Ultra High Density Magnetic Memory using Electrodeposition from Ionic Liquid into Porous Alumina

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1. Electrodeposition of Cobalt from Ionic Liquid : To obtain high purity Co and cobalt alloys by electrodeposition, ionic liquid from CoCl_2 and N-(n-butyl) pyridinium chloride (BPC) was used as an electrolyte. A mixture of CoCl_2 and BPC in the molar ratio between 1:2 to 1:1 had a melting temperature lower than 80℃. Electrodeposition of cobalt took place only in the ionic liquid of the molar ration less than 1:2. Current efficiency for the cobalt deposition exceeded 98% in these ionic liquid.2. Formation of Porus Alumina without Barrier Layer on Si/Ti/Au/Al Multi-layer : Since a Barrier layer formed at the bottom of porous alumina usually acts as an electric insulator, it is required to make a porous alumina without the barrier layer. It is also required to have an electronic contact at the pore bottom to make electrochemical reaction, a multi-layer of Ti(50nm), Au(200nm) and Al(2μm) was prepared on to a semiconducting silicon substrate. Two step anodic oxidation of the multi-layer specimen leads to form ordered nano-pored alumina. Pore widening was performed by a suitable chemical dissolution of oxide. Resulted porous alumina has a characteristics of 500nm height and 80nm pore diameter and without barrier layer at the bottom.3. Electrodeposition of Cobalt into Porous Alumina from Ionic Liquid : Far filling up cobalt into the pores of porous alumina, electrodeposition of cobalt from ionic liquid of AlCl_3-BPC-CoCl_2 was performed at a constant current condition. Cyclic voltamograms in the solution revealed that three peaks appeared in both cathodic and anodic scans, and these were corresponded to deposition and dissolution of pure cobalt, cobalt-aluminum alloy and pure aluminum, respectively. No considerable ohmic drop in the pore was observed. It needed to deposit cobalt layer thicker than that estimated from the pore depth, because a residual barrier layer disturb filling up cobalt.