Impedance Analysis of Controlled-Polarization-Type Ferroelectric-Gate Thin Film Transistor Using Resistor–Capacitor Lumped Constant Circuit

We propose a novel ferroelectric-gate field-effect transistor using a polar oxide semiconductor channel, which is called a controlled-polarization (CP)-type ferroelectric-gate thin film transistor (TFT). Although the CP-type ferroelectric-gate TFTs with a ZnO/YMnO3structure shows nonvolatile memory operation, the relationship between the electrical characteristics of the TFTs and the direction of spontaneous polarization of the ferroelectric layer (PSFe) below the channel has not been revealed. In this study, the direction ofPSFeis analyzed by the impedance spectra of the channel conductance because it can be expected that the channel conductance depends on the direction of thePSFe. The five conditions of the channel conductance are assumed and the impedances between the source electrode and the gate electrode of each condition are calculated by SPICE. The direction ofPSFeat various gate voltages is determined by the comparison of the calculated results and experimental results. It was found that the channel conductance of the ferroelectric-gate TFT has steep change by the change of the direction ofPSFe.