Ultra-Thin Fatigue-Free Bi₄Ti₃O₁₂ Films for Nonvolatile Ferroelectric Memories

Abstract

We have developed a new low temperature growth technique for Bi4Ti3O12 thin films using a MOCVD method in which an ultra-thin double buffer layer (5-nm thick Bi4Ti3O12/5-nm thick TiO2) is used to control the crystallization and fine grain structure. The 100-nm thick Bi4Ti3O12 thin films fabricated at 400°C showed an extremely smooth surface morphology and good electrical properties, namely, a large remanent polarization of P r=11 µC/cm2, a coercive field of E c=90 kV/cm and a low leakage current I L=7×10-9 A/cm2 at 3 V. Moreover, we successfully fabricated 50-nm ultra thin Bi4Ti3O12 films with P r=9 µC/cm2 and E c=120 kV/cm at 3 V. For the first time, the fatigue free property, which is very important for nonvolatile ferroelectric memory (NVFRAM) applications, was confirmed up to 1×1012 switching cycles.

Polarization switching behavior of Hf–Zr–O ferroelectric ultrathin films studied through coercive field characteristics

“…E C decreases with increasing thickness. This behavior is [52][53][54] and Bi 4 Ti 3 O 12 , [55][56][57][58][59][60][61] and HfO 2 9,12) and our results.…”

Atomic Layer CVD in the Bi–Ti–O System

“…However, there are reports on the use of triorthotolyl bismuth, Bi(o-C 7 H 7 ) 3 , [25] and bismuth iodide, BiI 3 , [26] as precursors for the deposition of Bi 4 Ti 3 O 12 . It is worth mentioning that BiCl 3 and Bi(CH 3 ) 3 have also been used as precursors in the CVD of Bi 2 Sr 2 CaCu 2 O 8+x , [27] and SrBi 2 -Ta 2 O 9 , [28] respectively.…”

The Preparation of a Fatigue-Free Bi4Ti3O12 Thin Film With Controlling Bi-Excess Using Sol-Gel Coating

“…Kijima et al [8,12] reported that fatigue-free BIT thin films could be obtained from MOCVD process, when the films had extremely smooth film surface consisting of very fine grains. Our result confirmed that such a film microstructure could improve fatigue endurance.…”