Incomplete Charge Transfer in Overlapping Gates Charge Coupled Devices

Citation

Mohsen, Amr Mohamed (1973) Incomplete Charge Transfer in Overlapping Gates Charge Coupled Devices. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/CEG6-AR39. https://resolver.caltech.edu/CaltechTHESIS:02012018-092625397

Abstract

We have developed a numerical simulation of the charge transfer in the overlapping gates charge coupled devices. The transport dynamics were analyzed in terms of thermal diffusion, self-induced fields and fringing fields under all the relevant electrodes and the interelectrode regions with time varying gate potentials. We have also developed a lumped circuit model of charge coupled devices. Using this model simple analytic expressions describing the charge transfer with various clocking waveforms are derived. This model can be used to study the charge transfer characteristics for other device structures, dimensions, clocking waveforms and voltages, thus providing practical charge coupled device and circuit design tools.

Using the numerical simulation and lumped circuit model, the influence of clocking waveforms and clocking schemes on CCD operation are studied. It is concluded that increasing the clocking scheme complexity allows a better control of the storage and transfer of the signal charge and hence improves the signal dynamic range and charge transfer characteristics. It is shown that the performance of charge coupled devices is better with push clocks (that push the charge from one storage site to another) than with drop clocks (that create deeper potential wells to transfer the charge). The performance of charge coupled devices is shown to be basically superior to the MOS bucket brigade.

We have also developed a simple model to study the incomplete charge transfer due to trapping in the interface states. Incomplete charge transfer due to trapping in interface states is shown to limit the performance CCDs at low frequencies. The most dominant effect is trapping in the interface states under the edges of the gates parallel to the active channel. The influence of the device parameters, dimensions and clocking waveforms on the signal degradation is discussed. Design features of CCD structures which would reduce the incomplete charge transfer due to interface states are presented. It is shown that increasing the clock voltages, increasing the signal charge or using dynamic push clock reduces the incomplete charge transfer due to interface states.

The contents of this thesis have been published under the following titles:

"Charge Transfer in Overlapping Gates Charge Coupled Devices" A. M. Mohsen, T. C. McGill and C. A. Mead, Journal of Solid State Circuits, SC-8, No. 3, June 1973.

"The Influence of Interface States on Incomplete Charge Transfer in Overlapping Gates Charge Coupled Devices", A. M. Mohsen, T. C. McGill , Y. Daimon and C. A. Mead, Journal of Solid State Circuits, SC-8, No. 2, April 1973.

"Push Clocks: A new approach to charge coupled device clocking", A. M. Mohsen, T. C. McGill, M. Anthony and C. A. Mead, Appl. Phys. Letters, 22, 4, February 15, 1973, pp. 172-175.

"Charge Transfer in Charge Coupled Devices", A. M. Mohsen, T. C. McGill and C. A. Mead, ISSCC Digest of Technical Papers 15, 1972, pp. 248-249

The contents of this thesis have also been presented in the following conferences:

"Physics of Charge Coupled Devices", Invited Review Talk given at the Gordon Research Conference, Meriden, New Hampshire, August 1972.

"The Influence of Clocking Waveforms of CCD Operation", presented at the International Device Research Conference at Edmonton, Canada, June 1972.

"Charge Transfer in Charge Coupled Devices", presented at the International Solid State Circuits Conference, Philadelphia, Pa., February 1972.

A motion picture simulation of the various stages of the charge trans­fer process with two-phase and four-phase clocking schemes was produced directly from the results of the numerical simulation developed in this thesis. The CCD movie has been presented in the conferences mentioned above and is included in the "Semiconductor Memory Course" prepared by Texas Instruments on video tapes. The CCD movie is published in the Journal of Solid State Circuits (June 1973) as three sequences of page-flip movie.

Thesis Files