitting diode (LED) lighting is widely used in current. However, lighting robustness is low in a series loop since the lighting shuts down as one LED fails. This study proposes a power chip for fault detection and isolation for enhancement of LED's fault-withstanding capability. The chip can automatically detect the failed LEDs and bypass them, and let others continue to work. The authors implemented four bypass loops using a power metal oxide semiconductor (MOS) on the single chip. This chip can drive 1 A with 4-bit current dimming, which includes four bypass power P-type MOSs, one power N-type MOS, schedule controller, level shifter and over voltage protection. The schedule controller with a state machine can quickly find which one LED fail and recover it soon. The prototyping chip was designed using TSMC 0.25 μm, which is the second generator high-voltage technology, and the resulting chip area with pads is only 1.3 × 1.7 mm2. The chip had been successfully implemented and measured to drive and bypass four LED components or modules.

Blue-Emitting Arylalkynyl Naphthalene Derivatives via a Hexadehydro-Diels-Alder Cascade Reaction.

We describe here three alkynyl substituted naphthalenes that display promising luminescence characteristics. Each compound is easily and efficiently synthesized in three steps by capitalizing on the hexadehydro-Diels-Alder (HDDA) cycloisomerization reaction in which an intermediate benzyne is captured by tetraphenylcyclopentadienone, a classical trap for benzyne itself. These compounds luminesce in the deep blue when stimulated either optically (i.e., photoluminescence in both solution and solid films) or electrically [in a light-emitting diode (LED)]. The photophysical properties are relatively insensitive to the electronic nature of the substituents (H, OMe, CO2Me) that define these otherwise identical compounds. Overall, our observations suggest that the twisted nature of the five adjacent aryl groups serves to minimize the intermolecular interaction between core naphthalene units in different sample morphologies. These compounds represent promising leads for the identification of others of value as the emissive component of organic LEDs (OLEDs).

Building blocks in creative computing: modularity increases the probability of prototyping novel ideas

Design is a cyclical journey from creative ideas to concrete realizations of those ideas though prototyping. Designers today have increasing access to low-cost technology toolkits within the electronic and computational domain. However, for technical novices, including electronic components in prototypes can hamper the ability to create novel ideas by introducing technical obstacles. Electronic modules can increase the probability of prototyping success, at the cost of reduced design flexibility. This research (1) presents the results of a pilot usability evaluation of (N = 68) participants making physical light emitting diode (LED) light creations with non-modular electronics components, and (2) uses this evaluation to motivate a creative prototyping study (N = 86) exploring the question: ‘How does prototyping tool modularity influence the creative result?’ Using a browser-based crowd platform (Amazon’s Mechanical Turk), participants created electric ‘creature circuits’ with LEDs in a virtual prototyping environment. We found that increasing the modularity of LED components (i) increased the novelty rating of prototypes as rated by a condition-blind panel, (ii) increased the quantity of prototypes created and the quantity of LEDs used by study participants, (iii) increased participants’ degree of perceived self-efficacy and cognitive flow, and (iv) reduced the number of errors due to LED polarity. The results highlight that novice prototyping with electronics is difficult due to the number of possible ways to fail. The findings show that modularity can reduce the chance of errors and improve the likelihood of creating novel prototypes.

Copper Aluminum Nano Junction Normal Temperature Processes and Methods Applied to the LED High Heat Transfer Performance

High-power light-emitting diodes (LED) have extremely broad applications. However, with the job requirements of high-brightness and high color temperature from light-emitting diodes, it must be followed to enlarge the operating current, thus heating up more rapidly. If its heat dissipation problem cannot be effectively solved, operation will be prone to bring about color shift, and it may even considerably shorten its life. Moreover, application value will therefore be greatly reduced. So in order to enhance the high-power LED luminous brightness and life to cope with the future development needs of high-power LED components, it is necessary to replace the use of conductive silver paste to stick thermally conductive Cu slug fixing grain and lead frame heat dissipation aluminum sheet. This is done by directly bonding thermally conductive Cu slug with pure aluminum, the formation of highly efficient direct heat conduction cooling structure. Therefore the topic points at the crux of the LED heat dissipation difficulty, puts forward of copper and aluminum bonding technology in the ordinary temperature and pressure, method to effectively improve thermal conductivity performance between LED die bond Cu slug and joining aluminum cooling module. This will ultimately make the LED's operation and applications perfect.

Formal Modeling and Verification of Smart Traffic Environment with Design Aided by UML

Issue challan in response to rules violation, LED (Light Emitting Diode) and Bridge components of this proposed Smart Traffic Monitoring and Guidance System are presented in this paper to monitor violation of rules, update users about traffic congestion through LED and to provide central hub to communicate with sensors to update server about the traffic situation. It involves the Wireless Sensors and actors to communicate with the system. The proposed components require fewer resources in terms of sensors and actors. Further sensors identify violation of rules through issue challan. Secondly, LED component provides information to users about the traffic situations. Thirdly, Bridge component is used to provide central hub to communicate with different components in the proposed model and to update the server. The proposed components of this model are implemented by developing formal specification using VDM-SL. VDM-SL is a formal specification language used for analysis of complex systems. The developed specification is validated, verified and analyzed using VDM-SL Toolbox.

Study of High-Brightness LED Samples Aged Under Stress Temperature Conditions: Electrical Characterizations and Signature Evolution Analysis

Light-emitting diode (LED) components used in lighting or backlighting applications remain operational for a long time, but in some cases, early catastrophic failures and degradation of the photocolorimetric characteristics are observed. Hence, manufacturers are highly interested in early detection of degradation mechanisms and the relationship between electrical signature evolutions and aging in order to predict the remaining lifetime of LED components. This paper describes a methodology to identify future characteristics degradation based on electrical signatures observed within the first hundred hours using an accelerating aging method. For that purpose, four kinds of high-power LEDs are submitted to temperature stress conditions that provide early aging electrical signatures. The first part of this paper describes the experimental setup and the aging protocol. In the second part, we present signatures obtained via current–voltage ( $I$ – $V$ ) and capacitance–voltage ( $C$ – $V$ ) data.

Light work for domestic LEDs

Light-emitting diode (LED) lightbulbs are becoming increasingly popular, but claims made by some manufacturers on longevity have been disputed. The EU brought in directives to increase the quality of LED construction as the lamps are more complex to manufacture and there are varying levels of quality. But there are anecdotal stories about poor quality construction. There are two distinct markets: the retail market, which is still relatively small because of the high price of LED bulbs; and the new build market, specifically builders who are incentivised to make new build homes as energy efficient as possible. The new build market is the larger of the two, although the retail market is expected to catch up. LED lamps have greater energy-efficient advantages over CFLs but without the problem of unflattering tones and uncomfortable flicker. However, unlike CFLs and incandescent products, the weakest component of LEDs is not the lamp, which can often last a great deal longer than some of the other intricate components.

Competing in the Global LED Industry: The Case of Taiwan

Light-emitting diode (LED) is a very essential application for energy-savings nowadays. The revenue of the Taiwan LED components industry is ranked top one in the world, followed by that of Japan and South Korea. Based on the advantage of their electronics industry, Taiwanese LED companies create a unique model to compete with the international firms. Large international LED companies achieve economies of scale by vertically integrating their operations. Taiwanese LED companies specialize and achieve an optimal efficiency by vertically disintegrating across the upstream, midstream, and downstream sectors in the value chains. Taiwanese LED companies create economies of scale and economies of scope through a complete industrial value chain.

Copper Aluminum Nano Junction Normal Temperature Processes and Methods Applied to the LED High Heat Transfer Performance

High-power light-emitting diodes (LED) have extremely broad applications. However, with the job requirements of high- brightness and high color temperature from light-emitting diodes, it must be followed to enlarge the operating current, thus heating up more rapidly. If its heat dissipation problem cannot be effectively solved, operation will be prone to bring about color shift, and it may even considerably shorten its life. Moreover, application value will therefore be greatly reduced. So in order to enhance the high-power LED luminous brightness and life to cope with the future development needs of high-power LED components, it is necessary to replace the use of conductive silver paste to stick thermally conductive Cu slug fixing grain and lead frame heat dissipation aluminum sheet. This is done by directly bonding thermally conductive Cu slug with pure aluminum, the formation of highly efficient direct heat conduction cooling structure. Therefore the topic points at the crux of the LED heat dissipation difficulty, puts forward of copper and aluminum bonding technology in the ordinary temperature and pressure, method to effectively improve thermal conductivity performance between LED die bond Cu slug and joining aluminum cooling module. This will ultimately make the LED's operation and applications perfect.

A novel Ba2MgMoO6:Eu3+ orange-red phosphor: Photoluminescence properties and mechanism of charge and energy transfer

Abstract