ECSE-6230 Semiconductor Devices and Models I Fall, 2012 S. Sawyer 1-1
ECSE-6230Semiconductor Devices and Models I
Lecture 3
Prof. Shayla M. Sawyer
Bldg. CII, Room 8225
Rensselaer Polytechnic Institute
Troy, NY 12180-3590
Tel. (518)276-2164
FAX (518)276-2990
e-mail: [email protected]
ECSE-6230 Semiconductor Devices and Models I Fall, 2012 S. Sawyer 1-2
MEDICI Lecture
Created by Jeff Langer
Edited by Peter Losee (F’05), Kamal Varadarajan (F’07) and Vipindas Pala (F’10)
ECSE-6230 Semiconductor Devices and Models I Fall, 2012 S. Sawyer 1-3
Overview
• Using ECSE servers– Logging in using SSH/Remote Desktop
• MEDICI Tutorial– Simulator overview
– MEDICI Example – Silicon pn junction diode
ECSE-6230 Semiconductor Devices and Models I Fall, 2012 S. Sawyer 1-4
Remote Access• Login remotely from your laptop
– 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
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Remote Access• Note if logging in from off-campus, VPN in
first
http://helpdesk.rpi.edu/update.do?artcenterkey=556
• If there are problems logging in with ts1…try any other of the machines, ts2, ts3, ts4, ts5
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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
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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.
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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
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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
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Simulation Procedure
• Device Structure Definition• 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
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Getting Started• First, grab the manual !
– 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
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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
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Suggested Procedure for Simulation (cont.)
• Plotting results– Load structures with MESH
– Load grid solution with LOAD
– Plot data, e.g. for IV/It, Vt
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1. Create the mesh• MESH, X.MESH, Y.MESH
2. Define material and electrode regions
• REGION, ELECTR
(0,0)
y
x
3. Specify Impurity Profiles• PROFILE
Sets impurity type, concentration and distribution including uniform, gaussian (default) or erfc
1. Define Device Structure
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1. Define Device Structure (cont.)
4. (Cont.)• INTERFACE
– QF - Interface fixed charge
– CLEAR - No interface fixed charge (default)
5. Set mobility and material parameters• MOBILITY
• MATERIAL
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1. Define Device Structure (cont.)
4. Set up contact and interface characteristics• CONTACT
– Resistance lumped
– Metal
– Metal work-function
– Barrier lowering
– Surface recombination velocity
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2. Simulate Device
1. Specify physical models• MODEL
2. Specify method of solution• SYMBOLIC
• METHOD
3. Set up file for logging IV data• LOG OUT.FILE=filename.iv
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2. Simulate Device (cont.)
4. 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
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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
3. Analysis of Simulation
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• 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
Example: Silicon pn Diode
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Example: Silicon pn DiodeTITLE 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
REGRID DOPING LOG RAT=3 SMOOTH=1 IN.FILE=MDEX3DS
REGRID DOPING LOG RAT=3 SMOOTH=1 IN.FILE=MDEX3DS
+ OUT.FILE=SDM1MSH
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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
Example: Silicon pn Diode
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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 Concentration @ V(Anode)=0.75V, X=0.5, Y=0 to Y=3"
+ COLOR=2
PLOT.2D FILL
CONTOUR FLOWLINES LINE.TYPE=3 COLOR=2 NCONT=20
Example: Silicon pn Diode
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1st PLOT Statement : PLOT.2D Shows the mesh structure Example: Silicon pn Diode
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2nd PLOT Statement : PLOT.3D Shows the doping profile
Example: Silicon pn Diode
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3rd PLOT Statement : PLOT.1D Shows the simulated I-V curveExample: Silicon pn Diode
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4th PLOT Statement : PLOT.1D Shows the simulated hole concentration in the n-type region under forward bias
Example: Silicon pn Diode
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5th PLOT Statement : PLOT.2D with CONTOUR Shows the simulated current “flow-lines” at forward bias
Example: Silicon pn Diode
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AIM-SPICE Lecture Outline
• AIM-SPICE Tutorial and Links
• AIM-SPICE Modeling
• Practical Applications
• Comparisons
• Summary
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Tutorial: AIM-SPICE
• Automatic Integrated Circuit Modeling Spice• Download from www.aimspice.com• 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 0-471-15778-3.
– K. Lee, M. Shur, T. A. Fjeldly, and T. Ytterdal, Semiconductor Device Modeling for VLSI, Prentice Hall, Englewood Cliffs, NJ (1993),
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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
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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
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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
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Tutorial: Basic Example• The SPICE model for the AC circuit below
AC circuit
vin 1 0 1 ac
r1 1 2 10k
r2 2 0 50k
c2 2 0 1n
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
C2R2
R1
vin
1 2
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• The SPICE model for a DC sweep: Diode circuit belowsimple diodevd 1 0 dc 0
d1 1 2 diode
vid 2 0 dc 0.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
Tutorial: Basic Example
vdvid
0
1
2