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For an electron packet, a sufficiently positive gate electric potential attracts electrons beneath the insulating layer of a MOS capacitor. The corresponding potential energy is $U=-e\varphi$, where $e>0$ is the magnitude of elementary charge: a larger electric potential gives a deeper potential well for electrons. A drawing of potential energy must therefore reverse the vertical sense of a drawing of electric potential.

A simplified three-phase transfer raises the adjacent gate's electric potential before lowering the old holding gate. This overlaps the accessible regions, then leaves the packet under the new gate. Repeat with the next gate to move it forward. Isolated wells with an intervening barrier would store the packet without transferring it.^[ref]

A charge-coupled device stores photoelectrons in potential wells and transfers the charge through clocked stages to an output amplifier. The transfer differs from independently addressed pixels in a hybrid infrared detector.

In an imaging charge-coupled device, absorbed photons produce mobile charge carriers in a semiconductor; collection stores an electric charge packet associated with each optical detector pixel. Closely spaced MOS capacitors allow applied electric potential differences to move the packet from site to site. Willard Sterling Boyle and George Elwood Smith described storage, transfer and detection as distinct operations, including imaging as one application.^[ref]

The useful architectural trick is that many optical detector pixels can send their electric charge to a shared output electronic amplifier. This makes repeatable conversion possible but makes fidelity depend on every transfer along the route. An active-pixel sensor made with CMOS technology instead uses circuitry at pixels to convert or buffer their signal and select it for readout; independent pixel addressing does not require transporting each packet through the whole image. This compares readout architectures, not whether either technology can use a photodiode.^[ref]

George E. Smith and Willard Boyle introduced the charge-coupled device, which stores information as electric charge packets in movable potential wells at a semiconductor surface. Changing electrode potentials transfers a packet to a neighboring storage region. Their 1970 paper describes electric charge creation, transfer and detection, and proposes both information-processing and imaging applications. The same electrical mechanism can therefore shift a stored signal through a device or carry light-generated electric charge toward a detector.^[ref]

A physicist researching semiconductor devices.^[ref]

Willard Boyle and George E. Smith devised the charge-coupled device around controlled storage and movement of electric charge. Adjacent electrodes create potential wells in a semiconductor; timed changes of their voltages move stored electric charge between the wells. The 1970 proposal treats electric charge packets as information and discusses a shift register as well as an imaging device. This links electrostatic control of a surface to the transport and detection of an optical signal.^[ref]

A physicist researching lasers and semiconductor devices.^[ref]