Scientists Seek Organic Cells for Ultrafast New Computer
Chemists and physicists throughout the country are working intensively on a new, radical way to build computers that would be thousands of times faster and more powerful than current models. Their efforts, if successful, could lead to more accurate weather forecasts, improved space exploration and perhaps even a more reliable Strategic Defense Initiative, to name a few of the possibilities.
Most scientists searching for faster and more powerful computers have concentrated on reducing the size of individual electronic components. But they are nearing the lowermost limits for the size of components produced from silicon and other semiconductors.
To bypass this size limitation, some scientists are turning to organic compounds similar to those found in living organisms.
‘Size of One Molecule’
Such an achievement would produce, for example, memory cells a millionth the size of the smallest ones now available. “What we would like to do is reduce the size of switching and memory components down to the size of one molecule,” said Forrest L. Carter of the Naval Research Laboratory in Washington.
Last year, Carter noted, researchers at IBM constructed silicon memory chips the size of a fingernail with a capacity of one megabyte--1 million letters or numbers. Within the next decade, he added, a 16-megabyte chip could be made using conventional technology, but higher densities are considered nearly impossible to achieve.
The problem is that if engineers try to cram any more components onto a chip, the components will short-circuit, according to IBM physicist Phillip Seiden. This happens because, as the components are moved closer together, minute electromagnetic fields created by them begin to impinge on nearby components, affecting their operation or altering stored data.
Organic molecules are less susceptible to such electromagnetic interference and can be stacked virtually one on top of another, allowing many more electronic components to be stuffed into a smaller area.
In the fastest supercomputers, Seiden added, speed of operation is limited primarily by the amount of time it takes an electronic signal to travel from one component to the next. Organic electronic components, called molecular electronic devices (MEDs), would reduce that time by enabling components to be closer together.
If 10 electronic components, such as transistors, can be compressed into the space formerly occupied by just one, then an electrical signal has to travel only a 10th as far to carry out a given operation, Seiden said, and the new circuit is 10 times faster. “Small means speed,” he added.
Such a small, MED-based computer, for example, might serve as a “brain” for unmanned spacecraft to make them self-sufficient on long missions, such as to a distant star. Existing computers are simply too large for this purpose, and so spacecraft must be controlled from Earth.
A new generation of ultrafast supercomputers based on MEDs could acquire more meteorological observations than existing computers and process them more rapidly, thereby producing more reliable weather forecasts.
Many scientists also point out that such enhanced supercomputers may be required by the Strategic Defense Initiative to track all the missiles and decoys that would be launched during an attack on the United States and to coordinate their destruction in the very short amount of time that would be available.
MED devices could also provide personal computer memories with much greater storage capacity and might even make possible briefcase-sized computers with far more power than today’s desk-top models.
The principal characteristic that an organic molecule must display for use in a MED is the ability to exist in two characteristic states--such as two different colors. In a memory device, those two states might represent the “0” and “1” of the binary code commonly used for storing and manipulating letters and numbers in computers.
Molecules Change Color
Many investigators are studying unusual molecules that can change colors when exposed to light. Chemist Robert R. Birge of Carnegie-Mellon University in Pittsburgh, for example, has been working with a pigment called bacteriorhodopsin that is part of the photosynthetic system of the purplish bacterium Halobacterium halobium.
Isolated from the bacterium, the pigment can exist in two states, one that absorbs green light and one that absorbs red. Shining green light on the green-absorbing state converts it to red-absorbing, and vice versa.
Information can be stored in the molecules and recalled with two laser beams, one red and one green.
In order to store a piece of information, clusters of molecules are irradiated with a green laser, changing the red molecules to green. The red laser can then be used to retrieve that information.
The MED memory is also much faster than a conventional magnetic memory, Birge said. Only 5 trillionths of a second are required for the molecules to change colors--about 1,000 times faster than information can be stored in a magnetic device.
Using this approach, Birge and Rick Lawrence of Hughes Aircraft have constructed a thumbnail-sized, high-density memory device by plating 1,000 layers of bacteriorhodopsin, each layer one molecule thick, on the surface of a quartz plate. “It looks like a piece of glass with a clear, deep, rich red coating,” Birge said. About 10,000 molecules are used for storing each bit of information.
Birge said the device has a storage capacity of nearly 1 billion bytes per square centimeter, or roughly equivalent to 100,000 times the number of letters in this article and about 100 times the storage density of the best magnetic devices used in large computers. A conventional floppy disk for a personal computer, in contrast, stores about 200,000 bytes per square centimeter.
Birge said memory devices based on this approach should be commercially available within two years.
The three primary difficulties associated with the use of MEDs are synthesizing the complex chemicals required, isolating them in the high purities that would be needed for use in electronic devices and building the devices.
To solve those problems, the government and industrial giants such as IBM, Westinghouse and Hughes Aircraft are investing about $100 million per year on MED research, according to the trade journal Chemical Week, and that figure that could grow to $1 billion annually by 1990. The governments of Japan, England, Italy, Germany and the Soviet Union are also developing the new technology.
By the year 2020, according to Technical Insights Inc., a Fort Lee, N.J., consulting firm, electronic devices incorporating large amounts of organic chemicals could account for 10% of the total computer market, or about $30 billion in sales.
But storing information is only one function of a computer. Scientists hope to manipulate such information faster by making MED forms of the semiconductor components now used for that processing, such as transistors and logic circuits.
At MIT, chemist Mark Wrighton and his colleagues have produced transistors based on organic compounds rather than on silicon. In the same way that MEDs have made possible smaller computer memories, the new transistors have the potential to speed up the processing of information.
Birge has also constructed organic molecules that, like silicon-based logic circuits, carry out mathematical operations such as addition and subtraction. “We think we could use these to build exceptionally small computers,” Birge said.
“That’s the goal of the semiconductor people as well,” he added. “But they are building from the top down, whereas we’re building from the bottom up.”
