Reduction of Leakage Current by HfO 2 High K Dielectric Film Stacked on the Ferroelectric Layer of a MFIS Structure

Abstract

We report here the reduction of leakage current through a thin ferroelectric layer by insertion of an HfO 2 film. We fabricated metal-insulator-ferroelectric-insulator-semiconductor (MIFIS) and metal-ferroelectric-insulator-metal (MFIS) structures. A Pb x La 1 m x TiO 3 (PLT) ferroelectric layer was deposited on a thermally oxidized p-type Si substrate with a Zr buffer layer. Adopting an HfO 2 layer on the ferroelectric layer of a MIFIS structure with an equivalent oxide thickness (EOT) of 5 nm resulted in a reduction by only 13 percent of the voltage distribution on the ferroelectric layer. Applying HfO 2 to the ferroelectric layer of a MFIS structure, however, led to a 70% decrease in leakage current: from 2.7 2 10 m 8 to 0.76 2 10 m 8 A/cm 2 at +1 V. An HfO 2 film, by itself, shows leakage that is 3 orders of magnitude smaller than that of PLT; clearly, insertion of the film impedes leakage through the ferroelectric layer. This characteristic is believed to contribute to extension of the retention time of MFMIS FETs.