Organic Molecules Challenge
Silicon\'s Reign as King of Semiconductors

There is a revolution fomenting in the semiconductor industry. It may take 30
years or more to reach perfection, but when it does the advance may be so great
that today\'s computers will be little more than calculators compared to what
will come after. The revolution is called molecular electronics, and its goal is
to depose silicon as king of the computer chip and put carbon in its place.

The perpetrators are a few clever chemists trying to use pigment, proteins,
polymers, and other organic molecules to carry out the same task that
microscopic patterns of silicon and metal do now. For years these researchers
worked in secret, mainly at their blackboards, plotting and planning. Now they
are beginning to conduct small forays in the laboratory, and their few successes
to date lead them to believe they were on the right track.

"We have a long way to go before carbon-based electronics replace silicon-based
electronics, but we can see now that we hope to revolutionize computer design
and performance," said Robert R. Birge, a professor of chemistry, Carnegie-
Mellon University, Pittsburgh. "Now it\'s only a matter of time, hard work, and
some luck before molecular electronics start having a noticeable impact."

Molecular electronics is so named because it uses molecules to act as the
"wires" and "switches" of computer chips. Wires, may someday be replaced by
polymers that conduct electricity, such as polyacetylene and
polyphenylenesulfide. Another candidate might be organometallic compounds such
as porphyrins and phthalocyanines which also conduct electricity. When
crystallized, these flat molecules stack like pancakes, and metal ions in their
centers line up with one another to form a one-dimensional wire.

Many organic molecules can exist in two distinct stable states that differ in
some measurable property and are interconvertable. These could be switches of
molecular electronics. For example, bacteriorhodpsin, a bacterial pigment,
exists in two optical states: one state absorbs green light, the other orange.
Shinning green light on the green-absorbing state converts it into the orange
state and vice versa. Birge and his coworkers have developed high density memory
drives using bacteriorhodopsin.

Although the idea of using organic molecules may seem far-fetched, it happens
every day throughout nature. "Electron transport in photosynthesis one of the
most important energy generating systems in nature, is a real-world example of
what we\'re trying to do," said Phil Seiden, manager of molecular science, IBM,
Yorkstown Heights, N.Y.

Birge, who heads the Center for Molecular Electronics at Carnegie-Mellon, said
two factors are driving this developing revolution, more speed and less space.
"Semiconductor chip designers are always trying to cram more electronic
components into a smaller space, mostly to make computers faster," he said. "And
they\'ve been quite good at it so far, but they are going to run into trouble
quite soon."

A few years ago, for example, engineers at IBM made history last year when they
built a memory chip with enough transistors to store a million bytes if
information, the megabyte. It came as no big surprise. Nor did it when they came
out with a 16-megabyte chip. Chip designers have been cramming more transistors
into less space since Jack Kilby at Texas Instruments and Robert Noyce at
Fairchild Semiconductor first showed how to put multitudes on electronic
components on a slab of silicon.

But 16 megabytes may be near the end of the road. As bits get smaller and loser
together, "crosstalk" between them tends to degrade their performance. If the
components were pushed any closer they would short circuit. Physical limits have
triumphed over engineering.

That is when chemistry will have its day. Carbon, the element common to all
forms of life, will become the element of computers too. "That is when we see
electronics based on inorganic semiconductors, namely silicon and gallium
arsenide, giving way to electronics based on organic compounds," said Scott E.
Rickert, associate professor of macromolecular science, Case Western Reserve
University, Cleveland, and head of the school\'s Polymer Microdevice Laboratory.

"As a result," added Rickert, "we could see memory chips store billions of bytes
of information and computers that are thousands times faster. The science of
molecular electronics could revolutionize computer design."

But even if it does not, the research will surely have a major impact on organic
chemistry. "Molecular electronics presents very challenging intellectual
problems on organic chemistry, and when people work on challenging problems they
often come up with remarkable, interesting solutions," said Jonathan S. Lindsey,
assistant professor of chemistry, Carnegie-Mellon University. "Even if the whole
field falls through, we\'ll still have learned a remarkable amount more about
organic compounds and their physical interactions than we know now. That\'s why I
don\'t have any