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Electro-Optical Na0.5K0.5NbO3 Films
KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Ferroelectric oxides are a group of advanced electronic materials with a wide variety of properties useful in applications such as memory devices, resonators and filters, infrared sensors, microelectromechanical systems, and optical waveguides and modulators.

Among the oxide perovskite-structured ferroelectric thin film materials, sodium potassium niobate or Na0.5K0.5NbO3 (NKN) has recently emerged as one of the most promising materials in radio frequency (rf) and microwave applications due to high dielectric tenability and low dielectric loss.

This thesis presents results on growth and structural, optical, and electrical characterization of NKN thin films. The films were deposited by rf-magnetron sputtering of a stoichiometric, high density, ceramic Na0.5K0.5NbO3 target onto single crystal LaAlO3 (LAO), Al2O3 (sapphire), SrTiO3, and Nd:YAlO3, and polycrystalline Pt80Ir20 substrates. By x-ray diffractometry, NKN films on c-axis oriented LaAlO3, SrTiO3 and Nd:YAlO3 substrates were found to grow epitaxially, whereas films on r-cut sapphire and polycrystalline Pt80Ir20 substrates were found to be preferentially (00l) oriented. The surface morphology was explored using atomic force microscopy.

Optical and waveguiding properties of the Na0.5K0.5NbO3/substrate heterostructures were characterized using prism-coupling technique. Sharp and distinguishable transverse magnetic and electric propagation modes were observed for NKN thicknesses up to 2.0 μm. The extraordinary and ordinary refractive indices were calculated together with the birefringence of the NKN material. The electro-optic effect in transverse geometry was measured in transmission, where the effective linear electro-optic response was determined to reff = 28 pm/V for NKN/Al2O3 with an applied dc field up to 18 kV/cm.

The ferroelectric state in NKN films on Pt80Ir20 at room temperature was indicated by a polarization loop with saturated polarization as high as 33.4 μC/cm2 at 700 kV/cm, remnant polarization of 10 μC/cm2, and coercive field of 90 kV/cm. Current-voltage characteristics of vertical Au/NKN/PtIr capacitive cells and planar Au/NKN/LAO interdigital capacitors (IDCs) showed very good insulating properties, with the leakage current density for an NKN IDC on the order of 30 nA/cm2 at 400 kV/cm. Rf dielectric spectroscopy demonstrated low loss, low frequency dispersion, and high voltage tunability. At 1 MHz, NKN/LAO showed a dissipation factor tan δ = 0.010 and a tunability of 16.5 % at 200 kV/cm. For the same structure the frequency dispersion was Δεr = 8.5 % between 1 kHz and 1 MHz.

Place, publisher, year, edition, pages
Stockholm: KTH , 2005. , xii, 91 p.
Series
Trita-FYS, ISSN 0280-316X ; 5299
Keyword [en]
Functional materials, ferroelectrics, sodium potassium niobates, thin films, rf-magnetron sputtering, waveguiding, refractive index, prism-coupling, electro-optic effects, dielectric tunability
Keyword [sv]
Funktionella material
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-193ISBN: 91-7178-007-6 (print)OAI: oai:DiVA.org:kth-193DiVA: diva2:7865
Public defence
2005-05-20, D1, KTH, Lindstedtsvägen 17, 2tr, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100928Available from: 2005-05-12 Created: 2005-05-12 Last updated: 2010-09-28Bibliographically approved
List of papers
1. High-performance epitaxial Na0.5K0.5NbO3 thin films by magnetron sputtering
Open this publication in new window or tab >>High-performance epitaxial Na0.5K0.5NbO3 thin films by magnetron sputtering
Show others...
2002 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 81, no 2, 337-339 p.Article in journal (Refereed) Published
Abstract [en]

Epitaxial Na0.5K0.5NbO3 (NKN) thin films have been grown on LaAlO3 substrates by rf magnetron sputtering of a stoichiometric, high-density, ceramic target. X-ray diffraction analysis showed c-axis oriented cube-on-cube growth. Micrometer size interdigital capacitor (IDC) structures were defined on the surface of the NKN film using photolithography. The electrical characterization at 1 MHz showed dissipation factor tan delta of 0.010, tunability 16.5% at 200 kV/cm and dielectric permittivity epsilon(r)=470. The frequency dispersion of epsilon(r) between 1 kHz and 1 MHz was 8.5% and the IDCs showed very good insulating properties with leakage current density on the order of 30 nA/cm(2) at 400 kV/cm. The polarization loop exhibits weak ferroelectric hysteresis with maximum polarization 23.5 muC/cm(2) at 600 kV/cm. These results are promising for tunable microwave devices based on rf sputtered NKN thin films.

Keyword
interdigital capacitors
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-21649 (URN)10.1063/1.1492854 (DOI)000176487400051 ()
Note
QC 20100525Available from: 2010-08-10 Created: 2010-08-10 Last updated: 2010-09-28Bibliographically approved
2. Rf-magnetron sputtered ferroelectric (Na,K)NbO3 films
Open this publication in new window or tab >>Rf-magnetron sputtered ferroelectric (Na,K)NbO3 films
2002 (English)In: Proceedings of the 13th IEEE International Symposium on Applications of Ferroelectronics / [ed] White, G.; Tsurumi, T., 2002, 195-198 p.Conference paper, Published paper (Refereed)
Abstract [en]

Sodium potassium niobate (Na,K)NbO3 (NKN) thin films were grown by rf-magnetron sputtering from stoichiometric Na0.5K0.5NbO3 target on LaAlO3 (LAO) single crystals and polycrystalline Pt80Ir20 (PtIr) substrates. NKN films on polycrystalline PtIr substrates were found to be preferentially (004 oriented while XRD measurements reveal epitaxial quality of NKN/LaAlO3 film structures. The ferroelectric state in NKN/PtIr films at room temperature is indicated by polarization loops with polarization as high as 33.4 muC/cm(2) at 700 kV/crn, remnant polarization of 9.9 muC/cm(2), and coercive field of 91 kV/cm. I-V characteristics of vertical Au/NKN/PtIr capacitive cells and planar Au/NKN/LAO interdigital capacitors (IDCs) showed very good insulating properties. For NKN IDC the leakage current density was in the order of 30 nA/cm(2) at 400 kV/cm. Rf dielectric spectroscopy demonstrates low loss, low frequency dispersion, and high voltage tunability both for vertical Au/NKN/PtIr and planar interdigital Au/NKN/LAO capacitors.

Keyword
Capacitors, Coercive force, Crystal orientation, Epitaxial growth, Insulation, Magnetron sputtering, Polycrystalline materials, Stoichiometry, Remnant polarization
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-5097 (URN)10.1109/ISAF.2002.1195903 (DOI)000183375500048 ()0-7803-7414-2 (ISBN)
Note
QC 20100928Available from: 2005-05-12 Created: 2005-05-12 Last updated: 2010-09-28Bibliographically approved
3. Optical waveguiding in magnetron-sputtered Na0.5K0.5NbO3 thin films on sapphire substrates
Open this publication in new window or tab >>Optical waveguiding in magnetron-sputtered Na0.5K0.5NbO3 thin films on sapphire substrates
Show others...
2003 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 82, no 3, 439-441 p.Article in journal (Refereed) Published
Abstract [en]

Preferentially oriented perovskite-structured Na0.5K0.5NbO3 (NKN) thin films have been deposited on hexagonal Al2O3(01 (1) under bar2) substrates using rf magnetron sputtering of a stoichiometric, high-density, ceramic target. Structural and film surface properties were measured using x-ray diffraction and atomic force microscopy, respectively. Optical and waveguiding properties were characterized using a prism-coupling technique. We observed sharp and distinguishable TM and TE propagation modes and measured the refractive index of NKN thin films of different thicknesses. The ordinary and extraordinary refractive indices were calculated to be n(o)=2.247+/-0.002 and n(e)=2.216+/-0.002 for a 2.0-mum-thick film at 632.8 nm. This implies a birefringence Deltan=n(e)-n(o)=-0.031+/-0.002 in the film. These first results show the potential use of rf-sputtered NKN films as an electro-optical active material.

Keyword
electrooptic characterization
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-22184 (URN)10.1063/1.1539295 (DOI)000180449100043 ()
Note
QC 20100525Available from: 2010-08-10 Created: 2010-08-10 Last updated: 2010-09-28Bibliographically approved
4. Rf sputtered Na0.5K0.5NbO3 films on oxide substrates as optical waveguiding material
Open this publication in new window or tab >>Rf sputtered Na0.5K0.5NbO3 films on oxide substrates as optical waveguiding material
2003 (English)In: Integrated Ferroelectrics, ISSN 1058-4587, Vol. 54, 631-640 p.Article in journal (Refereed) Published
Abstract [en]

Highly crystalline Na0.5K0.5NbO3 (NKN) thin films of 1-2 mum thickness were deposited by rf-magnetron sputtering of a stoichiometric, ceramic target on single crystal LaAlO3 (001) and Al2O3 (01 (1) under bar2) substrates. X-ray diffraction measurements revealed epitaxial quality of NKN/LaAlO3 film structures, whereas NKN films on sapphire substrates were found to be preferentially c -axis oriented. A prism-coupling technique was used to characterize optical and waveguiding properties. A bright-line spectrum at lambda = 632.8 nm, revealed sharp peaks, corresponding to transverse magnetic (TM) and electric (TE) waveguide propagation modes in NKN/LaAlO3 and NKN/Al2O3 thin films. Using a least mean square fit the refractive index for the films and film thickness were calculated. The extraordinary and ordinary refractive indices were determined to n(e) = 2.207 +/- 0.002 and n(o) = 2.261 +/- 0.002, and n(e) = 2.216 +/- 0.002 and n(o) = 2.247 +/- 0.002 at lambda = 632.8 nm for 2.0 mum thick NKN films on LaAlO3 and Al2O3 , respectively. This corresponds to a birefringence Deltan = n(e) - n(o) = -0.054 +/- 0.003 and Deltan = -0.031 +/- 0.003 in the films, where the larger Deltan for the NKN/LaAlO3 structure can be explained by the superior crystalline quality compared to NKN/Al2O3 . Atomic force microscopy images of the film surfaces revealed rms roughnesses of 2.5 nm and 8.0 nm for 1.0-mum thick NKN/LaAlO3 and NKN/Al2O3 films, respectively. We believe surface scattering is one of the main sources of waveguide losses in the thin films.

Keyword
Na0.5K0.5NbO3 films, rf-magnetron sputtering, prism coupling, waveguiding, refractive index, knbo3 thin-films, sapphire, light
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-23054 (URN)10.1080/10584580390259047 (DOI)000187625200013 ()
Note
QC 20100525Available from: 2010-08-10 Created: 2010-08-10 Last updated: 2010-09-28Bibliographically approved
5. Visible and IR light waveguiding in ferroelectric Na0.5K0.5NbO3 thin films
Open this publication in new window or tab >>Visible and IR light waveguiding in ferroelectric Na0.5K0.5NbO3 thin films
2005 (English)In: Integrated Ferroelectrics, ISSN 1058-4587, Vol. 69, 277-286 p.Article in journal (Refereed) Published
Abstract [en]

High-quality ferroelectric thin films are attractive materials for integrated optics applications including electro-optic waveguide modulators and frequency doubling secondharmonic generators. Several fefroelectric thin film materials, such as BaTiO3, KNbO3, LiNbO3, and (Pb,La)(ZrTi)O-3, have been investigated regarding their optical and waveguiding properties. Recently the first results on waveguiding in ferroelectric Na0.5K0.5NbO3 (NKN) thin films were presented. Perovskite NKN films have previously been investigated as electrically tunable material for low loss rf and microwave applications. Na0.5K0.5NbO3 thin films of thickness 0.5-1.0 mum have been deposited on Nd:YAlO3(001) and Al2O3(0112) substrates using rf-magnetron sputtering of a stoichiometric, high-density ceramic target. X-ray diffraction measurements confirmed films grown highly (00l) oriented on the perovskite Nd:YAlO3 substrate and preferentially c-axis oriented on the single crystal r-cut sapphire substrate. Optical and waveguiding properties were characterized using a Metricon 2010 prism-coupling apparatus with a rutile prism. Dark-line spectra were obtained at visible light (lambda = 632.8 nm) as well as at infrared optical communication wavelengths, lambda = 1319 nm and lambda = 1549 nm, in both transverse electric (TE) and transverse magnetic (TM) polarizations. Sharp dips corresponding to waveguide propagation modes in the thin film layers where observed for both substrates. The calculated refractive index values and corresponding birefringence (Deltan = n(TM) - n(TE) = n(e) - n(o)) as a function of wavelength has been compared. Generally a larger birefringence is observed for the NKN film on Nd:YAlO3, which is in agreement with the larger degree of preferential c-axis orientation measured by XRD.

Keyword
Na0.5K0.5NbO3 films, rf-magnetron sputtering, waveguiding, refractive index, birefringence, prism coupling, sapphire
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-14526 (URN)10.1080/10584580590899027 (DOI)000226933000031 ()2-s2.0-33644782690 (Scopus ID)
Note
QC 20100525 QC 20111011.Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-10-11Bibliographically approved
6. Electrooptic ferroelectric Na0.5K0.5NbO3 films
Open this publication in new window or tab >>Electrooptic ferroelectric Na0.5K0.5NbO3 films
2005 (English)In: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 17, no 8, 1638-1640 p.Article in journal (Refereed) Published
Abstract [en]

We report on waveguiding and electrooptic properties of epitaxial Na0.5K0.5NbO3 films grown by radio-frequency magnetron sputtering on Al2O3 (1102) single crystal substrates. High optical waveguiding performance has been demonstrated in infrared and visible light. The in-plane electrooptic effect has been recorded in transmission using a transverse geometry. At dc fields, the effective linear electrooptic coefficient was determined to 28 pm/V, which is promising for modulator applications.

Keyword
electrooptic effects, ferroelectric films, planar waveguides, thin-films, modulator, voltage, growth, knbo3
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-14941 (URN)10.1109/lpt.2005.851991 (DOI)000230799100018 ()2-s2.0-23844526785 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2010-09-28Bibliographically approved
7. Electro-optic effect in ferroelectric Na0.5K0.5NbO3 thin films on oxide substrates
Open this publication in new window or tab >>Electro-optic effect in ferroelectric Na0.5K0.5NbO3 thin films on oxide substrates
2006 (English)In: Integrated Ferroelectrics, ISSN 1058-4587, Vol. 80, no 1, 97-106 p.Article in journal (Refereed) Published
Abstract [en]

We have deposited Na0.5NbO3 (NKN) films oil single crystal Al2O3(1 (1) under bar 02) and SrTiO3(001) substrates using rf-magnetron sputtering of a stoichiometric, high-density ceramic target. Using x-ray diffraction it was confirmed that NKN grows preferentially c-axis oriented on sapphire substrate and epitaxially oil the perovskite SrTiO3(001) substrate. Electro-optical (EO) properties were measured in visible light through a transverse method. With an applied dc field up to 20 kV/cm, the effective linear EO response was determined to r(eff) = 28 pm/V for NKN/Al2O3 and r(eff) = I I pm/V for NKN/SrTiO3, where a superlinear dependence was observed.

Keyword
sodium potassium mobates, ferroelectric films, rf-rnagnetron sputtering, XRD, electro-optic effects, AFM, pulsed-laser deposition, knbo3
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-15800 (URN)10.1080/10584580600656569 (DOI)000238680700012 ()2-s2.0-33745751799 (Scopus ID)
Note
QC 20100525, QC 20110929. Conference: 17th International Symposium on Integrated Ferroelectrics .Shanghai, PEOPLES R CHINA. APR 17-20, 2005 Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-09-29Bibliographically approved

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