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To try to indicate how the invention of charge coupled devices CCDs in 1969 by W. S. Boyle and myself came about, it is first necessary to describe three important technologies being pursued at the time. Magnetic bubbles, the silicon diode array vidicon for the Picturephone, and metal oxide semiconductor MOS technology were all contributing factors to the invention of the device. Magnetic bubbles were formed by placing a special magnetic material, typically garnet, in a magnetic field so that circular magnetic domains could be formed as shown in Fig. 1. A Permalloy pattern was deposited on the surface which could capture the domain, and when a rotating magnetic field was applied in the plane of the slice, the bubble would be shifted along from one site to the next. With an input device to inject the presence or absence of bubbles representing 0’s or 1’s and a detection device at the end, one had a serial memory device. The second driving technology being worked on, which just happened to be in my department, was the silicon diode array camera tube, shown in Fig. 2. This was being developed for the Picturephone, which AT&T—Bell Labs parent and the major telephone provider at the time—thought would be a huge market once people discovered they could see as well as hear one another over the existing twisted pair phone lines. The initial imaging device considered was the standard commercial vidicon with an antimony trisulfide coating on glass accessed by an electron beam as the photosensitive element. This device was notorious for its lack of robustness and longevity. Instead, we were working on a tube with a silicon slice with millions of diodes placed on the surface, which were accessed by an electron beam in a similar manner. The silicon was an improvement; however, we strongly hoped to find an all solid state device to eliminate the electron beam. The third field being vigorously pursued was MOS transistor technology. This was the technology that finally became the basis of all modern integrated circuits. The metal oxide semiconductor capacitor that forms the gate of the MOS transistor is shown in Fig. 3. Basic studies of this structure were also being carried out in my department. To understand the atmosphere at the time, one must look at the structure of the Electronics Division at Bell Labs, which was under Vice President Jack Morton. This was split into two divisions, one for semiconductor devices and one for all others. Bill Boyle was Executive Director of the semiconductor part and I was a Department Head under him. Jack Morton was anxious to speed up the development of magnetic bubbles as a major memory technology, and there was talk of transferring resources from Bill’s division to the other where the bubble work was being done. For this not to happen, Morton demanded that Bill’s division come up with a semiconductor device to compete with bubbles. To address this demand, on October 17, 1969, Bill and I got together in his office. In a discussion lasting not much more than an hour, the basic structure of the CCD was sketched out on the blackboard, the principles of operation defined, and some preliminary ideas concerning applications were developed. The train of thought evolved as follows. First, the semiconductor analogy of the magnetic bubble is needed. The electric dual is a packet of charge. The next problem is how to store this charge in a confined region. The structure which came to mind, of course, was the simple MOS capacitor shown in Fig. 3. Charge can be introduced into this depletion region with the amount of charge stored being the magnitude of the signal. To understand this better, a plot of electron energy vs distance into the structure is shown in Fig. 4. As charge is introduced into the depletion region, the potential at the surface rises until the maximum allowable charge is reached. Any further charge added will flow into the substrate. The last problem was to shift the charge from one site to another, thereby allowing manipulation of the information. This is solved by simply placing the MOS capacitors very close together as shown in Fig. 5, one with

Nobel Lecture: The invention and early history of the CCD