The development of recording materials has been a critical component in the advancement of optical data storage. The continual need for improved performance in both consumer and business applications has pushed forward the capabilities of optical storage. In this issue of MRS Bulletin, we review some of the important developments in the materials behind established technologies such as compact discs, digital versatile discs, and magneto-optical recording; the emerging technology of blue recording; and two technologies that seek to extend the performance roadmap for optical storage, multilayer and holographic recording.

Optical data storage has become the mainstream technology during the past two decades for distributing audio, video, and software content as well as for recording and archiving personal data. The continuous demand for ever-higher storage capacities and faster data transfer has led to the development of three disc format families using infrared (compact discs), red (digital versatile discs), and blue lasers (Blu-ray discs or high-density DVDs). Substrate materials used in optical discs need to possess a complex property profile with sufficient optical, rheological, mechanical, and processing characteristics to ensure cost-efficient replication, good read/write performance, and long-term media stability. Bisphenol-A polycarbonate (BPA-PC) is the substrate material of choice and has undergone several optimization cycles to always meet new format specifications.

In the development of materials for blue recording, the issues for rewritable discs relate to speed and lifetime stability. Both aspects are connected with the properties of the phase-change recording layer. Higher data rates require faster erasure (i.e., recrystallization) of previously written marks. Increasing the Sb concentration or adding specific dopants to the phase-change material appears to accelerate the crystallization rate. Faster erasure rates should, however, not promote spontaneous recrystallization at room temperature, as this would adversely affect the lifetime stability. This roomtemperature stability can be estimated from an activation energy analysis. Excellent lifetime stability proves attainable by a judicious selection of the composition of the phase-change material.

For write-once discs, the choice of the recording material is between a spin-coated dye, a phase-change layer, and an inorganic alloy. While suitable dye materials for blue wavelengths are now being developed, research into the alternative of inorganic bilayers has yielded encouraging results. Thus far, good write-once recording performance has been demonstrated with Cu/Si as the recording medium.The mechanism of mark formation in such a bilayer will be addressed. Promising results obtained with optimized Cu/Si stacks illustrate the attractiveness of this type of write-once material for blue recording.

This article describes the characteristics and development of materials for magnetooptical (MO) recording. Magneto-optical recording is derived from thermomagnetic recording and readout by the magneto-optical effect. Rare-earth/transition-metal alloys, mostly Tb-Fe-Co, have been used for recording materials in MO discs. MO discs were first put on the market in 1988. Magnetic-field modulation for recording was introduced in MiniDisc (MD) systems in 1992. MO discs have an advantage in durability and achievability, because recording by magnetization reversal is not accompanied by any atomic movement. Magnetically induced super-resolution (MSR), reported in 1991, enabled resolving powers that are higher than the optical limit. MO discs based on MSR were commercialized as 3.5–in. discs for data recording and as 2–in. discs for digital cameras.

As extensions of MSR, DWDD (domain-wall displacement detection) and MAMMOS (magnetic amplifying magneto-optical system) have been proposed, in which the marks are expanded during readout for a large signal. DWDD technology has been used in Hi-MDs (high-density MiniDiscs), which were commercialized in 2004 with storage capacities of 1 Gbyte per 64-mm-diameter disc.

An attractive feature of optical discs is their capacity. Recent research has indicated that the capacity of optical discs can be increased by using multiple layers of bitwise data. Layers are spaced along the depth dimension of the discs. Individual layers are recorded and information is retrieved in a manner that is very similar to conventional optical disc systems using a single layer. The data capacity of each layer is nearly equal to the capacity of a single layer, thus increasing the capacity of a disc by a factor equal to the number of layers. In fact, dual-layer optical discs are already commercially available. With some storage materials, it is possible to record hundreds of data layers. However, system engineering trade-offs, like readout speed, are of concern. More conventional – materials can also be used for multilayer recording, but the number of layers is limited by the transmission properties of each layer. This article reviews the materials systems for multilayer recording, the interplay between materials properties and performance, and the optical systems used for multilayer recording.

Holographic storage is considered a promising successor to currently available optical storage technologies. Enabling significant gains in both data transfer rates and storage densities, holographic storage and its capabilities have gained a great deal of recent attention.One of the primary challenges in the advancement of holographic storage has been the development of suitable recording materials.In this article, we provide a brief introduction to holographic storage and its potential advantages over current technologies, outline the requirements for recording materials, and survey candidate materials.We end by highlighting recent progress in photopolymer materials that has produced materials that satisfy the requirements for holographic storage and have enabled significant demonstrations of the viability of this technology.

Recordable CDs and DVDs have become household items, and business depends on optical recording technologies for data interchange and archiving. This broad use of optical recording media has been enabled by the development of compatibility standards. Compliance with these standards enables data interchange between products from different manufacturers and between products of different vintages.

This article will discuss what optical recording standards are and describe the standard development organizations that exist to create them. Further, it will provide an overview of the most common standards development process for removable optical recording media. The article will conclude with a discussion of how optical recording media standards enable asset protection and how new optical recording media standards meet the market demand for higher capacities.

The following article is an edited transcript based on the plenary talk given by Alan I. Taub of General Motors Corp. on November 28, 2005, at the Materials Research Society Fall Meeting in Boston.

Fuel economy requirements, emissions regulations, and the push for energy independence are key factors driving the auto industry to increase vehicle efficiency. The main avenues to efficiency improvement are powertrain enhancements and mass reduction. This presentation details how General Motors is developing advanced propulsion systems and using lightweight materials to achieve greater vehicle efficiency. Taub, who is executive director of General Motors Research and Development, outlines GM's strategy for advancing propulsion technology, from improvements in the internalcombustion engine to hybridization to full vehicle electrification. He then describes the company's efforts to use lightweight materials such as aluminum and magnesium alloys, high-strength steels, and composites to reduce vehicle weight. Also highlighted is GM's success in employing novel materials in the development of advanced vehicle and powertrain systems to achieve additional efficiencies. One example is the application of smart materials, which enable new features and functions by way of mechamatronic solutions (the integration of smart materials with mechanical systems and electronics). Key technical hurdles that must be overcome to increase the use of these materials by the automotive industry are also discussed.