Sarah Eunkyung 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.

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.