• TCAD Examples

diodeex11.in : Effect of ionic species on small signal capacitance of MOS-C

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

This example shows how to include ionic species in the insulator of a MOS-C capacitor. The mobile species affect the small signal conductance and capacitance of the device as a function of bias and frequency. The deck builds a basic MOS-C structure using Atlas commands. Then an ionic species is added using the DOPING statement.
doping region=1 species1 gaussian conc=1e16 char=0.06 lat.char=0.15 peak=0.125
with the SPECIES1 parameter. Another species is initialised using the same syntax, and both species have an initial gaussian distribution. The PROBE statement is used to set up an integration of the species over the device. The generic ion transport model is selected on the MODELS statement
models srh nspecies=2 species1.z=2 species2.z=-1
where NSPECIES=2 indicates there are two species, and SPECIES1.Z=2 indicates that the first has a double positive charge and SPECIES2.Z=-1 indicates that the second has a single negative charge. The METHOD statement
method species.maxx=1.0e6 species.ins
restricts the species to the insulator and sets the maximum permissible update vector to be a ratio of 1.0e6.

The anode is biased to 1.0 V and the anode voltage is ramped to -2.0 V with the small signal parameters calculated at 100 Hz. This is then repeated with the small signal frequency being 1 GHz. These curves are compared to the MOS-C without ions in the insulator. In the latter case the Capacitance varies only slightly with the channel charge. With ionic species present, and at 100 Hz, the movement of ionic charge by the test signal gives a large capacitance. At an anode voltage of 1 V the negative ions are near the anode and the positive ions are near the semiconductor/insulator interface. As the anode bias changes to -2 V, this situation reverses and when the centre of charge is near the centre of the insulator the small signal capacitance is a maximum. With a test signal of 1 GHz the ionic species are not sufficently mobile to react and so the small signal capacitance is much reduced. The species density profiles are shown in the cutline of the plot of the structure file at 1.o and -2.0 V anode bias. The PROBE statements can optionally be selected in the first plot and show that the integrated density of each species is constant (because there are no reactions and the species are confined to the insulator). They also show the species concentration at the center of the insulating layer as a function of bias.

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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