|
|
|
|
|
Go To | Optical Storage | CD-ROM Storage |
Bulletin: 101 December 1996 DVD is a high density format for digital video storage, high density ROM (DVD-ROM) and next generation video games. The format has been defined by an industry consortium with input from both video content providers and computer manufacturers. There are four possible variations with increasing capacity, as shown in Table 1.
Each of the variations consists of two 0.6mm substrates which are bonded together. The 4.7 GB variation is shown in Figure 1. Depending on the capacity, the disc may have one to four information layers. In the 8.5 GB and 17 GB options, a semi-reflector is used in order to access two information layers from one side of the disc. The 4.7 GB and 8.5 GB options are shown in Figure 2.
Figure 1
Figure 2 The increased capacity relative to CD-ROM is the result of reduced track pitch and pit size (a shorter wavelength laser makes this possible) and reduced error correction overhead. Table 2 compares the basic parameters of DVD and today's current CD-ROM.
For the video application, which includes MPEG2 encoded video, Dolby® AC-3™ or MPEG audio and up to eight different languages and 32 sub-titles, the capacity of the single layer, single side, 4.7 GB option results in about 135 minutes, which is sufficient for 95% of today's movie releases. DVD Manufacturing The basic manufacturing process for DVD is similar to the current process for CD-ROM manufacturing, although some additional equipment is needed and tighter process controls are required. The manufacturing process, starting with injection molding, is shown in Figure 3. Prior to injection molding, a master must be created. Since the DVD features are less than half the size of CD-ROM features, higher resolution Laser Beam Recorders are required. Since tolerances on track pitch and jitter are also reduced, the mechanical control of the laser beam position and the rotation speed must also be more precise.
For injection molding, new molds are required to produce the 0.6mm substrates, and tighter process controls are necessary. For the 4.7 GB disc, bonding is the only additional process step needed which requires additional equipment. For higher capacity discs, process equipment must be added for both the
Dual Layer Process For the 8.5 GB DVD, the second information layer may be molded into the second substrate, as shown in Figure 4a, or may be added as a photopolymer (2-P) layer, as shown in Figure 4b. In either case, a semi-reflector layer is required to allow both information layers to be read from one side of the disc. For the 17 GB DVD, it is necessary to produce two dual-layer substrates, and bond them together, as shown in Figure 4c.
Semi-Reflector The semi-reflector that is required for the higher capacity DVD options is a critical process step. Though it is possible to produce a semi-reflective coating of aluminum, or other metals, it is very difficult to control the reflectivity to meet the requirements of the DVD specification. After conducting tests on various metal alloys, Imation, as a part of 3M, developed a unique semi-reflective coating that allows a much wider process window. Figure 5 shows reflectance as a function of layer thickness for both aluminum and the Imation semi-reflector. The Imation semi-reflector allows for a process window for layer thickness of approximately 10 times that required for aluminum. This unique technology will be a key factor in providing high production yields and reducing disc costs.
Figure 5 Summary DVD offers content publishers a new dimension in storage and distribution capability. It also provides a new means for high quality video distribution of full length feature films with six-channel surround-sound capability. DVD players are backwards compatible with current CD-ROMs, so one drive meets the needs for both new applications and existing CD-ROM applications. DVD discs can be manufactured on the same production lines as standard density discs, which allows manufacturers to balance their production load in the most efficient manner. Your Imation product carries with it all of the innovation, quality and service you've always counted on from Imation. Imation's innovative heritage passed on from 3M has allowed us to stay in the forefront of data storage technology for over 40 years. We were the first manufacturer of CD-ROM in the United States and our 25 year warranty is the longest available in the industry. Imation is a worldwide leader in providing a full range of optical and magnetic media products. We are ready to continue meeting our customers' increasing media needs through innovative, reliable data storage solutions.
For more information please contact: General Information Please contact Imation Technical and Customer Service at: 1-800-336-3636 or at 1-715-235-5567.
Copyright 1996 Imation. All rights reserved. 
|
