Usage: tracer inputfile tracefile [outputfile]
The trace specification file, tracefile, is similar to a PISCES or SUPREM input deck. Each line begins with a word designating what type of statement, or "card", it is. The four possibilities are CONTROL, FIXED, OPTION, and SOLVE. Also, a line may start with a "$" for comments. Such lines are ignored. The cards may appear in any order, and a card may be continued on following lines by placing a "+" at the beginning of each subsequent line. The "+" should be separated from the parameters on the line by at least one space.
Each option in a card should have the following structure: "param = paramvalue". Spaces separating the "=" sign are optional. The parameters for each card are described in the fol- lowing four sections. As with PISCES syntax, parameter names and values are not case- sensitive and may be abbreviated provided they remain unambiguous. Square brackets, [], enclosing a parameter indicate that it is optional (note that some of these parameters are only optional in the sense that they will default to a certain value if not specified in tracefile). A vertical line, |, represents a logical OR--only one of a list of parameters separated by "|" signs can be specified.
All electrodes in the device must have representation in the tracefile. Each electrode must appear as one, and only one, of the following: the CONTROL electrode, a FIXED electrode, or an open contact (OPENCONT1 or OPENCONT2) on the SOLVE card.
control num=3 begin = 0.0 initstep=-0.1 control=IMAX end=-3.0
control num=4 begin=0.0 initstep=0.5 control=step steps = 65
A FIXED card is used to designate an electrode whose bias remains fixed throughout the simulation. There should always be at least one FIXED electrode and usually there are two or more. The two types of bias conditions available are voltage sources and current sources. The value of the bias is arbitrary, with one exception: a zero-current source (open contact) should be specified through the open-contact option on the SOLVE card and not on the FIXED card. If non-zero current sources are used for some electrodes in a simula- tion, in inputfile the user must create contact cards with the "current" option for each of these electrodes (see Section A.7).
fixed num=1 type = voltage value=0.0 record =yes
An option card is used to specify convergence criteria and solution-method options for any open electrodes, parameters which affect the smoothness and step-size control of the trace, which PISCES solution files are saved, and whether extra solution data is saved in outputfile.
Simulations with one or two open contacts:
[ABSMAX=
Smoothness and step-size control:
[ANGLE1=
Control of output files:
[FREQUENCY=
option mincur=1e-14 itlim=12 verbose=no frequency=10 turningpoints=yes
option absmax=1e-16 relmax=1e-25
If the loaded solution is from a simulation using a zero-current bias condition, FIRST- SOLUTION=CURRLOAD should be used. In this case "current" should be specified on a contact card for each open electrode. As in the FIRSTSOLUTION=LOAD case, the existing inputfile load card is used by Tracer, which means the correct "infile" should be specified on a load card directly above the solve card in inputfile. Default: none.
solve opencont1=2 firstsolution=init simulator=pisc
solve firstsolution=load simulator=pisc opencont1=2 opencont2=4 + vopen1=0.641 vopen2=0.509
The input deck used by Tracer, inputfile, is a standard PISCES file, but Tracer has certain requirements. For understanding the basic flow of an input deck, consult the PISCES or TMA-MEDICI manual. The mesh, region, electrode, doping, and model cards must already be present in the input deck. Additionally, the Newton solution method must be specified in the symbolic card. Other requirements are described below.
Even if no contact cards are required in inputfile, a line starting with "$contact" must be present so that Tracer will know where to add a contact statement. This contact card is necessary because this is where the load resistance of the control electrode is specified by Tracer. There is no problem with placing a contact card for the control electrode in the input deck as long as it does not specify a resistance value (which should never happen). Note that at least the first five letters of "contact" must appear for Tracer (and PISCES) to recognize it.
Another option must be specified in the method card if TMA-MEDICI is used. In this simulator, if a solution is aborted MEDICI will try to solve for an intermediate solution and then retry the original solution. This is not desirable when using Tracer since Tracer needs to keep track of aborted solutions. Thus, "stack=0" should be specified in the method card of MEDICI so that it does not attempt intermediate solutions. Analogously, the "trap" option should not be specified on the method card in a PISCES-IIET deck.
Values in the next columns depend on which data are recorded. If requested in the FIXED statements of tracefile, current values of fixed-voltage electrodes and voltage values of fixed-current electrodes will be recorded for each solution point in outputfile. The order from left to right is from low to high electrode number.
After the electrode information is recorded, further columns contain information about each solution if VERBOSE=YES in the SOLVE card of tracefile. These columns are, from left to right, external control-electrode voltage, load resistance on the control electrode, differential resistance, normalized distance of the next projection, and the angle difference between the current and previous solution points (see [28] for a description of these parameters).
The FREQUENCY and TURNINGPOINTS parameters in the OPTION card allow data to be saved for certain specified solutions. In outputfile, those points which are saved are marked with an asterisk next to the solution number. The files saved are the input deck, input.i; the I-V data file, iv.i; and the solution file, soln.i; where i is the number of the solu- tion in outputfile.
In the trace file bvceo.tra (Fig. A.32), the FIXED card sets the voltage on the emitter electrode (num=1, as defined by bvceo.pis) to a constant value of 0.0V and states that the cur- rent through this electrode will not be recorded in outputfile. Electrode 3, the collector electrode, is designated as the control electrode. The CONTROL card states that the first solution will have a collector voltage of 0.0V, while the second solution will have a collector voltage of 0.1V. Tracing will continue until the collector voltage equals or exceeds 20V. If the initial step of 0.1V proves to be too large for convergence, Tracer will cut the step size in half, possible more than once, until it converges on a solution, and then will proceed from this solution.
In the SOLVE card, we specify that the base electrode (num=2) is to be treated as an open contact during the trace. Also, tracing will begin with a thermal-equilibrium solution and PISCES-IIET will be used for the simulation. Finally, the OPTION card specifies that only essential I-V data will be saved in the output file; the PISCES iteration limit is set to 15, agreeing with the PISCES deck in the input file; PISCES solutions will be saved for any turning points as well as for every fifth solution point; smoothness of the I-V curve will not be enforced until the collector current is greater than 5X10-12A/mm; and while voltage biasing is used on the open base contact, a solution will be accepted only if the current through the base is less than 5X10-19A/mm (unless the RELMAX condition pre- dominates).
To run Tracer, the following command is typed at the prompt:
machine-prompt% tracer bvceo.pis bvceo.tra bvceo.out
While Tracer is running, the output of the PISCES runs are sent to the standard output, along with messages announcing when solutions are written to the output file. The output file, named bvceo.out in the command line, is shown in Fig. A.33, and a plot of the collector current vs. collector voltage is shown in Fig. A.34. In bvceo.out, we see that every fifth solution, along with solutions 24 and 36 (the turning points), has been saved in files named soln.5, soln.10, etc. Additionally, the last solution was saved in the file soln.last, although there is no asterisk marking the last solution in bvceo.out.
At the top of bvceo.out, column headings mark the solution number, control-electrode (collector) voltage, control-electrode current, open-contact (base) voltage, and open-con- tact current as Soln, Vctrl, Ictrl, Vcurr, and Icurr, respectively. We see that the collector voltages for the first, second, and last solutions are 0.0, 0.1, and 20.18V, respectively. The final solution does not have a collector voltage of exactly 20V, as specified in bvceo.tra, because Tracer only guarantees that the curve will be traced out to at least 20V, not exactly 20V.
Other information regarding the trace must be inferred from the PISCES output displayed while Tracer is running (not shown). From this output we can see that voltage biasing was used on the open base contact for the first few solutions, in which the collector current is too small to allow stable use of zero-current biasing. A few PISCES simulations are actually run for each I-V point, with minor adjustments on the base voltage being made until the base current is less than ABSMAX. When the collector current is large enough, Tracer places a zero-current bias on the base. We can also see that a variable load resistor is placed on the collector when the collector current exceeds MINCUR. After this, the step sizes are regulated to produce a smooth curve.
For Tracer, another PISCES input deck must be created to use as the input file (Fig. A.37). In mesvg.5.pis the mesh file generated by mes.pis, mes.mesh, is read in, preempt- ing the mesh, eliminate, region, electrode, and doping cards. Since Tracer will be starting with a previous solution, the name of the solution file to load must be given in mesvg.5.- pis. This load statement appears directly above the solve card with the file name mes- vg.5.ini, the solution file generated by mes.pis.
The trace file mesvg.5.tra is shown in Fig. A.38. In the three FIXED cards, the voltages of the source and substrate (num=1 and num=4, respectively, as defined by mes.pis) have been fixed at 0V, while the gate voltage (num=2) has been fixed at -0.5V. The current through the gate electrode will be recorded for each solution in the output file. The CON- TROL card of mesvg.5.tra specifies that the drain (num=3) will be swept from 0.0V to a voltage where the current is greater than or equal to 4.1X10-4A/mm, with an initial drain voltage step of 0.2V. On the SOLVE card, FIRSTSOLUTION is specified as LOAD, consistent with the input file mesvg.5.pis, and PISCES-IIET is designated as the simulator to use. Since VERBOSE is NO on the OPTION card, only the essential I-V data will be recorded in the output file. The iteration limit is 30, consistent with mesvg.5.pis, and every ninth solution, as well as those corresponding to turning points, will have its solution file saved.
machine-prompt% tracer mesvg.5.pis mesvg.5.tra mesvg.5.out
Fig. A.39 shows the output file, mesvg.5.out, in which the solution number, drain voltage, drain current, and gate current have been recorded as Soln, Vctrl, Ictrl, and I2, respec- tively. The solution files of points 9, 18, 27, and 29 (a turning point), as well as of the last point (not marked in the output file) were saved as soln.9, soln.18, soln.27, soln.29, and soln.last, respectively. A plot of the drain current vs. drain voltage is shown in Fig. A.40.