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UBC Theses and Dissertations

Devices employing conductivity modulation in semiconductor films by ferroelectric polarization charging Teather, George Griffiths


Two types of devices employing ferroelectric modulation of a semiconductor thin-film have been realized and studied. The first consists of a cadmium selenide film with electrodes deposited on a barium titanate substrate together with a switching electrode on the other side of the substrate. This gives a two-valued resistor; in effect, a nondestructive readout of the state of the ferroelectric crystal which is regarded as a storage element. The second device is a thin-film transistor (TFT) deposited on a barium titanate crystal. A fourth counterelectrode - on the other side of the crystal allows changing between two opposite polarization directions in the crystal, thus giving a TFT with two sets of characteristics, roughly equivalent to a two-valued built-in gate bias. The read-in, or switching time, of the device is substantially determined by the barium titanate crystal and can be in the microsecond range for high switching fields. Readout of the devices can be continuous or not, as desired. Characteristics of the TFT, which is considered equivalent to a two-gate device, are analyzed in terms of the gradual channel approximation. Experimental results of the two devices are presented and discussed in relation to the predicted behaviour.

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