Hints & Trips

Q: How can solution quantities such as Electric Field by saved for plotting against applied bias?

A: There are two types of output files saved by ATLAS:

  • solution files contain physical quantities mapped to the simulation grid. One solution file is saved per bias point.
  • log files which traditionally have saved the terminal characteristics for all bias points.

A new feature of ATLAS 4.0 is the addition of a capability to save physical quantities at user-specified locations within the device grid to the log files. A new statement PROBE is used to specify the quantity to be saved and the location. For example to save the electron concentration rate at a location [1,0.1] the syntax is:

        PROBE NAME=my_e_conc N.CONC X=1.0 Y=0.5


The label specified by the NAME parameter is used to label the saved quantity in TonyPlot and subsequent EXTRACT statements.

For vector quantities the PROBE statement also requires a direction to be given using the DIR parameter. This is specified as an angle in degrees with the X axis as DIR=0. To find the electric field across an oxide layer the syntax is:

        PROBE X=1.2 Y=0.2 FIELD DIR=90 \ NAME=oxide_field


Figure 1 shows the resultant plot of electric field in a MOSFET gate oxide during a transient ESD pulse. This result shows the probability of oxide breakdown during the ESD stress without the need to examine many separate solution files.

Another advantage of the probe for vector quantities is that it reads the values directly from the simulator at the closest location to the specified XY coordinates. This avoids many issues of interpolation and averaging of vector quantities onto the simulation grid.

If two physical quantities are probed at the same location it is possible to plot them against each other to examine model settings. For example, impact ionization rate or mobility versus electric field. Figure 2 shows a plot of channel electron mobility in a submicron NMOS transistor versus the transverse electric field from the gate.

All of the primary solution quantities can be probed. A full list is given in the manual under the PROBE statement. In addition to values at point locations the PROBE statement also supports MIN and MAX parameters to find the minimum and maximum of a given quantity.

Figure 1. Electric field in MOS gate oxide during
a high current pulse on the drain.

 

Figure 2. Mobility (normalized) rolls off as
a high gate electric field is applied

 

 

Figure 3. Using a PROBE of electron concentration
allows a study of MOS width effect using 2D simulation.
An enhanced electron concentration is seen along slice 2.