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Abstract: An attractive alternative for extending the scaling of Flash-type memories is to replace the conventional floating gate (a poly-Si layer) by laterally isolated floating nodes in the form of nanoparticles. This floating-gate concept has led to the emergence of the so-called nanocrystal (NC) memories which have the potential of operating at lower voltages and higher speeds compared to the conventional non-volatile memories (NVMs) without compromising the criterion of non-volatility. NC memories also offer other advantages like a better immunity to the crosstalk effect arising from the floating-gate coupling of closely spaced adjacent cells and an increased design flexibility from which quantum confinement phenomena can be judiciously exploited for enhanced memory functionality. Among the different technological routes explored in the last few years for generating nanocrystals in the gate insulator of MOS devices, two major techniques have been utilized, namely deposition in vacuum and ion beam synthesis. During the last decade, we have extensively explored the ultra-low-energy ion-beam-synthesis (ULE-IBS) technique to produce single planes of Si-NCs in very thin (5–10nm) insulator layers. This review summarizes more than 10 years of research efforts we and other groups have dedicated to the fabrication of NCs memories using this original technique. By exploiting the flexibility of the ULE-IBS route, Si-NCs single-transistor NVM cells using “classical” gate oxides (SiO2) have been successfully realized. More recently, advanced dielectric stacks employing high-κ dielectric (HfO2) as tunnel oxide and SiN as control oxide and host matrix for Si and Ge-NCs, have been fabricated and show promising performance for low-voltage operating-NVM devices. Particular emphasis is placed herein on material science issues such as anomalous and controlled oxidation processes. While much research is still needed for making reliable and competitive NC NVMs, our systematic investigations based on the ULE-IBS option demonstrate that a tight control and understanding of the properties of NCs memory cells can be achieved, provided that deep structural characterization is coupled to electrical studies. [Copyright &y& Elsevier]

Abstract: Amorphization of germanium (Ge) substrates under ion implantation has been studied by transmission electron microscopy. Ge crystalline wafers were implanted with 150keV Ge ions with doses ranging from 1×1013–1×1016 cm−2. First a distribution of disordered zones appears, and then a continuous amorphous layer forms by damage accumulation and finally reaches the surface. The thickness of this layer increases while the roughness of the crystalline–amorphous interface decreases with further increase in the dose. For doses up to 5×1015 cm−2, Ge behaves like silicon and the amorphization of Ge can be described by using the critical damage energy density model. We show that the kinetics of Ge amorphization can be quantitatively predicted by assuming that amorphization occurs in regions which have received more than 5eV/atom. Yet for high doses, approximately from 5×1015 cm−2, the Ge surface undergoes a topology change and the well-known cellular structure appears. [Copyright &y& Elsevier]

Abstract: 2D arrays of Si nanocrystals embedded in the gate oxide (⩽10nm) of NVRAM-like transistors are synthesized by ultra-low-energy ion implantation (ULE-II). As we have shown previously, characteristics of trapping centers responsible for the memory performance such as type, depth location into the oxide, effective size and density could be obtained by using the two-level charge pumping (CP) technique performed versus frequency. It has also been demonstrated clearly that these trapping centers are the Si-NCs. However, in order to enhance the memory performances (i.e. charge retention and endurance to cycling), the synthesis of the Si-NCs must be carefully tuned, especially by adjusting the annealing conditions. In this paper, we demonstrate both that the Si-NCs are still responsible for the charge trapping while transistors are fabricated with strong NCs annealing conditions and that some memory performances recommended by the ITRS, more specifically the endurance criteria, are satisfied, with more than 106 erase/write cycles without degradation of the memory window. Therefore, our synthesis technique could provide high-performances non-volatile memories, ensuring the charge trapping in NCs. [Copyright &y& Elsevier]

Abstract: In this paper the capabilities of FIB systems as a tool for TEM studies of ancient pottery are explored, especially when the amount of available material is very limited and when, for instance, there is stringent demand for very accurate location of the electron-transparent area as is the case for investigation of outer surface layers, such as slips and patinas. The advantages of the two main FIB milling techniques (H-bar and Lift-out) are discussed in detail and illustrated through the study of metallic lustre decorations and a particular type of Roman Terra Sigillata coating. The H-bar technique is ideal for investigations where the features of interest are near the edges of a ceramic fragment. A significantly large area of surface decoration can be studied without any restriction on the size and the shape of fragment. On the other hand, the Lift-out technique is very powerful for extracting TEM membranes far from the edges. An added advantage of this technique is that the thickness of the foil is very uniform and that allows large tilts and makes it possible to obtain electron diffraction patterns of several zones axes from the same crystal, making crystallographic phase identification easier and precise, and identification of complex structures possible. We also show that the FIB system can be used to deposit very precise registration marks, allowing an experimenter to correlate results from TEM measurements with other complementary techniques, such as synchrotron based microdiffraction and μXANES. Combination of these complementary techniques is becoming a very powerful approach to probe the chemical and morphological microstructure of heterogeneous and complex material from the nanometre to millimetre scale. [Copyright &y& Elsevier]