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Purpose Light emitting diode (LED) has been the best resource for commercial and industrial lighting applications. However, thermal management in high power LEDs is a major challenge in which the thermal resistance (Rth) and rise in junction temperature (TJ) are critical parameters. The purpose of this work is to evaluate the Rth and Tj of the LED attached with the modified heat transfer area of the heatsink to improve thermal management. Design/methodology/approach This paper deals with the design of metal substrate for heatsink applications where the surface area of the heatsink is modified. Numerical simulation on heat distribution proved the influence of the design aspects and surface area of heatsink. Findings TJ was low for outward step design when compared to flat heatsink design (ΔT ∼ 38°C) because of increase in surface area from 1,550 mm2 (flat) to 3,076 mm2 (outward step). On comparison with inward step geometry, the TJ value was low for outward step configuration (ΔTJ ∼ 6.6°C), which is because of efficient heat transfer mechanism with outward step design. The observed results showed that outward step design performs well for LED testing by reducing both Rth and TJ for different driving currents. Originality/value This work is authors’ own design and also has the originality for the targeted application. To the best of the authors’ knowledge, the proposed design has not been tried before in the electronic or LED applications.

Purpose Polymer-based thermal interface materials (TIMs) are having pump out problem and could be resolved for reliable application. Solid-based interface materials have been suggested and reported. The purpose of this paper is suggesting thin film-based TIM to sustain the light-emiting diode (LED) performance and electronic device miniaturization. Design/methodology/approach Consequently, ZnO thin film at various thicknesses was prepared by chemical vapour deposition (CVD) method and tested their thermal behaviour using thermal transient analysis as solid TIM for high-power LED. Findings Low value in total thermal resistance (Rth-tot) was observed for ZnO thin film boundary condition than bare Al boundary condition. The measured interface (ZnO thin film) resistance {(Rth-bhs) thermal resistance of the interface layer (thin film) placed between metal core printed circuit board (MCPCB) board and Al substrates} was nearly equal to Ag paste boundary condition and showed low values for ZnO film prepared at 30 min process time measured at 700 mA. The TJ value of LED mounted on ZnO thin film (prepared at 30 min.) coated Al substrates was measured to be 74.8°C. High value in junction temperature difference (ΔTJ) of about 4.7°C was noticed with 30 min processed ZnO thin film when compared with Al boundary condition. Low correlated colour temperature and high luminous flux values of tested LED were also observed with ZnO thin film boundary condition (processed at 30 min) compared with both Al substrate and Ag paste boundary condition. Originality/value Overall, 30 min CVD processed ZnO thin film would be an alternative for commercial TIM to achieve efficient thermal management. This will increase the life span of the LED as the proposed material decreases the TJ values.

Thermal management in a heat source-based electronic package is a necessity for reliable, long-lasting performance, as it is compulsory to dissipate the generated heat effectively. In this study, a novel nickel–phosphorous (Ni–P) alloy coating on an aluminum substrate is proposed to obtain improved thermal properties such as thermal conductivity ( ${k}$ ), total thermal resistance ( ${R}_{{\mathrm {th-tot}}}$ ), and device junction temperature ( ${T}_{j}$ ). The performance of the electroless Ni–P coating is observed under different deposition times and test conditions. The morphology of Ni–P coating results in a cauliflower-like grown structure on a substrate with 91.2 wt% of Ni and 8.8 wt% of P. X-ray diffraction spectra indicate the presence of crystalline Ni (111) and (220) peaks and an average crystallite size of 541 nm. The thermal conductivity of the Ni–P coated substrate results in 14.42 W/mK, whereas bare Al results in 8.03 W/mK. The thermal transient measurement results in an impressive difference in both $\Delta {R}_{{\mathrm {th-tot}}}$ (6.31 K/W, 4.68 K/W) and $\Delta {T}_{j}$ (11.84 °C, 5.82 °C) under different test conditions. It is found that 0.33- $\mu \text{m}$ surface roughness with a 7.5- $\mu \text{m}$ coating thickness potentially improves the thermal behavior of Ni–P substrates, and it is believed that Ni–P is suitable for being used as an alternative coating option for electronic packages.

In response to the critical needs of high power density, advanced thermal gap fillers (TGF) are required for the long-term reliability of electronics packaging. In this study, dispensable thermal g...

Purpose Optimization of light-emitting diodes’ (LEDs’) design together with long-term reliability is directly correlated with their photometric, electric and thermal characteristics. For a given thermal layout of the LED system, the maximum luminous flux occurs at an optimal electrical input power and can be determined using a photo-electro-thermal (PET) theory. The purpose of this study is to extend the application of the luminous flux equation in PET theory for low-power (LP) LEDs. Design/methodology/approach LP surface-mounted device LEDs were mounted on substrates of different thermal resistances. Three LEDs were attached to substrates which were flame-retardant fiberglass epoxy (FR4) and two aluminum-based metal core printed circuit boards (MCPCBs) with thermal conductivities of about 1.0 W/m.K, 2.0 W/m.K and 5.0 W/m.K, respectively. The conjunction of thermal transient tester and thermal and radiometric characterization of LEDs system was used to measure the thermal and optical parameters of the LEDs at a certain range of input current and temperature. Findings The validation of the extended application of the luminous flux equation was confirmed via a good agreement between the practical and theoretical results. The outcomes show that the optimum luminous flux is 25.51, 31.91 and 37.01 lm for the LEDs on the FR4 and the two MCPCBs, respectively. Accordingly, the stipulated maximum electrical input power in the LED datasheet (0.185 W) is shifted to 0.6284, 0.6963 and 0.8838 W between the three substrates. Originality/value Using a large number of LP LEDs is preferred than high-power (HP) LEDs for the same system power to augment the heat transfer and provide a higher luminous flux. The PET theory equations have been applied to HP LEDs using heatsinks with various thermal resistances. In this work, the PET theory luminous flux equation was extended to be used for Indium Gallium Aluminum Phosphide LP LEDs attached to the substrates with dissimilar thermal resistances.

Oil bleed from silicone dispensable thermal gap filler may adhere to the electronic components and causes contamination of device substrates. A highly crosslinked silicone dispensable thermal gap f...

A high thermal conducting, electrically insulating, and non-oil bleed liquid thermal gap filler containing aluminum oxide (Al2O310 µm) and zinc oxide (ZnO0.6 µm) in polydimethylsiloxane (PDMS) has been fabricated. An effective method of mixing 93 wt% filler in 7 wt% PDMS was achieved without surface modification. It was found that the thermal conductivity, hardness, dielectric constant, and dielectric loss tangent values increased with the variation of filler ratio. The S5 hybrid composite exhibits the highest thermal conductivity of 3.38 W/m K, which was 21.1 times higher than that of pure PDMS. The corresponding dielectric constant and dielectric loss were 7.968 and 0.03076 at 1 MHz. TGA results revealed that the variation of Al2O3/ZnO filler ratio improved the maximum decomposition temperature of the composite. Furthermore, no oil bleed was observed for the entire composites after 1 month. Thus, fillers with different particle sizes provide more significant filler packing density in the matrix and lower thermal resistance between adjacent conductive filler, resulting in high thermal conductivity composites.

The semiconductor packaging field is evolving rapidly due to strong competition in customer demands for increased functionality and performance, further miniaturization, heightened reliability and lower costs. The lifetime reliability and sequential performance of solid-state products are mainly based on the device junction temperature (Tj). The main concerns of efficient thermal management in heat source-based electronic packages are controlling and reducing the device junction temperature and total thermal resistance (Rth). The optimization of process parameters to develop an anodic aluminium oxide nanopore (AAO-np) structure on an Al5052 alloy substrate using an electrochemical process (two-step anodization) is proposed based on the Taguchi orthogonal array (L9). The four major parameters are the electrolyte, anodization time, bath temperature, and applied voltage, which are varied at three different levels. This experiments aim to finalize suitable process parameters and their levels towards optimum Rth and Tj. The morphology of the step-wise preparation of AAO-np structure is discussed for the optimized conditions of 0.3 M oxalic acid, a 3 h anodization time, a 30 V applied voltage, and a bath at room temperature. The resulting AAO-np structure has a pore diameter of 40 to 55 nm and a height of 6 to 7 μm. This formation significantly reduces Rth by 24.58% and Tj by 24.66% for the electronic package compared to a bare Al substrate.

Increased heat generated in high-density electronic devices has intensified the search for advanced thermal management solutions. This urge has prompted various studies in thermal pad, liquid thermal interface material, gap fillers, and thermal coating, etc., with enhanced thermal performance. In this article, anodic aluminum oxide-nanopore (AAO-np) structure was grown on Al5052 alloy substrate electrochemically using two-step anodization process and it is used for efficient electronic packaging applications. It is observed that AAO-np substrate shows significant impact in thermal resistance (Rth) and junction temperature (Tj) of an electronic package. At 3.5 W input power with 14, 29, and 43 psi pressure condition the experimental results of AAO-np substrate resulted 15.11%, 14.58%, and 13.89% reduction in thermal resistance (ΔRth) and 15.53%, 14.85%, and 14.26% reduction in junction temperature (ΔTj) compared to bare Al5052 substrate. This enhanced thermal performance of AAO-np layer are due to high crystallinity, honeycomb-like morphology, nanopore oxide layer, and 0.35 µm rough surface which are effectively acting towards directional heat transport.

Hexagonal Boron Nitride (h-BN) thin film was deposited on flexible polyethylene terephthalate (PET) substrate using radio frequency (RF) magnetron sputtering system. Ceramic material h-BN was coated at three different thicknesses of 400 nm, 800 nm and 1200 nm on PET surface for a detailed comparative study. A clearer topography of the h-BN-coated surface on PET substrate was imaged using field emission scanning electron microscopy (FESEM) system, where it depicted well-developed grain boundaries. The existence of B–N components was ensured by peaks observed at 1442 and 817 cm−1 using Fourier-transform infrared spectroscopy (FTIR) study. X-ray diffractograms (XRD) confirmed the presence of (100) and (004) oriented BN phases in the prepared thin films. Increase in surface roughness (10.2–55.2 nm) from surface analysis and moderate improvement in thermal conductivity also obtained in this work was evident. Characterization studies support the novelty in the study of the deposition of h-BN thin film on flexible PET substrate with improved surface roughness and thermal conductivity. The conclusion was that BN thin film can be suggested as a potential object as heat spreader in flexible electronics for efficient thermal management devices such as electronic packaging applications.

Purpose The presence of voids in the solder layer has been considered as one of the main issues causing reliability problems in optoelectronic devices. Voids can be created due to trapped gas, clean-up agent residues (fluxes), poor wettability at interface or shortcoming of the reflow process. The voids hinder the heat conduction path and subsequently, the thermal resistance will increase. The purpose of this paper is to investigate the influence of lead-free water-washable Sn96.5Ag3.0Cu0.5 (SAC305) solder paste (SP) voids on the thermal and optical performance of white high-power (HP) surface-mounted device (SMD) light-emitting diode (LED). Design/methodology/approach Five LEDs are mounted on five SinkPAD substrates by using the SP. The SMT stencil printing is used to control the thickness of the SP and reflow oven for the soldering process. The fraction of voids in the SP layer is calculated using the X-ray machine software. The thermal parameters of the LEDs with different voids fraction and configuration are measured using a thermal transient tester (T3Ster) system. In addition, the optical characterizations of the LEDs are determined by the thermal and radiometric characterization of power LEDs (TeraLED) and the electroluminescence by using the spectrometer. Findings The results showed that the thermal performance and temperature distribution are improved for the LED with lower voids fraction and good filling state of soldering. In addition, luminous flux, efficacy and color shift of the LEDs with different fraction and configurations of voids on the SP layer are compared and discussed. It is found that the color shift of LED1 of low voids fraction and higher thickness are less than other LEDs. Originality/value The paper provides valuable information about the effect of water-washable SAC305 SP voids fraction and filling state of solder on the thermal and optical performance of ThinGaN HP SMD LED. A comprehensive overview of the outcomes is not available in the literature. It was shown experimentally that the voids fraction, height and configuration of the SP layer could strongly influence the heat dissipation efficiency and thermal resistance. This study can help in heat diffusion investigation and failure analysis of HP SMD LEDs.

Chemical vapor deposition (CVD) process was conducted for synthesis of boron (B) doped aluminum nitride (B-AlN) thin films on aluminum (Al) substrates. To prevent melting of the Al substrates, film deposition was carried out at 500 °C using tert-buthylamine (tBuNH2) solution delivered through a bubbler as a nitrogen source instead of ammonia gas (NH3). B-AlN thin films were prepared from three precursors at changing process parameters (gas mixture ratio). X-ray diffraction (XRD) technique and atomic force microscope (AFM) were used to investigate the structural and surface properties of B-AlN thin films on Al substrates. The prepared thin films were polycrystalline and composed of mixed phases {cubic (1 1 1) and hexagonal (1 0 0)} of AlN and BN with different orientations. Intensive AlN peak of high intensity was observed for the film deposited at a flow rate of the total gas mixture of 25 sccm. As the total gas mixture flow decreased from 60 sccm to 25 sccm, the crystallite size of AlN phase increased and the dislocation density decreased. Reduced surface roughness (10.4 nm) was detected by AFM for B-AlN thin film deposited on Al substrate using the lowest flow rate (25 sccm) of the total gas mixture.

This paper presents investigation on the effects of annealing temperature towards surface morphological and optical properties of black silicon (b-Si) fabricated by a two-step silver-assisted chemical etching process. Crystalline (c-Si) wafers are deposited with a thin film silver (Ag) layer. The c-Si wafers are annealed in nitrogen atmosphere for 40 min at different temperatures (200–260 ℃) to form Ag nanoparticles. The wafers are then etched in the aqueous solution of HF:H2O2:DI H2O at room temperature for 70 s. The results show that the surface morphologies of all samples are rough due to the presence of b-Si nanotextures. The b-Si wafers demonstrate significantly lower broadband reflection compared to the planar reference. The b-Si wafer annealed at 230 ℃ demonstrates the lowest reflection (3%) and highest absorption (97%) at the wavelength of 600 nm. This sample exhibits b-Si nanotextures with average width less than 50 nm and height of 245 nm. The enhanced broadband light absorption in the best b-Si wafer gives the highest maximum potential short-circuit current density (Jsc(max)) of 39.6 mA/cm2, or enhancement 50.6% compared to the planar c-Si reference wafer, calculated for wavelength region of 300–1100 nm.

In this work, NiO films of different layers (5, 10, 15 and 20) were coated on Al substrate by using sol-gel spin coating technique. The crystallinity of the films was improved with increasing the number of layers, as confirmed by the XRD and FESEM results. To investigate the thermal performance of NiO films, high power LED package was fixed on bare Al and NiO coated Al (NiO/Al) substrates. The rise in junction temperature (Tj) and total thermal resistance (Rth-tot) of the LED package were found to be lower on NiO/Al as compared to the bare Al. The Tj and Rth-tot on NiO/Al were increased by increasing the number of NiO layers. The lowest values of Tj and Rth-tot were obtained at 700 mA for the NiO film containing 5 layers. These values were lower than that of the bare Al by the difference of 14.31 °C and 5.73 K/W, respectively. Based on the thermal analysis results, NiO film is suggested to be a suitable thermal interface material for use in high power LED applications.

Though light-emitting diodes (LEDs) are gaining attention for implementation in various applications, thermal management remains a major concern in solid-state lighting devices. Thermal resistance and junction temperature are the critical parameters of LEDs, which should be maintained at nominal levels for its reliable and robust operation. In this paper, novel substrates were proposed to enhance the thermal performance of LEDs. Aluminum substrates with converging–diverging (CD) and diverging–converging (DC) geometries were fabricated using high-precision milling machine. Three different converge–diverge angles such as 45°, 60°, and 90° were used in CD and DC substrates. Numerical simulations were done using computational fluid dynamics software to gain more insights on heat distribution and flow dynamics in the proposed substrates. Thermal characterization was done using thermal transient method by mounting the LED on CD and DC substrates. The thermal performances of the proposed substrates were compared with bare aluminum substrate by measuring the thermal resistance and junction temperature of LED. Optical analysis on LED was done by utilizing still air chamber and spectrometer. From the analysis, DC substrates showed lower thermal resistance and junction temperature compared to the other two substrates due to the conjugate heat transfer effect. Precisely, DC substrate with 90° showed higher thermal and optical performance than any other substrates considered.

Purpose Thermal management of high-power (HP) light-emitting diodes (LEDs) is an essential issue. Junction temperature (TJ) and thermal resistance (Rth) are critical parameters in evaluating LEDs thermal management and reliability. The purpose of this paper is to study thermal and optical characteristics of ThinGaN (UX:3) white LED mounted on SinkPAD by three types of solder paste (SP): No-Clean SAC305 (SP1), Water-Washable SAC305 (SP2) and No-Clean Sn42/Bi57.6/Ag0.4 (SP3). Design/methodology/approach Thermal transient tester (T3Ster) machine is used to determine TJ and total thermal resistance (Rth–JA). In addition, the LED’s optical properties are measured via thermal and radiometric characterization of power LEDs (TeraLED) system. The LED is mounted on SinkPAD using SP1, SP2 and SP3 by stencil printing to control a thickness of SP and reflow soldering oven to minimize the number of voids. The LED with SP1, SP2 and SP3 is tested at various input currents and ambient temperatures. Findings The results indicate that at high input current, which equals to 1,200 mA, Rth–JA and TJ, respectively, are reduced by 30 and 17 per cent between SP1 and SP2. At same current value, Rth–JA and TJ are minimized by 42 and 25 per cent between SP1 and SP3, respectively. In addition, at an ambient temperature of 85°C, Rth–JA and TJ are decreased by 34 and 7 per cent between SP1 and SP2, respectively. Similarly, the reduction in Rth–JA and TJ between SP1 and SP3 is 44 and 10 per cent, respectively. Luminous flux, luminous efficacy and color shift of the LED with the three types of SPs are compared and discussed. It is found that the SP1 improves the chromatic properties of the LED by increasing the overall light efficiency and decreasing the color shift. Originality/value Thermal and optical performance of ThinGaN LEDs mounted on SinkPAD via three types of SPs is compared. This investigation can assist the research on thermal management of HP ThinGaN-based LEDs.

Purpose Proper thermal management is a key to improve the efficiency and reliability of light-emitting diodes (LEDs). This paper aims to report the influence of applying thermally conductive materials on thermal performance of indium gallium aluminum phosphide (InGaAlP)-based thin-film surface-mounted device (SMD) LED. Design/methodology/approach The LED thermal and optical parameters were determined using the combination of thermal transient tester (T3Ster) and thermal and radiometric characterization of power LEDs (TeraLED) instruments. The LED was mounted on FR4, 2W and 5W aluminum (Al) package substrates. Measurements were carried out by setting different boundary conditions: air between LED package and substrate and using thermally conductive epoxy (TIM A) and adhesive (TIM B) of thermal conductivity 1.67 and 1.78 W/mK, respectively. Findings For LED mounted on FR4 package, the total real thermal resistance is improved because of TIM B by 6 and 9 per cent at 50 and 100 mA, respectively. Likewise, the relative decrease in total thermal resistance of LED on 2W Al package is about 9 and 11 per cent. As well, for LED mounted on 5W Al package, the total real thermal resistance is reduced by 2 and 4 per cent. Originality/value No much work can be found in the literature on thermal interface material effects on thermal performance of low-power SMD LED. This work can assist in thermal management of low-power LEDs.

Thermal management in light-emitting diode (LED) has been extensively researched recently. This study is intended to develop an effective thermally conductive epoxy composite as thermal interface material (TIM) for headlamp LEDs. Silane-functionalized aluminum oxide (Al2O3) powder of different average particle sizes (44 and 10 µm) was studied for its feasibility as filler at its maximum loading. A detailed comparison of three different methods of particle dispersions, hand-mix, speed-mix and calendaring process (3-roll mill), has been reported. The dispersion of Al2O3 particles, the thermal conductivity and thermal degradation characteristics of the composites were investigated and explained in detail. At 75 wt.% filler loading, 10 and 44 µm Al2O3 achieved composite thermal conductivities of 1.13 and 2.08 W/mK, respectively, which is approximately 528 and 1055% of enhancement with respect to neat epoxy. The package-level thermal performance of the LED employing the Al2O3-filled TIMs was carried out using thermal transient analysis. The experimental junction-to-ambient thermal resistances (RthJ-A) achieved were 6.65, 7.24, and 8.63 K/W for Al2O3_44µm, Al2O3_10µm and neat epoxy, respectively. The results revealed that the Al2O3_44µm fillers-filled composite performed better in both material-level and package-level thermal characteristics.

PurposeThermal behavior of light-emitting diode (LED) device under different operating conditions must be known to enhance its reliability and efficiency in various applications. The purpose of this study is to report the influence of input current and ambient temperature on thermal resistance of InGaAlP low-power surface-mount device (SMD) LED.Design/methodology/approachThermal 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.FindingsAs input current increases from 50 to 90 mA at 25°C, the relative increase in LED package (ΔRthJS) and total thermal resistance (ΔRthJA) is about 10 and 4 per cent, respectively. In addition, at 50 mA and ambient temperature from 25 to 65°C, the ΔRthJSand ΔRthJAare roughly 28 and 22 per cent, respectively. A good agreement between simulation and experiment results of junction temperature.Originality/valueMost of previous studies have focused on thermal management of high-power LEDs. There were no studies on thermal analysis of low-power SMD LED so far. This work will help in predicting the thermal performance of low-power LEDs in solid-state lighting applications.

Purpose This paper aims to study the influence of the Cu-Al2O3 film-coated Cu substrate as a thermal interface material (TIM) on the thermal and optical behaviour of the light-emitting diode (LED) package and the annealing effect on the thermal and optical properties of the films. Design/methodology/approach A layer-stacking technique has been used to deposit the Cu-Al2O3 films by means of magnetron sputtering, and the annealing process was conducted on the synthesized films. Findings In this paper, it was found that the un-annealed Cu-Al2O3–coated Cu substrate exhibited low value of thermal resistance compared to the bare Cu substrate and to the results of previous works. Also the annealing effect does not have a significant impact on the changes of properties of the films. Research limitations/implications It is deduced that the increase of the Cu layer thickness can further improve the thermal properties of the deposited film, which can reduce the thermal resistance of the package in system-level analysis. Practical implications The paper suggested that the Cu-Al2O3–coated Cu substrate can be used as alternative TIM for the thermal management of the application of LEDs. Originality value In this paper, the Cu substrate has been used as the substrate for the Cu-Al2O3 films, as the Cu substrate has higher thermal conductivity compared to the Al substrate as shown in previous work.

In this study, metal-semiconductor-metal (MSM) ultraviolet photodetector based on NiO film was fabricated on n-type Si (100) substrate. The NiO film was deposited on Si (100) by using RF magnetron sputtering of NiO target at 100 °C. The film showed cubic bunsenite structure with (200) preferred orientation as confirmed through XRD analysis. The band gap of NiO film was evaluated from UV–vis reflectance specroscopy and it was found to be 3.38 eV. To study the photodetection performance of NiO film, Au metal contacts were deposited on the film through RF sputtering system. The photodetection characteristics of the photodetector such as spectral response, photosensivity, internal gain, rise and fall time were investigated. The Au/NiO/Au MSM UV device displayed maximum value of responsivity (4.5 A/W) upon exposure to 365 nm UV light at 5 V bias. The photosensivity was calculated to be 6.4 × 103% whereas the internal gain of the photodetector was estimated to be 6.5 × 101. In addition, the rising and falling time were found to be 266 ms and 200 ms, respectively. The fabricated device exhibited excellent stability and repeatability in its performance.

Thermal management stances a massive threat in solid-state lighting devices. With light-emitting diodes (LEDs) gaining attention for implementation in various applications, it is important to address its thermal issues. Thermal resistance and junction temperature are the critical parameters of LEDs which should be maintained at optimum ranges for its reliable operation. In this paper, novel substrates were proposed to minimize the thermal parameters of LEDs. Aluminum substrates with converging–diverging (CD) and Diverging–converging (DC) geometries were micromilled. Thermal characterization was done using thermal transient method by mounting LED on CD and DC substrates. The thermal performance of proposed substrates was compared with bare aluminum substrate by measuring the thermal resistance and junction temperature of LED. On analysis, DC substrates showed lower thermal resistance and junction temperature compared with the other two substrates due to conjugate heat transfer effect within the channels.

Nickel oxide (NiO) film was grown on Si (100) substrate through RF sputtering of NiO target in Ar plasma at various temperatures ranging from room temperature (RT) to 300 °C. The structural study revealed (200) oriented NiO diffraction peak at RT and at 100 °C, however, by increasing the substrate temperature to 200 °C, intensity of (200) NiO diffraction peak was decreased. At higher temperature (300 °C), crystalline quality of NiO was significantly degraded and the film was decomposed into Ni. The EDS results confirmed an increase of Ni atomic percentage with increase of the substrate temperature. The surface morphology of NiO film at RT and at 100 °C displayed cubical like grains that were changed into elongated grains with further increase of the substrate temperature. The UV–vis reflectance measurements of NiO revealed a small decrease in its band gap by increasing the substrate temperature to 200 °C.

The demands for high performance electronic devices have been increasing recently. This continuous demand simultaneously put forward stringent requirements for effective thermal management solutions. In this study, improved thermal and mechanical properties of epoxy composites consisting of milled carbon fiber (MCF) and polyhedral aluminium oxide (Al2O3) fillers have been reported. By adding 14.5 wt% MCF and 60 wt% Al2O3 particles into epoxy, the maximum thermal conductivity reached were 3.3 and 7.9 times that of neat epoxy respectively. To further improve the composite thermal conductivity, a mixture of the two fillers was utilized. Milled carbon fiber with high aspect ratio enables it to act as heat conducting bridges among 3-D Al2O3 irregular particles; contributing considerably to the formation of a more efficient percolating network for heat flow. This resulted in an exceptionally high thermal conductivity with relatively lower filler content. A thermal conductivity of ten times that of neat epoxy was obtained with 42 wt% Al2O3 + 8 wt% MCF thus not only break the bottleneck of further improving the thermal conductivity of epoxy composite but also broaden the application of MCF in the field of thermal management solutions.

Pure and calcium-doped zinc oxide thick films were deposited on Aluminium substrate by screen printing technique using nanocrystalline powder synthesized from co-precipitation method. Shear thinning phenomenon with increment of shear rate was observed during the rheological analysis for all pastes. X-ray diffraction results confirmed the formation of ZnO with preferred orientation along (101) plane. Peak shifting to lower angle was observed upon increment of doping concentration of calcium. Crystallite size of doped ZnO powder decreased in the range (from 35.4 to 42.4 nm) from 116.1 nm of pure ZnO. Surface morphology analysed by FESEM had revealed the reduction of voids with increasing doping concentration up to 7 wt% of doping, followed by a slightly increase in the number of voids at 9 wt% doping. AFM analysis showed that the surface roughness of films exhibited a decreasing trend with the increase of calcium dopant until 7 wt% but became rougher at 9 wt%. Peaks shifting of ZnO to lower wavenumber revealed by FTIR study indicated that doping had affected the lattice structure of ZnO in the films. Thermal characterization showed the introduction of calcium dopant had increased the thermal resistance of the thick films. This led to a better junction temperature (Tj) of LED of 46.4 °C when compared with Tj of pure ZnO film at 47.3 °C.

Magnesium-doped zinc oxide (MgZO) is one of the potential optical materials in enhancement of the band gap in solid state lighting. Undoped and Mg-doped ZnO thin film with various Mg concentrations (0.03 M:Mg, 0.05 M:Mg, 0.07 M:Mg) were synthesized using sol gel method on n-type silicon (111) and undergone annealing treatment at 450 °C and 550 °C using nitrogen gas for 1 h. The surface and optical properties of the thin films were investigated by field emission scanning electron microscopy (FESEM), Raman, UV-Vis spectroscopy, and Fourier transform infrared spectroscopy (FTIR). The undoped and Mg-doped ZnO thin film has hexagonal wurtzite structure with ZnO peaks (100), (002), and (101) that were identified by XRD analysis. The increment of Mg concentration resulted in the decrease of the intensity of the ZnO peaks. However, the intensity of the ZnO peaks increased with the increment of temperature. 0.07 M:Mg samples from both annealing temperatures have the largest crystallite size and the lowest dislocation density than that of the others. The crystallite size increased but the dislocation density decreased as annealing temperature was increased from 450 to 550 °C. FESEM results demonstrated that grain size of thin films reduced with increased doping concentration within the range of 25 to 65 nm and 26 to 44 nm for 450 °C and 550 °C annealing samples, respectively. Other than that, Raman spectra showed the decreased intensity of the mode vibration at peak 0.03 M:Mg but increased slowly with higher doping concentration. The influence of the annealing treatment also affect the mode position and intensity of Raman peak for undoped and Mg-doped ZnO thin films. The UV-Vis spectra revealed that no changes in band gap values at 450 °C for increased Mg doping concentration, but increment in band gap values within the range 3.35 ~3.60 eV was observed for samples annealed at 550 °C which occurs due to the improvement of crystallinity in samples. Characteristic vibrational mode of ZnO was observed in the absorption band in FTIR spectrum. Through this work, it is suggested that Mg-doped ZnO thin film could be a promising material in solid state and optoelectronic application.

The dielectric and optical properties of pure poly (3-hydroxybutyrate) and ZnO nanoparticle (15–30%)-reinforced poly (3-hydroxybutyrate) composite films were studied. Nanocomposites exhibit improved relative permittivity (e′ = 4.6720 @ 1 GHz) with acceptable loss tangent (tan δ

Effects of screen-printed AgxZn1−xO thick film deposited on Al substrate with composition 3 wt% ≤ x ≤ 9 wt% on the rheological, surface, vibrational and thermal properties were investigated in this paper. AgxZn1−xO powder with different doping concentration was synthesized through co-precipitation method and further mixed with solvent to form a thixotropic paste. The paste was screen-printed on Al substrate. Rheological behavior of pastes showed shear thinning phenomenon with increment of shear rate. Structural properties of pure and doped thick films were investigated by X-ray diffraction (XRD). It showed that (101) was a strong preferred orientation among other peaks. Field emission scanning electron microscopy (FESEM) results indicated the aggregated flake-like structure that become more prominent with increase of doping from 3 to 7 wt%. Surface roughness of the films exhibited a decreasing trend with the increase of silver content whereas the step analysis facilitated to identify the contact surface point of the film for thermal conduction in application purposes. By increasing the dopant’s concentration, peak position of ZnO had shifted within the range from 503 to 506 cm−1. FTIR spectra of the films showed no vibrational peaks related to AgO or Ag2O. Thermal characterization revealed a decreasing trend of film’s resistivity when the doping was increased to 7 wt%. The lowest achieved junction temperature with tested LED was measured at 47.32 °C at 7 wt% of silver doping.

A large amount of heat trapped inside Light Emitting Diode (LED) is the consequence of large thermal resistance between the heat source and the heat sink. Zinc oxide (ZnO) thick film was screen-printed from thixotropic paste that consisted of binder, filler and solvent to act as thermal interface material. Structural, surface morphology, vibrational and thermal properties of the samples were studied by means of Field Emission Scanning Electron Microscopy (FESEM), Atomic Force Measurement (AFM), Fourier Transform Infrared Spectroscopy (FTIR) and Thermal Transient Tester (T3ster). XRD analysis revealed that the formation of hexagonal wurtzite ZnO powder, which is free of hydroxide. FESEM results indicated that 50 wt% of filler loading in the thick film had created longer thermal transportation chain. The surface roughness of thick film displays variation in the range of from 64.8 to 218 nm. The presence of ZnO and binder were confirmed by FTIR spectrum at 518 cm−1 and 668 cm−1 to 2974 cm−1, respectively. Thermal characterization reveals a drop in film’s resistivity with the higher content of filler loading of 50 wt% and 55 wt%. The lowest rise in junction temperature of tested LED is reported to be 14.7 °C of 50 wt% of filler loading.

High scratch resistant nanorod nickel-phosphorous (Ni-P) sealing was fabricated using electroless deposition method on nanoporous anodic aluminum oxide (AAO-np). A two-step anodization process was preferred to develop an AAO-np template on Al alloy. Sensitization and activation processes were proceeded using SnCl2, PdCl2 respectively before Ni-P deposition. Concrete Ni-P was filled in and grown on AAO-np with a pore diameter of 40–60 nm at 6–7 μm height. A top view morphology confirms that the initial Ni-P clusters were transformed into a well-grown cauliflower-like structure during 1hr and 2 hr deposition times, respectively. Symmetric Ni-P nano-rods are formed at the beginning of porous structure in a side view. A possible formation of Ni-P nano-rods on AAO structure results in a potential improvement in indentation and scratch hardness as 3100 MPa and 3350 MPa, respectively.