1. ECSE-6230 Semiconductor Devices and Models I Lecture 3
Prof. Shayla M. Sawyer
Bldg. CII, Room 8225
Rensselaer Polytechnic Institute
Troy, NY
Tel. (518)
FAX (518)

2. MEDICI Lecture Created by Jeff Langer
Edited by Peter Losee (F’05), Kamal Varadarajan (F’07) and Vipindas Pala (F’10)

3. Overview Using ECSE servers MEDICI Tutorial
Logging in using SSH/Remote Desktop
MEDICI Tutorial
Simulator overview
MEDICI Example – Silicon pn junction diode

4. Remote Access Login remotely from your laptop Remote Desktop SSH
Login to any of :
ts1.ecse.rpi.edu
ts2.ecse.rpi.edu
ts3.ecse.rpi.edu
ts4.ecse.rpi.edu
ts5.ecse.rpi.edu
Remote Desktop
Windows XP / Older - Use remote desktop client
Windows 7 / Vista use the XP remote desktop client
SSH
From any terminal (Mac / Linux)
PUTTY for windows
From windows use an X-Window Client for to port graphics

5. Remote Access Note if logging in from off-campus, VPN in first
If there are problems logging in with ts1…try any other of the machines, ts2, ts3, ts4, ts5

6. MEDICI Introduction : What
A physics based device simulator
Output
I-V curves, capacitances, electrode charges (DC)
Gain, Capacitances, S Parameters (AC)
Light (Optical)
Solves simple circuits (CMOS Inverters etc)
Visualize internal physics (Carrier densities, carrier velocities, ionized charges, recombination/generation, …… )
Input
Device Geometry (2D)
Material properties (Doping, Mole Fractions, Mobilities …)
Originally developed in Stanford University (PISCES - Poisson and Continuity Equation Solver)
Similar tools : MEDICI, DESSIS, ISE, ATLAS, Sentaurus

7. MEDICI Introduction : Why
Modeling of device behavior
Understand mechanisms behind characteristics
Study extreme behavior like breakdown when measurement is difficult
Help understand the process corners
Because fabrication is never perfect
A typical question : How sensitive is the transistor gain to variation in doping ?
Device Optimization
Reduces the number of process spins and cost
Experiments with process are costlier and take more time
And most importantly, device design
Try your ideas without going through a fabrication process (play with geometry, materials)
A success in simulation does not guarantee a good prototype – models can capture most of physics but not all.

8. MEDICI Introduction : How
Finite element analysis
Divides the structure into a bunch of small triangular segments (grid)
Solves Poisson’s and Continuity Equations numerically for each grid point
Poisson’s equation : Electrostatics
Current into a volume – Current out of a volume = Charge generated – Charge recombined
Models :
Carrier transport (mobility)
Carrier generation recombination : SRH, Auger (or Impact Ionization), Radiative
Quantum effects (Fermi statistics) : Can also solve Schrodinger’s equation if needed
Materials :
Silicon (easiest, can use default material parameters), Ge
Compound semiconductors : SiGe, GaAs. GaN, SiC

9. MEDICI Introduction : How
Current version of MEDICI includes modules which allow
Anistropic modeling
Circuit analysis
Optical device simulation
Variable lattice temperature simulation
Hetero-junction simulation
Programmable device simulation

10. Simulation Procedure Device Structure Definition Device Simulation
Defined using a text file
Use an editor (vi, emacs, gedit)
Device Simulation
Run program : Apply bias conditions, run DC / AC / Transient simulations
Simulation time depends on : number of grid points, complexity of models
Analysis
1D Plots : Output currents, voltages
2D Plots : Physical variables (carrier concentration etc) for each grid point

11. Getting Started First, grab the manual ! To run Medici:
Location : in your account folder
Run an example code or two: under Medici_examples, also in account folder
To run Medici:
md3200 (or medici) file-maximum 3,200 grid points
md10000 file - 10,000 maximum grid points
md20000 file - 20,000 maximum grid points
For example: md3200 diode.inp

12. Suggested Procedure for Simulation
Define structure and save to file, e.g.
MESH OUT.FILE=filename.GRD
SOLVE OUT.FILE=filename.SOL (zero bias solution)
Simulate device and save data to files
Load structure
MESH IN.FILE= filename.GRD
LOAD IN.FILE= filename.SOL
Saving data
IV Data => LOG OUT.FILE= filename.IV
Grid Solution=> SOLVE v1=0 v2=0.1 OUT.FILE= filename.01

13. Suggested Procedure for Simulation (cont.)
Plotting results
Load structures with MESH
Load grid solution with LOAD
Plot data, e.g. for IV/It, Vt

14. 1. Define Device Structurex
1. Create the mesh
MESH, X.MESH, Y.MESH
2. Define material and electrode regions
REGION, ELECTR
(0,0) y
3. Specify Impurity Profiles
PROFILE
Sets impurity type, concentration and distribution including uniform, gaussian (default) or erfc

15. 1. Define Device Structure (cont.)
INTERFACE
QF - Interface fixed charge
CLEAR - No interface fixed charge (default)
Set mobility and material parameters
MOBILITY
MATERIAL

16. 1. Define Device Structure (cont.)
Set up contact and interface characteristics
CONTACT
Resistance lumped
Metal
Metal work-function
Barrier lowering
Surface recombination velocity

17. 2. Simulate Device Specify physical models Specify method of solution
SYMBOLIC
METHOD
Set up file for logging IV data
LOG OUT.FILE=filename.iv

18. 2. Simulate Device (cont.)
Solve device structure
SOLVE
Specify electrode voltages
Specify transient simulation parameters (e.g. time step, ramp time)
Specify output file name for solution to structure
OUT.FILE=filename

19. 3. Analysis of Simulation
Types of available plots
I-V
Distribution (e.g. potential, electric field, carrier conc.)
Transients
Contour plotting
Plot commands
PLOT.1D, PLOT.2D, PLOT.3D, 3D.SURFACE, CONTOUR, LABEL, CALCULATE, EXTRACT

20. Example: Silicon pn Diode
Complete example can be found on MEDICI Manual page 6-1 (mdex3) “Diode & Lumped Elements Example”
This example has been modified to show the I-V characteristics of a Silicon pn junction diode along with the hole concentration in the n-type region of the diode at forward bias (on-state)
With any text editor (pico, emacs, wordpad, vi etc.) create or save the following file shown on the next 3 slides

21. Example: Silicon pn Diode
TITLE Avant! MEDICI SDM-I Class Example - Diode I-V Simulation
COMMENT Create an initial simulation mesh
MESH
X.MESH X.MAX=3.0 H1=0.50
Y.MESH Y.MAX=3.0 H1=0.25
COMMENT Region and electrode statements
REGION NAME=Silicon SILICON
ELECTR NAME=Anode TOP X.MAX=1.0
ELECTR NAME=Cathode BOTTOM
$ Specify impurity profiles
PROFILE N-TYPE N.PEAK=1E15 UNIF OUT.FILE=MDEX3DS
PROFILE P-TYPE N.PEAK=1E19 X.MIN=0 WIDTH=1.0 X.CHAR=.2
Y.MIN=0 Y.JUNC=.5
$ Refine the mesh with doping regrids
REGRID DOPING LOG RAT=3 SMOOTH=1 IN.FILE=MDEX3DS
OUT.FILE=SDM1MSH

22. Example: Silicon pn Diode
PLOT.2D GRID TITLE="SDM-1 Diode Exmaple - Simulation Mesh" SCALE FILL
COMMENT Specify physical models to use
MODELS SRH AUGER CONMOB FLDMOB
COMMENT Symbolic factorization
SYMB NEWTON CARRIERS=2
COMMENT Create a log file for the static I-V data
LOG OUT.FILE=IV_LOG_FILE
COMMENT Perform a 0-volt steady state solution, then simulate
$ the static I-V characteristics for the diode.
SOLVE OUT.FILE=ZERO_BIAS_SOL
PLOT.3D DOPING LOG
+ TITLE="SDM-I Si Diode 3-D Doping Profile"
SOLVE ELEC=ANODE NSTEP=15 VSTEP=0.05
SOLVE V(Anode)=0.75 OUT.FILE=V_AN_1_SLN

23. Example: Silicon pn Diode
COMMENT Plot the diode current vs. anode voltage
PLOT.1D X.AXIS=V(Anode) Y.AXIS=I(Anode)
POINTS
TITLE="SDM-I Si Diode I-V Trace Example"
+ COLOR=2
LOAD In.file=V_AN_1_SLN
PLOT.1D holes x.start=0.5 x.end=0.5 y.start=0.5 y.end=3 POINTS
TITLE="Hole V(Anode)=0.75V, X=0.5, Y=0 to Y=3"
PLOT.2D FILL
CONTOUR FLOWLINES LINE.TYPE=3 COLOR=2 NCONT=20

24. Example: Silicon pn Diode
1st PLOT Statement : PLOT.2D Shows the mesh structure

25. Example: Silicon pn Diode
2nd PLOT Statement : PLOT.3D Shows the doping profile

26. Example: Silicon pn Diode
3rd PLOT Statement : PLOT.1D Shows the simulated I-V curve

27. Example: Silicon pn Diode
4th PLOT Statement : PLOT.1D Shows the simulated hole concentration in the n-type region under forward bias

28. Example: Silicon pn Diode
5th PLOT Statement : PLOT.2D with CONTOUR
Shows the simulated current “flow-lines” at forward bias

29. AIM-SPICE Lecture Outline
AIM-SPICE Tutorial and Links
AIM-SPICE Modeling
Practical Applications
Comparisons
Summary

30. Tutorial: AIM-SPICE Automatic Integrated Circuit Modeling Spice
Download from
Tutorial, Manual, and Download found on my website under AIM-SPICE download and AIM-Spice Tutorial
Two books for reference
T. A. Fjeldly, T. Ytterdal, and M. Shur, Introduction to Device Modeling and Circuit Simulation, John Wiley & Sons, New York, (1998), ISBN
K. Lee, M. Shur, T. A. Fjeldly, and T. Ytterdal, Semiconductor Device Modeling for VLSI, Prentice Hall, Englewood Cliffs, NJ (1993),

31. AIM-SPICE
Device models are defined in terms of equivalent circuits consisting of circuit elements such as current sources, capacitances, resistances etc.
Based on Berkley SPICE created in 1972
A vehicle for the new set of advanced device models for circuit simulation 31

32. Tutorial: AIM-SPICE
A circuit should be drawn (schematic) to determine nodes that define every device that is part of the circuit
Nodes must be numbered
Circuit is described by a sequence of lines that consist of statements that are responsible for:
definitions of power supply sources
single element or device
model parameters
Specification for output to be analyzed or analysis types

33. Tutorial: AIM-SPICE Input format is as follows: Circuit Title
Power Supplies
Signal Sources
Device/Element Descriptions
Model Statements
In order to run the simulation the devices (with devices with specific models) commands have to be included with a “dot” in front of the model command line
Order is arbitrary except for circuit title and model statements

34. Tutorial: Basic Example
The SPICE model for the AC circuit below
AC circuit
vin ac
r k
r k
c n
Click AC icon. For AC Analysis Parameters enter the following:
Click LIN
Number of points = 1000
Start frequency = 0
End frequency = 200k
Variables to plot, magnitude plot and v(2) voltage, Go to control and click start Simulation, Auto-Scale C2 R2 R1
vin 1 2

35. Tutorial: Basic Example
The SPICE model for a DC sweep: Diode circuit below
simple diode vd 1 0 dc 0
d1 1 2 diode
vid 2 0 dc MODEL diode d level=1
Click DC icon. For DC Transfer Curve Analysis Parameters:
Click 1. Source (default)
Source name: pull down vd
Start value = -5
End Value = 5
Variables in circuit i(vid) current (acts as ammeter to circuit), Go to control and click start Simulation, Zoom over region 1 vd 2
vid 35

36. Tutorial: Device Basic Example
Run the following nMOS circuit using the “DC” tool to give a DC analysis. The number code for a MOSFET is
Name D G S B that is (m ) in this case shown below
nMOS resistor circuit
vdd 3 0 dc 3
vgs 1 0 dc 1.0
*the voltage source vid is inserted to be used as an ammeter
vid 3 2 dc 0
rd k
m ntype l=1.0u w=4.0u
.model ntype nmos level=2 vto=0.5 kp=25e-6
Draw the schematic of this circuit

37. Tutorial: Device Basic Example
DC analysis parameters
1. Source
Source Name: vdd
Start Value: 0
End Value: 1.0
Increment Value: 0.02
2. Source (Optional)
Source Name: vgs
End Value: 1
Increment Value: 0.1
Select variables to plot drain current i(vid) Start simulation and autoscale