A Low-Dielectric-Constant Sr2(Ta1-x,Nbx)2O7 Thin Film Controlling the Crystal Orientation on an IrO2 Substrate for One-Transistor-Type Ferroelectric Memory Device

The compounds of the Sr2Nb2O7 (SNO) family are suitable for use as ferroelectric materials for ferroelectric memory field-effect transistors (FETs), because these substances have a low dielectric constant and high heat-resistance. A very low dielectric constant ferroelectric Sr2(Ta1-x,Nbx)2O7 (STN) film formation technology, which can be applied to a floating-gate-type ferroelectric random access memory (FFRAM), has been developed. Furthermore, a new technology that controls the orientation and the properties (a low dielectric constant and large coercive field) of STN has been developed. An MFMIS structure device with a large memory bias window (1.3 V) under ±5 V operation and a long retention time (>10 h) has successfully been fabricated.