Inter Device Leakage from Total Dose XRay Photonic Exposure

radex10.in : Inter Device Leakage from Total Dose XRay Photonic Exposure

Requires: VictoryProcess/VictoryDevice/REM
Minimum Versions: VictoryProcess 6.14.10.R, VictoryDevice 1.6.3.R

This examples demonstrates Inter Device Leakage from XRay Total Dose Exposure

For older technologies, one of the main effects of Total Dose Irradiation was the accumulation of positive charge in the gate oxide, resulting in threshold voltage shifts that either reduced current drive or increased off state leakage, depending on whether the device was a p- or n-MOS device respectively. For more agressive technologies, the gate oxides are so thin, that the major effect of Total Dose Irradiation is the trapping of positive charge in the trench isolation oxides, creating a parasitic current leakage path between trench isolated devices. The leakage path could be between the Source/Drain contacts of two seperate nMOS devices, or could be between the Source/Drain contact of an nMOS device and the n-Well isolation of a p-MOS device. In this example, we demonstrate the creation of a current leakage path between two nMOS devices. Leakage betwen an nMOS and pMOS n-Well is essentially the same phenomenon.

VictoryProcess is used to create the two nMOS devices, seperated and electrically isolated by a trench and p-well with associated trench implants.

There are several basic input file set up requirements for simulating total dose effects in VictoryDevice:

  • the effected insulators must be simulated as wide bandgap semiconductors
  • any doping in the insulator therefore needs to be removed
  • insulator trap densities, characteristics and locations need to be defined
  • the radiation source and dose rate needs to be defined
  • the parameter "radiation" needs to be invoked on the solve statement

To convert an insulator to a wide bandgap semiconductor, the material statement is used. For example:
material material=oxide semiconductor

To remove any existing doping from the insulator, which would cause erroneous conduction, the "doping replace" syntax is used. For example:
doping material=oxide replace uniform net concentration=-1

Two types of insulator traps can be defined, bulk insulator traps, using the oxidecharging statement and interface insulator traps, using the intoxidecharging statement in a direct analagy to defect and intdefect statements. Two model implementations are also available, the "Jmodel" and the "Vmodel". The user is directed to the manual to gain a full understanding of the meaning of all the parameters in these statements and the model implementation, as a full description is too lengthy for this brief example description.

The radiation source and dose rate are defined in the radiation statement. Here a 10keV XRay source and a dose rate of 1 Rad per second is defined, using the radiation statement: radiation doserate=1 XRay

The convenience of defining a dose rate of 1 Rad per second is that the total dose will be the same as the elapsed transient time in the solve statement, if the parameter "radiation" was invoked in the transient from the start.

The simulation shows how the leakage between the two trench isolated nMOS devices, increases after a total dose of 3 MRads.

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.