Piezoelectric
Characterization in an AFM
Joe T. Evans, Jr,
Radiant Technologies, Inc.
Radiant Technologies, Inc.
Introduction
• Radiant has developed a special packaged die containing
thin PZT film capacitors constructed to aid piezoelectric
characterization in an AFM.
• The capacitors have exposed top electrode and exposed
PZT surfaces over bottom electrode to allow PFM
characterization.
• The devices may also be used to execute more
conventional piezoelectric measurements such as the
butterfly loop.
• All of the characterization techniques that may be
executed on one of these reference devices will be
described in the following presentation.
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Foundation Process
One half of a
micrometer of PZT,
TiOx, & glass as
protection
Half of a
micrometer of
Silicon Dioxide as
a foundation
Top
Electrode
Bottom
Electrode
Ferroelectric
material
Silicon wafer
• Radiant has an established process for thin PZT film
capacitors with platinum electrodes, top glass passivation,
and chrome/gold metal interconnect (not shown).
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20/80 PZT
P o la r iz a t io n (µ C /c m 2 )
80
70
60
50
40
30
20
10
0
-1 0
-7 .5
-5 .0
-2 .5
0 .0
V o lt a g e
2 .5
5 .0
7 .5
• Typical hysteresis loop for Radiant 0.26 20/80 PZT with
platinum electrodes.
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Reference Process
Top
Electrode
Bottom
Electrode
Ferroelectric
material
Silicon wafer
• The reference is fabricated without the ILD passivation
layer to allow electrical access directly to the top electrode.
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The Reference Die
The completed die has multiple capacitors ranging from
10x10 up to 100,0002. The film is 0.26 20/80 PZT.
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Packaging
The die is mounted on a TO-18 transistor header without a lid. The
bottom electrode is bonded to the COMM pin. Any of the other
capacitors may be bonded to the other two free pins.
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Packaging
TO-18
Cap A
Common Cap B
Top view
COMMON
CAP A
CAP B
CASE
The TO-18 package provides a convenient format for handling and
connecting to the integrated capacitors. The packages shown above
have lids. The PFM references do not.
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Mounted in the AFM
• The header (package without a lid) can be soldered to an
experiment board or placed in a socket for alignment under the
AFM cantilever.
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Electrical Connection
With a conductive cantilever tip, the PZT over the bottom electrode
without a top electrode my be scanned and poled.
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PFM of Un-electroded PZT
The un-electroded PZT over bottom electrode as made exhibits the
theoretical distribution of 50:50 polarization orientation.
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PFM of Un-electroded PZT
The un-electroded PZT over bottom electrode as made exhibits the
theoretical distribution of 50:50 polarization orientation.
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PFM of Un-electroded PZT
Using a
conductive tip,
the exposed
PZT over
bottom
electrode can
be poled UP or
DOWN with
the application
of a bias
voltage.
In the image above, the rim outside the poled region is virgin and
was not poled in the opposite direction.
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PFM of Electroded PZT
The electroded PZT may be electrically stimulated either with a
conductive tip or through one of the TO-18 package pins.
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Electrical Connection
TO-18
Bottom electrode
Cap A
Common Cap B
PFM Stimulus Signal
The common is the bottom electrode connection. The PFM signal
can be applied to one of the capacitor top electrodes through a
package pin. In this situation, the cantilever tip provides
displacement information only.
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Electrical Connection
TO-18
Bottom electrode
PFM Stimulus Signal
Cap A
Common Cap B
The common is the bottom electrode connection. The PFM signal
can be applied to one of the capacitor top electrodes through a
package pin. In this situation, the cantilever tip provides
displacement information only.
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PFM of Electroded PZT
Phase maps of the same region poled UP and DOWN yields
information about the presence and distribution of defects.
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PFM of Switching Polarization
P o la r iz a t io n (µ C /c m 2 )
80
70
60
50
40
30
20
10
0
-10
-7.5
-5.0
-2.5
0.0
2.5
V o lt ag e
5.0
7.5
All of the new PFM tools may be applied to the reference.
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PFM of Switching Polarization
Asylum Research
tested a new
software protocol to
capture this movie.
The data took three
hours to collect.
The software
protocol used
landmark
recognition to
correct any X:Y
drift of the stage
between scans.
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Reference Applications
With its high signal-to-noise ratio, a reference may be used
for a variety of applications:
•
•
•
•
•
Activation at less than 10 volts.
Verification of equipment operation
Verification of procedures
Evaluating test procedures on a known-good sample
Materials and polarization switching studies
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Other Measurements
AFM Output Signal
By connecting the Z-output of an
AFM to a polarization tester, a large
array of other tests may be executed
to parallel the PFM measurements.
AFM
Conductive
Tip
Polarization Tester
SENSOR
DRIVE
Insulator
RETURN
Chuck
A wire must run directly
between system grounds.
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Butterfly Loop
1.0 PNZT with platinum electrodes, shown above, moves
approximately 15 Angstroms at 20 volts. The 0.26 20/80 PZT is
expected to move approximately 3 Angstroms at 9 volts.
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Electrical Properties
Hysteresis Parameters
uC/cm^2, uA/cm^2, uF/cm^2
50
40
30
20
10
Rhyst
0
-6
-4
-2
-10
0
2
4
6
SW CV*10
nSW CV*10
-20
SW IV*2.5
-30
nSW IV*2.5
-40
Volts
• Using the AFM as a probe station, the polarization, remanent
polarization, small signal capacitance, and leakage vs voltage
may be measured on the same sample as are the piezoelectric
measurements.
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Conclusion
• It is now possible to measure all electrical and
piezoelectric properties on a single capacitor.
–
–
–
–
–
–
–
Polarization hysteresis
Small signal capacitance hysteresis
Current vs Voltage
Butterfly loop
Small signal displacement
PFM amplitude and phase maps
PFM d33 loop
• Measurement and comparison of these measurements on a
single sample will improve our understanding of the nature
of piezoelectric materials.
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Acknowledgements
An Asylum Research MFP-3D AFM with an Arc2 controller
were used to capture the images in this presentation. Radiant
would like to acknowledge Asylum Research and its employees for
their assistance in this work.
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