• TCAD Examples

sonosex01.in : Nitride charging dependence on capture cross-section

Requires: S-Pisces
Minimum Versions: Atlas 5.28.1.R

The example shows :

  • How to create a simple SONOS structure.
  • How to activate and specify the parameters for the DYNASONOS model.
  • How to charge a SONOS structure.
  • How to specify and interpret the SONOS logfile output.

Typical Atlas meshing commands are used to set up a MOSFET-like structure. The main difference is the presence of a layer of Silicon Nitride in the gate stack. The insulating layer between the Nitride and the channel is termed the tunnel oxide, and the insulating layer between the Nitride and the contacts is called the blocking layer. The Atlas SONOS model is invoked using the INTERFACE N.I DYNASONOS statement. The value of DYNASONOS flag is enabed by default, and so it is not necessary to specify this explicitly.

To use the DYNASONOS model, the insulators in the gate stack must be changed to (wide-gap) semiconductors and given values for density of states, mobility and effective mass. The effective mass values strongly affect the tunneling current through the gate stack.

Additionally, one must use the NITRIDECHARGE statement to set up the parameters of the nitride traps. The density of traps can be set with the parameters NT.N (acceptor-like traps) and NT.P (donor-like traps). In this deck we want to trap electrons and so specify a non-zero value for NT.N. The parameter SIGMAT.N gives the cross-section for trapping the electrons in the Nitride conduction band and is set to 4 different values within this deck.

The parameter ELEC.DEPTH specifies the energy depth of the electron trap below the conduction band. The parameter TAU.N gives the characteristic timescale for emission from the trap level to the conduction band.

The parameter SIGMAN.P controls hole capture from the valence band and is set to zero with loss of generality.

The Nitride traps are charged up by ramping the bias to 16 V over 1 nanosecond and then maintaining this for 1 millisecond.

The stored charge as a function of time (nettcharge) is plotted for the four different values of SIGMAT.N. The larger the cross-section then the more charge is stored. The stored charge should be the integrated difference between the current entering the Nitride region from the channel and that leaving to the gate contact. This can also be seen in the other plots, and by using the TonyPlot integrate tool you can obtain an estimate of the nett stored charge to compare (within truncation errors) with nett charge.

As the trapping cross-section increases, less charge arrives at the interface with the blocking insulator and the out current decreases and is delayed, as can be seen in the plots of in and out current at the different values of capture cross-section. In all cases a steady state is obtained where in and out current are matched and the nett charge is constant.

The structure files of the charged device are plotted, the user can use the TonyPlot cutline tool to view the Trapped Insulator Charge, Electron Charging Rate and other relevant parameters

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

Additional Info:

Input Files
Output Results
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