HIGH GROWTH
FORECAST FOR
STORAGE SYSTEM CHIPS
Battles over data-storage formats for the next generation of
consumer electronics and PCs are gradually being resolved. The
DVD optical system now appears to have become the main
medium-term solution – displacing videocassettes in home
multimedia applications and offering effective high-capacity
storage for PCs. However, in the longer term, next-generation
storage may well be based on the Blu-ray Disc, which offers more
than five times the capacity of a DVD. This standard was
announced in 2002 by nine of the world’s leading consumer
electronics manufacturers covering Europe, the USA and AsiaPacific. Novel storage systems are also being developed for newgeneration personal digital assistants (PDAs) and other mobile
multimedia applications.
Analyst IDC sees DVD semiconductors as one of the healthier electronic application sectors. In a recent
study of the worldwide DVD semiconductor market, it forecasts a projected compound annual growth of
19.3% from 2002 until 2007 – when the global market should be worth nearly € 9 million, principally in DVD
writers. At the same time, IDC sees DVD drives for PCs continuing to predominate over those for
consumer electronics, despite growing convergence between the two areas. The fastest growing segment
is likely to be integrated drive-management and image-management chips. And there will be continuing
high demand for analogue application-specific chips (ASICs), SRAM and flash memory.
MEDEA+ identified future storage as a key area for research in the initial White Book outlining reasons and
content for the initiative. The MEDEA+ A202 future storage (FUST) project is already coming to an end.
The aim of this important research effort is to strengthen Europe’s ability to deliver system-on-chip (SoC)
devices for future mass storage systems. To achieve this it has had to focus on new formats, general chip
architectures and the development of suitable building blocks and standards to ensure maximum flexibility.
Main trends identified in the FUST project are the switch to fully digital applications and enormous
increases in storage density possible with both optical and hard disks. The main uncertainties have arisen
from the choice of formats, both for optical drives and for the audio and video compression systems –
including MP3, MPEG-2 and MPEG-4.
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New components developed to prototype stage in this MEDEA+ project include channel Codec SoCs for
optical storage, audio-visual Codec devices for high-density hard disks (HDD) to enable time-shift
applications, improved mechanical systems for linear magnetic tape systems aimed at multimedia use,
and alternative storage devices to tape for camcorders. Application Codecs have also been developed
from both DVD and HDD, including video and audio compressors, decoders and copy protection, as well
as optical and HDD interface systems.
In addition, tools have already been developed for authoring, verification and testing of hardware-software
co-design of system architecture for the new DVD+R/RW, super audio CD (SACD) and Blu-ray disc
formats. And IP libraries have been assembled that should speed design and therefore time to market for
the chips to support new equipment.
DVDs now seem set to be the storage system of choice for the medium term – able to handle the
requirements of both computer and multimedia applications, with sufficient capacity for standard definition
TV and films. HDDs also have an important role in time-shift off-air recording and in the growing number of
residential gateway computer systems in the home.
However, the relatively long development time for new drives means that drive manufacturers must stay
well ahead of developments in storage systems so that they can get products to market quickly once a
particular format gains market acceptance. Several leading manufacturers have already demonstrated
prototype Blu-ray Disc drives for consumer products such as video recorders that can read and write DVD
and Blu-ray Discs, and PC drives that can offer high capacity while both reading and writing CD, DVD and
Blu-ray Discs.
The success of the FUST project has ensured that European component and systems manufacturers now
have access to the technologies required, whatever the storage medium. And, as importantly, many
MEDEA+ participants – including Philips, STMicroelectronics and Thomson, all partners in the FUST
project – are closely involved in the formulation of the new storage and compression standards. This
involves work through bodies such as the DVD forum, the ISO Moving Picture Experts Group (MPEG)
working group and the Blu-ray Disc industry group.
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Article
BLU-RAY DISC OFFERS RADICAL ADVANCE IN HIGH CAPACITY
STORAGE
Blu-ray Disc (BD) is a radically new optical storage medium, jointly developed by nine of the world’s leading
1
consumer electronics and optical storage companies . It should not be considered a replacement for DVD
formats, which are expected to meet the requirements of standard definition TV (SDTV) recording and film
distribution for many years to come, but as a basis for future even higher quality recording products.
In terms of storage capacity, Blu-ray Disc is as different to the DVD as the DVD was to the compact disc
(CD). High-definition video recording may be the starting point for Blu-ray Disc, but it is certainly not the
only application that will ultimately leverage its very high storage capacities – over 25 GB compared with
the 4.7 GB of DVDs – and high-speed data transfer rates in the order of 36 MB/s.
Blue laser precision
In order to play back full-length feature films, DVDs store digitally encoded video and audio information in
the form of ‘pits’ and ‘bumps’ that are pressed into a recording track that spirals out from the centre of the
disc to its edge. The different reflectivity of these pits and bumps enables the laser pick-up to read
information from the disc.
To provide similar length playback of high-definition TV (HDTV) pictures, at least four times the storage
capacity of a standard DVD is required. To achieve the bit density necessary to put this amount of data on
a low-cost single-sided 12-cm optical disc, the size of the pits pressed into it must be smaller. It must also
be possible to focus the illuminating laser well enough to create a correspondingly small ‘laser-spot’ that
can reliably read the smaller pits on the disc.
A fundamental law of physics states the diameter of the laser spot is directly proportional to the wavelength
of the laser light and inversely proportional to the numerical aperture of the objective lens – a figure that
depends on the diameter of the lens, its radius of curvature and the material from which it is made. To
reduce the size of the laser spot requires use of a shorter wavelength laser or a higher numerical aperture
lens. Better still is a combination of both, which is the approach adopted in the Blu-ray Disc specification.
Blu-ray Disc drives use a 405-nm wavelength blue laser and a lens with a numerical aperture of 0.85,
instead of the 650-nm red laser and 0.60 numerical aperture lens used in current DVD drives – see Figure
1. This allows a Blu-ray Disc drive to read reliably pits on the disc that are a mere 0.15-µm long – more
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than 2.5 times shorter than the shortest pits on a DVD. Together with the longer recording track achieved
by reducing the track pitch from 0.74 µm to 0.32 µm, this allows a single-layer Blu-ray Disc to store up to
25 GB of data – enough to provide two to thee hours of HDTV recording and playback.
DVD (4.7 GB)
BD (25 GB)
substrate
minimum
pit length
0.4 mm
track pitch
0.74 mm
minimum
pit length
0.15 mm
recording
layer
optical transmission & protection layer
track pitch
0.32 mm
* in case of 27GB
Figure 1 – By reducing track pitch and pit length, Blu-ray Disc provides five times more
recording capacity than DVD
Blu-ray Disc is not just a technological solution. It has been designed with commercial considerations in
mind. The blue laser diodes it uses are now available, while the optical assemblies and servo mechanisms
needed are compatible with current high-volume manufacturing techniques. In addition, Blue-ray discs can
be mechanically pressed on the same equipment used to produce prerecorded CDs and DVDs.
Unlike CDs and DVDs, where compatibility issues have arisen because of the need to add recordable and
rewritable format extensions to an initial read-only concept, Blu-ray takes the rewritable format as the
starting point for the entire specification. Using phase-change recording technology similar to that
developed for DVD+RW, Blu-ray also features random access for both reading and writing, enabling high
compatibility across PC and consumer product domains and across data and audio/video applications.
The Blu-ray recording layer
One of the features that differentiates Blu-ray Disc from DVD recording systems is the position of the
recording layer within the disc. For DVDs, the recording layer is sandwiched between two 0.6-mm thick
layers of plastic – typically polycarbonate. The objective is to shift surface scratches, fingerprints and dust
1
Hitachi Ltd, LG Electronics Inc., Matsushita Electric Industrial Co. Ltd, Pioneer Corporation, Royal Philips
Electronics, Samsung Electronics Co. Ltd, Sharp Corporation, Sony Corporation and Thomson Multimedia
Page 4 of 6
particles to a position in the optical pathway where they will have negligible effect – that is, well away from
the point of focus of the laser. However, burying the recording layer 0.6 mm below the surface of the disc
also has disadvantages.
The injection moulding process used to produce CDs leads to stress-induced birefringence in the
substrates. Birefringence can lead to the splitting of the single incident laser light into two separate beams
– if this splitting is excessive, the drive cannot read data reliably from the disc. Consequently, the injection
moulding process has always been a critical part of CD and DVD production. Another crucial
manufacturing parameter, particularly for DVDs, is the flatness of the disc, because the laser beam
becomes distorted if the disc surface is not perpendicular to the beam axis – a condition referred to as disc
tilt. This distortion increases as the thickness of the cover layer grows and for higher numerical aperture
lenses.
To overcome these disadvantages, the recording layer in a Blu-ray Disc sits on the surface of a 1.1-mm
thick plastic substrate, protected by a 0.1-mm cover layer. With the substrate material no longer in the
optical pathway, birefringence problems are eliminated. In addition, the closer proximity of the recording
layer to the drive’s objective lens reduces disc tilt sensitivity. This only leaves the problem of surface
scratching and fingerprints, which can be prevented by applying a hard coat on top of the cover layer. This
protective coat is hard enough to prevent accidental abrasions and also allows fingerprints to be removed
by wiping the disc with a tissue. Both the cover layer and hard coat can be applied by low-cost
manufacturing techniques such as spin-coating.
Disc manufacturing
Despite the fact that Blu-ray Discs require the application of a cover layer and an optional hard coat, this
should have little overall impact on manufacturing costs. DVD production currently requires the injection
moulding of two 0.6-mm discs (one of which must meet stringent birefringence limits), the application of a
recording layer to one of the discs, and a gluing operation to bond the two discs together.
Blu-ray Discs require only the injection moulding of a single 1.1-mm substrate with non-critical optical
characteristics – reducing moulding costs. This saving offsets the additional cost of applying the cover
layer and hard coat, while the techniques used for applying the recording layer remain the same. As a
result, the overall cost of manufacturing a Blu-ray Disc should be no more than that of producing a DVD,
while some equipment such as injection moulding machines can actually be used more efficiently.
Because of the thinness of the cover layer, surface-flatness tolerances become far less stringent, while
relative cover-thickness tolerances remain almost the same as for current DVD production.
Drive compatibility
Although no blue-laser disc will be readable using a red laser, combined blue-/red-laser drives are perfectly
feasible. Servo-mechanisms that are capable of meeting Blu-ray Disc’s track positioning will be more than
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capable of meeting DVD requirements, while it should also be possible for both the blue and red lasers to
share part of the optical pathway.
There is no doubt that existing red-laser technology will be extended to increase further the versatility of
the DVD format. Several developments in this area are already under way. However, while they may
extend playback times for SDTV, provide short film HDTV playback or resolve incompatibility problems,
none of these developments is likely to achieve the capability for high-definition playback of full-length
blockbuster films.
With Blu-ray Disc, 25 GB is the starting point for a format that already has the requirements built in for a
next-generation optical recording format – two- to three-hour HDTV playback, real-time HDTV recording,
rewritable, recordable and read-only versions, random access, cross-platform compatibility, and x2 singlesided capacity extension.
CD
DVD
l = 780 nm
BD
l l==650
650nm
ll==400
405nm
nm
1.2 mm substrate
0.6 mm substrate
0.1 mm substrate
0.7 GB
4.7 GB
25 GB
Figure 2 – Comparison between CD, DVD and Blu-ray Disc
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