Du-hyun Lee

The fabrication of Co-Pt electro-deposited bit patterned media with nanoimprint lithography.

Bit patterned media with 25 nm hole diameter and 50 nm pitch size were fabricated with serial processes comprising master patterning with electron-beam lithography, a Si etching process, multi-layer soft stamp replication, and UV nanoimprinting, followed by Co-Pt magnetic material filling by electro-deposition. From these processes, the designed patterns were well defined, and perpendicular magnetic anisotropy of the fabricated bit patterned media was obtained.

Nano-pore arrays of anodic aluminum oxide fabricated using a Cr mask

Anodic aluminum oxide (AAO), typical material with a self-organized porous structure, has recently attracted due to its many potential technical applications such as magnetic, electronic, and optoelectronic device (Whitney et al., 1993 and Rahman and Yang, 2003). There is a great demand for highly ordered and patterned nano-pore arrays. These studies have been reported by prepatterning the Al films and lithographical approaches (Sun and Kim, 2002 and Yasui et al., 2005). To array alumina pore, in this study, Cr and SiO2 layer deposited on Al thin film, which were patterned by electron beam lithography and ion milling and were used as anodizing mask before anodizing. The effects of mask pattern on alumina pore array were investigated by the various shape and size of Cr mask and different anodic voltage during the anodizing process.

30nm full field quartz template replicated from Si master for FLASH active layer NIL

38nm half pitch pattern was replicated from Si master pattern to quartz blank template. It is a novel approach different from typical quartz to quartz replication. This replication concept is expected to alleviate the burden not only in cost but also resolution for NIL template fabrication. In this study, full field Si master fabricated by ArF immersion lithography, UV-transparent hard mask for quartz blank template and core-out quartz blank template were applied to prove the concept. And the replica template was evaluated with NIL and subsequent etching.

Fabrication and MFM study of 60 nm track-pitch discrete track media

Discrete track magnetic recording media with a 60 nm track pitch and prewritten servo patterns were fabricated and tested for read/write performance, and a feasibility analysis of the embedded servo was performed. The fabrication process consisted of ultraviolet nanoimprint lithography (UV-NIL) and sequential ion beam etching on a conventional perpendicular magnetic recording medium. Magnetic patterns were written to the fabricated tracks at 700 kilo flux changes per inch (kFCI) using a spin stand and were read using magnetic force microscopy (MFM), with a resulting signal-to-noise ratio (SNR) of 12.15 dB. The servo pattern was also visualized with MFM. These results demonstrated the feasibility of writing to a 30 nm wide discrete data track and the workability of the embedded servo pattern.

Dependence of exchange bias on various annealing conditions in Mn-Ir-Pt based spin valves

In this paper, we have investigated the annealing conditions for a Mn-Ir-Pt based top and bottom conventional SVs and have evaluated the blocking temperature and the thermal stability of H/sub ex/ at the ramped temperature. The change of an interface was confirmed from a RBS study.

Effect of surface roughness on plasma oxidation behavior of Al layer and tunneling magnetoresistance

In this paper, we evaluated the variation of magnetic properties and junction resistance R/sub j/. And the oxidation behavior was analyzed by a high resolution transmission microscopy (HR-TEM) study.

The Effect of the Interface Impurity in Fabrication of Spin Dependent Tunnel Junction

Ferromagnetic-insulator-ferromagnetic tunneling was measured in two types of Co/Al2O3/Co/NiFe junctions. For type 1 junction (two times of interface exposure to air), the maximum tunnel junction magnetoresistance (TMR) ratio was 16.5% at room temperature. Junctions with a relatively thicker Al layer showed a lower resistance and a higher TMR ratio. Whereas, junctions with a relatively thinner Al layer showed a fast increase of barrier width. The passivation effect of Al2O3 in oxidation process enhanced the TMR ratio. As the oxidation time is increased, the coercivity of Co bottom electrode is also increased. So the effect of CoO formation in the interface of the Co bottom electrode and the Al2O3 is discussed in three possible assumptions. For type 2 junction (just one time of interface exposure to air), the maximum TMR ratio was 21% at room temperature. And the TMR ratio was decreased to half at 550 mV. These junctions have potential use as low-power field sensors and memory elements.