Sungdong Kim

The effects of heat treatment on room temperature ferromagnetism in a digitally Co doped ZnO thin film

The effects of heat treatment on room temperature ferromagnetism of Co-doped ZnO were investigated with a (ZnO 20Å/Co x Å)20 multilayer structure where x = 1.5, 3, 4.3, 6 and 9 Å. As the thickness of the Co sub-layer increased, the ZnO/Co multilayer changed its magnetic state from diamagnetism at Co 1.5 Å and 3 Å to weak ferromagnetism at Co 4.3 Å and strong ferromagnetism at Co 6 Å and 9 Å. The heat treatment, in a vacuum at 400°C, changed the diamagnetic property into a ferromagnetic one, resulting in room temperature ferromagnetism for all Co sub-layer thicknesses. The improvement in ferromagnetism could be ascribed to the exchange coupling between dispersed Co atoms through XRD, optical transmittance and TEM analysis.

The Effect of Vacuum Annealing of Tin Oxide Thin Films Obtained by RF Sputtering

Tin oxide thin films were deposited by rf reactive sputtering and annealed at 400℃ for 1 h in vacuum. To minimize the influence such as reduction, oxidation, and doping on tin oxide thin films during annealing, a vacuum ambient annealing was adopted. The structural, optical, and electrical properties of tin oxide thin films were characterized by X-ray diffraction, atomic force microscope, UV-Vis spectrometer, and Hall effect measurements. After vacuum annealing, the grain size of all thin films was slightly increased and the roughness (R a ) was improved, however irregular and coalesced shapes were observed from the most of the films. These irregular and coalesced crystal shapes and the possible elimination of intrinsic defects might have caused a decrease in both carrier concentration and mobility, which degrades electrical conductivity.

Characterization and Fabrication of Tin Oxide Thin Film by RF Reactive Sputtering

Tin oxide thin films were prepared on borosilicate glass by rf reactive sputtering at different deposition powers, process pressures and substrate temperatures. The ratio of oxygen/argon gas flow was fixed as 10 sccm / 60 sccm in this study. The structural, electrical and optical properties were examined by the design of experiment to evaluate the optimized processing conditions. The Taguchi method was used in this study. The films were characterized by X-ray diffraction, UV-Vis spectrometer, Hall effect measurements and atomic force microscope. Tin oxide thin films exhibited three types of crystal structures, namely, amorphous, SnO and SnO2. In the case of amorphous thin films the optical band gap was widely spread from 2.30 to 3.36 eV and showed n-type conductivity. While the SnO thin films had an optical band gap of 2.24-2.49 eV and revealed p-type conductivity, the SnO2 thin films showed an optical band gap of 3.33-3.63 eV and n-type conductivity. Among the three process parameters, the plasma power had the most impact on changing the structural, electrical and optical properties of the tin oxide thin films. It was also found that the grain size of the tin oxide thin films was dependent on the substrate temperature. However, the substrate temperature has very little effect on electrical and optical properties.

Evaluation of wafer level Cu bonding for 3D integration

Alignment from an aligner, bond spacer removal during bonding, and wafer warpage are found to be the influential issues for the misalignment in wafer level bonding process. Also, Cu surface pre-treatment, thermo-compression bonding conditions such as temperature, pressure, ambient gas, annealing time, and Cu CMP process affect significantly a bonding quality.