The document describes a reference die containing thin film PZT capacitors that can aid in piezoelectric characterization using an atomic force microscope (AFM). The die has exposed top electrodes and PZT surfaces to allow piezoelectric force microscopy (PFM) characterization. The packaged die is mounted in an AFM to demonstrate PFM techniques like visualizing polarization switching and domain imaging of the PZT film.

1. Piezoelectric
Characterization in an AFM
Joe T. Evans, Jr,
Radiant Technologies, Inc.
Radiant Technologies, Inc.

2. 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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3. Foundation Process
One half of a
micrometer of PZT, Top Bottom
TiOx, & glass as Electrode Ferroelectric
Electrode
protection material
Half of a
micrometer of
Silicon Dioxide as Silicon wafer
a foundation
• 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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4. 20/80 PZT
80
P o la r iz a tio n (µ C /c m 2 ) 70
60
50
40
30
20
10
0
-1 0
-7 .5 -5 .0 -2 .5 0 .0 2 .5 5 .0 7 .5
V o lt a g e
• Typical hysteresis loop for Radiant 0.26µ 20/80 PZT with
platinum electrodes.
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5. Reference Process
Top Bottom
Electrode Ferroelectric
Electrode
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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6. The Reference Die
The completed die has multiple capacitors ranging from
10µx10µ up to 100,000µ2. The film is 0.26µ 20/80 PZT.
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7. 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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8. 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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9. 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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10. 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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11. 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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12. 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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13. 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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14. 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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15. 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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16. 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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17. 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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18. PFM of Switching Polarization
80
70
60
P o la r iz a tio n (µ C /c m 2 )
50
40
30
20
10
0
-10
-7 .5 -5 .0 -2 .5 0 .0 2 .5 5 .0 7 .5
V o lt a g e
All of the new PFM tools may be applied to the reference.
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19. 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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20. 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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21. Other Measurements
AFM Output Signal
AFM
By connecting the Z-output of an
Conductive
AFM to a polarization tester, a large Tip
array of other tests may be executed
to parallel the PFM measurements.
Polarization Tester
SENSOR Insulator
DRIVE RETURN
Chuck
A wire must run directly
between system grounds.
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22. Butterfly Loop
1.0µ PNZT with platinum electrodes, shown above, moves
approximately 15 Angstroms at 20 volts. The 0.26µ 20/80 PZT is
expected to move approximately 3 Angstroms at 9 volts.
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23. Electrical Properties
Hysteresis Parameters
50
40
uC/cm^2, uA/cm^2, uF/cm^2
30
20
10
Rhyst
0
-6 -4 -2 0 2 4 6 SW CV*10
-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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24. 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.
Radiant Technologies, Inc.
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25. 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.
Radiant Technologies, Inc.
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