We have been fabricated and characterized a ferroelectric-gate thin-film transistors (TFTs) using ZnO as a channel polar semiconductor and YMnO(3) as a ferroelectric gate. A typical n-channel transistor property showing clear drain current saturation in I(D)-V(D) (drain current - drain voltage) characteristics was recognized When the 3 V of the gate voltage is applied under the 4 V of drain voltage, the large dram current of about 1.1 mA is obtained These controlled-polarization-type ferroelectric-gate TFTs using ZnO-channel TFTs operate in the accumulation-depletion mode and the ON/OFF state of the ferroelectric-gate TFTs strongly depends on the polarization switching of Psi,. In this paper, therefore, the polarization switching of P(SFe) in the TFT is carefully examined and the relationship between the polarization switching and the carrier accumulation (depletion) state is discussed using impedance spectroscopy and Capacitance-Voltage (C-V) measurements at applied the gate voltage (C) 2009 Elsevier B V All rights reserved