Transcript 1/f Noise Measurements - MOS-AK

1/f Noise Measurements
Falk Korndörfer
IHP
Im Technologiepark 25
15236 Frankfurt (Oder)
Germany
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
www.ihp-microelectronics.com
© 2007 - All rights reserved
Outline
•
Measurement system
Noise current measurement with Stanford SR570
•
Wiring considerations
Capacitive coupling
Resistive coupling/ground loops
Inductive coupling
•
Systematic errors
Imperfections of amplifier
System noise floor
•
Conclusion
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
www.ihp-microelectronics.com
© 2007 - All rights reserved
Measurement System
based on Agilent proposal
SR570 low noise current preamplifier
with Agilent 35670A
dynamic signal analyzer
SR570
ICOMP
DUT
VGate
from SMU
DSA
Agilent
35670A
1 Hz
filter
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
VBIAS
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Wiring Problem – Capacitive Coupling
Stray Capacitance
Noise
Source
DUT
iCStray t   CStray
SR570
d VCStray
dt
   CStray VNoise
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
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Wiring Solution – Capacitive Coupling
•
Turn off noise source if possible, e.g. TFT screens
•
Reduce stray capacitance by increasing distance to noise source
•
Use a metal box for shielding
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
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Wiring Problem – Resistive Coupling, Ground Loops
SR570
Finite conductivity
of ground wire
V1
DUT
V2
Noise
Source
V1  V 2
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
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Wiring Solution – Resistive Coupling, Ground Loops
•
Star configuration
central ground point
•
Use heavy ground bus to increase conductivity of ground
connections
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
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Wiring Problem – Microphonics
•
Vibrations can change the cable capacitance due to small changes in
geometry
current is generated
Q  C V
dQ
dV
dC
i (t ) 
C
V
dt
dt
dt
•
•
Ensure stable placement of equipment
Use high quality cable
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
www.ihp-microelectronics.com
© 2007 - All rights reserved
Wiring Problem – Inductive Coupling 1
B(t)
SR570
•
•
DUT
Noise
Source
Most critical for on-wafer measurements
Occurs even if electrically isolated
Is like a transformer with 1 secondary winding
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
www.ihp-microelectronics.com
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Wiring Problem – Inductive Coupling 2
B(t)
VIND(t)
dA
d
vIND t     B  d A
dt A
iIND t   rDUT
d
   Bd A
dt A
iIND t    g DUT
•
d
  Bd A
dt A
Disturbance depends on DUT conductivity
Measurements of high conductive DUTs are most influenced
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
www.ihp-microelectronics.com
© 2007 - All rights reserved
Wiring Solution – Inductive Coupling
•
Turn off noise sources, e.g. coolers/heaters
•
Minimized the area of the pick-up loop
use twisted pairs cables
Consider usage of RF probes (GS or GSG)
no loop from coaxial cable
minimal area for magnetic field
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
www.ihp-microelectronics.com
© 2007 - All rights reserved
Wiring – on-Wafer
•
Twist cables as good as possible
Minimized pick-up loop area
Usually coaxial cable does not shield magnetic fields

IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
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On-Wafer Wiring Example
Twisted triaxial cable
Central ground point
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
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© 2007 - All rights reserved
On-Wafer Wiring Considerations
•
How many connections to protective earth conductor?
Ground loop(s) if more than one
Check wafer prober, SMU, signal analyzer, current amplifier
Check triax/coax adapters if used
•
Use only one central ground point
RF probes are highly recommend
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
www.ihp-microelectronics.com
© 2007 - All rights reserved
Recommendations
•
Prevent loops in wiring
twist cables
use star configuration
•
Use short, high quality cable
•
Use RF probes (GS or GSG configuration)
•
Place everything in a metal box
use shielded wafer prober
•
Switch off unnecessary equipment
Is thermo chuck really necessary?
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
www.ihp-microelectronics.com
© 2007 - All rights reserved
Systematic Errors 1
•
Imperfections of the current preamplifier
ICOMP
ideal
SR570
Current compensation
source has finite source
impedance
Real
SR570
VCOMP
RCOMP
ICOMP
RIN
VBIAS
VBIAS
Input resistance is not zero
(depending on gain)
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
www.ihp-microelectronics.com
© 2007 - All rights reserved
Systematic Errors 2
•
Small signal equivalent circuits of DUT (MOSFET) and SR570 current
amplifier input stage
gIN
gOUT
Real
SR570
VCOMP
RCOMP
RCOMP
RIN
ICOMP
IMEAS
RIN
VBIAS
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
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Systematic Errors 3
DUT
Inoise
SR570
gOUT
RCOMP
RIN
IMEAS
•
3 paths for current flow
Measured current is only a part of the noise current
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
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Systematic Errors 4
•
•
RIN and RCOMP are known from amplifier settings
gOUT is derived from DC measurement
gOUT
•
DUT
d I DS

d VDS
Inoise
SR570
gOUT
RCOMP
RIN
Inoise can now be calculated
g IN
IMEAS
1

RIN
g COMP 
1
RCOMP
gTOTAL  g IN  g COMP  g OUT
Inoise  I MEAS  RIN  gTOTAL 
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
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Systematic Errors 5
•
System noise floor and noise from compensation current source
Compare with measured data with system noise
System Noise Floor without
Compensation Current
Sensitivity
100 nA/V
1 µA/V
10 µA/V
100 µA/V
1 mA/V
1E-19
INOISE in A²/Hz
1E-17
1E-21
1E-23
1E-25
1E-27
1E-19
INOISE in A²/Hz
1E-17
System Noise Floor with
5 mA Compensation Current
1E-21
Sensitivity
100 nA/V
1 µA/V
10 µA/V
100 µA/V
1 mA/V
1E-23
1E-25
1E-27
1E-29
1E-29
1
10
100
1k
10k
100k
1
Frequency in Hz
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
10
100
1k
Frequency in Hz
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10k
100k
Example Measurement
Plot UntitledModel0/UntitledDUT0/UntitledSetup0/UntitledPlot0
Inoise.m System_Noise.m [LOG]
1E-14
PO
A
1E-15
p-MOSFET at 2 different BIAS points
1E-16
1E-17
1E-18
VG=-1.2, VD=-1.2
1E-19
VG=-0.9, VD=-1.2
1E-20
1E-21
1E-22
1E+0 1E+1 1E+2 1E+3 1E+4 1E+5
X
freq [LOG]
Y
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
www.ihp-microelectronics.com
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Conclusion
•
Current based noise measurement system was presented
•
Potential wiring problems and solutions
•
Guidelines for on-wafer wiring
•
Imperfections of the measurement equipment
System noise floor
•
Example of noise measurement
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
www.ihp-microelectronics.com
© 2007 - All rights reserved
1/f Noise Measurements
Thank you for your attention
IHP Im Technologiepark 25 15236 Frankfurt (Oder) Germany
www.ihp-microelectronics.com
© 2007 - All rights reserved