We have developed a numerical simulation of the charge transferin the overlapping gates charge coupled devices. The transport dynamics were analyzed in terms of thermal diffusion, self-inducedfields and fringing fields under all the relevant electrodes and theinterelectrode regions with time varying gate potentials. We have also developed a lumped circuit model of charge coupled devices. Usingthis model simple analytic expressions describing the charge transferwith 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 providingpractical charge coupled device and circuit design tools.
Using the numerical simulation and lumped circuit model, theinfluence of clocking waveforms and clocking schemes on CCD operationare studied. It is concluded that increasing the clocking schemecomplexity allows a better control of the storage and transfer of thesignal charge and hence improves the signal dynamic range and chargetransfer characteristics. It is shown that the performance of chargecoupled devices is better with push clocks (that push the charge fromone storage site to another) than with drop clocks (that createdeeper potential wells to transfer the charge). The performance ofcharge coupled devices is shown to be basically superior to the MOSbucket brigade.
We have also developed a simple model to study the incomplete charge transfer due to trapping in the interface states. Incompletecharge transfer due to trapping in interface states is shown to limitthe performance CCDs at low frequencies. The most dominant effectis trapping in the interface states under the edges of the gatesparallel 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. Itis shown that increasing the clock voltages, increasing the signalcharge or using dynamic push clock reduces the incomplete charge transfer due to interface states.
The contents of this thesis have been published under thefollowing 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 andC. 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 Papers15, 1972, pp. 248-249
The contents of this thesis have also been presented in the followingconferences:
"Physics of Charge Coupled Devices", Invited Review Talk given at the Gordon Research Conference, Meriden, NewHampshire, August 1972.
"The Influence of Clocking Waveforms of CCD Operation",presented at the International Device Research Conferenceat Edmonton, Canada, June 1972.
"Charge Transfer in Charge Coupled Devices", presented atthe International Solid State Circuits Conference,Philadelphia, Pa., February 1972.
A motion picture simulation of the various stages of the charge transferprocess 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 mentionedabove and is included in the "Semiconductor Memory Course" prepared by Texas Instruments on video tapes. The CCD movie is published inthe Journal of Solid State Circuits (June 1973) as three sequences of page-flip movie.
