Self-assembly of metal nanocrystals on ultrathin oxide for nonvolatile memory applications

Abstract

The self-assembly of metal nanocrystals including Au, Ag, and Pt on ultrathin oxide for nonvolatile memory applications are investigated. The self-assembly of nanocrystals consists of metal evaporation and selective rapid-thermal annealing (RTA). By controlling process parameters, such as the thickness of the deposited film, the post-deposition annealing temperatures, and the substrate doping concentration, metal nanocrystals with density of 2-4 ϫ 10 11 cm Ϫ2 , diameter less than 8.1 nm, and diameter deviation less than 1.7 nm can be obtained. Observation by scanning-transmission electron microscopy (STEM) and convergent-beam electron diffraction (CBED) shows that nanocrystals embedded in the oxide are nearly spherical and crystalline. Metal contamination of the Si/SiO 2 interface is negligible, as monitored by STEM, energy dispersive x-ray spectroscopy (EDX), and capacitance-voltage (C-V) measurements. The electrical characteristics of metal, nanocrystal nonvolatile memories also show advantages over semiconductor counterparts. Large memory windows shown by metal nanocrystal devices in C-V measurements demonstrate that the work functions of metal nanocrystals are related to the charge-storage capacity and retention time because of the deeper potential well in comparison with Si nanocrystals.

Recent progress in gold nanoparticle-based non-volatile memory devices

“…This is a very simple way to fabricate gold nanoparticle-based memory devices, and the device performance is reported to be good in terms of program/erase characteristics. However, metallic contamination in the gate oxide layer and/or diffusion of metallic components to the interfaces of the memory devices can occur during synthesis of metallic nanoparticles [42]. In addition, the size distribution of metallic nanoparticles is normally very high, the size control is difficult, and generally there are some undetectable nanoparticles, so the calculation of trap density is very difficult.…”

“…However, the process is compatible with conventional semiconductor device fabrication and one can achieve very high-density nanoparticle layers, thus many studies have been performed using this method. For example, Lee et al reported on the nonvolatile memory effects using self-assembled gold nanoparticles [42]. Thin tunnelling oxide layer (SiO 2 of ~3 nm) was employed and a 1.2 nm-thick gold layer was deposited by e-beam evaporation.…”

Floating nanodot gate memory fabrication with biomineralized nanodot as charge storage node

“…In addition to the exploitation of semiconductive property of Co 3 O 4 , part of Co-BND reduced to metal Co during the device processing made semiconductor Co 3 O 4 BND to the metal/semiconductor hybrid Co-BND. Since an improved charge storage capacity is reported by the utilization of metal nanoparticle in FNGM, 11 coexistence of metal Co will facilitate the charge storage ability of our device. Therefore, it can be anticipated that the utilization of metal Co/semiconductor Co 3 O 4 hybrid Co-BND will enable the gate bias controlled charge programming to the semiconductor Co-BND and large charge capacity in the metal Co. We fabricate Co-BND embedded memories, such as Co-BND MOS capacitors and MOS field effect transistors ͑MOS-FETs͒, and examine the electrical characterization of fabricated MOS memories.…”

“…1,2 The discrete charge storage elements utilized in such devices are usually isolated silicon or germanium nanocrystals fabricated by chemical vapor deposition, [1][2][3][4] low energy ion implantation, 5,6 annealing of silicon rich oxide, 7 thermal oxidation of SiGe, 8 aerosol nanocrystal formation, 9 traps in nitride film, 10 or self-assembled metal nanoparticles. 11 The performance and the success of floating nanodot gate memories strongly depend on the structural characteristics of fabricated nanodots such as size, shape, and in-plane ordering and density of them in the MOS stacked structure. Therefore, highdensity array of monodisperse and homogeneous nanodots is needed.…”

Mesoscopic phenomena in Au nanocrystal floating gate memory structure

“…1,2 Undoubtedly, metal nanocluster embedded in high-k materials could work as promising floating gate memory. Apart from this application, metal nanocrystals ͑NC͒ could also be used as well-controlled test laboratories to study the interplay between different types of order.…”