Abstract

Data storage technologies such as HDD and optical recordings are key to the information-oriented society, and the demand for their technological developments will be undoubtedly more strongly increasing. For mass-data storage applications, the capacity or areal density of drives will be more demanded. With increasing areal density, both track pitch and bit-length must be decreased (Fig.1). Given this trend, one would expect a bit-length for densities close to 100 Gbits/in² in HDD is expected to become 20-30nm or even less. For such small bit-length, a grain size of a medium must also be smaller than that bit-length, thus a thermal decay of magnetization due to super-paramagnetic effect becomes serious. Recently, a multi-layer type medium, utilizing a ferro-antiferro coupling, has been developed to demonstrate a better thermal stability. Perpendicular magnetic recording (PMR) has been receiving much attention, and a recent work demonstrated the performance of 63 Gb/in². Yet, serious issues remain to be solved before any drives will be commercially available. They may be: i) thermal instability of magnetization at low recording densities, leading to large noise, ii) a so-called antenna effect, which is the enhancement of noise due to stray fields externally generated, and iii) lack of suitable media in conjunction with manufacturability. Another approach to high-density recording is a patterned medium, which consists of small-scale dots isolated physically and magnetically. One of them is that can be fabricated by using lithography or ion/electron-beam technique or self-assemble manner. Though these techniques may provide another way to increase density, drawback related to compatibility and cost-performance must be addressed. For optical recording technology, the current areal recording density level (MO and DVD) is about 4-5 Gb/in². Recent works using blue laser and high NA demonstrated densities of about 20 Gb/in². As seen in Fig.1, optical recording of the current products has an advantage of narrower track pitch, as compared to HDD. This may not be any longer the case, since recent works of HD head fabrication indicate the manufacturability of a narrow track head (100nm), which is comparable to what the current optical recording might have been able to do in a few years. The current trend for high-density recording is to combine blue-laser and high NA optical head, together with MSR and MFM/LIM. Various techniques such as MAMMOS, DWDD, SIL/Super Rens-Near Field Optics and multi-values recording have been being intensively developed. For phase change recording, novel media capable for high-speed writing and small marks have been developed, leading to higher density than that of DVD.

© 2001 IEEE