Byung-Kyu 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.

Dependence of sputtering power and soft underlayer on magnetic properties in CoCrPtO perpendicular recording media

In this paper, sputtering power dependence on magnetic properties and microstructure of CoCrPtO perpendicular recording media was examined. Also, change of magnetic properties of CoCrPtO layers on two different soft underlayers was investigated. As the oxygen gas ratio increases, coercivity (Hc) increases regardless of the variation of the sputtering power up to a certain critical oxygen gas ratio which depends on the sputtering power. Then, Hc drops sharply in all cases. The higher the power is, the higher the critical oxygen gas ratio is. As the oxygen gas ratio increases, exchange slope also decreases more rapidly at the lower sputtering power than higher power. The small grains of the size of /spl sim/7 nm with thick amorphous-like grain boundaries are observed in the media sputtered at the power of 75 W. It is considered that the selective oxidation of grain boundary is performed more effectively at low sputtering power. CoCrPtO layer on NiFeNb soft magnetic underlayer (SUL) showed higher Hc of 5000 Oe and well isolated grain in comparison with CoCrPtO layer on CoZrNb SUL. This difference of coercivity behavior may be associated with difference CoCrPtO layer on residual stress or surface roughness.

The effect of Pd buffer layers on magnetic exchange energy of Co/Pd multilayered films for perpendicular magnetic recording

A Co/Pd multilayered film is one of the promising perpendicular magnetic recording (PMR) media with high magnetic squareness, due to interfacial magnetic anisotropy energy. However, the lack of a magnetic decoupling factor in the Co/Pd film, unlike a compositionally decoupled CoCr based alloy film, possesses large magnetic exchange energy which results in large magnetic domain sizes and high noise source. In this research, we investigate a domain isolation parameter (α) to control the magnetic exchange energy and domain sizes in terms of the deposition pressures of a Co/Pd recording multilayer and a Pd buffer layer in a PMR disk. The high pressure in the Pd buffer layer is effective to isolate and reduce the Co/Pd domain sizes with a low α value. The observations with a magnetic force microscope (MFM) and a cross sectional transmission electron microscope (TEM) prove that the physically decoupling effect originated from the surface roughness of the Pd buffer layer, plays a major role in creating a fine domain pattern in the Co/Pd multilayer. The dynamic read/write performances of the Co/Pd multilayered disk by a merged giant magneto resistive (GMR) head show that the low α value disk with magnetically decoupled grains has a low medium noise level, compared with the high α value disk.

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.

Recording physics of perpendicular recording with single layered medium and ring head

In this article, the recording physics of a ring head with a single layered perpendicular medium (Ring/SL) is studied and the results are compared with a single pole head with a double layered perpendicular medium (SPT/DL) by using various simulations and experiments. The Ring/SL has much lower effective medium coercivity than the SPT/DL due to the substantial longitudinal field component of ring head and the incoherent rotation mode of medium magnetizations. Furthermore, switching time of the Ring/SL is estimated as only 10%∼30% of the SPT/DL. In the Ring/SL, the head field gradient of 40 Oe/nm is enough for maximizing SNR. The Ring/SL shows very low noise characteristics especially at high linear density. The signal output of the Ring/SL is smaller than the SPT/DL, but it is large enough to be detected. Therefore, it can be concluded that the combination of single layered perpendicular medium and ring head is highly promising for ultrahigh density recording.

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.

New design of perpendicular magnetic recording media: hybrid media

To achieve both the high anisotropy energy and high SNR performance at ultra high areal recording density, we have studied paired recording layered PMR media named as hybrid media. Hybrid media consist of 1/sup st/ recording layer and 2/sup nd/ recording layer. 1/sup st/ recording layer and 2/sup nd/ recording layer have low noise properties and high anisotropy energy, respectively. 1/sup st/ and 2/sup nd/ recording layer are continuously and coherently stacked on the top of the underlayer.

The effect of hybrid media to achieve both good thermal stability and excellent read/write performance

In this paper, hybrid media to achieve both good thermal stability and excellent read/write performance were analyzed. Hybrid media consist of 1/sup st/ recording layer having low noise properties and 2 /sup nd/ recording layer having high anisotropy energy.

Enhancement of signal to noise ratio by underlayer control in CoCr-based perpendicular magnetic recording media

In this paper, enhancement of signal to noise ratio by underlayer control in CoCr-based perpendicular magnetic recording media was discussed. Underlayer control for SNR, thermal stability, magnetic hysteresis, structure of the media also investigated.