Nanocluster Based Memories

The talk starts with a short survey of the concepts for non-volatile memories designed for nanoelectronics. Among different approaches memories based on the charge storage in small semiconductor quantum dots are of particular interest, as they offer an opportunity for integration in the present CMOS-technology. Following this route the "Nanocrystal Memory" - which was first introduced by IBM in 1996 - is discussed in detail regarding its working principle and the corresponding technological challenges. One of the critical points is the fabrication of a shallow band of small semiconductors in the gate oxide of a FET very close, but well separated to the Si/SiO2-interface. Different deposition and ion beam techniques have been successfully applied to realize small Si or Ge nanoclusters with a typical size of 2-5 nm and a density between 10E11…10E12 cm-2. One very promising technique is the ion beam synthesis of nanoclusters, which is mainly applied in the Forschungszentrum Rossendorf. Microstructural investigations have shown, that IBS enables the fabrication of delta-like nanocluster bands, which fulfill very well the requirements for a "nanocrystal" memory. Electrical investigations revealed, that cluster containing thin SiO2 films show a remarkable storage effect even at room temperature, which are characterized by the shift of flatband or threshold voltage of MOS- or FET-structures, respectively. Despite these successful results main questions are still open, so that hopes and challenges are close together.