D. Mutharasu

Study on thermal performance of high power LED employing aluminum filled epoxy composite as thermal interface material

The demand for high power light emitting diodes (LEDs) has spawned a dramatic revolution in illumination industry. However, the miniaturization of electronic devices especially LEDs have increased the need for highly sophisticated yet cost effective thermal management solutions in order to sustain this technological advancement. This paper elucidates the thermal behaviour of an LED employing metal filled polymer matrix as thermal interface material (TIM) for an enhanced heat dissipation characteristic. Highly thermal conductive aluminium were incorporated in bisphenol A diglycidylether (DGEBA) epoxy matrix to identify the effect of filler to polymer ratio on the thermal performance of high power LEDs. The curing behaviour of DGEBA was optimized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The dispersion nature of the Al fillers into polymer matrix was verified with Field Emission Scanning Electron Microscope (FESEM). The thermal performance of synthesized Al filled polymer composite as TIM was tested with 5W green LED employing thermal transient measurement technique. Comparing the filler to polymer ratio, the rise in junction temperature for 60 % Al filled composite was higher by 11.0 °C than 50 % Al filled composite at cured state. In addition, it was also observed from the structure function analysis that the total thermal resistance was 10.96 K/W higher for 60 % Al filled composite compared to 50 % Al filled composite. On the other hand, a significant rise of 9.46 °C in the junction temperature between cured and uncured samples of 50 % Al filled polymer TIM was observed and hence the importance of curing process of metal filled polymer composite for effective heat dissipation has been discussed extensively in this work.

Performance Testing of 3-W LED Mounted on ZnO Thin Film Coated Al as Heat Sink Using Dual Interface Method

In high-power electronic devices, thermal interface material (TIM) helps to conduct heat effectively from the chip to ambient by connect the discrete points of the two mating solid surfaces. This paper demonstrates the use of zinc oxide (ZnO) thin film as TIM prepared on Al substrate using RF sputtering. The total thermal resistance (Rth-tot) measured by dual interface method is lower for ZnO coated than for bare and thermal paste applied Al substrates. The thickness of ZnO thin film also influences the thermal resistance as Rth-tot decreases with increased thickness at high driving current. Junction temperature (TJ) is also reduced noticeably for ZnO coated substrates and ATJ between bare and 800-nm ZnO thin film coated substrate is 3.33°C as high for other combinations. The thermal resistance of ZnO interface (Rth-b-hs) is also calculated from the transient curve and observed low resistance with 800-nm ZnO thin film measured at 700 mA. The observed correlated color temperature values are low for ZnO thin film coated Al substrates measured at >350 mA. ZnO thin film is supported to enhance the luminosity of the given light emitting diode and suggested for the replacement of thermal paste based interface material.

Thermal Performance of High Power LED on Boron Doped Aluminium Nitride Thin Film Coated Copper Substrates

Aims: The paper is aim to study the thermal performance of Boron doped Aluminium Nitride (B-AlN) thin film coated over Copper (Cu) substrate to improve surface configuration of the interface between two materials with different synthesis parameters. Study Design: Synthesis of Boron doped AlN thin film by sputtering and post processed for various temperatures. The processed samples were characterized to study the behavior of B doping as well as the annealing temperature in changing the properties of B doped AlN thin film. The structural and surface properties were studied and reported. Place and Duration of Study: Nano Optoelectronic Research Laboratory, School of Physics, University Sains Malaysia, Penang 11800, Malaysia, between December 2013 and July 2014. Methodology: B-AlN thin films were prepared with five different gas ratios over Cu substrates by DC-RF coupled sputtering method and suggested for thin film based thermal interface material Original Research Article Ong et al.; JSRR, 5(2): 109-119, 2015; Article no.JSRR.2015.078 110 (TIM). 3W green LED package was tested with B-AlN thin films coated Cu substrates through thermal transient and surface analysis. The results are compared with the performance of bare Cu substrates. Results: The thin film prepared with gas ratio of Ar 7: N2 13 coated at 200°C showed the lowest thermal resistance Rth (53.27 K/W), board to ambient thermal resistance RthB-A (36.03 K/W) and the lowest junction temperature Tj(120.98°C) at higher driving current (700 mA). Surface analysis results show that the thin film mentioned above exhibits low in surface roughness (8 nm) and range of valley depth (30-80 nm), which contribute in thermal performance of LED. Conclusion: Overall, B-AlN films coated with gas ratio of Ar 7: N2 13 are more favorable in reducing both total thermal resistance and junction temperature (Tj) of LED.

Paper study on thermal conductivity of Al 2 O 3 thin film of different thicknesses on copper substrate under different contact pressures

Thermal interface resistance of solids is an important factor for heat conduction from one solid to another. Interface resistance disrupts heat flow in systems like CPUs and various solid state devices like LEDs. Interface materials play an important role in heat transport through interface. In this study, Al203 with different thickness was coated on a copper substrate. The overall thermal conductivity of the material is measured at different contact pressures. It was observed that overall thermal conductivity of the system was affected by thickness of the Al2O3. It was also observed that the overall thermal conductivity increases with increasing pressure.

Study on the variation in thermal resistance and junction temperature of GaN based LEDs using thermal transient measurement

Proper heat management in solid state lighting (SSL) is vital to enhance its efficiency and reliability. The ease of heat flow through the LED package was described in terms of the thermal resistance, Rth. In this study white and green LEDs were used to investigate the variation in junction temperature and junction-to-ambient thermal resistance, RthJA. It was reported that the green LED always shows higher junction temperature and thermal resistance compared to the white LED. This is due to current crowding effect at the p-n junction of the green LED. At 700mA, the RthJA of green LED was increased about 3KW compare with white LED. Furthermore, the die attach quality also influences the temperature rise and thermal resistance of the LED packages. Due to poor die attach, the RthJA rises about 7K/W when compared with good die attach sample.

The influence of still air environment on thermal transient measurement of high power LED

The surrounding air influence on the thermal transient measurement was studied. The measurements were carried out by setting two boundary conditions where one was measured in open air condition and another transient was captured under still air environment. The data obtained were analysed using structure function evaluation. Analysis of the experimental methods reveal that the thermal resistance of the high power LED is much lower in still air condition compared to open air condition. For the same driving current of 600mA, the total thermal resistance for open air was 8.07692K/W whereas as for still air condition the value was much lower, 7.26577K/W.

Electrodeposited three dimensional tin nano wire anode for thin film Li-Ion micro batteries

The tin wire grown over anodic aluminium oxide template is used as anode for Li ion batteries. This work entails porous template formation through double step electrochemical oxidation method optimized by design of experiment and Tafel polarization. The X-ray diffraction results of different anodized specimens show amorphous alumina layer formation. The pores in alumina matrix and the filamentous outward projection of Sn wires are observed from micrographs. The initial discharge capacity of Sn wire and Sn planar thin film is observed to be around 850 and 531 mA h/g respectively. The 50th cycle capacity of Sn wire is observed to be around 494 mA h/g which is very high when compared to theoretical capacity of graphite anodes.

Heat transfer in high-power LED with thermally conductive particle-filled epoxy composite as thermal interface material for system-level analysis

This paper elucidates the thermal behaviour of an LED employing different particles filled epoxy as thermal interface material (TIM) for enhanced heat dissipation. Highly thermal conductive metal filler of aluminium (Al) and ceramic fillers of aluminium nitride (AlN) and aluminium oxide (Al2O3) were incorporated in bisphenol A diglycidylether (DGEBA) epoxy resin to identify the effect of the filler materials as TIM on the thermal performance of high power LEDs. From the thermal transient analysis of a 3W warm white LED, it was observed that the Al filled composite exhibits the lowest junction temperature of 38.3 °C compared to the other two fillers. The total thermal resistance of the package with AlN filled composite and Al2O3 filled composite were 13.77 and 15.50K/W respectively. This paper too suggests that the total thermal resistance of the LED package increases when the particle size of the fillers decrease.

Influence of the heat sink orientation and fins arrangement on the thermal behavior of high power LED

Heat management in Light Emitting Diodes (LED) is necessary to enhance its optical performance and stability. The usage of external heat sink is one of the efficient ways to reduce the thermal effect on the LED packages at low cost.

Antibacterial Activity and Electrical Properties of Gold Nanoparticle Doped Ceria-Rice Husk Silica (Au/Ce-Silica) Nanocomposites Derived From Biomass

The present study deals with synthesis and characterization of gold doped in ceria-silica, derived from rice husk silica biomass materials. Large amount of silica recovered from waste rice husk silica was utilized. The silica materials derived from waste product can be used as low cost supporting material for potential applications such as catalytic oxidations and low-k dielectric material development. Gold doping on ceria-mixed silica derived from rice husk is carried out by an in situ method (Au/Ce-Silica-A) as well as by co-precipitation method (Au/Ce-Silica-B). The physicochemical characterization and antibacterial activity of as prepared material have been studied.