NBIS(Negative Bias Illumination Stress)

tftex18.in : NBIS(Negative Bias Illumination Stress)

Requires: Vicitorydevice

Minimum Versions: Victorydevice 1.12.1.R

In this example, we demonstrate the Negative Bias Illumination Stress simulation due to ionization of oxygen vacancy and interstitial oxygen. In Victorydevice, we simulate the electrochemical reaction formula for explaining the negative threshold voltage shift by ionization process.

The oxygen vacancy ionization is described in chemical ion reaction formula as "Vo2+ + 2e- <-> Vo". Here Vo is neutral oxygen vacancy. The interstitial oxygen ionization is Io + 2e- <=> Io2-. Here Io is neutral oxygen and Io2- is double negative charged trap state.

Victorydevice Ion Reaction and Transport Simulation

First step is to define each ion's charge state.
species formula="In:Ga:Zn:O" charge=+2 name="Vo2+"
species formula="In:Ga:Zn:O" charge=0 name="Vo"
species formula="In:Ga:Zn:O" charge=-2 name="Io2-"
species formula="In:Ga:Zn:O" charge=0 name="Io"

Next step is to define the initial ionization concentration before reaction in IGZO region.

doping reg=4 species.name="Vo" uniform conc=1.3e17
doping reg=4 species.name="Io2-" uniform conc=9.5e16
# initial vo2+/Io should be the same as ngd doping reg=4 species.name="Vo2+" uniform conc=2e16
#acceptor-like trap doping reg=4 species.name="Io" uniform conc=2e5

For drift-diffusion simulation of hydrogen atom during applied bias and temperature, we need to define the diffusion coefficient. Other ion species is immobile. The ion's diffusion coefficient is defined in material statement.
# diffusivity material material=IGZO species.name="Vo" species.ea=2.36 species.af=1e7 species.hop=1e-6 material material=IGZO species.name="Vo2+" species.ea=1.7 species.af=1e7 species.hop=1e-6 material material=IGZO species.name="Io" species.ea=1.14 species.af=1e5 species.hop=1e-6 material material=IGZO species.name="Io2-" species.ea=1.14 species.af=1e5 species.hop=1e-6

Finally, we define the chemical reaction formula using "reaction" command.
# Vo => Vo2+ + 2e- reaction formula="Vo2+ + 2e- <=> Vo" forward.ea=1.0 forward.rate=1e7/1e19 \ reverse.ea=0.7 reverse.rate=5e18*1e7/1e18
# Io neutral acceptor-like trap reaction formula="Io + 2e- <=> Io2-" reverse.ea=0.0 reverse.rate=5e18*1e5/1e18 \ forward.ea=0.83 forward.rate=1e-15

The simulation starts to get the intial threshold voltage. Then, NBIS simulaton proceeds with stress voltage of "Vgs=-20V + intial threhold voltage" to maintain the constant stress voltage. During stress time simulation, the time evolution of each ion's concentration is plotted to see the change of ion concentration. It is plotted on tftex18_1.log. After obtaining stress solution, it is saved to different structure file to get the final threshold voltage shift at each time. It is plotted on tftex18_2.log for each stress time at 0 sec(initial), 2000 sec and 10,000 sec.

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.