Memory Characteristics of Al2O3/La2O3/SiO2 Multi-Layer Structures for Charge Trap Flash Devices

Abstract

The Charge Trap Flash (CTF) memory device is a replacement candidate for the NAND Flash device. In this study, Pt/<TEX>$Al_2O_3/La_2O_3/SiO_2$</TEX>/Si multilayer structures with lanthanum oxide charge trap layers were fabricated for nonvolatile memory device applications. Aluminum oxide films were used as blocking oxides for low power consumption in program/erase operations and reduced charge transports through blocking oxide layers. The thicknesses of <TEX>$SiO_2$</TEX> were from 30 <TEX>$\AA$</TEX> to 50 <TEX>$\AA$</TEX>. From the C-V measurement, the largest memory window of 1.3V was obtained in the 40 <TEX>$\AA$</TEX> tunnel oxide specimen, and the 50 <TEX>$\AA$</TEX> tunnel oxide specimen showed the smallest memory window. In the cycling test for reliability, the 30 <TEX>$\AA$</TEX> tunnel oxide sample showed an abrupt memory window reduction due to a high electric field of 9<TEX>$\sim$</TEX>10MV/cm through the tunnel oxide while the other samples showed less than a 10% loss of memory window for <TEX>$10^4$</TEX> cycles of program/erase operation. The I-V measurement data of the capacitor structures indicated leakage current values in the order of <TEX>$10^{-4}A/cm^2$</TEX> at 1V. These values are small enough to be used in nonvolatile memory devices, and the sample with tunnel oxide formed at <TEX>$850^{\circ}C$</TEX> showed superior memory characteristics compared to the sample with <TEX>$750^{\circ}C$</TEX> tunnel oxide due to higher concentration of trap sites at the interface region originating from the rough interface.