Computer Modeling of Charge-Coupled Device Characteristics

With the invention 1 and initial investigation 2,3 of charge-coupled devices (CCDs), it became apparent that although conventional one705 706 T H E BELL SYSTEM T E C H N I C A L J O U R N A L , MARCH 1972 dimensional considerations can lead to qualitative and heuristic arguments concerning the device operation, the phenomenon of charge coupling laterally along a semiconductor surface is essentially twodimensional in nature and any quantitative understanding of the effect must begin with this premise. The purpose, therefore, of the present work is to use the solutions of the two-dimensional PoissonBoltzmann equation obtained within the bounds of certain reasonable approximations to try to infer the basis of operation for the structures reported in the literature as well as to study new structures and predict their anticipated performance. Such inferences are obviously dependent upon a large number of considerations. For purposes of tractability, however, attention will be restricted to what is believed to be the key attributes of the device. Central to our considerations, therefore, will be the static surface potential and electric field profiles. These will be obtained through numerical iteration of the two-dimensional equations. In addition, the analysis is limited to the simple three-phase devices as originally described. The question of charge motion is then treated for the case of a sufficiently small charge density so that the fields are not appreciably altered by its presence.