Bubbles for the Future

By inventing the transistor 21 years ago, researchers at the Bell Telephone Laboratories paved the way for most of the sophisticated electronic marvels of the 1960s--most notably the miniaturized, high-speed computer. Now they may have done it again. A versatile new device conjured up by the wizards at Bell may eventually make current computers as old-fashioned as the abacus.

For several years, Bell scientists have been experimenting with thin wafers of crystalline materials known as orthoferrites, which are compounds of iron oxides and such rare-earth minerals as ytterbium, thulium and samarium-terbium. They found that when a strong enough magnetic field is applied, orthoferrites display an extraordinary property: tiny cylinder-shaped areas, or "bubbles," of magnetism are formed in the wafer, their polarity opposite to that of the surrounding material. Often smaller in diameter than a human hair, the magnetic bubbles can be maneuvered and positioned into an almost endless variety of patterns.

Therein lies the secret of their usefulness. Because their presence or absence at specific points in the wafer can be precisely controlled and electronically detected, bubbles can be used to carry coded messages in the on-off binary language of the computer, store reams of data and perform myriad mathematical calculations. Moreover, controlling the position of the bubbles is relatively simple. One method is to send small electric currents through tiny circuits printed on the surface of the crystalline wafer; the currents generate magnetic fields that cause bubbles to form at predetermined locations in the wafer. Currents passed through different branches of the printed circuits can form new bubbles, or move or erase existing bubbles. The same result can be achieved by the controlled motion of a magnetic field outside the crystal; this method eliminates the need for any electrical connections to the wafer.

Thousands of Bits. Not only do the crystals have the advantage of simplicity of operation, but they could also be extremely compact computer components. In a recent demonstration at their Murray Hill, N.J., headquarters, the Bell scientists showed that a thin crystal, only one-tenth of an inch square, could carry 10,000 bits of information. Even the tiniest conventional computer circuitry, explained Bell Labs Vice President Jack A. Morton, is able to achieve only 10% of that density. In addition, the crystals need just a fraction of the power required by ordinary computers.

These properties could make possible extraordinarily small, efficient equipment. "We can imagine a data-storage file," says Morton, "holding 15 million coded bits of information in one or two cubic inches and run by forty-thousandths of a watt of power." The same job now would require a closet full of equipment and hundreds of watts.

Bell officials do not anticipate the first commercial application of their new technique for several more years. They concede that much work must still be done before the crystals can be produced in commercial size and quantities. Nonetheless, they are convinced that this is one technical bubble that is unlikely to burst once it leaves the lab.

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