U.S. Philips Corporation

Agnes C Kleimann

Jan T Bosiers

Edwin Roks

It is known to reduce the leakage current or dark current in charge-coupled devices with buried channels such as, for example, charge-coupled imaging devices by bringing the surface to the inverted state. In such a device, however, it is not possible to empty the channel completely locally in usual manner in that the charge is drained off through the substrate by means of a voltage pulse applied to the gates (charge reset). To be able to carry out charge reset nevertheless, the voltage pulse is applied between the substrate and the intermediate zone interposed between the substrate and the CCD channel. Since this voltage pulse is active over the entire range of the device, the device also prevents charge from being removed in locations where this is not desired when the pulse is applied. It is possible in this manner to carry out charge reset, for example, in the imaging section only, in imaging devices without removing the information which is simultaneously in store in the memory section and/or in the read-out register.

Charge-coupled device having charge reset

It is known to bring the surface into the inverted state in CCD imaging devices with buried channels during the integration period in order to keep the dark current low (All Gates Pinning). The desired potential profile, with wells in which the charge is integrated bounded by potential beers, is obtained through the use of a two-phase structure with a doping profile in the channel or with a gate oxide having thickness differences. Owing to limiting conditions which hold for the clock voltages used for charge transport, serious limitations are imposed on the depth of the potential wells and thus also on the charge storage capacity of the pixels. This disadvantage is counteracted by the operation of the device not as a two-phase but, for example, as a four-phase CCD according to the invention, whereby a d.c. shift is present between the clock voltages for compensating the built-in, comparatively great potential differences described above. An imaging device is obtained thereby with a low dark current, a great charge storage capacity per pixel, and a high transport efficiency.

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Eindhoven, Netherlands

Agnes C Kleimann