SiO2 doped Ge2Sb2Te5 thin films with high thermal efficiency for applications in phase change random access memory

This study examined the various physical, structural and electrical properties of SiO(2) doped Ge(2)Sb(2)Te(5) (SGST) films for phase change random access memory applications. Interestingly, SGST had a layered structure (LS) resulting from the inhomogeneous distribution of SiO(2) after annealing. The physical parameters able to affect the reset current of phase change memory (I(res)) were predicted from the Joule heating and heat conservation equations. When SiO(2) was doped into GST, thermal conductivity largely decreased by ～ 55%. The influence of SiO(2)-doping on I(res) was examined using the test phase change memory cell. I(res) was reduced by ～ 45%. An electro-thermal simulation showed that the reduced thermal conductivity contributes to the improvement of cell efficiency as well as the reduction of I(res), while the increased dynamic resistance contributes only to the latter. The formation and presence of the LS thermal conductivity in the set state test cell after repeated switching was confirmed.     

Thermoelectric properties of Bi2Te3-In2Se3 composite thin films prepared by co-sputtering

Bi2Te3-In2Se3 films were prepared by co-sputtering followed by annealing, and their structural and thermoelectric properties were investigated. The immiscible nature of the two alloys results in precipitation of the second phase, thus leading to structures with self-assembled dots that are a few nanometers in scale. HAADF-STEM and HRTEM were used to confirm that In2Se3 nanodots that were a few nanometers in size did indeed form in the Bi2Te3 thin film. It was found that the incorporation of these nanodots can reduce the thermal conductivity of the thin film.     

Three-Dimensional Bi2Te3 Nanocrystallites Embedded in 2D Bi2Te3 Films Grown by MOCVD

Two- (2D) and three-dimensional (3D) growth of nanostructured Bi₂Te₃ films was performed on 4° tilt (100) GaAs substrates using a metalorganic chemical vapor deposition system. To obtain 3D Bi₂Te₃ crystallites embedded in 2D planar film, we alternately changed the gas flow rate in the reactor. By repeating two steps, 3D Bi₂Te₃ crystallites embedded in 2D planar Bi₂Te₃ film were obtained. The thermoelectric properties in terms of the thermal conductivity, electrical conductivity, and Seebeck coefficient were investigated at room temperature. The thermal conductivities of the nanostructured Bi₂Te₃ films were from 0.63?W/(m?K) to 0.94?W/(m?K) at room temperature, which are low compared with that of film without nanostructure [1.62?W/(m?K)]. The thermal conductivity of the film was effectively decreased with the decrease of size and increase of density of 3D crystallites. The results of this study open up a new method to fabricate nanostructured thermoelectric films with high thermoelectric figure of merit.     

Life-time estimation of high-power blue light-emitting diode chips

We have proposed a new concept of metal package by which we can estimate the lifetime of blue light-emitting diode (LED) chips with high accuracy. Components in conventional LED package which may obscure the degradation behavior of LED chip itself were removed or replaced by other materials or components. Three kinds of chips from different manufacturers were analyzed in this study using proposed metal packages. In this paper, the optical and electrical characteristics such as light-output degradation and reverse leakage current of high-power blue LED chip were investigated and analyzed. Also, the relationship between light-output degradation and electrical characteristics of LED chip was described. With aging time of 5000 h, only one kind of blue LED chip shows enough light-output degradation to estimate life-time.