What Is Blu-ray Disc?

TDK Corporation has commenced shipments of mass-production samples of so-called bare-type (i.e., cartridge-less) versions of its BD-R (write-once type) and BD-RE (rewritable type) Blu-ray DVD media. The four new products include the BD-R25 (single-side, single-layer, 25GB) and BD-R50 (single-side, dual-layer, 50GB) write-once types and BD-RE25 (single-side, single-layer, 25GB) and BD-RE50 (single-side, dual-layer, 50GB) rewritable types.

For the Blue-ray Discs, which achieves significantly higher density recording, scratches or dirt can have fatal consequences to the data, so it was initially introduced utilizing a protective cartridge. The BD-R and BD-RE Blu-ray Discs launched this time make use of DURABIS 2, TDK's originally developed hard coating technology. This achieves a recording surface with extremely high resistance to scratches and dirt (particularly fingerprint smudges), thus enabling anxiety-free use of a cartridge-less disc.

For the forming of the cover layer above the disc's recording layer, an original high-precision spin coating is utilized, realizing smoothness at the nano-level while achieving stabilized recording and playback characteristics.

The BD-R write-once type, moreover, makes use of an inorganic material in the recording layer, entirely different from the organic dye used in previous types of write-once type discs. Because the recording layer is not affected by light, it realizes a disc with outstanding archivability. Furthermore, the BD-RE rewritable type utilizes a high-sensitivity phase-change material that realizes stabilized characteristics, in the form of a low error rate, even after 10,000 overwrites.

In addition, the single-sided, dual-layer disc realizing 50GB capacity harnesses high-precision stacking technology resulting from years of work at optical disc development, to achieve precision forming of its respective functioning layers. The upper layer (Layer 1) and lower layer (Layer 0) are combined in terms of high sensitivity and recording layer transparency ratio, realizing stabilized recording and playback characteristics.

The commitment of TDK's advanced optical disc technology has resulted in creation of the world's first 25GB and 50GB high-capacity discs capable of 2X recording speed. TDK is confident that the BD-R and BD-RE, freed from the confines of a cartridge, will offer their large capacities with greater facility, thus greatly expanding the potential of optical recording.



Blu-ray, a next-generation optical disc format, also known as Blu-ray Disc (BD). Blu-ray has a storage capacity of 25GB on a single-layer disc and 50GB on a dual-layer disc. While DVD, DVD-R, DVD+R rely on a red laser to read & write data, Blu ray disc uses a blue-violet laser instead. The benefit of using a blue-violet laser (405nm) is that it has a shorter wavelength than a red laser (650nm), which makes it possible to focus the laser spot with even greater precision. This allows data to be packed more tightly and stored in less space, so BR-D can fit more data even though it's the same size as a CD/DVD.

Main features of BD-R and BD-RE Blu-ray Disc

1. Use of DURABIS 2 coating designed for bare (cartridge-less) Blu-ray Discs provides significantly greater resistance to scratches and dirt (particularly fingerprint smudges), ensuring safe use even without a cartridge.
Since the area of the laser spot on the Blu-ray Disc is small (about one-fifth that of the DVD), scratches or dirt on the recording surface can have a much more severe effect than on DVDs, causing interference with the irradiation of the laser beam and, in worst cases, even loss of irreplaceable data. For the recording surfaces on the BD-R and BD-RE, the DURABIS 2 coating specially developed for the bare Blu-ray Disc is utilized. Along with significantly higher resistance to scratches, it is also extremely resistant to dirt (particularly fingerprint smudges), ensuring safe use even without a protective cartridge. (Figs. 1, 2 and 3.)

2. Original high-precision spin coating creates a cover layer with nano-level smoothness, realizing stabilized recording and playback.
The Blu-ray Disc is constructed of a 1.1mm thick substrate with a 0.1mm thick cover layer. For the laser beam to penetrate the cover layer to the recording layer, the cover layer assumes the function of a lens, so to speak. For this reason, in the Blu-ray Disc, which uses a blue-violet laser with significantly shorter wave length, the precision and smoothness of the cover layer, from the standpoint of accurate laser irradiation, is extremely important. To form this cover layer, TDK utilizes an originally developed high-precision spin coating. The thickness precision is controlled at the nano-level, and an outstanding cover layer with extreme smoothness is formed. As a result, the load on the focus servo circuit used to correct laser beam position is reduced, making possible more stabilized recording and playback. (Figs. 4, 5)

3. The BD-R write-once type utilizes a recording layer of inorganic material. Since it is unaffected by exposure to light, it boasts outstanding archivability.
Previous types of write-once type discs such as the CD-R, DVD-R and others utilized organic dye for their recording layer. The BD-R write-once type is based on a completely new concept for the recording layer utilizing a two-layer structure composed of silicon (Si) and copper alloy (Cu) inorganic materials. When heated by the recording laser beam, these melt and the Si and Cu alloy become a composite forming recording marks. Because the material is inorganic, it is not affected by light, thus realizing a disc with outstandingly high reliability in terms of archivability. (Fig. 6)

4. The rewritable BD-RE utilizes a high-sensitivity phase-change material in the recording layer that realizes stabilized characteristics even after as many as 10,000 rewrites.
In the BD-RE rewritable type disc, exclusively designed high-sensitivity phase change recording material and a layer structure for high-density recording are utilized to realize excellent recording/playback characteristics and overwrite characteristics. Even after 10,000 rewrites, stabilized characteristics are realized. (Fig. 7)

5. High-precision stacking technology precisely overlays disc layers having respective functions. Stabilized characteristics on the upper (Layer 1) and lower (Layer 0) are realized in a single-sided, dual-layer (50GB) disc.
The single-sided, dual-layer disc realizing a tremendous 50GB capacity was achieved through the high-precision stacking technology developed from TDK's years of accumulated experience in optical discs. The respective recording layers, Layers 0 and 1, each composed of recording and dielectric layers, plus a spacer layer and a cover layer, are formed with high precision in thickness that totals 0.1mm (100µm). By this, both Layer 0 and Layer 1 are matched in terms of precision and recording layer transparency ratio, realizing stabilized recording and playback characteristics. (Figs. 8, 9)

BD-R, BD-RE Blu-ray Disc Information

[ Fig. 1 : Structural diagram of the Blu-ray Disc (single-sided, single-layer) using DURABIS 2 coating ] DURABIS 2 coating is formed by spin coating atop the cover layer.

[ Fig. 2 : DURABIS 2 coating boasts awesome resistance to scratches ] Here is a comparison of disc surfaces after rubbing with a steel wool pad. The disc using a DURABIS 2 coating is practically free of scratches.

[ Fig. 3 : DURABIS 2 coating boasts awesome resistance to fingerprint smudging ] Artificial fingerprints were affixed to the disc surface and viewed with a microscope The DURABIS 2 coating resists fingerprints and even when they adhere, they form small particles and do not interfere with laser penetration.

[ Fig. 4 : Comparison of cover layer thickness distribution ] The diagram at the left is a measurement of the thickness of the cover layer of the Blu-ray Disc from the inner (20mm from the center) to the outer sections (60mm from the center). Here it can be seen that with the previous method of spin coating, the inner section was thinner and the outer section thicker, whereas TDK's new spin coating method results in the forming of a uniform, high-precision coating 100 μm thick. The cover layer of the TDK Blu-ray Disc formed by the original spin coating method realizes precision on the nanometer level. This is why the blue-violet laser can achieve accurate irradiation of the recording layer.

[ Fig. 5 : Comparison of focus servo signals ] Because the cover layer of the TDK Blu-ray Disc is extremely uniform in thickness and possesses superb smoothness, an outstanding focus servo signal can be obtained. This makes possible stabilized recording and playback (RF signal). TDK Blu-ray Disc (Stable waveform) Disc having cover layer with poor precision (Waveform is unstable)

[ Fig. 6 : A write-once type recording system ] 1. When the recording laser makes contact, its heat melts the Si and Cu alloy, which become mixed. 2. When the mixture cools, the hardened Si and Cu alloy become a composite, in which the recording mark is formed.

[ Fig. 7 : Eye pattern after repeated recordings (BD-RE) ] Even after 10,000 overwrites, the rewritable BD-RE realizes stabilized characteristics. 10 recordings 10000 recordings

[ Fig. 8 : Structural diagram of the write-once type single-sided, dual layer Blu-ray Disc ] Layer 0 and Layer 1 incorporate two recording layers

[ Fig. 9 : Eye patterns on Layer 0 and Layer 1 ] Both the two layers show clean eye patterns, attesting to the disc's outstanding characteristics. Layer 0 Layer 1

Main specifications

Item	Unit	BD-R25	BD-R50	BD-RE25	BD-RE50
Type	-	Write-once		Rewritable
Recording capacity	GB	25 (single-layer)	50 (dual-layer)	25 (single-layer)	50 (dual-layer)
Recording wavelength	nm	405 (blue-violet laser)
Disc diameter	mm	120
Disc thickness	mm	1.2
Cover layer thickness	mm	0.1
Track pitch	μm	0.32 (groove recording)
Data transfer rate	Mbps	36(1X) / 72(2X)
Reflectance	%	12-24	4-8	12-24	4-8
Linear velocity	m/s	4.9(1X) / 9.8(2X)

* Dimensional specifications are nominal.

* TDK logo is a trademark or registered trademark of TDK Corporation.
* DURABIS is a registered trademark of TDK Corporation.