Memory characteristics of Al₂O₃/LaAlO₃/SiO₂ multilayer structures with tunnel oxide thickness variation

Charge trap flash (CTF) memory devices are candidates to replace NAND flash devices. In this study, Pt/Al₂O₃/LaAlO₃/SiO₂/Si multilayer structures with lanthanum aluminate charge traps were fabricated for nonvolatile memory device applications. An aluminum oxide film was used as a blocking oxide for low power consumption in the program/erase operation and to minimize charge transport through the blocking oxide layer. The thickness of SiO₂ as tunnel oxide layer was varied from 30 to 50 Å. Thicknesses of oxide layers were confirmed by high resolution transmission electron microscopy (HRTEM) and all the samples showed amorphous structure. From the C–V measurement, a maximum memory window of 3.4 V was observed when tunnel oxide thickness was 40 Å. In the cycling test for reliability, the 30 Å tunnel oxide sample showed a relatively large memory window reduction by repeated program/erase operations due to the high electric field of ~10 MV/cm through tunnel oxide. The other samples showed less than 10% loss of memory window during 10⁴ cycles.