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

1. 离子液体电沉积钴：以CoCl_2和N-（正丁基）氯化吡啶（N-(N- butyl) pyridium chloride， BPC）为电解液制备高纯度钴和钴合金。当CoCl_2与BPC的摩尔比为1:2 ~ 1:1时，熔点低于80℃。钴的电沉积只发生在摩尔比小于1:2的离子液体中。在离子液体中沉积钴的电流效率超过98%。在Si/Ti/Au/Al多层上形成无阻挡层的多孔氧化铝多层：由于多孔氧化铝底部形成的阻挡层通常起到电绝缘体的作用，因此需要制造无阻挡层的多孔氧化铝。在半导体硅衬底上制备了Ti（50nm）、Au（200nm）和Al（2μm）的多层材料，同时要求在孔底有电子接触才能进行电化学反应。对多层试样进行两步阳极氧化，形成有序的纳米多孔氧化铝。通过适当的化学溶解氧化物来扩孔。所得多孔氧化铝具有高500nm、孔径80nm、底部无阻隔层的特点。离子液体电沉积钴到多孔氧化铝：将钴填充到多孔氧化铝的孔洞中，在恒流条件下，用AlCl_3-BPC-CoCl_2离子液体电沉积钴。溶液中的循环伏安图显示，在阴极扫描和阳极扫描中均出现三个峰，分别对应于纯钴、钴铝合金和纯铝的沉积和溶解。孔中没有观察到明显的欧姆下降。由于残留的屏障层阻碍了钴的填充，因此需要沉积比孔隙深度估计的更厚的钴层。

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.