IEEE Spectrum April, 2014 - 67

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time
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BETTEr THAN TuBEs: This 1955 report, published in 1956, informed the
computer-engineering community of Buck's new magnetic switching element.

Gating Element," contained broad claims
for the cryotron and its use in computers.
At this point, Buck's cryotron research expanded beyond MIT, albeit just down Memorial Drive. He signed a consulting agreement
on cryotron technology with the contractresearch firm Arthur D. Little. Named after
its MIT chemist founder, A.D. Little was adjacent to the MIT campus and in the 1950s
had become a leading producer of cryostats
for the production of liquid helium. With
NSA sponsorship, Buck and researchers at
A.D. Little began development of Buck's
cryotron recognition unit, starting with a
smaller proof-of-concept memory array.
Through the rest of 1955, Buck's personal
cryotron research at MIT focused on creating miniature cryotrons, and even integrated cryotron arrays, using evaporated
thin films. Instead of winding small wires
about one another, he wanted to evaporate
metal through a mask, like a stencil, onto a
substrate to create a patterned thin film of
superconducting material. Atop this film, he
would evaporate the control wiring through
another mask. He would thus be able to print
cryotrons, arrays of them.
In preparation, Buck tested a variety of films
made of alloys of lead, bismuth, strontium, indium, and other elements. During these experiments, he produced a 100-nanometer-thick
film of a lead-bismuth-strontium alloy that
could switch between superconducting and

resistive states in 0.1 microsecond-a tenth the
speed of the fastest transistor at the time. Buck
also designed a wide range of binary circuits
that could be constructed solely from cryotrons, including flip-flops, gates, multivibrators, adders, and accumulators.
With his patent filed and significant research completed, Buck was ready to announce the cryotron to the world. He
submitted a paper titled "The Cryotron-
A Superconductive Computer Component" to
the Institute of Radio Engineers, one of IEEE's
predecessor organizations, in November 1955.
In the paper, Buck detailed the wire-wound
cryotron and a range of basic digital circuits
that could be made with it, stressing the implications for this superconductive device in
computing. "The cryotron in its present state
of development...can be used as an active
element in logical circuits," Buck wrote. He
did not restrain himself from sharing his conviction that, in the near term, "a large-scale
digital computer can be made to occupy one
cubic foot.... The power required by such a
machine extrapolates to about one-half watt."
Buck's discussion of switching speeds
in this paper was, in contrast, coy: "The
device is at present somewhat faster than
electromechanical relays, but far slower
than vacuum tubes and transistors. A program is under way to increase the speed."
Although he had already tested thin-film
cryotrons that could come close to the fast-

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Table of Contents for the Digital Edition of IEEE Spectrum April, 2014

IEEE Spectrum April, 2014 - Cover1
IEEE Spectrum April, 2014 - Cover2
IEEE Spectrum April, 2014 - 1
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IEEE Spectrum April, 2014 - Cover3
IEEE Spectrum April, 2014 - Cover4
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