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ECSE-6230 Semiconductor Devices and Models I Lecture 3

ECSE-6230 Semiconductor 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: ssawyer@ecse.rpi.edu. MEDICI Lecture. Created by Jeff Langer

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ECSE-6230 Semiconductor Devices and Models I Lecture 3

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  1. ECSE-6230Semiconductor Devices and Models ILecture 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: ssawyer@ecse.rpi.edu

  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 • Logging in using SSH/Remote Desktop • MEDICI Tutorial • Simulator overview • MEDICI Example – Silicon pn junction diode

  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

  5. 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

  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 • 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 ! • 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 Structure x • 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.) • (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 • MODEL • 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 REGRID DOPING LOG RAT=3 SMOOTH=1 IN.FILE=MDEX3DS 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 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

  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 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),

  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

  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. R1 1 2 vin R2 C2 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

  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 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 1 vd 2 vid 0

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