Two-Silicon-Nanocrystal Layer Memory Structure with Improved Retention Characteristics

Abstract

It was demonstrated in the literature that the use of self-aligned doubly-stacked Si dots improves retention characteristics of a nanocrystal memory. In this paper, we show that a similar effect may be obtained by using two distinct layers of silicon nanocrystals within the gate dielectric of the MOS structure, if the nanocrystal density in each layer is high enough (above 1012 dots/cm2) so as to get an average effect of at least one smaller dot underneath each larger one. The relative distance of the layers and their position from the silicon substrate and the gate metal are critical for optimum memory operation. Two different double-nanocrystal-layer structures were investigated. In the first structure the two nanocrystal layers were close together and they were composed of dots of different size (lower layer: 3 nm, upper layer: 5 nm), while in the second structure the dot layers were composed of dots of equal diameter (d = 3 nm) and their inter-distance was much larger. In both cases, the retention characteristics of the structure were improved compared with a single dot layer structure. In the second case this improvement was significantly larger than in the first case. Extrapolation of the data to ten years memory operation, showed that the charge loss after this time was only ≈ 12%.

Temperature-dependent electron transport in highly ordered Co/Al2O3 core-shell nanocrystal memory synthesized with di-block co-polymers

“…[2][3][4] Nonvolatile memory with discrete-trap type storage nodes, particularly nanocrystal (NC) trap storage nodes, has attracted much attention as a promising candidate for future low power electronics. [5][6][7][8][9] New types of NC floating dots, such as double Si dots, 10 Ge nanocrystals, 11 metal 12 or metal-like 13 dots, and dielectric NCs (Al 2 O 3 , HfO 2 , Si 4 N 3 , etc. ), [14][15][16] have been proposed to achieve memory devices with long retention performance.…”

Memory characteristics of ordered Co/Al2O3 core-shell nanocrystal arrays assembled by diblock copolymer process

“…2 Due to excellent memory performance and high scalability, nanocrystal ͑NC͒ floating gate memory devices have attracted considerable attention. 3 Different types of NCs such as double Si dots, 4 Ge NCs, 5 metal NCs, [6][7][8] silicide NCs, [9][10][11][12] and dielectric NCs ͑Ref. 13͒ have been proposed to achieve memory devices with longer retention performance.…”

Determination of critical points on silicon nanofilms: surface and quantum confinement effects

“…Especially, this multiple excitons generation in nanocrystalline Si at lower photon energies in the visible region has the potential to increase the power conversion efficiency in Si-based photovoltaic cells towards a thermodynamic limit of 44% at standard AM1.5 solar intensity. Furthermore, Si-NCs of sizes 3-6 nm embedded in SiO 2 have been used to fabricate non-volatile memory devices [3] with considerable advantages. However, in spite of this breakthrough effort towards the use of Si-NCs in photovoltaics and memory applications, very few fundamental properties of the band structure of material are well known.…”