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: ssawyer@ecse.rpi.edu

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)

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Overview

• Using ECSE servers– Logging in using SSH/Remote Desktop

• MEDICI Tutorial– Simulator overview

– MEDICI Example – Silicon pn junction diode

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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