The metal/ferroelectric material/metal/oxide insulating material/Si substrates (MFMIS) structure was realized by using Pb(Zr0. 4Ti0. 6)O3 (PZT) thin film. PZT(330 nm thick) thin film was sandwiched between the upper electrode of Ti/Pt-Rh (about 380 nm thick and 123 microns in diameter) and the lower electrode of Pt-Rh/Ti (about 380 nm thick and 378 microns in diameter). The MFM structures mentioned above were prepared on metal oxide semiconductor (MOS structures). Pt-Rh and Ti lower electrodes were directly deposited on a poly-Si MOS electrode with sputtering, and PZT layer was prepared using the sol-gel method. In order to maximize induced charge density in the MOS gate, diameters of the upper and the lower electrodes were adjusted, and the MFM area-to-MOS area ratio was optimized. By using the area ratio of 0. 11 a memory window of 2. 4 V was obtained.

In this paper, we discuss ferroelectric materials suitable for a metal ferroelectric metal insulator semiconductor FET (MFMIS FET). It is important for a ferroelectric material to have a low dielectric constant to enable the application of sufficient electric field to a ferroelectric layer. Films of Sr2Nb2O7 (SNO) and Sr2(Ta1-xNbx)2O7 (STNO) were prepared by the sol-gel method on Pt/IrO2 electrodes for an MFMIS FET. The ferroelectricities of STNO films were confirmed in the range of x=0. 1-0. 3. In case of x=0. 3, the largest remanent polarization was obtained in the hysteresis loop. The remanent polarization and the coercive field are 0. 5 µ C/cm2 and 44 kV/cm, respectively. The film had a low dielectric constant (ε=53). It is considered that the characteristics of STNO thin films are suitable for MFMIS FET.