At the ISOM/ODS '05 event, Toshiba Corp. presented recording and readout results of the HD DVD-R DL, the company's new double layer HD DVD-R disc with a capacity of 30 GB.
The International Symposium on Optical Memory and Optical Data Storage was held
this year (July 10-14) at the Hyatt Regency in Waikiki Honolulu, Hawaii.
Toshiba revealed details of the prototype, following a press meeting in May
2005, at which the company only showed its playback signals. Along with the
development of an organic dye for the recording layer, the company also
established a manufacturing process requiring lower costs than the previous
DVD-R DL manufacturing process.
To make an HD-DVD disc double-layered, the company needed to reduce the
thickness of the Ag reflection layer, located close to the optical head so
thatthe laser beam can reach the other layer (Layer 0) more easily. However,
the thinner the Ag reflection layer gets, which also works as a heat sink, the
weaker its heat releasing effects become; and therefore the larger the heat
interferences between recorded marks grow. Toshiba overcame these problems with
an organic dye with good heat conductivity, newly developed in conjunction with
raw material manufacturers. This dye is a low to high polarity dye, which
increases reflection when exposed.
Conventional 2P (photopolymer) process is used to form the middle layer. In
existing double layer DVD-R media, disposable polyolefin stampers are used to
transcribe the recording layer's concavities and convexities onto the
photopolymer. Toshiba has employed 0.6 mm-thick, polycarbonate injection molded
stampers instead of the polyolefin stampers. As a result, polycarbonate once
used in stampers can be reused as alternative dummy substrates.
The Blu-Ray response
At the same time, Philips showcased the latest developments and results of its
research work on behalf of the rival Blu-Ray camp. The Philips research team
announced their successfull testing on BD-R (Blu-Ray Recordable) recording
Unlike the BD-RE (Blu-Ray Rewritable) disc which is based on the phase-change
layer technology, and alternatively to the use of a dye layer, Philips proposed
the usage of a Cu/ Si bilayer to be applied as the recording medium in a
write-once Blu-ray Disc (BD-R). The write process basically comprises the
formation of a CuSi alloy containing 25?30 at. % Si, while any excess Si is
left behind as unreacted film. Auger analyses of the laser-written layers
indicate that recording consists primarily of the diffusion of Si into Cu.
The results coming from Philips labs indicate that this technology offers
adequate results in terms of disc readability and high recording speeds. The
very low jitter levels of typically 4%, proved to be achievable with equally
thick films of Cu and Si as recording medium.
Philips has successfully tested first recordings on Cu/Si bilayer BD-R media at
1x-7x speeds (25GB, single layer). Note that 7x BD-R speed equals 10x for DVD
and 30x for CD. The results indicate that the shortest possible recording time
was given at a rotational speed fixed at 10800 rpm, which is equal to 200 km/h!
At the same time, the linear velocity at 7x is aproximatelly 35m/sec. To make
things clear, this means that 25GB of data can be recorded at 7x in just 14
The most suitable writing strategy for 7x recording, according to Philips,
should be the so-called "Castle Write Strategy". Hence, for speeds of 1X-2X it
will use the improved (n-1) writing strategy and for 4X - 7X the Castle
writing strategy just mentioned.