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Slide 1
1
Developing Reliable Device Simulation Models
using ADS
ADS User Meeting Böblingen, 14.05.2009
Dr. Thomas Gneiting
AdMOS GmbH
Frickenhausen
Dr. Franz Sischka
Agilent Technologies
Böblingen
(C) Bildarchiv der Stadt Böblingen
ADS User Meeting BöblingenMay 2009
Slide 2
2
- The difference between selecting a model and extracting model parameters.
- Trusted, verified measurements.
- contact resistance- self-heating effects
- linear S-parameter- de-embedding
- Example of a device modeling sequence
Developing reliable device simulation models using ADS
AGENDA
Slide 3
3
Semiconductor Device Models (Nonlinear Models):
- BJT Models: HICUM 2, HICUM 0, MEXTRAM, VBIC, Gummel-Poon, ST BJT,
Agilent EEBJT2
- Diode Models: PN diodes, Philips JUNCAP, Agilent Root, PIN
- MESFET/HEMT Models: TOM3, Angelov, Agilent EEFET3 and EEHEMT1,
Agilent Root MESFET/HEMT (HPFET), TOM scaleable, Curtice quadratic
and cubic, Advanced Curtice, Statz et al. (Raytheon), Materka, Modified
Materka (Rizzoli), Tajima
- MOSFET Models: BSIM3, BSIM4, BSIM3SOI, BSIM4SOI, PSP, HiSIM2,
HiSIM-HV, Philips MOS Model 11, Philips MOS Model 30, Philips MOS,Model 9, Agilent Root MOSFET, Agilent EEMOS1, BSIM1, BSIM2,
MOS Level 1,2,3
Which modelto select ?
There are many models available, even for the same device !
Slide 4
4
Model A Model B?
Which model is better ?
Only reliable measurementsprovide good simulation models
You may think of using rather model_A than model_B.
However, as we will show with the following slide set, the main topic is to perform reliable, verified
measurements. This is the very base of any good model implemented in a design kit of a manufacturer.
Of course, some models feature equations to better fit a certain effect (thermal self-heating, non-linear
large-signal RF behavior).
But also here applies the statement of above: if the measurements are not available, the ‘better’ model
does not help.
And if the measurements are not ‘qualified and verified’, the ‘better’ mdoel does not help too.
Slide 5
5
DCspacecharge
RS
diffusioncapacitancevD vDint
iD
−⋅= 1eIi vt*N
v
SD
intD
M
J
intD
JOs
V
v1
CC
−
= DT
intD
DTD i
vtN
1T
v
iTC ⋅
⋅⋅=
∂
∂⋅=
What is a model ?
Is ... Model Parameter
Model equations
DC
Junction Cap
Diff.Cap (Transit Time)
Ohmic Losses
( )
D
intDDS
i
vvR
∂
−∂=
( )273.15 + TEMP 5-8.6171E = vt ⋅
A set of equations describing the principal electrical behavior of a device represents what is commonly
called a device model.
NOTE: A ‘SPICE simulation model’ is a name for a model available in UCB Spice (University of
California, Berkeley), and thus typically available in all of today’s simulators.
For a real device, only the model parameters like e.g. IS, NF are adjusted to get a simulation results
close to the real behavior.
Additionally, the instance parameters (e.g. L, W) describe the geometry and structure of a device.
If no model parameters or instance parameters are specified, the simulator takes default parameter
values. They shall prevent the simulator from numeric errors (e.g. divide by zero) and represent an
ideal device (the specific model effect is ‘switched-off’).
Caution: Default parameter are in most cases DC bias and frequency independent!!
Slide 6
6
Plot diode_basics/DC/forward/ia_va
va [E+0]
ia.m [LOG]
0.0 0.2 0.4 0.6 0.8 1.01E-15
1E-14
1E-13
1E-12
1E-11
1E-10
1E-9
1E-8
1E-7
1E-6
1E-5
1E-4
1E-3
1E-2
1E-1
What is model parameter extraction ?
2.3*N*vt
−⋅= 1vt*N
v
SD
D
eIi
Is
1 decade
Fitting the model equation to the measured data
by varying the model
parameters.
NOTE: The model
equation specifies the
measurement setup (what to measure)!
Slide 7
7
Device Instance(L, W, geometry, lithography, size of the production masks)
Device Model (typically process-dependent Model Parameters: VTH, U0, CDS etc.)
Model Parameters and Instance Parameters
W
L
SA, SB
IMPORTANT NOTE:
when not specified, the instance and model parameter values used in the simulation will be the ‘default values‘,
i.e. the effect is switched off (CDS=0F, RTH=0ΩΩΩΩ, VAF=infinite), or the simulation is standardized (L=1).
Slide 8
8
- The difference between selecting a model and extracting model parameters.
- Trusted, verified measurements.
- contact resistance- self-heating effects
- linear S-parameter- de-embedding
- Example of a device modeling sequence
Developing reliable device simulation models using ADS
AGENDA
Slide 9
9
IC-CAP/ADS
Contact resistance of on-wafer measurements
(C) Cascade Microtech
One of the most important preconsiderations regarding accurate device modeling is to characterize the
contact resistance of the probes to the contact pads on the wafer. This is especially important for silicon
processes, where the on-wafer contacts are made from aluminum (III/IV processes use typically gold).
When not considering these contact resistances, their effect will be included in the ohmic parameters of
the model, (they will become too big). This will badly affect any chip design.
Slide 10
10
Plot ADS_simul_types/DC_mdlg/idvd/idvsvd
vd [E+0]
id.M
id simulated without Rc id with simulated Rc [E-3]
0.0 0.5 1.0 1.5 2.00
10
20
30
40
50
The effect of contact resistance
Behavior of the final model in design kit = real device behavior !
(without contact resistance)
Measurement and Simulation
including contact resistance
IMPORTANT NOTE:Including the contact
resistance is mandatory during
the modeling process
Gate
Rcontact1MOSFET1
Drain
Rcontact2
id w
itho
ut
Rco
nta
ct
id
inclu
din
g R
co
nta
ct
[1E
-3]
NOTE: do not confuse these measurement-related contact resistances with the device‘s inner, ohmic
model parameters (e.g. RD, RS etc.)
Slide 11
11
Self-heating with DC measurements
infinite
4 µsec
2 µsec
1 µsec
Measurements
at various pulse
widths
VCE (V)
Silicon Bipolar Transistor on wafer
Hint: 50mA device current: beginning of self-heating
Ic (mA)
Only a few models can handle self-heating: MOS: BSIMSOI3, BSIMSOI4, HiSIM-HV
BJT: VBIC, HiCUM
MESFET/HEMT:Angelov, ...
Model Parametersto model the self-heating: RTH, CTH
pulse period: 1msec
As a general observation, currents above ~25mA will cause self-heating effects with transistors.
Rule of thumb: 25mA with typically 2V equals already 50mΩ for that tiny transistor on the wafer!
Self-heating can only be avoided when applying pulsed DC measurements. However, the max. duration
for such a DC pulse is 100ns, followed by typically 1ms wait time.
If you have to live with self-heating, make sure to have repeatable measurements for the DC Settings
(currents for the transfer and for the output characteristics must be identical for identical bias
conditions !!). Furthermore, the self-heating during the (very often fast measured (!)) DC
measurements must be the same as with the (slowly performed) S-parameter measurements !!
-> measure your DC curves as slowly as later the DC-biased S-parameters.
Slide 12
12
Transistor and Diode S-Parameter measurements are performed including a DC bias.Due to the nonlinear transistor behavior, a too big AC amplituderesults in a distorted output signal. These distortions will shift the DC operating point !
iD
vGS
DC oper.point w/o RF signal
DC oper.point shifted by too big an RF signal
S-parameter measurements
The energy for the harmonics of a non-linear behavior is provided
- by the DC bias
- by the applied RF signal.
In any case, when harmonics occur, the DC bias is affected. The currents provided by the DC power
supply will become a function of the distortion of the RF signals.
Slide 13
13
If the RF signal is small enough,it does not disturb the DC
biasing of the S-parameter measurements !
-20dBm: RF signal disturbs DC traces
-30dBm: correct RF signal level for this transistor
Find Out The Max. Applicable RF Signal to obtain
linear S-parametersSimultaneous measurement of DC behavior
with overlaid S-parameter signal
From the plot above, we can determine 2 important things for obtaining linear S-parameters:
the max. applicable RF signal level for the S-parameter measurements for a given DC operating point,
or, inversely, the minimum applicable DC bias for a given RF signal.
Slide 14
14
NWA Calibration, applpying the identified RF power
After the standard calibration,
the calibration plane is at the end of the GSG probes.
Probes and calibration substrate must match !
ISS calibration substrate
Cal.Plane
Slide 15
15
G
D
S=B
S=B
Unfortunately, our transistor is not directly
at the probe contact location …
NWA Cal Plane
In the above slide, in the magnified view, is the inner transistor, which we want to characterize. All the
rest has to be de-embedded, i.e. to be stripped-off.
In other words, the NWA calibration plane, obtained by the NWA calibration so far, has to be shifted
from the GSG probe contact location down to the beginning of the device.
Slide 16
16
De-embedding:
Shifting NWA Calibration Plane vs. DUT
-> The influence of the parasitic
components between the NWA
calibration plane and the
transistor is eliminated by
de-embedding.
Source + Substrat
DrainGate
Source + Substrat
Ground
Ground
Ground
Ground
SignalSignal
el iminateparasitic
effects
through de-embedding
Ground
Ground
Signal
Referenceplane of
NWA por t 1
Ground
Ground
Signal
Referenceplane of
NWA por t 1
Reference plane ofcircuit library element
The simulation model shall only
describe the behavior of the DUT
without any influence of the
surrounding pads
(C) www.ihp-microelectronics.com
Slide 17
17
measured data of device and pad
after de-embedding
De-embedding: Measurement Data
The two diagrams demonstrate the effect of the de-embedding.
The left one shows the input and output reflection S11 and S22 before and after the de-embedding.
Looking at S22, the difference in both, phase and magnitude can be seen very clearly.
A similar behavior can be observed in the transmission behavior. The original measured data of the
forward transmission S21 clearly has an increased phase shift and a decreased magnitude with
increasing frequency, compared to the de-embedded data.
As a summary, it is absolutely necessary to perform a correct de-embedding to get the real transistor
data as a base for accurate modeling.
Slide 18
18
De-embedding: Principal Teststructure Layouts
OPEN SHORT
THRU
OPEN andSHORT are a must forde-embedding
The THRU deviceis for verifying thede-embedding quality:-> After de-embedding
from OPEN and SHORT,the THRU S-parametersmust represent a short transmission line.
These facts should be widely
known and are explained in
many publications.
However, we still see many
cases, where de-embedding
cannot be done correctly due to bad de-embedding
structures !!
(C) www.ihp-microelectronics.com
The pre requisite for a correct de-embedding is that certain test structures are available on a wafer
together with the device under test (DUT) itself.
Depending on the selected de-embedding method, an OPEN, a SHORT and a THROUGH dummy pad
structure must be available and must be measured.
The principle layout of these structures are given above.
RECOMMENDATION: the on-wafer THROUGH is an ideal, golden de-embedding verification
device. Compared to a diode or transistor, the de-embedded THRU is
- DC bias independent
- not suffering from self-heating
- not susceptible to large RF signals etc.
In other words, when the THRU, de-embedded from the OPEN or the OPEN/SHORT represents a
short strip line, with its characteristic appearance in both, the Smith Chart (S11, S22) and the Polar
Diagram (S21, S12), it can be assumed that when replacing that little piece of aluminum by the diode
or the transistor, that the de-embedding will work OK also for these very devices.
Slide 19
19
measuredDUT
G G
S S
G G
The measured S-parameters
of the DUT describe the behavior
of the device plus the pads
de-embedded DUT
The DUT to-be-modeled
is without the pads
Wrap-up:
De-embedding, the step after NWA calibration
Layout screen shots:(C) www.ihp-microelectronics.com
the DUT itself (!)
Slide 20
20
measured Spar
DC data converted to S-parameter, f=0Hz
If this starting point check fails, verify:-> too much RF signal
-> self-heating-> voltage drop in S-par testset-> accurate DC contact resistance-> DC modeling was performed at different bias range than the S-par modeling !
Device Modeling:
The extrapolated starting points of the S-par (0Hz)are determined by the DC fitting !!
fmin=100MHz
Since S-parameter modeling means (black-and-white) characterizing ‘the speed’ from going from the
DC biasing to freq->infinite, the capacitors and the transit time are the only parameters to adjust. And
these capacitors and the transit time, although bias dependent, describe ‘just’ the phase(freq) and
magnitudes(freq) of the S-parameters with increasing frequency.
-> The extrapolated 0Hz starting points are 100% determined by the DC fitting !
Slide 21
21
- The difference between selecting a model and extracting model parameters.
- Trusted, verified measurements.
- contact resistance- self-heating effects
- linear S-parameter- de-embedding
- Example of a device modeling sequence
Developing reliable device simulation models using ADS
AGENDA
Slide 22
22
Typical Device Modeling Flow
Parametric Tests
Measurements
for Modeling
Parameter
Extraction
Quality Assurance
Documentation
Statistical Modeling
- Golden Die selection
- Mismatch & statistical analysis
- Process stability
Adjust model to
process targets.
Adding corner cases
and statistical
distributions
Test model
- in dedicated simulators
- for specified operating conditions
- outside specifications (model robustness)Generate a
final report with
a comparison
measurement /
simulation
Perform all
necessary
measurements
Extract model
parameters
topics discussed
in this presentation
Slide 23
23
• Parameter extraction for state-of-the-art CMOS processes (e.g. 65nm) is a highly complex task.
• To fulfill all require-ments with respectto accuracy and statistical behaviordedicated softwareis a must.
• The screenshotshows the PSP Modeling Packageof IC-CAP
IC-CAP: Dedicated Software to Support Modeling
Slide 24
24
• The following slides show different examples how parameters are adjusted.
• A typical RF CMOS process with a minimum feature length of 130nm was taken as a test vehicle.
• We demonstrate from which characteristics certain model parameters are extracted.
• In the same simulation setup, the influence of the extracted parameter to other regions of operation are visualized.
• For this purpose, the following measurements/simulations are taken into account:– DC, S-parameter, Harmonic Balance, Minimum Noise Figure
Examples of Parameter Extractions (RF CMOS)
Slide 25
25
Influence of Contact Resistance on DC, S21, ...
Simplified MOS model
Drain
Rcontact2
Gate
Rcontact1
Rs
Rgate Rearly
Rd
Cgs
gmCgd
Slide 26
26
Influence of Contact Resistance on DC, S21, ...
Rcontact:
3Ω(=correct value)
10Ω
Extraction: From DC
Measurementsof an on-wafer
SHORT dummy
Slide 27
27
Influence of Gate Resistance on S11, NFMIN
Simplified MOS model
Drain
Rcontact2
Gate
Rcontact1
Rs
Rgate Rearly
Rd
Cgs
gmCgd
Slide 28
28
Rshg:
4.45Ω/(=correct value)
10Ω/
Extraction: From S11, Y11
NOTE:Rshg is the Gate Sheet Resistor.
Influence of Gate Resistance on S11, NFMIN
Slide 29
29
Influence of DC Parameter to Id-Vd, gds, S21, S22, Pout, NFmin
Simplified MOS model
Drain
Rcontact2
Gate
Rcontact1
Rs
Rgate Rearly
Rd
Cgs
gmCgd
PCLM 0.3 .. 1.3
Slide 30
30
PCLM:
1.3(=correct value)
0.1
Extraction from:Id-Vd, gds
NOTE:PCLM is a DC related parameter (Early voltage). It affects all regions of operations !
Influence of DC Parameter
to Id-Vd, gds, S21, S22, Pout, NFmin
Slide 31
31
Simplified MOS model
Drain
Rcontact2
Gate
Rcontact1
Rs
Rgate Rearly
Rd
Cgs
gmCgd
Influence of Capacitance Parameter
Slide 32
32
CGDL:
493pF/m
(=correct value)
5nF/m
Extraction from:
S12 and CV
Influence of Capacitance Parameter
Slide 33
Modeling Services
CMOS TechnologyDesign libraries for CMOS and other technologies:- Advanced Processes down to 45nm- RF CMOS- High voltage devices- Silicon on Insulator- Packaged devices
Passive DevicesSimulation models for: - On-chip passives (inductors, ...) - PCB elements for high speed circuits- Connectors- IC packages
The principal services and products of Adanced Modeling Solutions are in the area of device modeling
and connector design (signal integrity).
Slide 34
34
AdMOS Company Information
AdMOS GmbHAdvanced Modeling SolutionsIn den Gernaeckern 8D-72636 Frickenhausen/Germany
Phone: +49 (7025) 911698-0Fax: +49 (7025) 911698-99
email: [email protected]://www.admos.de
• AdMOS was founded in 1997 by Dr. Thomas Gneiting.
• AdMOS is focused on:
– Software development of tools
for model parameter extraction of CMOS and other devices.
– Modeling and simulation service for complex devices and systems.
– Engineering service for design and test of RF and high speed components.
• Actually, we employ 5 highly qualified engineers
for our modeling serviceand software development activities.
• Due to our ongoing expansion, we moved to a new office building in December 2007.
Advanced Modeling Solutions is a young startup company, which focuses on the aspects of device
modeling for circuit simulation. It was founded in 1997 by Dr. Thomas Gneiting.
Advanced Modeling Solutions is located pretty close to Stuttgart, which is well known for its famous
car manufacturers and a lot of high tech industry.
Slide 35
35
- The difference between selecting a model and extracting model parameters.
- Trusted, verified measurements.
- contact resistance
- self-heating effects- linear S-parameter
- de-embedding
- Example of a device modeling sequence
Developing reliable device simulation models using ADS
Wrap-Up
