Insulator-thickness dependence of a metal-ferroelectric-insulator-semiconductor field effect transistor using (Bi,La)4Ti3O12 thin films as the ferroelectric material

Studies on the electrical properties of pulsed-laser-deposited Bi3.25La0.75Ti3O12 thin films were conducted on thermally oxidized 8-nm- and 15-nm-SiO2-coated Si substrates. Characterizations of the ferroelectric-gated field effect transistors (FeFET) were evaluated from measurements extracted from capacitance-voltage and current-voltage properties. It has been found that the FeFET has an inverted hysteresis property and that the characteristics from 8-nm-SiO2/Si were much more stable than those from 15-nm-SiO2/Si substrates. The memory window values showed that FeFETs with 15-nm-SiO2/Si required a higher operating voltage, considered to be a drawback in device applications. However, relatively large memory window values of 0.3 V, 2.5 V, 5.0 V, and 7.0 V were extracted at the respective bias voltages of ± 5 V, ± 7 V, ± 10 V, and ± 12 V for FeFETs made from 8-nm-SiO2/Si. The properties of FeFETs made from both substrates and the effects of reducing the insulator thickness are discussed.