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Article
Publication date: 4 August 2014

Krzysztof Górecki

The purpose of this paper is to present a new method of measuring thermal resistance of power light-emitting diodes (LEDs). Properties of power LEDs strongly depend on…

Abstract

Purpose

The purpose of this paper is to present a new method of measuring thermal resistance of power light-emitting diodes (LEDs). Properties of power LEDs strongly depend on their internal temperature. The value of this temperature depends on the cooling conditions characterized by thermal resistance.

Design/methodology/approach

The new method of measuring the value of this parameter belongs to the group of electric methods. In this method, the problem of estimating the value of electrical power converted into light is solved. By comparing the values of the case temperature obtained for the LED operating in the forward mode and the reverse-breakdown mode, the thermal power is estimated. On the basis of the measured value of the thermally sensitive parameter (the LED forward voltage) and the estimated value of the thermal power, thermal resistance is calculated.

Findings

The elaborated method was used to measure thermal resistance of the selected types of power LEDs operating at different cooling conditions. The correctness of the elaborated measurement method was proved by comparing the results of measurements obtained with the use of the new method and the infrared method.

Research limitations/implications

On the basis of the obtained results of measurements and the catalog data of the tested diodes, the dependence of the measurement error of thermal resistance of the LED on its luminous efficiency is discussed.

Originality/value

The new measurement method is easy to use and more accurate than the classical method of thermal resistance measurement of the diode.

Details

Microelectronics International, vol. 31 no. 3
Type: Research Article
ISSN: 1356-5362

Keywords

Article
Publication date: 7 August 2020

Przemysław Ptak, Krzysztof Górecki, Agata Skwarek, Krzysztof Witek and Jacek Tarasiuk

This paper aims to present the results of investigations that show the influence of soldering process parameters on the optical and thermal parameters of power LEDs.

Abstract

Purpose

This paper aims to present the results of investigations that show the influence of soldering process parameters on the optical and thermal parameters of power LEDs.

Design/methodology/approach

The power LEDs were soldered onto metal core printed circuit board (MCPCB) substrates in different soldering ovens: batch and tunnel types, characterized by different thermal profiles. Three types of solder pastes based on Sn99Ag0.3Cu0.7 with the addition of TiO2 were used. The thermal and optical parameters of the diodes were measured using classical indirect electrical methods. The results of measurements obtained were compared and discussed.

Findings

It was shown that the type of oven and soldering thermal profile considerably influence the effectiveness of the removal of heat generated in the LEDs tested. This influence is characterized by thermal resistance changes. The differences between the values of this parameter can exceed 20%. This value also depends on the composition of the soldering paste. The differences between the diodes tested can exceed 15%. It was also shown that the luminous flux emitted by the diode depends on the soldering process used.

Practical implications

The results obtained could be useful for process design engineers for assembling power LEDs for MCPCBs and for designers of solid-state light sources.

Originality/value

This paper presents the results of investigations into the influence of the soldering profiles and soldering pastes used on the effectiveness of the removal of heat generated in power LEDs. It shows and discusses how the factors mentioned above influence the thermal resistance of the LEDs and optical parameters that characterize the light emitted.

Details

Soldering & Surface Mount Technology, vol. 32 no. 4
Type: Research Article
ISSN: 0954-0911

Keywords

Article
Publication date: 19 July 2021

Mohd Ann Amirul Zulffiqal Md Sahar, Zainuriah Hassan, Sha Shiong Ng, Way Foong Lim, Khai Shenn Lau, Ezzah Azimah Alias, Mohd Anas Ahmad, Nur Atiqah Hamzah and Rahil Izzati Mohd Asri

The aims of this paper is to study the effects of the V/III ratio of indium gallium nitride (InGaN) quantum wells (QWs) on the structural, optical and electrical…

Abstract

Purpose

The aims of this paper is to study the effects of the V/III ratio of indium gallium nitride (InGaN) quantum wells (QWs) on the structural, optical and electrical properties of near-ultraviolet light-emitting diode (NUV-LED).

Design/methodology/approach

InGaN-based NUV-LED is successfully grown on the c-plane patterned sapphire substrate at atmospheric pressure using metal organic chemical vapor deposition.

Findings

The indium composition and thickness of InGaN QWs increased as the V/III ratio increased from 20871 to 11824, according to high-resolution X-ray diffraction. The V/III ratio was also found to have an important effect on the surface morphology of the InGaN QWs and thus the surface morphology of the subsequent layers. Apart from that, the electroluminescence measurement revealed that the V/III ratio had a major impact on the light output power (LOP) and the emission peak wavelength of the NUV-LED. The LOP increased by up to 53% at 100 mA, and the emission peak wavelength of the NUV-LED changed to a longer wavelength as the V/III ratio decreased from 20871 to 11824.

Originality/value

This study discovered a relation between the V/III ratio and the properties of QWs, which resulted in the LOP enhancement of the NUV-LED. High TMIn flow rates, which produced a low V/III ratio, contribute to the increased LOP of NUV-LED.

Details

Microelectronics International, vol. 38 no. 3
Type: Research Article
ISSN: 1356-5362

Keywords

Article
Publication date: 2 August 2021

Nur Atiqah Hamzah, Mohd Anas Ahmad, Rahil Izzati Mohd Asri, Ezzah Azimah Alias, Mohd Ann Amirul Zulffiqal Md Sahar, Ng Sha Shiong and Zainuriah Hassan

The purpose of this paper is to enhance the efficiency of the LED by introducing three-step magnesium (Mg) doping profile. Attention was paid to the effects of the Mg…

Abstract

Purpose

The purpose of this paper is to enhance the efficiency of the LED by introducing three-step magnesium (Mg) doping profile. Attention was paid to the effects of the Mg doping concentration of the first p-GaN layer (i.e. layer close to the active region). Attention was paid to the effects of the Mg doping concentration of the first p-GaN layer (i.e. layer close to the active region).

Design/methodology/approach

Indium gallium nitride (InGaN)–based light-emitting diode (LED) was grown on a 4-inch c-plane patterned sapphire substrate using metal organic chemical vapor deposition. The Cp2Mg flow rates for the second and third p-GaN layers were set at 50 sccm and 325 sccm, respectively. For the first p-GaN layer, the Cp2Mg flow rate varied from 150 sccm to 300 sccm to achieve different Mg dopant concentrations.

Findings

The full width at half maximum (FWHM) for the GaN (102) plane increases with increasing Cp2Mg flow rate. FWHM for the sample with 150, 250 and 300 sccm Cp2Mg flow rates was 233 arcsec, 236 arcsec and 245 arcsec, respectively. This result indicates that the edge and mixed dislocations in the p-GaN layer were increased with increasing Cp2Mg flow rate. Atomic force microscopy (AFM) results reveal that the sample grown with 300 sccm exhibits the highest surface roughness, followed by 150 sccm and 250 sccm. The surface roughness of these samples is 2.40 nm, 2.12 nm and 2.08 nm, respectively. Simultaneously, the photoluminescence (PL) spectrum of the 250 sccm sample shows the highest band edge intensity over the yellow band ratio compared to that of other samples. The light output power measurements found that the sample with 250 sccm exhibits high output power because of sufficient hole injection toward the active region.

Originality/value

Through this study, the three steps of the Mg profile on the p-GaN layer were proposed to show high-efficiency InGaN-based LED. The optimal Mg concentration was studied on the first p-GaN layer (i.e. layer close to active region) to improve the LED performance by varying the Cp2Mg flow rate. This finding was in line with the result of PL and AFM results when the samples with 250 sccm have the highest Mg acceptor and good surface quality of the p-GaN layer. It can be deduced that the first p-GaN layer doping has a significant effect on the crystalline quality, surface roughness and light emission properties of the LED epi structure.

Details

Microelectronics International, vol. 38 no. 3
Type: Research Article
ISSN: 1356-5362

Keywords

Article
Publication date: 3 August 2015

Krzysztof Górecki and Przemysław Ptak

– The purpose of this paper is to present an electrothermal model of the module containing power light emitting diodes (LEDs) situated on a common base.

Abstract

Purpose

The purpose of this paper is to present an electrothermal model of the module containing power light emitting diodes (LEDs) situated on a common base.

Design/methodology/approach

The electrothermal model of this device, which takes into account both self-heating and mutual thermal coupling between the diodes situated in this module, is described.

Findings

The correctness of the presented model is verified experimentally, and a good agreement of the calculated and measured optical and thermal characteristics of the considered module is obtained.

Research limitations/implications

The presented model can be used for different structures of the LED module, but electrical inertia in the diodes is omitted.

Practical implications

The presented model was used to calculate electrical, thermal and optical waveforms of the module OSPR3XW1 containing three power LED situated on the common base.

Originality/value

The presented model takes into account thermal inertia in the considered LED module and its cooling systems with mutual thermal coupling between all the diodes situated in the same module.

Details

Microelectronics International, vol. 32 no. 3
Type: Research Article
ISSN: 1356-5362

Keywords

Article
Publication date: 1 October 2018

Zhiwei Li

The purpose of this paper is to find an effective route to fabricate high transparent top electrode in quantum dots light-emitting diodes (QLEDs).

Abstract

Purpose

The purpose of this paper is to find an effective route to fabricate high transparent top electrode in quantum dots light-emitting diodes (QLEDs).

Design/methodology/approach

Al-doped ZnO (AZO) top cathode with high transparency have been deposited by an atomic layer deposition (ALD) method at 140°C for 1 h. The products are studied by UV-vis spectrometer and atomic force microscopy (AFM). The electroluminescence spectra of QLED are recorded using an Ocean Optics high-resolution spectrometer (HR4000). The devices were measured under ambient conditions without encapsulation.

Findings

The AZO-based QLED shows excellent performance with high luminance and current efficiency.

Originality/value

The AZO obtained by ALD method is a promising cathode candidate for application in QLEDs.

Details

Microelectronics International, vol. 35 no. 4
Type: Research Article
ISSN: 1356-5362

Keywords

Article
Publication date: 2 March 2015

Inese Parkova, Ivars Parkovs and Ausma Vilumsone

Flexible light-emitting textile display is designed with floats for electronic elements covering and electronic contacts insulation what at the same time provides an…

Abstract

Purpose

Flexible light-emitting textile display is designed with floats for electronic elements covering and electronic contacts insulation what at the same time provides an opportunity to develop aesthetic design of the display in the single piece construction of material. The paper aims to discuss these issues.

Design/methodology/approach

Display consists of interwoven electrically conductive yarns, non-conductive yarns and SMD LEDs connected to conductive yarns. Industrial jacquard weaving machine have been used, weave patterns were designed in PC-Edit software.

Findings

Weave can be used as a tool to build and evolve electrotextile. Exploring weaving techniques and perceiving electronic circuit as a weave pattern, new approaches can be developed in electrotextile design field.

Research limitations/implications

Connections of electronic elements and conductive textile materials still is actual problem what should be explored in further research.

Practical implications

Flexible light emitting textile display can be used as output interface integrated into communication clothing by representing different animated images directly on clothing. Display also can be used for accessories, room and auto interior etc. applications.

Originality/value

Paper describes method of light source integration directly into textile structure, combining functional and visual design of textile display.

Details

International Journal of Clothing Science and Technology, vol. 27 no. 1
Type: Research Article
ISSN: 0955-6222

Keywords

Article
Publication date: 14 November 2012

Do Chung, Nguyen Dinh, Tran Thao, Nguyen Nam, Tran Trung and David Hui

Polymeric nanocomposite films from PEDOT and MEH-PPV embedded with surface modified TiO2 nanoparticles were prepared, respectively for the hole transport layer (HTL) and…

Abstract

Polymeric nanocomposite films from PEDOT and MEH-PPV embedded with surface modified TiO2 nanoparticles were prepared, respectively for the hole transport layer (HTL) and emission layer (EL) in Organic Light Emitting Diodes (OLED). The composite of MEH-PPV + nc-TiO2 was used for Organic Solar Cells (OCS). The results from the characterization of the properties of the nanocomposites and devices showed that electrical (I-V characteristics) and spectroscopic (photoluminescent) properties of the conjugate polymers were enhanced due to the incorporation of nc-TiO2 in the polymers. The OLEDs made from the nanocomposite films would exhibit a larger photonic efficiency and a longer lasting life. For the OSC made from MEH-PPV + nc-TiO2 composite, the fill factor (FF) reached a value as high as 0.34. Under illumination of light with a power density of 50 mW/cm2, the photoelectrical conversion efficiency (PEC) was found to be of 0.15% corresponding to an open circuit voltage VOC = 1.15 V and a short-cut circuit current density JSC = 0.125 mA/cm2.

Article
Publication date: 7 October 2019

Hui Yuen Peng and Fong Kwong Yam

In general, lighting application, white light emitting diode (LED) usually exposed to an extreme operating temperature of above 90°C. It is well-known that luminous…

Abstract

Purpose

In general, lighting application, white light emitting diode (LED) usually exposed to an extreme operating temperature of above 90°C. It is well-known that luminous efficacy and spectral characteristic of white LED are dependent on the temperature, causing thermal effects on luminous efficacy and color shift of white LED become a critical application checkpoint to be addressed by white LED manufactures. Thus, the purpose of this paper is to minimize the thermal stability issue affecting white LED luminescence during operation by introducing phosphor sedimentation process.

Design/methodology/approach

The LED samples were assembled and sent for centrifugation with 0, 5 and 10 revolutions per second (rps), respectively, during phosphor sedimentation process. Luminescence properties of these LED samples were then characterized at a varying temperature to investigate the effect of phosphor sedimentation on the luminescence stability of LED samples. The LED samples were also cross-sectioned and analyzed to understand the phosphor sedimentation mechanism. Computational fluid dynamics (CFD) was applied to study the temperature distribution of the non-phosphor sediment (NPS) and phosphor sediment (PS) LED during operation to validate the hypotheses based on experimental data.

Findings

Experimental results show that the luminous intensity of PS LED samples degrades less significant at high temperature. The experimental results also show that the color coordinate for PS LED samples is more stable and is less blue-shifted than NPS LED samples as the temperature increased. These are because the heat generated by phosphor particles during operation can be dissipated effectively throughout a high thermal conductivity substrate after phosphor sedimentation. Thus, the phosphor temperature of PS LED is lower than NPS LED during operation as validated with the thermal simulation.

Practical implications

The study of this paper is applicable as a reference for industries who intend to resolve the thermal stability of white LED during operation. The luminescence properties changes as a function of the temperature study in this paper can be used to predict the application performances of white LED accurately. Apart from that, the analysis method of temperature distribution using CFD simulations can be extended by other CFD users in the future.

Originality/value

Implementation of phosphor sedimentation to reduce thermal instability issue of white LED has yet to be reported on previous studies. Most literature just studied the thermal instability issue of either assembled LED or raw material, without suggesting any solution to tackle the issue.

Details

Microelectronics International, vol. 37 no. 1
Type: Research Article
ISSN: 1356-5362

Keywords

Article
Publication date: 6 July 2012

Sucheng Liu, Luowei Zhou, Weiguo Lu and Anxin Li

The purpose of this paper is to model and analyze energy transfer through near‐field resonant coupling for high power lightemitting diode (HPLED) illumination, with the…

Abstract

Purpose

The purpose of this paper is to model and analyze energy transfer through near‐field resonant coupling for high power lightemitting diode (HPLED) illumination, with the intention to increase the appreciation and use of the coupled mode theory (CMT) other than the usual equivalent circuit method.

Design/methodology/approach

The CMT is extensively used to analyze the wireless energy transfer system because of its generality, simplicity, accuracy and intuitive understanding of near‐field resonant energy coupling mechanism.

Findings

The CMT forms a general way to model and analyze the non‐radiative magnetic resonant coupling systems. It is suitable not only for low frequency coupling but also for high frequency (of million‐Hertz) in which the circuit parameters are not easily obtained. Optimal coupling condition corresponding to the maximum power transfer is identified based on the CMT, and the multiple limit cycle phenomenon caused by the nonlinear nature of the HPLED is also described on the CMT model.

Originality/value

This paper takes advantages of CMT, i.e. generality, simplicity, accuracy and intuitive understanding to analyze the near‐field resonant energy coupling system. Key characteristics of the systems are explored based on the CMT, not the usual equivalent circuit method. The influence of nonlinear nature of the high power LED on energy transfer is also investigated. This work seeks a more general way than conventional equivalent circuit method to model and analyze the resonant magnetic system and the results obtained could facilitate better understanding of the resonant magnetic coupling mechanism and optimal design of the near‐field energy transfer system.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 31 no. 4
Type: Research Article
ISSN: 0332-1649

Keywords

1 – 10 of 975