The most common method of making white light emitting diode (LED) is to mix the blue light from the LED die and the
wavelength converted yellow light from the phosphor layer. The color conversion efficiency depends on the geometry
and concentration of the phosphor layer including phosphor material. Thus the optimization of the phosphor geometry
and concentration make increase the luminous efficiency of the white LED. In this paper, the remote phosphor scheme is
optimized focusing on increasing the luminous efficiency in high power. The phosphor layer is separated by the silicone
resin from the LED die. The silicone resin covers the LED die with dome shape to increase the extraction efficiency. The
phosphor layer has very large volume with dilute concentration. The separation of phosphor layer from LED die and
very large volumetric dilute phosphor layer were great important role in increasing the luminous flux. The improved
luminous flux was 15% for 1mm<sup>2</sup> LED die at 700mA.
We report on the development of GaN-based violet laser diodes (LDs) for the high-capacity optical storage application and blue LDs for the laser projection display application. InGaN LDs with emission wavelength of ~405 nm are already being adopted for next-generation optical-storage systems. We present results on >400 mW single-mode output power under pulsed operation which can be employed in 100 Gbyte multi-layer BD systems. We designed LD layer structures to exhibit high level of catastrophic optical damage (COD) and small beam divergence. In addition, GaN-based blue LDs with emission wavelength of ~450 nm have also been developed for the application to the blue light sources of laser display systems. We demonstrate single-mode blue InGaN LDs with >100 mW CW output power. Interestingly, we observed anomalous temperature characteristics from the blue InGaN LDs, which has shown highly-stable temperature dependence of output power or even negative characteristic temperature (T<sub>0</sub>) in a certain operation temperature range. This unusual temperature characteristic is attributed to originate from unique carrier transport properties of InGaN QWs with high In composition, which is deduced from the simulation of carrier density and optical gain.
The enhanced output power with improved lifetime is required for the GaN-based blue-violet laser diode (LD) as a light source for Blu-ray Disc or HD-DVD. In this paper, the output power levels and aging behaviors in GaN-based LDs grown on sapphire substrates were compared in epi-up and epi-down bonding. At low current level, the two bondings
show little differences in L-I characteristics. At high current level, however, the epi-up bonding shows a rapidly decreased slope efficiency in L-I characteristics with increasing current injection. On the contrary, the slope efficiency in epi-down bonding is not so much deteriorating as that in epi-up bonding. The differences in junction temperature between epi-up and epi-down bonding are large at higher current levels. The junction temperature of epi-up bonding is
about two times higher than that of epi-down bonding, implying efficient heat dissipation in epi-down bonding. At aging test, the epi-down bonding LD shows lower degradation rate at the aging slope than that of epi-up bonding LD. The degradation rate is accelerated by poor heat dissipation in epi-up bonding. Thus, for the higher power and longer lifetime, it is necessary to employ efficient heat dissipation structures such as epi-down bonding for the GaN-based LD
on sapphire substrate.
Electronic packaging is increasingly becoming a vital part of the electronics industry, representing a key barrier to cost reduction and performance improvement. Flip-chip joining using conductive polymeric adhesives have been identified as a key technologies for future electronics assembly and manufacturing. The purpose of this study is to investigate optimum conditions to achieve the best electrical performance in conductive adhesive joints. Therefore, the quality and reliability tested in conductive adhesive joints were performed at various current densities with different curing conditions. Differential scanning calorimetry and resistance measurement were used to monitor curing condition in conductive adhesives. Accelerated life testing of conductive adhesive joints made of the selected conductive adhesive using different curing conditions was performed with various current densities. The current-induced degradation of conductive adhesive joints was investigated through optical microscope and resistance measurements. Results show a shift in contact resistance depending on curing condition and current density. The contact resistance shift is found to be due to the migration of conducting particles in the adhesive joint.
A study of both thickness dependent optical and dielectric properties of a low-dielectric constant polycrystalline polymer thin film is investigated. It is demonstrated that the refractive index increase with increasing film thickness, but for thickness < 200 nm, abnormal decrease of the refractive index with increasing film thickness is observed. It is also found that the dielectric strength has a strong dependance on film thickness, which decrease with increasing film thickness. Optical spectroscopy and current ramping voltage test are involved to investigate thickness dependence of optical and dielectric properties. The observations are discussed in terms of our and other models for film thickness dependent of dielectric strength as well as refractive index.
Thermal stability is a critical issue for polymer thin films being used as interlevel dielectrics (ILDs) in deep- submicron multilevel interconnection. One of crucial parameters to predict thermal stability is the glass transition temperature (T<SUB>g</SUB>). Unfortunately the glass transition in polymer thin films is still not clearly understood. In this work, a simple model is developed for the thickness dependence of T<SUB>g</SUB> of polymer thin and ultrathin films. It is predicted that T<SUB>g</SUB> of polymer thin films can either be reduced or enhanced in comparison with its bulk values, depending on the polymer-substrate and polymer-surface interactions. In addition, the thickness- dependent T<SUB>g</SUB> of polymer thin films can exhibit a minimum as a function of thickness. Experimental data from technologically important ILD films are obtained to support the theoretical model.