Ångstrom-level piezoelectric measurement...radiant technologies, inc. Ångstrom-level piezoelectric...

Radiant Technologies, Inc.

Ångstrom-Level Piezoelectric

Measurement

Joe T. Evans, Jr., Scott Chapman, Bob Howard, Spencer

Smith, Michelle Bell

Presented May 08 at the 2013 International Workshop on Acoustic

Transduction Materials and Devices at Penn State University

Summary

• Motivation

• Equipment Architecture

• Calibration

• Piston Displacement

• MEMs Measurement

• Future Objectives

All of the test samples shown

below were fabricated by

Radiant.

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.

Measurement Techniques

• Atomic Force Microscope

Piston motion of capacitor

surface.

• Laser Vibrometer

- 5 .0

- 2 .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 ]

V o l t s

-30 -20 -10 0 10 20 30

Displacement - Averaged [ Smoothed and Z-corrected ]

Smoothed Average

Asylum SA

Polytec OFV534/OFV5000

Noise is Ever Present

• Averaged and Smoothed

• Original Data

-30 -20 -10 0 10 20 30

Displacement - Averaged [ Smoothed and Z-corrected ]

Smoothed Average

Even on an exceptionally

quiet commercial AFM,

noise is significant.

• 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.

System Architecture

Digital microscope camera

Light lever

Sample holder

Z-piezo element Manual sample

positioning

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)

PZT Actuator

Custom Sample Holders

Because the system is

inexpensive, we can safely

experiment with different

mounting techniques for different

samples.

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.

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.

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.

-30 -20 -10 0 10 20 30

Polytec Laser Vibrometer vs PNDS

Polytec

1m-thick 4/20/80 PNZT with platinum electrodes – 1kHz.

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

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.

Noise Filtering

Raw data vs filtered loop.

- 5 .0

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 ]

V o l t s

- 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

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

MEMs Cantilever Measurement

Cantilever Motion

PNDS cantilever capturing butterfly motion of resonator

-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 ]

V o l t s

Average of ten 1-second loops.

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.

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.

0.0 2.5 5.0 7.5 10.0 12.5 15.0

cessed P

iezo D

0.0 2.5 5.0 7.5 10.0 12.5 15.0

cessed P

iezo D

0.0 2.5 5.0 7.5 10.0 12.5 15.0

cessed P

iezo D

0.0 2.5 5.0 7.5 10.0 12.5 15.0

cessed P

iezo D

Complex Cantilever Motion @ 110kHz

Because the structure and the support arms are so thin, the

device has very complex mechanical motion.

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

Repeatability

-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

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

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.

Future Efforts

• Calibration procedures must be fully verified.

• Custom sample mounts must be completed.

• Documentation and operating procedures must be

finished.

Acknowledgement

• The authors would like to thank Gabe Smith at Army

Research Laboratory Adelphi for the movie of the

piezoMEMs dynamic motion.

Ångstrom-level piezoelectric measurement...radiant technologies, inc. Ångstrom-level piezoelectric...

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