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Radiant Technologies, Inc.
Ångstrom-Level Piezoelectric
Measurement
Joe T. Evans, Jr., Scott Chapman, Bob Howard, Spencer
Smith, Michelle Bell
Radiant Technologies, Inc.
Presented May 08 at the 2013 International Workshop on Acoustic
Transduction Materials and Devices at Penn State University
Radiant Technologies, Inc.
Summary
• Motivation
• Equipment Architecture
• Calibration
• Piston Displacement
• MEMs Measurement
• Future Objectives
All of the test samples shown
below were fabricated by
Radiant.
Radiant Technologies, Inc.
Why Measure Ångstroms?
• Thin ferroelectric and piezoelectric films have great
potential to impact the future economy.
More sensitive sensors
Tiny machines
Autonomous memory
• Radiant already offers advanced piezoelectric tasks to
interface existing AFMs, vibrometers, and other
displacement meters with our testers.
• After years of looking, we have now found an affordable
instrument to measure absolute Ångstroms.
Radiant Technologies, Inc.
Measurement Techniques
• Atomic Force Microscope
Piston motion of capacitor
surface.
• Laser Vibrometer
- 5 .0
- 2 .5
0 .0
2 .5
5 .0
7 .5
1 0 .0
1 2 .5
- 2 0 - 1 5 - 1 0 - 5 0 5 1 0 1 5 2 0
D i s p l a c e m e n t - A v e r a g e d[ S m o o t h e d a n d Z - c o r r e c t e d ]
An
gs
tr
om
s
V o l t s
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
-30 -20 -10 0 10 20 30
Displacement - Averaged [ Smoothed and Z-corrected ]
Smoothed Average
Nan
om
ete
rs
Volts
Asylum SA
Polytec OFV534/OFV5000
Radiant Technologies, Inc.
Noise is Ever Present
• Averaged and Smoothed
• Original Data
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
-30 -20 -10 0 10 20 30
Displacement - Averaged [ Smoothed and Z-corrected ]
Smoothed Average
Nan
om
ete
rs
Volts
Even on an exceptionally
quiet commercial AFM,
noise is significant.
Radiant Technologies, Inc.
Goal
• Find a method to
Inexpensively measure ferroelectric and piezoelectric
displacement loops of thin films.
Create a system that the average university lab could
afford.
Guarantee a level of absolute displacement accuracy.
Radiant Technologies, Inc.
System Architecture
Digital microscope camera
Light lever
Sample holder
Z-piezo element Manual sample
positioning
Radiant Technologies, Inc.
Control System Operation
• For Ångstrom-level displacements, the PNDS looks directly at the
Error Function. The test is run faster than the GPID can respond.
• For MEMs-level displacements, the PNDS looks at the Control Signal.
The test is run slowly so the GPID can respond.
Quad Cell Laser
Reference
GPID HVA
-
+
Error Function
(Piston)
Control Signal
(pMEMs)
Chuck
PZT Actuator
Radiant Technologies, Inc.
Custom Sample Holders
Because the system is
inexpensive, we can safely
experiment with different
mounting techniques for different
samples.
Radiant Technologies, Inc.
In-Contact Surface Scan
• We are interested in putting the cantilever in one spot in contact mode. A small
in-contact surface scan capability allows small features to be found and targeted.
Radiant Technologies, Inc.
Piston Displacement The vertical displacement of the top surface of the capacitor with voltage
application: converse d33.
Because the capacitor is
clamped by the substrate, we
assume that a single-sided
measurement is reasonably
accurate.
Radiant Technologies, Inc.
Compare
The Polytec laser vibrometer has an absolute distance reference in the
wavelength of its laser light. Amplitudes of the PNDS measurements
when properly calibrated compare well with the laser vibrometer.
-10
-5
0
5
10
15
-30 -20 -10 0 10 20 30
An
gstr
om
s
Volts
Polytec Laser Vibrometer vs PNDS
Polytec
PNDS
1m-thick 4/20/80 PNZT with platinum electrodes – 1kHz.
Radiant Technologies, Inc.
Calibration
Step #1: Do a surface scan of a calibrated reference sample to
calibrate the piezo Z-element.
Step #2: Execute a FORCE-DISTANCE curve pushing
on the cantilever with the now calibrated piezo
Z-element to calibrate the photo-sensor
App Nano SHS-0.1-3 1000Å Reference Grid Force-Distance Measurement AFM Workshop
Radiant Technologies, Inc.
Noise Reduction
The measurements are noisy at such small displacements.
Noise reduction procedure:
Make multiple measurements
Move each loop to the origin
Remove “tilt” in the loop due to Z-drift
Average all of the loops.
Smooth the averaged loop.
Radiant Technologies, Inc.
Noise Filtering
Raw data vs filtered loop.
- 5 .0
-2 .5
0 .0
2 .5
5 .0
7 .5
1 0 .0
-2 0 -1 5 -1 0 -5 0 5 1 0 1 5 2 0
A d v a n c e P i e z o A v g 4 0 @ 2 m s B e f o r e R e c o v e r y[ T y p e A C W H I T E ]
An
gs
tro
ms
V o l t s
- 40
- 30
- 20
- 10
0
10
20
30
40
50
- 20 - 15 - 10 - 5 0 5 10 15 20
A d v a n c e P ie z o A v g 4 0 @ 2 m s
An
gs
tr
om
s
V o l t s
R a w D i s p 1 R a w D i s p 2 R a w D i s p 3 R a w D i s p 4 R a w D i s p 5 R a w D i s p 6 R a w D i s p 7
R a w D i s p 8 R a w D i s p 9 R a w D i s p 1 0 R a w D i s p 1 1 R a w D i s p 1 2 R a w D i s p 1 3 R a w D i s p 1 4
Radiant Technologies, Inc.
MEMs Cantilever Measurement
1.2mm
Radiant Technologies, Inc.
Cantilever Motion
PNDS cantilever capturing butterfly motion of resonator
edge.
- 5 0
-2 5
0
2 5
5 0
7 5
1 0 0
-1 5 -1 0 -5 0 5 1 0 1 5
A c tu a to r E d g e D is p la c e m e n t[ p M E M s - 1 2 0 1 R S 1 o n T O - 1 8 ]
An
gs
tro
ms
V o l t s
Average of ten 1-second loops.
Radiant Technologies, Inc.
Complex Cantilever Motion
By measuring at different parts of the resonator as it is flexed in pseudo-
static piezoelectric motion, more complex behavior is revealed.
Radiant Technologies, Inc.
Complex Cantilever Motion
Construct of cantilever motion. Single-sided voltage
application should make the cantilever bend upwards in a
smooth curve. This cantilever does not.
-100
-75
-50
-25
0
25
50
75
100
0.0 2.5 5.0 7.5 10.0 12.5 15.0
-100
-75
-50
-25
0
25
50
75
100
0.0 2.5 5.0 7.5 10.0 12.5 15.0
Pro
cessed P
iezo D
ispla
cem
ent
-100
-75
-50
-25
0
25
50
75
100
0.0 2.5 5.0 7.5 10.0 12.5 15.0
Pro
cessed P
iezo D
ispla
cem
ent
-100
-75
-50
-25
0
25
50
75
100
0.0 2.5 5.0 7.5 10.0 12.5 15.0
Pro
cessed P
iezo D
ispla
cem
ent
-100
-75
-50
-25
0
25
50
75
100
0.0 2.5 5.0 7.5 10.0 12.5 15.0
Pro
cessed P
iezo D
ispla
cem
ent
Radiant Technologies, Inc.
Complex Cantilever Motion @ 110kHz
Because the structure and the support arms are so thin, the
device has very complex mechanical motion.
Radiant Technologies, Inc.
e31 Measurement
• Radiant is going to pursue a possible e31 measurement
using the Kanno method.1
• The technique derives e31 from the displacement of the tip
of a cantilever due to voltage application.
• Accuracy depends upon the cantilever acting “perfectly”.
• For this technique to work, the silicon substrate under the
cantilever must be thick enough to force proper “arching”
of the cantilever.
1I Kanno, H Kotera , K Wasa, “Measurement of transverse piezoelectric properties of PZT
thin films”, Sensors and Actuators A 107 (2003) 68–74
Radiant Technologies, Inc.
Repeatability
-100
-50
0
50
100
150
-15 -10 -5 0 5 10 15
p M E M s - 1 2 0 1 R S 1 o n T O - 1 8
Dis
pla
ce
me
nt
V o lt ag e
Ad v P -15 V 1s -M o n o p o l a r : P o l a r i z a t i o n (µC / c m 2): Ad v P 15 V 1s +M o n o p o l a r : P o l a r i z a t i o n (µC / c m 2 ): 1
Ad v P 15 V 1s B i p o l a r : P o l a r i z a t i o n (µC / c m 2): 1
Radiant Technologies, Inc.
True AFMs and Vibrometers
• The PNDS is intended to be an inexpensive
system for small materials programs.
• All of the measurement techniques described here
work with more advanced commercial AFMs and
with sensitive laser vibrometers.
Radiant Technologies, Inc.
Future Efforts
• Calibration procedures must be fully verified.
• Custom sample mounts must be completed.
• Documentation and operating procedures must be
finished.
Radiant Technologies, Inc.
Acknowledgement
• The authors would like to thank Gabe Smith at Army
Research Laboratory Adelphi for the movie of the
piezoMEMs dynamic motion.