The objective of this study is to quantitatively evaluate the impacts of LED components on the overdriving reliability of high power white LED chip scale packages (CSPs). The reliability tests under room temperature are conducted over 1000 h in this study on CSP LEDs with overdriving currents. A novel method is proposed to investigate the impact of various components, including blue die, phosphor layer, and substrate, on the lumen depreciation of CSP LEDs after aging test. The electro-optical measurement results show that the overdriving current can lead to both massive light output degradation and significant color shift of CSP LEDs. The quantitative analysis results show that the phosphor layer is the major contributor to the failure in early period aging test. For the long-term reliability, the degradations of phosphor and reflectivity of substrate contribute significantly on lumen depreciation. The proposed reliability assessment method with overdriving loadings can be usefully implemented for LED manufacturers to make a cost- and effective-decision before mass production. ... Read more

Using the analogue of the electric inductance, we reveal the properties of the thermal inductance in GaN-based light-emitting diode devices by testing their transient thermal behaviors. We find that the devices exhibit a transient thermal response under step-down or step-up currents and observe notable inductive phenomena of the temperature response as time evolves from start up to some hundred microseconds. We define thermal inductance as the rapid change in device temperature that is opposite to the temperature change expected from the power input. These findings can promote new temperature measurements, and novel thermal analyses of high-frequency semiconductor devices that combining the thermal resistances, thermal capacitances, and thermal inductances. ... Read more

We report a molecular modeling study to evaluate and select conducting polymers (CPs) for use as the sensing layer for carbon dioxide (CO2) sensor. The interactions between gases and sensing materials and the adsorptions of small gas molecules on polymer sensing films are described and investigated. Polymers considered for this work include emeraldine base polyaniline (EB-PANI) and unprotonated sodium polyaniline salt (NaSPANI) with sulfur to nitrogen ration (S/N) of 0.4, 0.5 and 0.6 Gases studied include CO2, humidity (H2O). Comparative studies of NaSPANI and PANI show differences on the polymer-gas interaction energy and gas sorption number because of the -So3NA groups on the phenyl rings. ... Read more

This chapter aims at developing molecular modeling methodology to select a thiol-based self assembly monolayer (SAM) as a coupling agent for achieving a reliable epoxy-copper interfacial adhesion under moisture conditions. Moisture diffusion and interfacial energy is evaluated using molecular dynamics simulations. The qualitative agreement of the calculated interfacial energy with the experimental adhesion energy demonstrates that the molecular dynamics method is an effective way in selecting the coupling agent candidates. ... Read more

Molecular dynamics (MD) and molecular mechanical (MM) analysis are carried out to provide reliable and accurate model for emeraldine base polyaniline. This study validate the forcefields and model with the physical and mechanical properties of the polyaniline. The temperature effects on non-bond energy, potential energy and solubility parameter during the transformation from the rubbery to the glassy state have been analysed in this work. A new method using the solubility versus temperature (delta-T) curve for predicting the Tg of polymer are suggested. Keywords: Emeraldine base; molecular dynamics; forcefields; glass transition. ... Read more