microcircuits, which, in turn, allowed chipmakers a wider selection of materials. Further improvements will be necessary, however, for generating such things as diamond thin films for use in flat-panel displays. Improvements in the deposition of organics and thin films are vital to improving the performance of the next generation of electronic devices. Today, the material to be deposited restricts the choice of technology used. A more universal deposition technique would offer a significant advantage.

Nonvolatile RAMs

Recent years have seen a surge of interest in developing inexpensive, fast, durable, and nonvolatile random access memories and in the use of a solid-state technology called magneto-electronics to replace volatile and nonvolatile semiconductor memories and mechanical storage. Most of this work is focused on giant magnetoresistance (GMR) and magnetic tunnel junction technology. GMR materials have the advantage of a strong signal, nonvolatility, and compatibility with integrated circuit technology. Magnetic tunnel junction devices have the potential to serve as nonvolatile memories with speeds comparable to those of today’s dynamic random access memories (DRAMs). Much of the research on magneto-electronic memories has emphasized hybrid devices that utilize a magnetic memory and semiconductor electronics. But one start-up company has gone all-metal, developing a magnetic RAM in which the memory arrays and the electronics are all made of GMR materials. The device is based on electron spin rather than electric charge.

Data Density

More bits per square inch is almost a mantra in the computer data-storage field. But as with photolithography, traditional magnetic and optical storage techniques are approaching their own physical limits, which will require innovative solutions to overcome. In 1999, IBM forecast that it would achieve an areal magnetic storage density of 40 gigabits per square inch (Gb/in.2) by the middle of this decade. Beyond this density, magnetic storage encounters the instability of superparamagnetism, a phenomenon in which the magnetic orientation energy equals the surrounding thermal energy. As a result, magnetic bits flip spontaneously at normal operating temperatures. In May 2001, IBM announced it had developed a new coating for its hard disk drives that bypasses the problem—a three-atom-thick layer of ruthenium sandwiched between two layers of magnetic material. IBM predicted that the material would enable a storage density of 100 Gb/in.2 by 2003.

Optical storage faces its own physical barrier—the diffraction limit, at which the size of the optical bits is limited by the wavelength of light used to record



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