Investigation of the Pb depletion in Single and Dual Pulsed Laser

Deposited Epitaxial PZT Thin films and their Structural characterizationDevajyoti Mukherjee, R. Hyde, T. Dhakal, S. Hariharan, P. Mukherjee and S. Witanachchi

Department of Physics & Center for Integrated Functional Materials (CIFM), University of South Florida, Tampa, FL 33620.

Dual-Laser PLD with the ICCD Imaging System

UV Detector

Excimer Laser

CO2 Laser

IR Detector

Oscilloscope

Rotating Target

Vacuum

ChamberSubstrate

Heater10.00ns

Lens System

Digital Delay

Generator

ICCD

Sync Out

Trig In

Trig InICCD Sync

Control PC

0

50

100

150

200

250

300

350

400

450

0 100 200 300 400 500 600 700 800 900 1000

Time (ns)

Vo

lta

ge (

mV

)

UV

IR

100ns

The time-resolved oscilloscope traces of the

excimer and CO2 laser pulses from the UV and

IR detectors.

Photograph of laser

ablated plume

Experimental Details

Problem !!

High volatility of Pb in PZT leads to Pb depletion

in deposited films lowering ferroelectric

properties.

Solution !!

Dual laser ablation to produce high Pb

content films with less particulates using

low excimer energy.

??

Advantages of Pulsed Laser Deposition technique :

Stoichiometric transfer of materials from target to films

Fast and versatile method for in-situ hetero-structure growth

Plume of highly energetic materials have sufficient ion

mobility for the growth of epitaxial thin films

Ferroelectric / ferromagnetic hetero-structures

Laser ablation for film growth

FIB image of Cobalt Ferrite-PZT bilayer

PZT (100)

Cobalt Ferrite (100)

MgO (100)

IntroductionMotivation: Increasing demands for high-quality defect- free

epitaxial lead zirconium titanate PbZr0.52Ti0.48O3 (PZT) thin

films in present market

Applications : PZT thin films are successfully used in

non-volatile random access memory devices (FeRAM)

micro actuators and ultrasonic sensors

Pulsed laser deposition (PLD) to grow multi- layered

PZT based hetero-structures for multi-ferroic device

applications

NEW

UV 1 J/cm2 IR 2 J/cm2 UV 2 J/cm2 IR 2 J/cm2 UV 3 J/cm2 IR 2 J/cm2 UV 1 J/cm2 IR 2 J/cm2

SEM images of irradiated target surfaces after 1000 pulses using dual laser

ablation for different excimer fluences and 2 J/cm2 CO2 laser and 100 ns peak to

peak interpulse delay in 500 mT O2 ambient.

Chemical compositions using EDS analysis of the ablated target surfaces versus

fluence. (Dual laser ablation)

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

0 1 2 3 4 5Excimer Fluence (J/cm 2)

Ato

mic

% P

b/(

Zr+

Ti)

0.38

0.42

0.46

0.50

0.54

0.58

0.62

0 1 2 3 4 5Excimer Fluence (J/cm 2)

Ato

mic

%/(

Zr+

Ti)

Zr

Ti

Dual Laser Ablation

ACKNOWLEDGMENTSThis work was supported in part by the National Science Foundation under the grants

DMI-0217939, DMI-0078917 and by the Department of Defense under the grant W81XWH- 07-1-0708.

Conclusion

Using a dual laser ablation process high Pb content, particulate free, smooth

and epitaxial PZT films with the desired perovskite structure and no impurity

phases were grown.

This technique could be generalized to all multi-component thin film growth

where high volatility of one of the elements leads to non-stoichiometric transfer

of materials in the PLD process.

Optical-plume diagonostics

0 (µs)

1 cm

1 (µs)

1 cm

2(µs)

1 cm

4 (µs)

1 cm

6 (µs)

1 cm

8 (µs)

1 cm

Time gated ICCD images using 200 ns exposure time of single laser ablated

plumes from PZT target using 2 J/cm2 fluence under 500 mT O2 gas. (Plume

propagation)

1 cm

UV 1 J/cm2 UV 2 J/cm2 UV 3 J/cm2 UV 4 J/cm2

1 cm1 cm 1 cm

1 cm 1 cm 1 cm 1 cm

UV 1 J/cm2 IR 2 J/cm2 UV 1 J/cm2 IR 2 J/cm2 UV 1 J/cm2 IR 2 J/cm2 UV 1 J/cm2 IR 2 J/cm2

ICCD images of total visible emission spectra of single laser plumes (top row)

varying the excimer (UV) fluences from 1 to 4 J/cm2 and dual laser plumes

(bottom row) varying excimer fluences keeping 2 J/cm2 CO2 (IR) fluence and

100 ns peak to peak inter-pulse delay

Thin film properties

20 30 40 50 60 70 80

ST

O (100)

ST

O (200)

ST

O (300)

PZT

(003)

PZT

(002)

PZT

(001)

2222ThetaThetaThetaTheta(deg )(deg )(deg )(deg )

ln(Int

ensit

y)(

arb. u

nit )

ln(Int

ensit

y)(

arb. u

nit )

ln(Int

ensit

y)(

arb. u

nit )

ln(Int

ensit

y)(

arb. u

nit )

Single laser 5 J/cm2

Dual laser 1 J/cm2UV 2 J/cm

2IR

Single laser 2 J/cm2

-1.5 -0.5 0.5 1.5

ɷ (deg)

Inte

nsit

y (

arb

. u

nit

)

Single

laser

Dual laser

XRD ϴ-2ϴ scans and rocking curves about PZT (200) plane for single and dual

laser deposited films grown on SrTiO3 (STO) (100) substrates.

S 5 J/cm2

FWHM = 0.536˚̊̊̊

D 1J/cm2UV 2J/cm2IR

FWHM = 0.541˚̊̊̊

(a) (c)(b)0

25 nm

5 μμμμm5 μμμμm 5 μμμμm

0 0

30 nm 150 nm

AFM images of PZT films deposited using single laser fluences (a) 2J/cm2 (b)

5J/cm2 and (c) dual laser ablation. Surface roughnesses for (a), (b) and (c) are 3

nm, 12 nm and 2 nm respectively.

SEM images and chemical compositions of the PZT films grown on STO

substrates at 550˚C and 500mT O2 pressure using single and dual laser

ablation. Film thicknesses about 350nm.

0

0.2

0.4

0.6

0.8

1

Single laser 2J/cm2 Single laser 5J/cm2 Dual laser

Films under different conditions

At.

% P

b

References1. P. Mukherjee et al., Appl. Surface Science 127-129 (1998) 620-625

2. S. Witanachchi et al., Appl. Phys. Lett. 66, 1469 (1995)

3. X. Y. Chen et al., Appl. Phys. A 69 [Suppl.], S523-S525 (1999)

4. S. Witanachchi et al., J. Vac. Sci. Technol. A, Vol 13, No. 3 (1995)

5. P. Mukherjee et al., Appl. Phys. Lett. 74, 1546 (1999)

Laser-Target Interactions

Results

0.5

0.7

0.9

1.1

1.3

1.5

0 1 2 3 4 5 6

Excimer Fluence (J/cm 2)

Ato

mic

% P

b/(

Zr+

Ti)

0.40

0.45

0.50

0.55

0.60

0 1 2 3 4 5 6

Excimer Fluence (J/cm 2)

Ato

mic

%/(

Zr+

Ti)

PZT (+ 30 at. % PbO)

PZT

Zr

Ti

Chemical compositions using EDS analysis of the ablated target surfaces versus

fluence. (Single laser ablation)

Single Laser Ablation

SEM images of a PZT target surface after irradiation by 1000 pulses of a KrF

laser beam in 500 mT O2 ambient at different UV fluences.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

T1 T2 T3 T4 T5 T6 T7 T8 T9T10 T11 T12 T13 T14 S

1S2

S3

S4

S5

S6

S7

S8

S9

S10

S11

S12

S13

S14

Spectrum

At.

%

At.% Pb

At.%Ti

At%Zr

Cone tops Cone sides

Point ID EDS of column tops and sides : Cone tops were Pb deficient

UV 1J/cm2 UV 5J/cm2UV 4J/cm2UV 2J/cm2

20 25 30 35 40 45 50 55 60

[001/1

00]

[101/1

10]

[111]

[002/2

00]

[102/2

01]

[112/2

11]

Inten

sity (

arb. u

nits )

Inten

sity (

arb. u

nits )

Inten

sity (

arb. u

nits )

Inten

sity (

arb. u

nits )

2222ThetaThetaThetaTheta ( deg ) ( deg ) ( deg ) ( deg )

Pb

O [

002]

Pb

O [

220]

Pb

O [

020]

Pb

O [

111]

PbZr0.52

Ti0.48

O3 (+ 30 at.% PbO) target

PbZr0.52

Ti0.48

O3 target

(Left) XRD data for the PZT targets.

(Top) SEM images of typical PZT target surface

before/after irradiation by laser.

Before ablation

2 m

m

3 mm

Peak to peak Interpulse Delay in Dual Laser Ablation

0.0

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0.8

0.9

1.0

0 100 200 300 400 500 600 700 800 900 1000

Time (ns)

No

rm

ali

zed

Vo

lta

ge .

0.0

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1.0

0 100 200 300 400 500 600 700 800 900 1000

Time (ns)

No

rm

ali

zed

Vo

lta

ge .

0.0

0.1

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0.3

0.4

0.5

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0.7

0.8

0.9

1.0

0 100 200 300 400 500 600 700 800 900 1000

Time (ns)

No

rm

ali

zed

Vo

lta

ge .

0.0

0.1

0.2

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0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 100 200 300 400 500 600 700 800 900 1000

Time (ns)

No

rm

ali

zed

Vo

lta

ge .

100 ns 50 ns 0 ns - 50 ns

Chemical compositions of the ablated target surfaces versus peak

to peak interpulse delay.

0.4

0.5

0.6

0.7

0.8

0.9

1

-100 0 100 200 300

Peak to peak Delay (ns)

Ato

mic

%

Pb

Zr

Ti

←--------------------------------------------- Time (ns) ----------------------------------------------→