Optical data storage tape is now a commercial reality. The world's first successful development of a digital optical tape system is complete. This is based on the Creo 1003 optical tape recorder with ICI 1012 write-once optical tape media. Several other optical tape drive development programs are underway, including one using the IBM 3480 style cartridge at LaserTape Systems. In order to understand the significance and potential of this step change in recording technology, it is useful to review the historical progress of optical storage. This has been slow to encroach on magnetic storage, and has not made any serious dent on the world's mountains of paper and microfilm. Some of the reasons for this are the long time needed for applications developers, systems integrators, and end users to take advantage of the potential storage capacity; access time and data transfer rate have traditionally been too slow for high-performance applications; and optical disk media has been expensive compared with magnetic tape. ICI's strategy in response to these concerns was to concentrate its efforts on flexible optical media; in particular optical tape. The manufacturing achievements, media characteristics, and media lifetime of optical media are discussed

Duffy, Joseph F.

Mclean, Robert A.

English

NASA Technical Reports Server

ICI Imagedata /o
ICI Optical Data Storage Tape
Robert A McLean
Joseph F Duffy N93- 15037
1. Introduction to flexible optical media
Optical data storage tape is now a commercial reality. The world's first successful
development of a digital optical tape system is complete. This is based on the Creo 1003
optical tape recorder with ICI 1012 write-once optical tape media. Several other optical tape
drive development programs are underway, including one using the IBM 3480 style cartridge
at LaserTape Systems.
In order to understand the significance and potential of this step change in recording
technology, it is useful to review the historical progress of optical storage. This has been slow
to encroach on magnetic storage, and has not made any serious dent on the world's mountains
of paper and microfilm. Some of the reasons for this are:
• The long time needed for applications developers, systems integrators and end users to
take advantage of the potential storage capacity.
• Access time and data transfer rate have traditionally been too.slow for high-performance
applications.
• Optical disk media has been expensive compared with magnetic tape.
As one of the world's major international chemical companies, ICrs strategy in response to
these concerns has been to concentrate its efforts on flexible optical media; in particular
optical tape.
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https://ntrs.nasa.gov/search.jsp?R=19930005848 2020-03-17T08:35:10+00:00Z
ICI Imagedata
2. Manufacturing achievements
Flexible optical media offers many benefits in terms of manufacture; for a given capital
investment, continuous, web-coating techniques produce more square meters of media than
batch coating. The coated layers consist of a backcoat on the non-active side; on the active
side there is a subbing layer, then reflector, dye/polymer and transparent protective overcoat.
All these layers have been tailored for ease of manufacture, and specific functional
characteristics.
3. Media characteristics _ :
The media can contribute to high system performance over a very wide range of capacities,
depending on the drive design and media format. In addition to low cost/MegaByte, the
media offers the archivability and indelibility that is vital for many storage applications. Thus,
the media permits the development of systems that provide a unique set of features:
• Low on-line costtMB: 10¢ to 40¢/MB depending on the format.
• Low media cos_: ._¢ to I¢/MB at first, falling with time.
High performance in access time: the low track spacing and high longitudinal speed of
f'Lxed head optical tape drives allows search rates between 2 GB/s and 20 GB/s. This
compares very favorably with helical scan magnetic drives.
• High data rate: a single laser channel can achieve 4 MB/s with 60 mW on the media
surface, and this can readily be increased with the use of multiple lasers.
• High volumetric efficiency: flexible optical media offers efficiencies a factor of 10 higher
than advanced helical magnetic recording.
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• Indelible media: the original information cannot be erased and altered.
• Unlimited read cycles: non-contact recording means that the data will survive in excess
of 30,000,000 read cycles. The number of tape wind cycles is very high.
• Long media lifetime: the use of chemically stable materials has allowed us to predict a
lifetime in excess of 15 years.
4. Media lifetime
Optical media based on organic, dye/polymer materials is well-known for its chemical stability.
An unfortunate consequence of this is the difficulty in predicting a lifetime. Several
accelerated aging techniques are in common usage: steady-state elevated temperature and
humidity with Arrhenius extrapolation; elevated levels of temperature plus corrosive gases (the
"Battelle" test); and chemical stability investigations.
We have used all of these extensively, both to attempt to predict an absolute lifetime limit,
and in comparisons with magnetic tapes: iron oxide, cobalt modified iron oxide, chromium
dioxide and metal particle formulations. We have also compared our media with rigid optical
disks, including stability to uv light.
The Arrhenius test is performed at various constant conditions of elevated temperature and
humidity (Ref. 1). The test assumes the following relationship, where failure is dominated by
one chemical process with a given activation energy: 1/time = A{e_T}. Our initial criteria for
failure was a change in absolute reflectivity of 5% (Fig. 2) or a drop-off in the Carder-to-
Noise Ratio (CNR) by 3 dB (Fig. 3). This level of failure was not detected for any of the
samples. A better way of detecting failure is to measure the raw BER on a drive; we are
now doing this on the Creo drive.
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To generate an Arrhenius estimate (Fig. 1), we looked for any deviation from the starting
values that was significant compared with the measurement accuracy. There was no
measurable change for the sample at 55 °C. The sample at 95 *C was well above the glass
transition temperature of the PET base film, and so was badly warped, and this led to
inaccurate reflectivity measurements and prevented us from doing a CNR measurement. The
Arrhenius graph slope gives an activation energy of 1.12 eV. This implies that a sample kept
at conditions of 20 *C and 60 %RH would survive for 393 years. A comparison with other
forms of optical media is shown in Table 1.
We have used two UV stability tests. The Blue Wool Test was developed for dyes used in the
clothing industry, and has now been formalized as British Standard BS1006. It assesses light
fastness on a scale of 1 (low) to 6 (high). ICrs media measures > 4 with the test still
continuing. By comparison, the average textile dye measures < 4.
Another UV test was used by Sony to test their optical disk media (Ref. 2). This exposes a
sample to 120 hours of UVA light at 45 *C and 60 %RH, and is equivalent to 70 days of
sunshine. We saw 1% drop in reflectivity - a result similar to that for Sony Century Media.
We also compared our media to metal particle and metal oxide tapes, and examined,
respectively, recording characteristics and chemical stability.
The metal particle tapes were stored under accelerated aging conditions, and the recording
characteristics were assessed by looking for any changes in the magnetic properties. We
bought two tapes; tape "A" is consumer R-DAT and tape "B" is 8 mm video, both were
different major Japanese brands. The test method consisted of storing the tapes at a constant
60 °C and 80 %RH for 3 and 6 weeks, while keeping a Control tape at room conditions. The
magnetic properties were then measured in a high saturation field VSM. This work was done
for ICI by the Fulmer Research Company in England, and is summarized in Table 2. The
signal strength dropped by up to 22% after 6 weeks.
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We performed an analogous test on the ICI optical tape out to 9 weeks (Fig. 4). The signal
strength was unchanged, and the CNR curves did not change within the measurement
accuracy. In addition, we used a Time Interval Analyzer (TIA) to look for an increase in the
intrinsic error rate by measuring a Geometric Error Rate (GER) on unwritten media, and
looking for changes. The GER is directly proportional to the sum of the defective areas.
Figure 5 displays this against the detector threshold level, normalized to unwritten media at
100%. Points below 100% are dark defects, and those above are light defects. ICI media
darkens upon writing and a typical detector threshold level is 60%, so the GER increased by
less than a factor of 2.
Temperature cycling tests can be used to test not only the chemical stability of the media, but
also the mechanical integrity of the structure. It is not possible to infer a lifetime from cycling
tests. We subjected the optical tape media to 20 temperature cycles defined by Figure 6. We
again looked for changes in the signal characteristics. There was 1 or 2 dB drop in the CNR
(Fig. 7), which is just greater than the measurement accuracy. The time interval results in
Figure 8 showed a corresponding increase in the signal jitter (standard deviation) of 3 ns.
The "(+/-)" refers to the signal's rising-to-falling half cycle, and "(-/+)" is the other half cycle.
A range of oxide magnetic tapes were stored under accelerated aging conditions, and any
degradation was assessed by looking for any decomposition products. This work was also done
by Fulmer Research. We tested three tapes; tape "C' is iron oxide instrumentation tape, tape
"D" is cobalt modified iron oxide VHS consumer video tape, and tape "E" is chromium dioxide
IBM 3480 type data cartridge tape.
The test method was to store the tapes at a constant 60 *C and 80 %RH for 3 and 6 weeks,
and keep a Control tape at room conditions. Standard solvent extraction techniques were
used to look for decomposition products. One meter samples were immersed for two hours
in a Soxhlet extraction by Delifrene; then soluble extract was weighed. This was followed by
a further two hours in acetone and weighing the extract.
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The results are presented in Table 3. The initial extract is a baseline, and the percentage
increase above this is a measure of chemical decomposition in the binders. These results can
be put into perspective through a paper by Bertram and Cuddihy (Ref. 3). This states that
after aging, an increase in extract of 1.4 % by weight corresponds with a degradation in tape
performance. When our results are compared with Bertram and Cuddihy's, there was very
good agreement for the Tape "C'.
We performed a similar chemical stability test on the optical tape. Again, the test method was
to store at a constant 60 *C and 80 %RH, and also 80 *C and 80 %RH for 1, 2 and 3 weeks,
and keep a Control tape at room conditions. We were unable to detect any decomposition
products at a constant 60 *C and 80 %RH, which was why the test was repeated at the more
severe conditions of 80 *C and 80 %RH.
We devised an extraction technique suitable to the solubility of the dye/polymer material. This
involved immersing 500 cm _ samples for 72 hours in a Soxhlet extraction by ethanol. Samples
and extract were then weighed and analyzed by sensitive FTIR techniques. Using FFIR, we
could detect binder degradation only at the harsher conditions of 80 *C and 80 %RH, and this
for a minor component of the protective overcoat, not the recording layer. The quantities
were too small to be weighed.
Another test we used is the Battelle Class H accelerated aging test, performed under contract
at the Battelle Institute in Ohio. This test has been correlated to aging of materials in cities
and other locations where combustion byproducts form a mix of corrosive gasses. A fully
assembled open reel ICI 1012 optical tape, without the protective sealed storage and shipping
box was kept at a constant 23 *C and 70 %RH in a flowing mixed gas environment consisting
of 10 ppb HzS, 10 ppb C1, and 200 ppb NOz for 30 days. This environment has been
correlated to 15 years lifetime. We detected no damage in terms of corrosion, reflectivity or
modulus.
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ICI Imagedata
5. Conclusion
Optical tape systems can offer a unique set of attributes to potential end-users. The use of
chemically stable recording materials, indelible write-once technology, plus the advantages of
non-contact reading and writing, yield a very robust and archival medium. Our lifetime studies
have concentrated on measurement techniques and comparisons with magnetic technologies
that are independent of the drive and read/write channel. The comparisons with magnetic
tape technologies are favorable:
• No deterioration in optical recording characteristics after 9 weeks, 60 *C and 80 %RH.
• Metal particle magnetic formats show up to 22 % deterioration in magnetic capability
after only 6 weeks.
• No binder hydrolysis in the optical tape recording layer after severe environmental
exposure and extraction process.
• Minor hydrolysis present in the overcoat after 3 weeks at 80 *C and 80 %RH.
• Clear evidence of deterioration in magnetic oxide tapes under an industry standard
hydrolysis test.
We plan to extend these studies to raise the lifetime prediction for ICI 1012 optical tape from
15 to 30 years, and to characterize any changes in the raw BER through the read/write
channel on the Creo 1003 optical tape recorder.
References
1. A B Marchant, Optical recording: a technical overview, Addison-Wesley Publishing Company,
pp 380-382, 1990.
2. Sony Publication Recording Principle and Reliability Study of Sony Century Media, Sony
Corporation of America, Park Ridge, N J, April 1988.
3. H N Bertram and E F Cuddihy, "Kinetics of the Humid Aging of Magnetic Recording
Tape", IEEE Trans Magn, vol MAG-18, no 5, pp 993-999, Sept 1982.
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Company
Table 1
Media Type Test Method Activation
Energy in eV
Sony Metal Alloy BER i. 5
ICI Dye/polymer %R and CNR I. 12
OITDA* Multi WORM %R i. 0
, . ..
Hitachi 12" WORM BER I. 0
Magneto-optic DERNEC 0.97
*OITDA = Japanese Standard Committee for the Optical Data Disk
Tape Time
i •
Control
3 weeks
6 weeks
IIAII
liB-
Control
3 weeks
6 weeks
Table 2
Ms % fall
0 0
10.64 11.30 0.74
18.84
Mr % fall
0
20.34
Sq % fall
1.84
0 0 0
4.20 4.38 0.19
22.35 22.31 -0.015
Table 3
Tape Time Total Extract Increase in %
in %
Contro i 1.20 0
"C" 3 weeks 2.35 1.15
.rr
6 weeks 3.49 2.29
Contro i 1.24 0
"D" 3 weeks I. 45 0.21
6 weeks i. 86 0.62
lw
Control 1.53 0
"E" 3 weeks 2.04 0.51
6 weeks 2.55 1.02
ICI Imagedata
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2.6
Arrhenius Relationship
ICI 1012 Optical Tape: Steady State Environmental Test
60 %RH at differerd temperatures
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3.1
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_I_85"C (53days)
[] 95"C (19days)
Fleflectivity vs Time
ICI 1012 Optical Tape: Steady State Envkonmental Test
60 'X,J:IHat different temperatures
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CNR vs Wdte Power
ICI 1012 Optical Tape: Steady State 60
3.75 MHz, 8.5 m/s, 50% duly cycle, 30kHz bandwidth
,, ...._ j41
.....|ll :__
4 6 8 10 12 14 16
Write Powar in mW
X Control
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• e5"C (" (_,Xs)
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8
CNR vs Write Power
ICI 1012 Opticsl Tape: Steady State 60 "CABO%RH
3.75 MHz, 8.5 m/s, 50% duty cycle, 30 kHz bandwidth
10 11 12 13 14 15
Write Pow_ in mW
154
Rg. 4
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X Con_ol
1121 Days
• 42 Days
4,, s3 Days
ICI Imagedata
Fig. 5
|
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R 10
0.01
Geometric Error Rate ,,mTh4reehold
ICI 1012 Optical Tape: Steady State 60 "C/80 %RH
0 20 40 60 80 100 120
"rhfeshold (% of unwritten)
140
Temperature vs "13me
IC11012 Optical Tape: Temperature Cycle Teat
Constant 8O
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Fig. 7
C
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4O
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8
CNR vs Write Power
ICI 1012 Ol_iCai Tape: 20 Tempe(alu_e Cycles
4.4 MHz, 8.5 m/s, 50% duty cycle, 30 kHz bandwidth
_ ..... II --'. I ! ..... I[----_ ..... || ..... |
10 11 12 13 14
Write Pow_' in mW
15 16
[] Befo4re
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175
T
i 150
m 125
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n 50
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25
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Time Interval Anal_ vs Write
IC11012 Optical Tape: 20 Temperature Cycle==
4.4 MHz, 8.5 m/s, 50% duly cycte
i_- ...... II - ..... I
"--_ ...... __..... __
..... --_ ...... ,(
10 11 12 13 14 15 16
Write Power in mW
[] (+/-) Mean - before
• (+/-) Mean - after
A (-I+) Idean- befo,'e
A. (4+) Mean- alter
(+I-) Jitt= - bef_e
• (+/-) Jitter-_e,'
156
Fig.8


ICI optical data storage tape

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