STUDY OF TRANSPARENT STUDY OF TRANSPARENT FERROELECTRIC THIN FILMS BY FERROELECTRIC THIN FILMS BY OPTICAL REFLECTOMETRY AND OPTICAL REFLECTOMETRY AND

ELLIPSOMETRYELLIPSOMETRY I. AulikaI. Aulika

Institute of Solid State Physics, University of Latvia, Riga, LatviaInstitute of Solid State Physics, University of Latvia, Riga, Latvia

Ferrolectric thin films are used:high dielectric constant capacitorsnon-volatile memoriesinfrared sensors electro-optic devices

Optical properties for ferroelectric thin films have been relatively rarely studied.

Are investigated:Dielectric and optical properties for ferroelectric bulk materialsDielectric properties for ferroelectric thin films

Reflective coefficient

R

Main ellipsometric angles ,

Reflactive n and absorbtion k coefficients,

thickness

Light in the Light in the visible spectrum visible spectrum

regionregion

Computer with Computer with CCD spectrometerCCD spectrometer

SampleSample

Optical fibre Optical fibre inputinput

Illustrative sham for Illustrative sham for reflectometry measurementsreflectometry measurements

Ellipsometer shamEllipsometer sham

//44 lamina lamina

PolarizerPolarizer

CompensatorCompensator

SampleSample

AnalyserAnalyser

DetectorDetector

He-Ne laser He-Ne laser 632.8nm632.8nm

00 00

Reflective index:

Rp = M21p / M11p

Rs = M21s / M11s

Idea of the matrix methodMij s,p = I01 s,p L1 I12 s,p L2 I23 …Iij s,p Lj Ij+1

Last layer1st layerBoundary interface

2nd layer

Ellipsometric formula:

tg e = Rp / Rs

Multilayer modelMultilayer model

Mean square error = (fexp-fteor)2

BaTiOBaTiO33 BTBT derivation tech.: derivation tech.: laser laser ablation ablation 11))

Pb(TiPb(Ti0,480,48ZrZr0,520,52)O)O33 PZT sol-gel PZT sol-gel22)), laser , laser ablation ablation

Pb(MgPb(Mg0.660.66NiNi0.340.34)O)O3 3 PMN rf sputteringPMN rf sputtering33))

1)1) In collaboration with Solid state and material research institute in Dresden, In collaboration with Solid state and material research institute in Dresden, IFM-Dresden, GermanyIFM-Dresden, Germany2)2) In collaboration with Yosef Stefan Institute in Slovenia In collaboration with Yosef Stefan Institute in Slovenia3) 3) In collaboration with University of Sarland, GermanyIn collaboration with University of Sarland, Germany

Samples

SiO2

Au

PZT PtTi

Si

300 400 500 600 700 8002,8

3,0

3,2

3,4

3,6

3,8

4,0

0,00

0,01

0,02

0,03

0,04

0,05

0,06

k

n

, nm

BT P532A n = n()

k = k()

ResultsResultsRefraction Refraction nn and absorption and absorption kk coefficients for BT thin film coefficients for BT thin film (thickness 340 (thickness 340 7nm as calculated from reflectometric data; 7nm as calculated from reflectometric data; sol-gel technique).sol-gel technique).

300 400 500 600 700 8002,4

2,5

2,6

2,7

2,8

2,9

3,0

0,00

0,01

0,02

0,03

0,04

0,05

PZT, L36, sol-gel technique n = n()

k

n

, nm

PZT, P582A, laser ablation technique n = n()

k = k()

k = k()

The refractive index The refractive index nn and extinction coefficient and extinction coefficient kk of of PZT PZT deposited by laser ablation (thickness 250nm) and so-gel deposited by laser ablation (thickness 250nm) and so-gel (thickness 300nm ) technique.(thickness 300nm ) technique.

300 400 500 600 700 8002,5

2,6

2,7

2,8

2,9

3,0

3,1

k

n

, nm

PMN C25 n = n()

0,00

0,04

0,08

0,12

0,16

0,20

k = k()

Refraction Refraction nn and absorption and absorption kk coefficients for PMN thin film coefficients for PMN thin film (thickness 770(thickness 770 10nm, as calculated from reflectometric data 10nm, as calculated from reflectometric data laser ablation technique). laser ablation technique).

0 100 200 300 400 5002,48

2,49

2,50

2,51

2,52

2,53

2,54

k

t0C

n

PZT L36 n = n(t)

0,000

0,002

0,003

0,005

0,006

0,007

0,009

k = k(t)

Temperature dependence of refractive Temperature dependence of refractive nn and absorption and absorption kk indexes of PZT film indexes of PZT film (thickness 300nm)(thickness 300nm) at at wavelengthwavelength 632,8nm. 632,8nm. Temperature slowly raised at average rate 4°C/minute.Temperature slowly raised at average rate 4°C/minute.

ConclusionsConclusions

Ellipsometric and reflectometric measurements has been Ellipsometric and reflectometric measurements has been successfully applied for the thickness, refractive and absorption successfully applied for the thickness, refractive and absorption coefficient determination of BT, PZT, PMN thin films. Optical coefficient determination of BT, PZT, PMN thin films. Optical properties and thickness are well described by multilayer model. properties and thickness are well described by multilayer model.

Slight variation of refractive index by factor 1.02 and Slight variation of refractive index by factor 1.02 and absorption coefficient by factor of 1.04 has been observed in absorption coefficient by factor of 1.04 has been observed in comparison of sol-gel and laser ablation deposited samples, comparison of sol-gel and laser ablation deposited samples, respectively. respectively.

ObservedObserved temperature dependence of temperature dependence of the the refractive index refractive index and and the absorption coefficient in the temperature range above the absorption coefficient in the temperature range above 400°C 400°C isis described by described by diffuse ferroelectric/paraelectric phase diffuse ferroelectric/paraelectric phase transitiontransition

AckowledgementAckowledgement

The author is thankful V.ZaulsThe author is thankful V.Zauls1)1), K.Kundzins, K.Kundzins2)2) for for valuable discussions. valuable discussions.

This work was supported by This work was supported by K.K.Morberg Morberg scholarshipscholarship of Latvian University. of Latvian University.

1, 2)1, 2) Institute of Solid State Physics, University of Latvia Institute of Solid State Physics, University of Latvia

400 500 600 700 8000

20

40

60

80

R,%

, nm

300 400 500 600 700 800800

1200

1600

2000

2400

2800

, nm

nd, n

m

0 20 40 60 80 10010

20

30

40

50

60

70

80

90

, (

0 )

0, (0)a)

0 20 40 60 80 100

-200

-150

-100

-50

0

50

100

150

200

0, (0)b)

, (

0 )

Thank you for attention !