6T SRAM SEU Simulation using MixedMode3D

radex15.in : 6T SRAM SEU Simulation using MixedMode3D

Requires: VictoryProcess2D / DevEdit 3D / VictoryDevice3D / MixedMode3D
Minimum Versions: VictoryProcess 7.6.6.R / Devedit 2.8.23.R / VictoryDevice 1.8.2.R

This example is a variant of radex14, where instead of using pure Spice to simulate an SEU strike on a 65nm SRAM cell, the SEU simulation section uses MixedMode3D instead.

The Mixedmode3D simulation uses the same 65nm nMOS TACD structure that was calibrated against a PDK Spice model in radex14, and wraps the rest of the SRAM circuit around this TCAD structure using Mixedmode3D's Spice syntax. The TCAD structure is struck with a 1 LET single event when it is in it's low power configuration with an applied supply voltage of 0.85 volts, which represents the state of highest sensitivity to being upset by a single event.

The data flow in this particular example occurs in the following sequence:

  • The calibrated 65nm nMOS TCAD structure is the same one used in the previous radex14 example
  • The 65nm nMOS TCAD only structure is biased into it's high sensitivity, low power off state, with Vd=0.85 Volts and Vs,Vg=0 Volts. This TCAD only structure, in this biased state, is then saved.
  • A new device simulation, this time in MixedMode3D, which contains the rest of the SRAM circuit, is then specified, and the previously saved biased TCAD structure is loaded, and it's biased condition initializes the circuit state. The line which loads the TCAD structure intial state is: .OPTIONS loadsolutions
  • After the MixedMode3D simulation is complete, the solutions are plotted at the end.

The energy of the Single Event Strike is characterized by a parameter called the "Linear Energy Transfer", or LET. The higher the LET, the greater the energy of the incoming particle or photon. In this example, the LET value of the incoming strike is set up as a variable, by the line "set LET=1", which creates a variable called "$LET" and assigns it a unity value. In order to convert the units of LET into units of pico Coulombs/cm3 of track charge density, the LET value needs to be multiplied by 0.01035 for silicon material. A second variable called "$density" is assigned this converted pico coulomb value. Lastly, the units of the strike are specified to be these same pico coulomb units, by the parameter "pcunits" in the "singleeventupset" statement that describes the time and track positional properties of the strike.

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.