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Impact of time and space evolution of ion tracks in nonvolatile memory cells approaching nanoscale
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Image of FIG. 1.
FIG. 1.

Spatial distribution of ionization in carbon, taken from Ref. 32. The energy deposited at radius t, in erg per gram, by an ion of atomic number Z moving at speed is: where and are derived from the left and right graphs of this figure, and z is the effective charge obtained from (1). See Ref. 32 for further details.

Image of FIG. 2.
FIG. 2.

Schematic diagram of an industry-standard flash memory cell. Left: vertical section along the MOSFET width; top left: section along line; bottom right: view from top.

Image of FIG. 3.
FIG. 3.

distributions for a T1 device before and after irradiation with iodine ions per centimeter square.

Image of FIG. 4.
FIG. 4.

Average charge loss for T2 devices irradiated at SIRAD as a function of ion LET (right) and electric field across the tunnel oxide (left).

Image of FIG. 5.
FIG. 5.

Probability density function for a T2 device before and after irradiation with iodine ions per centimeter square. In the after irradiation characteristics, only FGs in the secondary peak are those directly hit by ions.

Image of FIG. 6.
FIG. 6.

Elaboration of the statistical model for a T2 device irradiated with iodine. Crosses are the experimental data, whereas lines are either fittings or calculations. (a) Experimental pdf of the charge loss from FG, , fitted with a Gaussian. (b) Experimental pdf for after irradiation.

Image of FIG. 7.
FIG. 7.

Probability distribution of the threshold voltage shift, , for grazed FGs in T2 devices irradiated with different ions.

Image of FIG. 8.
FIG. 8.

First principle sketch of the two mechanisms involved. Left: quick discharge due to the ion tracks which act like a conductive pipe. Right: slow discharge due to a path of defects left by the ion (RILC).

Image of FIG. 9.
FIG. 9.

Cumulative probability plots for a T2 device irradiated with iodine and reprogrammed.

Image of FIG. 10.
FIG. 10.

Retention experiments on T2 devices irradiated with iodine ions and re-programmed FGs were divided into two populations (hit and grazed): only the hit FGs exhibit RILC.

Image of FIG. 11.
FIG. 11.

Probability densities of the excess FG charge, , for a T2 device programmed with a physical checkerboard pattern and irradiated with 316 MeV Kr. We recall that in the “0” state there are excess electrons in the FG (net negative charge, with our definition), while in the “1” state there are excess holes (net positive charge, ).

Image of FIG. 12.
FIG. 12.

distributions for different devices irradiated at tilted angles at the same fluence of .

Image of FIG. 13.
FIG. 13.

Maps of the distribution of “hit” (black) and “grazed” (white) FGs above small chip areas, for devices irradiated with 1217 MeV Xe at different angles. Non hit FGs are shown as gray squares. Each square represent a single FG.

Image of FIG. 14.
FIG. 14.

First principle sketch of the timings determining hit and grazed FGs: right after strike (left) and after a short while (right) the different densities of track and the different mechanisms mediating energy exchange result in two population of FGs (hit, grazed).

Image of FIG. 15.
FIG. 15.

Distribution of the length of traces for device irradiated at different angles with Kr and Xe ions.

Image of FIG. 16.
FIG. 16.

First principle sketch of the impact of the ratio between trace diameter and tunnel oxide thickness on the discharge current at tilted angles. When (left) discharge current decreases because path length increases, which is not true when (right).

Image of FIG. 17.
FIG. 17.

Probability densities of for two T2 devices irradiated with ions of similar surface LET but different energies.

Image of FIG. 18.
FIG. 18.

Geometrical description of the formation of traces as a function on impinging angle.

Image of FIG. 19.
FIG. 19.

Average outside track diameter (“lines” of adjacent FGs showing charge loss), for T2 devices irradiated with Xe and with Kr. Error bars correspond to the spread of traces diameter, as obtained on different devices.

Image of FIG. 20.
FIG. 20.

Histogram of deposited energy in 10 nm (that is, in the tunnel oxide of used devices) by 2.25 MeV/amu iodine ions. 18 178 events were considered to compute the statistics.

Image of FIG. 21.
FIG. 21.

Spatial distribution of energy deposition for the two ions used in Fig. 17.

Image of FIG. 22.
FIG. 22.

Straggling of deposited energy in a 10 nm layer from 266 MeV Ag ions and 1217 MeV Xe ions: (a) in an infinite layer, 10 nm thick; and (b) in a layer 10 nm thick and having the FG dimension.

Image of FIG. 23.
FIG. 23.

Track pair densities generated at different time-intervals for 1217 MeV Xe ions. The large drop in the density is shown to overlap with the experimental range of the inner track diameter (responsible for hit FGs). The oscillations in the densities are apparently due to the use of small bins in the temporal discretization of the deposition events.

Image of FIG. 24.
FIG. 24.

Track densities at , where t is the time after ion hit, compared with the range of size for the outer track diameter (responsible for grazed FGs).


Generic image for table
Table I.

Main characteristics of used ion beams (calculated with SRIM).

Generic image for table
Table II.

Main characteristics of used devices.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Impact of time and space evolution of ion tracks in nonvolatile memory cells approaching nanoscale