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A metal-ferroelectric-insulator-emiconductor (MFIS) feld-effect transistor structure has been fabricated by using ferroelectric Bi3:25La0:75Ti3O12 thin flm and thermally oxidized SiO2 insulating layer. We found that the electronic transport properties differ greatly with the different types of Si substrates (boron-doped p-type and phosphorus-doped n-type). Capacitance-voltage (C-V) curves were measured at a frequency of 1 MHz at various bias voltages, which resulted in an inverted memory window characteristic for n-type structure while an ideal clockwise loop was observed from p-type structure. These di erences in C-V measurements have been found to be reliable since current-voltage (I-V) measurements for both structures resulted in identical plots. Such a result ensures that MFIS structures prepared on n-type substrates are consistent with effects from ferroelectric polarizations.