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The charge-coupled device (CCD) was invented October 19, 1969, by Willard S. Boyle and George E. Smith at Bell Telephone Laboratories. Figure 1.1 (a) shows their original laboratory notebook entry describing the idea. Jack Morton, vice-president of Bell Labs Electronics Technology, was an important motivator behind the CCD. Jack was a strong proponent of the magnetic bubble memory and wondered if an analogous device could be made with a semiconductor. He encouraged Boyle and Smith to look into a potential connection. At the same time, the Picture-phone was being developed using diode arrays in silicon. Charge storage on individual diodes had been a problem that prompted some new research. The CCD was born with these two existing technologies in mind. As the story goes, Boyle and Smith brainstormed on the blackboard for approximately a half hour, producing the CCD structure. The first notebook drawing of the device is shown in Fig. 1.1 (b), which presents a basic three-phase configuration. The original timing diagram presented also accurately describes today's CCD and is used throughout this book.
A few weeks later, a three-phase device was designed, fabricated and tested: a simple row of nine 100-μm metal plates separated by 3-μm spacings. The first gate electrode was used to inject charge into the second plate. The ninth plate was used to detect charge. Plates 2â8 were clocked to demonstrate the transfer process. The experiment was a success.
The first public announcement, which lasted only five minutes, was made at the New York IEEE convention held March 1970. The ideas were subsequently reported by Boyle and Smith in the April 1970 issue of the Bell System Technical Journal. This paper was important because it introduced potential problems behind the invention. For example, limitations in storage time caused by dark current generation were discussed. Also, they found three important factors that limited charge transfer efficiency: surface interface state trapping, thermal diffusion and fringing fields. The bubble memory analogy was introduced by shifting digital information in the form of charge and implemented with a serial shift register with p-n inputs and outputs. Also very important was the idea that the CCD could be used for imaging using linear and array areas.
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