Electrodeposition of CoCu Nanostructures

Abstract

Electrodeposition is a key component in the microelectronic industry because it has the following advantages: low cost, easy operation and the capability to deposit into irregular geometries such as recessed and curved areas. In this dissertation, CoCu alloys were investigated to fabricate multilayers, microdevices and microposts. All of these multilayer structures were composed of nanometric copper and cobalt-rich layers in order to obtain magnetoresistance, a phenomenon where the resistance of multilayer structures decreases with increases of external magnetic field. An investigation was carried out in order to evaluate appropriate plating conditions during multilayered thin film deposition, with the aim to obtain higher magnetoresistance at lower magnetic field. The effects of layer size, pH, bilayer number, seed layer and nickel component on the magnetoresistance of multilayered thin films were experimentally explored. A magnetoresistance of 5 % was obtained with the saturation field of less than 3000 Oe on the multilayered thin films by a conventional pulse method. An alternative electrodeposition process, which is referred to as pulse train in this dissertation, was first applied to study its effect on magnetoresistance of multilayered thin films. A pulse train control deposition of the cobalt layer during the fabrication of CoCu/Cu multilayers can improve magnetoresistance over the conventional square-wave pulse. A maximum 7-8 % magnetoresistance was obtained. The conditions that resulted in the best GMR in thin films were employed to fabricate a multilayered microdevice by combining UV lithography and electrodeposition. The geometric effects of the microdevices on their magnetoresistance were investigated in detail. The pulse train control method was also employed to improve the magnetoresistance of the microdevices. High aspect ratio CoCu/Cu multilayered microstructures were also electrodeposited. A single sulfate electrolyte with sodium citrate was employed to successfully fabricate 500 ìm tall microposts prepared by x-ray lithography. A giant magnetoresistance of 4 % was demonstrated in a single 500 ìm tall micropost. It is the first demonstration of GMR in a micropost exceeding a 10 ìm. A detailed investigation of the effects of the layer thickness, plating potentials, nickel component and the pulse train method on the magnetoresistance of microposts was performed.