piezo responce force microscopy

Radiant Technologies, Inc.

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.


Foundation Process

• Radiant has an established process for thin PZT film capacitors with platinum electrodes, top glass passivation, and chrome/gold metal interconnect (not shown).

Silicon wafer

Half of a micrometer of

Silicon Dioxide as a foundation

One half of a micrometer of PZT,

TiOx, & glass as protection

Top Electrode

Bottom Electrode Ferroelectric

material


20/80 PZT

• Typical hysteresis loop for Radiant 0.26 20/80 PZT with platinum electrodes.

-10

0

10

20

30

40

50

60

70

80

-7.5 -5.0 -2.5 0.0 2.5 5.0 7.5

Po

lari

za

tio

n (

µC

/cm

2)

Voltage


Reference Process

• The reference is fabricated without the ILD passivation layer to allow electrical access directly to the top electrode.

Silicon wafer

Top Electrode

Bottom Electrode Ferroelectric

material


The Reference Die

The completed die has multiple capacitors ranging from 10x10 up to 100,0002. The film is 0.26 20/80 PZT.


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.


Packaging

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.

Top view

COMMON CAP A

CAP B CASE

Cap A Cap BCommon

TO-18


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.


Electrical Connection

With a conductive cantilever tip, the PZT over the bottom electrode without a top electrode my be scanned and poled.


PFM of Un-electroded PZT

The un-electroded PZT over bottom electrode as made exhibits the theoretical distribution of 50:50 polarization orientation.



The un-electroded PZT over bottom electrode as made exhibits the theoretical distribution of 50:50 polarization orientation.



In the image above, the rim outside the poled region is virgin and was not poled in the opposite direction.

Using a conductive tip, the exposed PZT over bottom electrode can be poled UP or DOWN with the application of a bias voltage.


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.



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.

Cap A Cap BCommon

TO-18

PFM Stimulus Signal

Bottom electrode


PFM of Electroded PZT

Phase maps of the same region poled UP and DOWN yields information about the presence and distribution of defects.


-10

0

10

20

30

40

50

60

70

80

-7.5 -5.0 -2.5 0.0 2.5 5.0 7.5

Po

lari

zati

on

(µ

C/c

m2

)

Voltage

PFM of Switching Polarization

All of the new PFM tools may be applied to the reference.


PFM of Switching PolarizationAsylum 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.


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


Other Measurements

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.

Polarization Tester

RETURN

SENSOR

DRIVE

Insulator

Chuck

Conductive Tip

AFM

A wire must run directly between system grounds.

AFM Output Signal


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.


Electrical Properties

• 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.

Hysteresis Parameters

-40

-30

-20

-10

0

10

20

30

40

50

-6 -4 -2 0 2 4 6

Volts

uC

/cm

^2

, uA

/cm

^2

, uF

/cm

^2

Rhyst

SW CV*10

nSW CV*10

SW IV*2.5

nSW IV*2.5


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.


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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