The most serious challenge to achieving the target densities (Table 4.1) is reduced head-media spacing. The effective head to media spacing must be reduced from the present value of 80-100 nm to <30 nm. This includes head gap erosion, media roughness and air entrapment at high tape to head speeds. No obvious solution to these requirements has been identified.

Thin film heads expose a variety of soft and hard materials to the abrasive tape surface. Highly desirable would be a thin (<10 nm) head overcoat which was highly wear resistant. Thicker overcoats are now used in ME tapes to reduce wear and corrosion. Sony is the world's leader in this area and presumably would have knowledge of the efficiency of head overcoats as well. Several U.S. companies, including IBM, Seagate and StorageTek, make tape heads and presumably are studying this problem.

Peak media roughness, not the average roughness, limits the spacing between the head and media. It is now about 20 nm and must be reduced by improved processing to <10 nm.

Traditionally, tape heads were made with long throat heights, which wore away during use. This is one reason VCRs eventually fail. Thin film heads have very short throat heights (<1.5 µm) so a more creative solution must be found. The head slider used in an HDD is a very sophisticated, aerodynamic form designed to keep the head "flying" close to the media surface. Similar analysis must be employed to minimize the flying height of the head over the tape at high tape-head speeds. The United States is in a strong position in this area because of its leadership in HDDs.

2X Improvement in Stability


Fig. 4.3. Substrate stability-capacity/data rate trade-offs.
Published: June 1999; WTEC Hyper-Librarian