Relationship between Sr2(Ta1-x,Nbx)2O7 Crystal Phase and RF-Sputtering Plasma Condition for Metal–Ferroelectric–Insulator–Si Structure Device Formation

Sr2(Ta1-x,Nbx)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 °C, the metal element of STN and Si react mutually during crystallization annealing. As a result, perovskite STN cannot be fabricated. We have clarified the relationship between a ferroelectric crystal phase on amorphous SiO2 and an rf-sputtering plasma condition. On the basis of the results obtained, STN film formation technologies on SiO2, which can be applied to metal–ferroelectric–insulator–Si field-effect transistor-type ferroelectric random access memories, have been developed by controlling the properties of rf-sputtering plasma and the application of microwave-excited plasma.