Development of Low Dielectric Constant Ferroelectric Materials for the Ferroelectric Memory Feild Effect Transistor

In this paper we discuss ferroelectric materials suitable for a metal-ferroelectric-metal- insulator-semiconductor feild effect transistor (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 and Sr₂(Ta_1-xNb_x)₂O₇ were prepared by the sol-gel method on Pt/IrO₂ electrodes for an MFMIS FET. The ferroelectricities of Sr₂(Ta_1-xNb_x)₂O₇ films were confirmed to be in the range of x=0.1–0.3. In the case of x=0.3, the largest remanent polarization was obtained in the hysteresis loop. The values of the remanent polarization and the coercive field are 0.5 µC/cm² and 44 kV/cm, respectively. The film has a low dielectric constant (ε _r=53). The characteristics of Sr₂(Ta_1-xNb_x)₂O₇ thin films are suitable for MFMIS FET.