MarcoBombenTCADTechniques

Coupled Defect Level

Coupled Defect Level Recombination Model

This model is a modification of the SRH model to the situation where there is charge transfer between two defect levels. This can lead to large excess currents in devices. The model has explained some anomalous diode characteristics 228. Figure 3-5 shows the assumptions about the trap levels.

• Figure 3-5: Trap Level Assumptions:
  

If there is no coupling between the two defect levels, then the recombination total recombination rate is just the sum of two SRH terms, R1 + R2, where

where the denominators are:

[snip]

To enable the model, use either the CDL parameter or the CONCDL parameter on the MODELSstatement. If you set CDL, then the values used for the lifetimes are those set by CDL.TN1, CDL.TN2, CDL.TP1 and CDL.TP2. If you set CONCDL, then the lifetimes used are doping dependent and are derived from Equations 3-303 and 3-304 with the lifetimes being CDL.TN1, CDL.TN2, CDL.TP1 and CDL.TP2, instead of TAUN0 and TAUP0. The default values for the other parameters are shown in Table 3-65.

SRH and CDL are mutually exclusive parameters. If you enable CDL, the CDL recombination rate is output to a structure file in the SRH slot and are added to the output of total recombination rate.

Restarting from a previous bias point

Re-initializing ATLAS at a Given Bias Point (page 93 of ATLAS manual)

Each SOLVE statement will begin with the device biased at the previous value solved. To begin a solution at a previously solved bias point, re-load the structure file saved at that point. This is accomplished in the following manner:

LOAD INFILE=<filename> MASTER

Information about that solution point will be displayed in the Output Window. This command is useful for solving a set of I/V curves. For example, to solve a family of Id / Vd (at various Vg), ramp the gate with zero drain bias. A structure file is then saved at each desired value of Vg. These structure files can be reloaded in turn while a Vd sweep is performed.

Note: An ATLAS input file cannot start with a LOAD statement. Before loading the structure file, use the MESH statement to load the device mesh for the same structure. Also, the same

• MODELS,
• MATERIAL, and
• CONTACT settings are required when the files are saved by ATLAS.

WORKING EXAMPLE

CurveTrace

2.9.5 Advanced Solution Techniques

Obtaining Solutions Around The Breakdown Voltage

Obtaining solutions around the breakdown voltage can be difficult using the standard ATLAS approach. It requires special care when choosing voltage steps and interpreting the results. The curve tracer described in “The Curvetrace Capability” on page 85 is the most effective method in many cases.

The Curvetrace Capability (page 85 of ATLAS manual)

The automatic curve tracing algorithm can be invoked to enable ATLAS to trace out complex IV curves. The algorithm can automatically switch from voltage to current boundary conditions and vice versa. You can use a single SOLVE statement to trace out complex IV curves, such as breakdown curves and CMOS latch-up including the snapback region and second breakdown. The algorithm is based upon a dynamic load line approach.

For example, typical CURVETRACE and SOLVE statements to trace out an IV curve for the breakdown of a diode would look like:

CURVETRACE CONTR.NAME=cathode STEP.INIT=0.5 NEXTST.RATIO=1.2 \
MINCUR=1e-12 END.VAL=1e-3 CURR.CONT
SOLVE CURVETRACE

• CONTR.NAME specifies the name of the electrode, which is to be ramped.
• STEP.INIT specifies the initial voltage step.
• NEXTST.RATIO specifies the factor used to increase the voltage step in areas on the IV curve away from turning points.
• MINCUR sets a small current value above that activates the dynamic load line algorithm. Below the MINCUR level, using the STEP.INIT and NEXTST.RATIO determines the next solution bias.
• END.VAL stops the tracing if the voltage or current of the ramped electrode equals or exceeds END.VAL.

Note: To set a sweep of increasingly negative voltage in CURVETRACE, you only need to set STEP.INIT to be negative. Since all parameters are multiplier of STEP.INIT, the whole voltage sweep will be negative.

When you plot the log file created by the CURVETRACE statement in TONYPLOT, select the internal bias labeled int.bias for the ramped electrode instead of plotting the applied bias, which is labeled Voltage.

IMPURITY REFINE

MANDATORY TO USE IT: otherwise errors will appear when using mesh in ATLAS.

Reading MASTER format file struct.str from DEVEDIT.
 Read 82618 nodes.
 Read 163980 triangles.
 Read 10 regions.
 Read 7 electrodes.
 74762123 net bytes allocated during read.


Warning: In line #   1
Too many boundary conditions added. Maximum =****

and then an error:

Error: Error in mesh definition.
Insufficent number of grid points.

ATLAS version 5.16.3.R finished at Thu Aug 25 16:44:02 2011
0.78user 0.08system 0:02.90elapsed 30%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+22907minor)pagefaults 0swaps
0.787u 0.089s 0:02.90 29.6%     0+0k 0+0io 0pf+0w

devedit 2.8.7.R (Fri Apr  4 17:46:09 PDT 2008)
Version:  atlas 5.16.3.R (Thu Apr 22 13:33:30 PDT 2010)

• USAGE:

IMPURITY.REFINE IMPURITY=<C> [ID=<N>] SENSITIVITY=<N> \
[scale=<C>] [transition=<N>]

• Below transition nothing is done
• If an impurity’s value changes more than sensitivity, smaller triangles are created.
• If an impurity’s scale is logarithmic, sensitivity is in powers of ten.
• For donor and acceptors: transition=1e10, scale=log, sensitivity=8.0

Refractive Index (Complex)

Absorption

IMAG.INDEX

Specifies the imaginary portion of the refractive index of the semiconductor (see Equation 10-12). Wavelength dependent defaults exist for certain materials as documented in Appendix B “Material Systems”.

[...]

• is the wavelength.
• c is the speed of light.
• is the absorption coefficient given by Equation 10-12:

where k is the imaginary part of the optical index of refraction.

Reflection

Material real and imaginary refractive index

Temperature

/Users/bomben/work/Silvaco/lpnsilvaco/simulations/boris/iv_temp_t300_Eg1.08.txt

/Users/bomben/work/Silvaco/lpnsilvaco/simulations/boris/110701/diode_tempeg1.12/t293.15/true_diode.in

/Users/bomben/work/Silvaco/lpnsilvaco/simulations/boris/110701/diode_tempeg1.12/t300/true_diode.in

  MATERIAL region=2 TAUP0=4.0e-5 TAUN0=4.0e-5 EG300=1.12  

• IV at different temperature, reweighted:
  

Extract

extract init inf="ninp_fluence=4e+15_bias=1700-1400.str"
extract name="max_pot" max.conc.file impurity="potential" x.step = 0.1 \
 material = "silicon" outfile="potential.out" x.min=-25 x.max=25
extract name="max_field" max.conc.file impurity="e field" x.step = 0.1 \
 material = "silicon" outfile="efield.out" x.min=-25 x.max=25
extract name="max field position" 2d.max.conc impurity="e field" \
  material = "silicon" datafile="max_efield_point.out"
  extract x.pos
  extract y.pos
extract name="max field position" 2d.max.conc impurity="potential" \
  material = "silicon" datafile="max_potential_point.out"
  extract x.pos
  extract y.pos
extract name="max conc position" 2d.max.conc  \
  material = "silicon" datafile="max_conc_point.out"
  extract x.pos
  extract y.pos
extract name="max P position" 2d.max.conc impurity="Phosphorus" \
  material = "silicon" datafile="max_P_point.out"
  extract x.pos
  extract y.pos

Models

TRAP.TUNNEL

• Trap-Assisted Tunneling models the trap-to-band phonon-assisted tunneling effects for Dirac wells. At high electric fields, tunneling of electrons from the valence band to the conduction band through trap or defect states can have an important effect on the current.
• It increases the slope for the bulk current

-- MarcoBomben - 07-Oct-2011