IEEE Spectrum November, 2014 - 43

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success of semiconductors. No surprise, then, that every on an oscilloscope. Normally, magnetic resonance is helpful
sizable tech-oriented company in the world had a super- in studying the physical and chemical properties of a mate-
rial in the presence of a powerful magnet. A given material
conductivity group.
A giant step toward commercializing superconductivity will emit a distinctive pattern of signals, or spectra. In this
came in 1962 when Brian Josephson, a graduate student at the case, though, the sample began emitting signals immediately,
University of Cambridge, theorized that a superconducting while the magnet was still off.
Cole later gave this account in an oral history interview: "Sud-
current, or supercurrent, could tunnel through an insulating
barrier between two superconductors without any resistance, denly, before they even turned the magnet on, they began to
thereby completing a superconducting circuit. Once the super- see what looked like magnetic resonance spectra coming out
current exceeded a certain critical current, however, an AC of their apparatus. They noticed that even with the power off,
voltage would develop across the junction, with a frequency if they rotated the magnet, these lines seemed to move around,
approaching 500 gigahertz. The following year, Philip W. move back and forth in the spectral domain. They turned the
Anderson and John M. Rowell at Bell Labs built the first such magnet on. They were seeing not dozens of lines, which was
circuit, subsequently named the Josephson junction. A com- not unusual, but thousands, tens of thousands of lines. A mys-
mercially viable Josephson junction then became the goal of tery! They had looked at the spectrum in a nearly identical
many industry researchers. An electronic circuit fashioned sample just before. How could something change that much?"
Puzzled, Lambe consulted with some colleagues. The silicon
from Josephson junctions would be capable of switching at very
high speeds-particularly desirable for computer logic chips. sample had indium solder contacts, and so the team "decided
Ford's Dearborn lab wasn't caught up in the fervor sur- it had something to do with superconductivity, because they
rounding superconductivity, but much like the more estab- began to appear temperature-wise at about the transition
lished corporate labs, it had a research program in cryogenics temperature of indium," Silver later recalled.
They then experimented with different thin-film samples.
and nuclear magnetic resonance. Lab managers had been
very successful at recruiting top scientific talent, who were When the samples had no cracks or other f laws, no lines
well funded and relatively unfettered in their investigations. appeared. But when they were damaged even slightly, the
When later asked what magnetic resonance research had to effect returned. "Eventually we patterned the films...we cut
do with cars, Terry Cole, a member of the Ford magnetics little notches in them," Silver said. The oscilloscope readings
group, replied, "It really didn't matter." Indeed, none of the from these intentionally notched films were even stronger
Ford researchers responsible for the SQUID-a group that than those from the original sample.
Mercereau, a Caltech Ph.D. who had worked on diffraction
included Robert Jaklevic, John Lambe, James Mercereau,
Arnold Silver, and James Zimmerman-was drawn to the work waves in liquid helium for his thesis, had a possible explana-
tion for this puzzling phenomenon. He had just come back
because of its possible commercial applications.
Lambe made the first crucial observation, which came from a low-temperature physics conference, where he had
about like many a noteworthy discovery: by accident. In met Brian Josephson. He suggested that they had in fact cre-
1963, he was studying nuclear double resonance-the inter- ated a Josephson junction.
Realizing that their creation was sensitive to tiny magnetic
action between the nuclear and electron spins of an atom-
fields, the researchers set about fashioning
in silicon-29. After placing the silicon sample
a Josephson-junction device that could actu-
in his magnetic resonance instrument, he
ally measure the intensity of those fields-
cooled it to 4 K and then watched the signals
baCK to basICs :
an interferometer, in other words.
An aerial shot of the
Ford Motor Co.'s
To build the device, Jaklevic started by
Scientific Research
depositing
a film of tin onto a glass micro-
Laboratory in Dearscope slide; he patterned the film by passing
born, Mich., in 1967,
where the SQUID had
it through a stainless steel mask, which he
been invented four
had cut with a razor blade. Next he painted
years earlier.
on a mask of Formvar (a type of plastic) and
deposited a second tin film to cover the first
film. The plastic mask was now the insulator between the two
films, and the junction was created through an opening in the
plastic between the bottom film, which oxidized in air, and
the top film. The device was placed in liquid helium, a coil
was inserted to apply magnetic fields to the device, and the
resulting signals were viewed on an oscilloscope. The result
was the world's first functioning SQUID, as described by the
team in an article in Physical Review Letters in early 1964. This
type of SQUID would subsequently be referred to as a DC SQUID
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Table of Contents for the Digital Edition of IEEE Spectrum November, 2014