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UBC Theses and Dissertations

A GaAs cermet gate charge-coupled device LeNoble, Maurice


The design, implementation and evaluation of a 64-pixel, 4-phase GaAs cermet gate charge-coupled device ( CMCCD ) are described. It is demonstrated that the signal charge confinement and the signal charge capacity of the CMCCD are maximized when thin, highly doped active layers are used for implementing the device. The cermet/GaAs junction within an interelectrode gap of the CMCCD forms a barrier similar to a metal/GaAs Schottky barrier, as revealed by an investigation of the dc current-voltage characteristic of a cermet/GaAs Schottky barrier diode. A transmission line model is described for the cermet/GaAs junction within an interelectrode gap of the CMCCD and is used to demonstrate the relationship of the surface potential variation along the gap as a function of the clock frequency and the material parameters. It is shown that the surface potential variation is monotonic for all frequencies, which is desirable for minimizing the formation of energy troughs within the active layer. Energy troughs trap and release charge from passing charge packets, causing unwanted signal dispersion. A two-dimensional computer model is used to determine a theoretical maximum frequency of operation of the CMCCD. It is shown that a short transport electrode length for a fixed transport electrode pitch is preferable as it results in the maximum high frequency performance of the CMCCD for the lowest clock power. A computer simulation of a single electrode transfer of a charge packet is demonstrated using the two-dimensional computer model. The computer simulation indicates that efficient charge transfer takes place, suggesting that the CMCCD will have good performance. A GaAs CMCCD with an on-chip GaAs MESFET source follower amplifier has been produced using a six mask level fabrication procedure. The CMCCD and the output source follower amplifier are demonstrated to operate at 100 MHz. Charge transfer efficiencies of 1.00 and 0.998 for 100 MHz operation are obtained for the CMCCD using the impulse response method and the insertion loss method.

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