worked by injecting magnetic 
domains into garnet patterned with 
an array of ferromagnetic bars. 
Applying an alternating magnetic 
field caused these domains, or bub-
bles, to hop within the garnet from 
underneath one bar to the next, 
like packages on a conveyor belt. By 
taking the presence or absence of a 
bubble to represent a 1 or a 0, respec-
tively, such a device could be used to 
store a series of digital bits. 

Boyle and Smith spent barely 
an hour at the blackboard devising 
an electronic alternative. Instead of 
magnetic bubbles, they proposed 
to use electronic charges injected 
into metal-oxide-semiconductor 
(MOS) capacitors grown on silicon. 
By placing two capacitors close to 

‘Revolutionary’ is used too often 
to describe advances in science. 
When applied to the invention of 
the charge-coupled device (CCD) 
array by Willard Boyle and George 
Smith, however, it is not far off. Yet, 
the CCD was not originally intended 
for applications in digital imaging, 
for which Boyle and Smith received 
the 2009 Nobel Prize in Physics, but 
rather as a potential new form of 
digital memory. 

In the late summer of 1969, Boyle 
and Smith, who were working at Bell 
Laboratories, were told to come up 
with a semiconductor memory that 
could compete with the so-called 
‘magnetic bubble’ memory that was 
being developed by a rival group 
of their division. Bubble memory 

each other and applying electric 
voltages they could induce the charge 
to move from one to the next. In 
this way, packets of charge could be 
passed down a linear array of ‘charge-
coupled’ MOS capacitors, mimicking 
the operation of a bubble array. 

Ironically, although the operation 
of the device was a success, neither it 
nor bubble memory ever took off as a 
means of storing digital information. 
But it did not take long for Boyle and 
Smith to realize that it might have 
other uses. At around the same time, 
Bell Laboratories was working hard 
to develop the Picturephone, which 
was a crude videoconferencing sys-
tem. The commercial cathode-ray-
tube cameras used were notoriously 
unreliable and a more dependable 
alternative was eagerly sought. The 
CCD provided the solution. 

The simplicity of fabricating large 
sensor arrays, combined with the 
linear optical response to even the 
most faint light sources, has meant 
that 40 years after their invention 
they are still used in large-scale opti-
cal telescopes, including the Hubble 
space telescope. It has also allowed 
them to become cheap enough to be 
integrated into most modern mobile 
phones — a fact that news agencies 
increasingly rely on for important 
events. So, although the revolution 
might not be televised, thanks to 
the CCD it will almost certainly be 
photographed.

Ed Gerstner,  
Senior Editor, Nature Physics

ORIGINAL RESEARCH PAPERS Boyle W. S. & 
Smith, G. E. Charge coupled semiconductor 
devices. Bell Syst. Tech. J. 49, 587–592 (1970) | 
Amelio, G. F., Tompsett, M. F. & Smith, G. E. 
Experimental verification of the charge coupled 
device concept. Bell Syst. Tech. J. 49, 593–600 
(1970)
FURTHER READING Smith, G. E. The invention 
and early history of the CCD. Nucl. Instr. Meth. 
Phys. Res. A 607, 16 (2009)

 M I L E S T O N E  1 4

Digital photography is born

The CCD inventors, Willard 
Boyle (left) and George 
Smith (right). Image courtesy 
of Alcatel-Lucent/Bell Labs

M i l e s t o n e s

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