MFIS Structure Device with a Low Dielectric Constant Ferroelectric Sr2(Ta1−x,Nbx)2O7 Formed by Plasma Physical Vapor Deposition and Oxygen Radical Treatment

A low dielectric constant ferroelectric Sr2(Ta1 −x,Nbx)2O7 film formation technology which is applied to FFRAM has been developed. The high ferroelectric performance of the STN capacitor has been achieved by plasma physical vapor deposition and microwave-excited (2.45 GHz) high-density (> 1012 cm−3) low electron temperature (< 1 eV) Kr/O2 plasma (oxygen radical treatment). Oxygen radical treatment can oxidize STN effectively at 400°C. Furthermore, we have successfully developed a new technology that crystallizes a ferroelectric material on an insulator layer such as SiO2 and Si3N4 directly by oxygen radical treatment. Using this technology, MFIS device operation has been successfully achieved and its retention time is more than 24 hours.