NEW MEDIA

For high-density storage, the leading candidates are acicular metal particle (MP) tape and metal evaporated tape ME (Fig. 4.2). Because of the process difficulties manufacturers experienced in making particulate tape coatings thinner than ~2 µm, ME appeared in the early 1990s to have a significant advantage. However, the revolutionary use by Fuji Film of co-cast multi-layer technology derived from photographic film processing to produce magnetic layers <200 nm thick swung the advantage back to particulate tape. It was felt to be cheaper to produce, because of the relatively faster coating speeds, and more durable. Barium ferrite particles have also been considered for many sound scientific reasons, but the performance of MP and its availability have dampened interest in barium ferrite. However, Fuji Film has provided double-coat barium ferrite tapes for specific applications (e.g., ARKIVAL Technology Corp., Nashua, NH) where the environmental reliability is a dominant issue.


Fig. 4.2. High performance tape media.

ME has been dogged by repeated reports of low thresholds for wear and corrosion. However, in the panel's visit to Sony, panelists were told that the problem had been solved. Japanese manufacturers seem to have targeted ME for future DV consumer applications. Sony is installing an ME production line in its Dothan, AL plant and JVC has switched its focus in Japan to ME. At the present time, no ME tape is manufactured in the United States, and there is no indication that either Quantegy or Imation have any plans to do so.

In the United States, the only manufacturers of MP tape are Quantegy and Imation. However, the only supplier of the very thin "double coat" MP tape is Fuji Photo Film. Sony has licensed the technology but only for a new 200 MB floppy product. Imation researchers feel confident that they have the technology in place and will be a supplier of tape cartridges to specific formats when a market demand is evident. Fuji has an extensive patent portfolio surrounding the "double coat" process that restricts other manufacturers like Quantegy. Clearly, if the only supplier of the highest performance MP tape is Japanese, U.S. system designers will be at a severe disadvantage.

To achieve 300 kbpi with particulate tape, particles <50 nm in length must be available. Commercial tapes with 100 nm MP particles are available, and experimental tapes with 80 nm particles have been tested. However, although SEM images of 50 nm particles have been shown by Toda, no data on the particle characteristic has been published. All of the major particle suppliers are Japanese including the former U.S. companies Pfizer and Hercules, which were acquired by Japanese manufacturers. Thus, U.S. tape manufacturers do not have a domestic supplier of advanced magnetic particles.

The progress proposed in Table 4.3 will require improved substrate materials which are thinner, stronger mechanically and more dimensionally stable. At the present time, there are products using PET (polyethylene terephthalate), PEN (polyethylene naphthalate) and PA (polyamid). PET dominates low performance particulate tapes; PEN, which is stiffer, is used in several advanced products both for MP and ME; PA, which is even stiffer, is used in the SONY microcassette at a thickness of only 2.5 µm. However, the cost of PET is half that of PEN and a tenth that of PA. Both PET and PEN are manufactured in very high volume for other commercial applications, which results in lower cost for the tape market. If an entirely new, more exotic material is discovered, it will be difficult for the industry to afford the development and manufacturing costs if significant commercial applications cannot be identified. The major substrate manufacturers are Toray and Teijin, both Japanese. There is no supplier in the United States of high-quality tape substrate materials.

Table 4.3
Thinner Substrates

High End MP

Now

+5 Years

+10 Years

Substrate Material

PET/PEN/PA

PEN/PA

PA or better

Substrate Thickness

14 m m

5-6 m m

4-5 m m

Total Thickness

18 m m

8-9 m m

6-7 m m

       

Mid-Low Range MP

Now

+5 Years

+10 Years

Substrate Material

PET/PEN/PA

PEN/PA

PA or better

Substrate Thickness

4.5 m m

3-4 m m

2-3 m m

Total Thickness

7 m m

4-5 m m

3-4 m m


PET = polyethylene terephthalate $PET = 1/2 $PEN = 1/10 $PA
PEN = polyethylene naphthalate
PA = polyamid (aramid)

The data rate capacity product in a multi-track recorder is limited by the dimensional stability of the tape, dominated by the substrate. Present materials which experience several mechanisms of instability have an overall quality figure of ~1000 PPM. In a new material with the quality figure reduced to 500, the gain could be translated into a 2X increase in capacity or data rate or some combination of both. This is easily seen by examination of Fig. 4.3, which depicts the situation when a previously written pattern is read with a multi-track head. Assume the media has expanded so that the outermost channels of the multi-track head are off-track but at the limit of detectability. Only the track width and the head span matter. If the substrate was replaced by a medium with twice the stability (half the distortion), either the track width could be halved and the number of tracks on the tape doubled (2X capacity) or the head span and therefore the number of channels could be doubled (2X data rate).

The industry faces a major challenge in the development of improved but cost-effective substrate materials. The clear necessity to increase cost effectiveness conflicts with the expected higher costs of new materials.


Published: June 1999; WTEC Hyper-Librarian