Charging a SONOS device using the Lucky Electron model

sonosex06.in : Charging a SONOS device using the Lucky Electron model

Requires: S-Pisces
Minimum Versions: Atlas 5.22.1.R

The example shows:

  • How to charge the device using lucky electron gate current
  • How to obtain the threshold voltage for different charging times

The device structure is set up to be the same as in sonosex05. The difference is that the gate stack materials are changed to semiconductors and the necessary parameters are set. This example uses lucky electron gate current and the values of effective mass in the tunnelling insulator do not affect the simulation (they may if set to be unphysically small).

The NITRIDECHARGE statement is used to specify electron traps at a uniform density of 5x10^19 /cm^3, and sets up various parameters for the capture cross-section and emission rates. The emission rates are in fact overridden because on the MODELS statement the PF.NITRIDE flag is specified. With this choice, the emission rates are calculated using the Poole-Frenkel formula (see the DYNASONOS section in the manual). The HEI flag is also used to select a hot carrier gate current calculation using the lucky electron approximation along with the drift-diffusion simulation.

The gate bias is set to 8V and the drain is ramped to half of this. At the channel/insulator interface, the hot electron current is calculated and the electric field lines are used to determine where the current arrives at the interface between the Silicon Nitride and the surrounding insulator. The Nitride is then charged at its interface according to the amount of hot carrier current arriving there.

The structure file is saved to file at certain preset simulation times. The SONOS.RATES flag was set on the OUTPUT statement and so you can see the location of the Nitride charging at each output time. Only a subset of structure files are output by the example, but you can also view the other ones if desired.

The next part of the deck uses dbinternal to obtain the threshold Voltage for each of the saved structure files. It does this in the file sonos06_aux.in. The advantage of using dbinternal is that the data file containing the threshold values can be plotted using TonyPlot. These threshold voltages are plotted against charging time. The logfiles Idrain versus Vgate are also saved to file and can be viewed in TonyPlot.

To load and run this example, select the Load example button in DeckBuild. This will copy the input file and any support files to your current working directory. Select the run button to execute the example.