Recently, nonvolatile memory devices having a ferroelectric gate structure have considerable attention from the view points of nonvolatile, high-speed, high-density, and obeying the scaling rule. Sr₂(Ta_1-x,Nb_x)₂O₇ (STN, x=0.3) is suitable for use as a ferroelectric material for ferroelectric memory field-effect transistors, because it has a low dielectric constant. However, the fabrication of STN on an amorphous insulator, such as SiO₂, is difficult. In particular, in the case of STN, because its crystallization annealing temperature is 950℃, the metal element of STN and Si react mutually during crystallization annealing. We have already developed and reported [1] the STN formation technology on amorphous SiO₂ and MFIS structure device operation. These were realized using (1) a thin seed layer formed by rf sputtering and microwave-excited plasma treatment, and (2) by the formation of a ferroelectric film, whose oxygen vacancy is reduced by ferroelectric multilayer stack (FMLS) deposition. This plasma treatment can oxidize the surface of the film and supply ion bombardment energy to the surface of the film. In this work, we report imprint and data-programing properties of the MFIS structure device. Threshold voltage shipt of the device is within 10mV and 30 mV after writing operation of 10⁹ and 10¹⁰ cycles, respectively.

[1] I. Takahashi et. al., Japanese Journal of Applied Physics, Vol. 45, pp. 3207-3212, 2006

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