Shanmugan Subramani

Influence of AlN Thin Film as Thermal Interface Material on Thermal and Optical Properties of High-Power LED

An AlN thin film was fabricated and used as a thermal interface material (TIM) for a high-power light-emitting diode (LED) application. The AlN thin film was stacked with an Al thin film on Al substrates and used as a heat sink. The thermal behavior of a 3-W green LED mounted on the AlN and AlN/Al stack thin-film-coated substrates was tested using a dual interface method. A low value in junction temperature (TJ) of the LED was observed with an AlN/Al stack used as the interface. The observed total thermal resistance (Rth-tot) was low for the AlN/Al-stack-coated Al substrates compared to the bare and thermal-paste-applied Al substrates. The interface thermal resistance (Rth-b-hs) was influenced by the driving currents and observed a low value with the AlN-based coatings. Improved luminosity was observed from the LED with the AlN/Al stack as the TIM. The observed correlated color temperature (CCT) was low for the AlN/Al stack at all driving currents. No significant change was observed in the color rendering index (CRI) and peak wavelength (λpeak).

Thermal resistance studies of surface modified heat sink for 3W LED using transient curve

Purpose – Surface configuration at the interface between two materials makes a huge difference on thermal resistance. Thermal transient analysis is a powerful tool for thermal characterization of complex structures like LEDs. The purpose of this paper is to report the influence of surface finish on thermal resistance.Design/methodology/approach – Surface of heat sink was modified into two categories: machined as channel like structure; and polished using mechanical polisher and tested with 3W green LED for thermal resistance analysis.Findings – The observed surface roughness of rough and polished surface was 44 nm and 4 nm, respectively. Structure function analysis was used to determine the thermal resistance between heat sink and MCPCB board. The observed thermal resistance from junction to ambient (RthJA) value measured with thermal paste at 700 mA was lower (34.85 K/W) for channel like surface than rough surface (36.5 K/W). The calculated junction temperature (TJ) for channel like surface and polished ...

Thermal Transient Analysis of High-Power Green LED Fixed on BN Coated Al Substrates as Heatsink

Boron nitride (BN) thin film was deposited over Al substrate and used as a heatsink for high-power LED. The rise in junction temperature TJ was evaluated from transient cooling curve and observed as a low value for BN coated substrates rather than for bare and thermal paste (TP) applied substrate measured at 700 mA. Total thermal resistance (Rth-tot) was also observed as a low value for BN samples. The BN thin film interface influenced the wavelength peak shift toward a higher value. Noticeable increment on luminosity of the LED was also observed for BN coated Al substrate with respect to driving currents. The observed results were suggested the use of BN thin film as thermal interface materials as an alternative for TP.

Structural and surface analysis of AlInN thin films synthesized by elemental stacks annealing

This paper presents the synthesis of AlInN thin films on Si (100) substrates using elemental stacks annealing (ESA) process. Single stack InN films were grown on Si (100) substrates by reactive radiofrequency (RF) magnetron sputtering using pure indium target in Ar–N2 environment and then an Al stack layer was deposited on the InN films by direct current (dc) sputtering of pure aluminum target in Ar atmosphere at room temperature. Annealing of the deposited films was carried out at 400 °C for 2, 4 and 6 h in a tube furnace under N2 atmosphere. X-ray diffraction (XRD) results reveal that annealing for 2 h does not produce a well-defined AlInN film, however, with the increase of annealing time to 4 h and to 6 h, (002) and (103) oriented highly crystalline AlInN films are formed with wurtzite structures. Field emission scanning electron microscopy (FESEM) results indicate a uniform film structure with grains growth by increasing the annealing time. Energy dispersive x-ray (EDX) analysis shows higher Al (atomic %) in the film as compared to In and N. Atomic force microscopy (AFM) results show a decrease in the surface roughness with increase of the annealing time.

Structural, morphological, optical and electrical properties of NiO films prepared on Si (100) and glass substrates at different thicknesses

In this work, structural, surface, optical and electrical properties of NiO films were studied at different film thicknesses. The NiO films of different thicknesses in the range 330–920 nm were prepared on Si (100) and glass substrates by using radiofrequency magnetron sputtering of NiO target at 100 °C. The structural study through XRD indicated polycrystalline NiO films with preferred orientation along (200) plane. The crystalline quality of the films was improved with increase of the film thickness on both substrates, however, the films prepared on Si (100) displayed better crystallinity as compared to the films prepared on the glass. The morphological features of the film as studied through FE-SEM displayed an increase of grain size with increase of its thickness, however, the grain size of the film on Si (100) was found to be slightly larger than that of the glass. The band gap of NiO film was decreased with increase of the film thickness on both the substrates. The films grown on Si (100) exhibited superior electrical properties as compared to the films prepared on glass at all film thicknesses.

Testing and Analysis of Boron-Doped Aluminum Nitride Thin-Film-Coated Al as Thermal Substrates in PCB Fabrication for LED Application

Chemical vapor deposition was used to coat boron-doped AlN thin film on Al substrates and used as thermal substrates in the fabrication of printed circuit boards (PCBs). Conventional screen printing method was used to deposit dielectric, conductor, and protective coating on thin-film-coated Al substrate for the printed metal PCBs (MPCBs). Commercial light emitting diode (LED) was fixed on MPCB and tested for thermal and optical properties under various driving currents. The observed results are compared with those of commercial metal-core printed circuit board (MCPCB). The measured total thermal resistance (Rth-tot) of the LED was low for MPCB and recorded good difference in Rth-tot (ARth-tot = 7.55 K/W) when compared with MCPCB. An impressive difference on rise in junction temperature (TJ) was noticed (ΔTJ = 13.72) with MPCB at 700 mA as compared with MCPCB. As a result of reduced TJ, an improved light output was recorded for MPCB in all driving currents and a higher value also with MPCB. Hence, B-AlN thin-film-coated Al substrate could be used as thermal substrates in PCB fabrication for efficient electronic packaging in LED industries.

Variation of thermal resistance with input current and ambient temperature in low-power SMD LED

Purpose Thermal behavior of LED device under different operating conditions must be known to enhance its reliability and efficiency in various applications. The influence of input current and ambient temperature on thermal resistance of InGaAlP low-power SMD LED is reported in this study. Design/methodology/approach Thermal parameters of the LED were measured using thermal transient measurement via Thermal Transient Tester (T3ster). The experimental results were validated using computational fluid dynamics (CFD) software. Findings As input current increases from 50 to 90 mA at 25 ℃, the relative increase in LED package 〖(∆R〗_thJS) and total thermal resistance (〖∆R〗_thJA) is about 10% and 4%, respectively. In addition, at 50 mA and ambient temperature from 25 to 65 ℃, the 〖∆R〗_thJS and 〖∆R〗_thJA is roughly 28% and 22%, respectively. A good agreement between simulation and experiment results of junction temperature. Originality/value Most of previous studies have focused on thermal management of high-power ...

Performance of Cu-Al2O3 thin film as thermal interface material in LED package: thermal transient and optical output analysis

Purpose The paper aims to study the influence of the Cu-Al2O3 films coated Cu substrate as thermal interface material on the thermal and optical behaviour of the LEDs package and the annealing effect on the thermal and optical properties of the films. Design/methodology/approach Layer stacking technique is used to deposit the Cu-Al2O3 films through magnetron sputtering and annealing process were conducted on the synthesized films. Findings In this paper, it is found that un-annealed Cu-Al2O3 coated Cu substrate exhibited low value of thermal resistance compared to the bare Cu substrate and previous work. Also the annealing effect does not have significant impact on the changes of properties of the films. Research limitations/implications It is deduced that the increase of Cu layer thickness can further improved the thermal properties of the deposited film, which can reduced the thermal resistance of the package in system level analysis. Practical implications The paper suggested that the Cu-Al2O3 coated C...

Thermal performance of LED fixed on CVD processed ZnO thin film on Al substrates at various O 2 gas flow rates

Zinc oxide thin films were deposited on aluminium (Al) substrates by chemical vapor deposition (CVD) method and used as thermal interface materials in LED packages. Various driving current were used to test the thin film performance on LED and measure the parameter, such as thermal resistance and junction temperature. Field Emission Scanning Electron Microscopy analysis of ZnO thin film surface prepared at 5 sccm showed dense and uniform particles, and this is verified by Atomic Force Microscopy analysis. Energy dispersive X-ray Analysis of the thin films confirmed that the thin film are Zn rich. Low thermal resistance (33.92 K/W) and high value of difference in junction temperature (∆T j = 4.8 ℃) were noticed with ZnO thin film prepared at 5 sccm gas flow for 700 mA when compared with bare Al boundary conditions. Overall, ZnO thin film at 5 sccm flow can be effectively used as thermal interface material for high power LEDs.

THERMALLY-DRIVEN STRUCTURAL CHANGES OF SPUTTERED COPPER ALUMINUM OXIDE FILMS (Cu–Al2O3) GROWN BY LAYER STACKING METHOD

Copper aluminium oxide (Cu–Al2O3) films were synthesized on Si(111) substrates through RF magnetron sputtering by using the layer stacking technique. Cu and Al2O3 targets were used to deposit Cu and Al2O3 thin films under Ar atmosphere, respectively and the deposited films were then annealed under N2 environment at 350∘C, 450∘C and 550∘C for 6h. The structural properties of the films were investigated by using X-ray diffraction (XRD) while the surface morphology and topography of the deposited films were examined through Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray (EDX) and Atomic Force Microscopy (AFM). XRD analysis revealed the existence of multiple phases of CuO, Al2O3 and CuAl2O4 in the deposited films on Si(111) substrates. As a result of the annealing effect, the peak intensities of CuO, Al2O3 and CuAl2O4 were found to be increased along with the shifting of peak positions. Williamson–Hall (WH) analysis was also implemented to analyze the structural properties such as crystallite size, stress, strain, and energy density. Based on the three models used in WH analysis, the changes in the crystallite size and strain of the films were indicated to be anomalous with the changes in the annealing temperature. Moreover, the strain of films was also showed to be changed from compressive strain into tensile strain. The FESEM results also indicated the formation of various surface morphologies under various annealing temperatures whereas EDX analysis showed an increased atomic percentage of Cu, Al, and O due to the effect of increase in annealing temperature. The AFM analysis showed that the surface roughness of the deposited films increased with the increase in the annealing temperature.