An MOS (metal oxide semiconductor) capacitor structure with double-layer heterogeneous nanocrystals consisting of semiconductor and metal embedded in a gate oxide for nonvolatile memory applications has been fabricated and characterized. By combining vacuum electron-beam co-evaporated Si nanocrystals and self-assembled Ni nanocrystals in a SiO2 matrix, an MOS capacitor with double-layer heterogeneous nanocrystals can have larger charge storage capacity and improved retention characteristics compared to one with single-layer nanocrystals. The upper metal nanocrystals as an additional charge trap layer enable the direct tunneling mechanism to enhance the flat voltage shift and prolong the retention time.

TiO2 and HfO2 with different electrical conductivity were used as buffer layer for phase change memory (PCRAM) cell, where Si‐Sb‐Te alloy was used as storage medium in the PCRAM cell. The electrical properties of the cells with and without buffer layer were compared through resistance‐voltage measurements. It is found that the PCRAM cell with both TiO2 and HfO2 buffer layer has relative low operation voltage. Furthermore, the inserting TiO2 buffer layer can also improve the device stability. It is considered that buffer layer with suitable electrical conductivity is needed for the PCRAM cell, especially in future high density storage. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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