Semianalytical model of tunneling in nanocrystal-based memories

Abstract

The purpose of this paper is to study single electron charging of a floating gate composed of nanocrystals in a metal-oxide-semiconductor transistor. We present a three-dimensional model of electron tunneling into quantum islands that are spherical in shape. This model can be numerically solved through a two-dimensional finite element approach. In this way, extensive and accurate numerical experimentations can be carried out due to the reduced computer time cost. The curves of tunneling time versus bias voltage exhibit complex serrated shapes, related to both the energy subbands of the channel and the energy states of the nanocrystal. The results are discussed for different channel doping densities.

Transient charging current measurements and modelling in silicon nanocrystal floating gate devices

“…This hypothesis was evoked for the first time only a few years ago [11] although it is very common to measure and model this kind displacement currents in usual Flash memories [26,27]. This interpretation of the peaks in I G -V G curves was then used in other studies on nanocrystals based memories [24,28], and this behaviour was also theoretically modelled [28,29]. In this paper, we present a model which enables one to extract some structural parameters of the dot planes directly from the experimental data.…”

Low-voltage onset of electroluminescence in nanocrystalline-Si/SiO2 multilayers

“…The tunneling times were calculated within the WentzelKramers-Brillouin approximation. However, tunneling time dependence on bias voltage has a more complex serrated shape, 25 and so this argument should be taken with some precaution.…”

“…4,23,24 For example, single electron injection current into a spherical nanocrystal having a diameter of 5 nm with a 1.5 nm tunneling oxide could be a few femtoamperes at the applied voltage of about 3 V. 25 Multiplying this value by a typical density of the nc-Si in the ML structure, which is of the order of 10 12 cm −2 , and by the area of our device, the injection current amounts to a few microamperes, which well compares with the measured tunneling currents in Fig. 2.…”

Modeling of Single Electron Charging in Nanocrystal Memories

“…The dielectric permittivity and the effective mass for the where X;: and em are known analytically [23]. electron correspond to the bulk values of each material considered, since no better value for dimensions in the Equation (2) thus becomes: nanometer scale is available.…”