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ECSE-6230 Semiconductor Devices and Models I Lecture 3

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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 : 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 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.)
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

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