Browsing by Author "Chiu, Shang-Jui"

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Enhancement of epitaxial LaNiO3 electrode on the ferroelectric property of La-doped BiFeO3/SrTiO3 artificial superlattice structure by rf sputtering
(2013-04-01)
Chiu, Shang-Jui
;
Liu, Yen-Ting
;
Yu, Ge-Ping
;
Lee, Hsin-Yi
;
Huang, Jia-Hong
Improvement of ferroelectric property by LaNiO3 (LNO) electrode on superlattice films was shown in this study. High quality asymmetric multiferroic 5 at% La-doped BiFeO3 (BFO) and paraelectric SrTiO3 (STO) superlattice structure was deposited on LNO electrode by rf magnetron sputtering system. High crystalline quality of the La-doped BFO/STO artificial superlattice structure on LNO electrode have been confirmed by clear main feature and satellite features around (0 0 2) STO substrate Bragg peak shown in (0 0 2) radial scan spectrum. The results of in-pane crystal truncation rod (CTR) spectrum and the rocking curve indicated that superlattice films with high crystal quality behaved in-plane strain closed to fully strained state on both LNO and Nb-doped STO electrode. The epitaxial relation between the La-doped BFO and STO layers in the superlattice was examined through a (1 0 3) azimuthal scan and (1 0 3) Lscan. The results show a four-fold symmetry and slight distorted of gamma angle of the BFO unit cell, confirming the pseudocubic structure of the La-doped BiFeO3 structure. The measurement of hysteresis loops showed that La-doped BFO superlattice structure on LNO electrode behaved lower, but stable and saturated ferroelectric properties than that of films with Nb-doped STO substrate in our previous study. The measurement of resistivity and leakage current density of superlattice films demonstrated that resistivity of electrode is the main factor to determine the leakage properties of films. The superlattice films behaved larger piezoelectric coefficient (d(33)) on LNO electrode than films on Nb-doped STO substrate, which indicated the enhancement of intrinsic ferroelectric properties in La-doped BFO/STO superlattice films. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.
Fabrication and ferroelectric properties of BiFeO3/LaNiO3 artificial superlattice structures grown by radio-frequency magnetron-sputtering
(2013-02-01)
Liu, Yen-Ting
;
Chiu, Shang-Jui
;
Lee, Hsin-Yi
;
Chen, San-Yuan
;
材料科學與工程學系
Symmetric superlattice structures of multiferroic BiFeO3 and conductive LaNiO3 sublayers were grown on a Nb-doped SrTiO3 substrate with radio-frequency magnetron-sputtering. The formation of a superlattice structure was confirmed from the appearance of satellite lines on both sides of the main line in the X-ray diffraction pattern. X-ray measurements show that these superlattice films become subject to greater tensile stress along the c-axis and to increased compressive stress parallel to the surface plane with a decreasing thickness of the sublayer. The smaller is the thickness of the sublayer, the greater is the crystalline quality and the strain state. The hysteresis loops show a large leakage current at frequencies of 0.5 and 1 kHz; the polarization decreases with an increasing frequency. (C) 2012 Elsevier B.V. All rights reserved.
Growth of BiFeO(3)/SrTiO(3) artificial superlattice structure by RF sputtering
(2011-11-01)
Chiu, Shang-Jui
;
Liu, Yen-Ting
;
Lee, Hsin-Yi
;
Yu, Ge-Ping
;
Huang, Jia-Hong
Asymmetric superlattice structures consisting of multiferroic BiFeO(3) (BFO) and paraelectric SrTiO(3) (STO) sublayers were grown on a Nb-doped STO substrate by RF magnetron sputtering at temperatures in the range 500-800 degrees C. For substrate temperatures less than 500 degrees C and at 800 degrees C, only poorly crystalline films resulted, whereas a BFO/STO superlattice structure film of great crystalline quality was obtained for a substrate temperature in the range 550-750 degrees C. The formation of a superlattice structure was confirmed through both the appearance of Bragg lines separated by Kiessig fringes in X-ray reflectivity curves and the satellite features of a (002) diffraction pattern. The clearly discernible main and satellite features on both sides of the substrate about the (002) STO Bragg peak of superlattice films indicate the high quality of the BFO/STO artificial superlattice structure. For BFO/STO superlattice films deposited at 600-700 degrees C, the increased crystalline quality with smaller interface roughness correlates with larger lattice strain and remanent polarization of the film. The lattice strain and interface quality might be important factors that influence the leakage and ferroelectric properties in BFO/STO artificial superlattices. (C) 2011 Elsevier B.V. All rights reserved.
Growth of BiFeO3/SrTiO3 artificial superlattice structure by RF sputtering
(2011-11-01)
Chiu, Shang-Jui
;
Liu, Yen-Ting
;
Lee, Hsin-Yi
;
Yu, Ge-Ping
;
Huang, Jia-Hong
Asymmetric superlattice structures consisting of multiferroic BiFeO3 (BFO) and paraelectric SrTiO3 (STO) sublayers were grown on a Nb-doped STO substrate by RF magnetron sputtering at temperatures in the range 500-800 degrees C. For substrate temperatures less than 500 degrees C and at 800 degrees C, only poorly crystalline films resulted, whereas a BFO/STO superlattice structure film of great crystalline quality was obtained for a substrate temperature in the range 550-750 degrees C. The formation of a superlattice structure was confirmed through both the appearance of Bragg lines separated by Kiessig fringes in X-ray reflectivity curves and the satellite features of a (002) diffraction pattern. The clearly discernible main and satellite features on both sides of the substrate about the (002) STO Bragg peak of superlattice films indicate the high quality of the BFO/STO artificial superlattice structure. For BFO/STO superlattice films deposited at 600-700 degrees C, the increased crystalline quality with smaller interface roughness correlates with larger lattice strain and remanent polarization of the film. The lattice strain and interface quality might be important factors that influence the leakage and ferroelectric properties in BFO/STO artificial superlattices. (C) 2011 Elsevier B.V. All rights reserved.
Preparation of a BiFeO(3)/LaNiO(3) multiferroic oxide superlattice structure by RF magnetron sputtering
(2011-12-25)
Liu, Yen-Ting
;
Chiu, Shang-Jui
;
Lee, Hsin-Yi
;
Chen, San-Yuan
;
材料科學與工程學系
Artificial superlattices consisting of multiferroic BiFeO(3) (BFO) and conductive LaNiO(3) (LNO) were grown epitaxially on a Nb-doped SrTiO(3) (STO) (001) single-crystal substrate at temperatures in a range 560-810 degrees C with a RF magnetron sputtering system. The superlattice contained 30 periods of symmetric BFO/LNO bilayers with a thickness of 2 nm of each individual layer. Ferroelectric and conductive superlattice materials of this type can serve for an investigation of the strain dependence of ferroelectric properties of BFO layers in superlattice structures. Measurements of X-ray reflectivity and X-ray diffraction at high resolution were employed to characterize the microstructure of these films. The formation of a superlattice structure was confirmed by the appearance of Bragg peaks separated by Kiessig fringes in the X-ray reflectivity curve and a diffraction pattern. The clearly discernible main feature and satellite features on both sides of the substrate feature about the (002) STO Bragg peak indicate the high quality of the BFO/LNO artificial superlattice structure formed on a STO substrate at all deposition temperatures. X-ray measurements show that these superlattice films become subject to greater compressive strain in the in-plane direction, and possess increased crystalline quality when increasing the deposition temperature to 660 degrees C. The measurement of hysteresis loops shows that the largest remanent polarization (P(r)) occurs at 660 degrees C. (C) 2011 Elsevier B.V. All rights reserved.
Preparation of a BiFeO3/LaNiO3 multiferroic oxide superlattice structure by RF magnetron sputtering
(2011-12-25)
Liu, Yen-Ting
;
Chiu, Shang-Jui
;
Lee, Hsin-Yi
;
Chen, San-Yuan
;
材料科學與工程學系
Artificial superlattices consisting of multiferroic BiFeO3 (BFO) and conductive LaNiO3 (LNO) were grown epitaxially on a Nb-doped SrTiO3 (STO) (001) single-crystal substrate at temperatures in a range 560-810 degrees C with a RF magnetron sputtering system. The superlattice contained 30 periods of symmetric BFO/LNO bilayers with a thickness of 2 nm of each individual layer. Ferroelectric and conductive superlattice materials of this type can serve for an investigation of the strain dependence of ferroelectric properties of BFO layers in superlattice structures. Measurements of X-ray reflectivity and X-ray diffraction at high resolution were employed to characterize the microstructure of these films. The formation of a superlattice structure was confirmed by the appearance of Bragg peaks separated by Kiessig fringes in the X-ray reflectivity curve and a diffraction pattern. The clearly discernible main feature and satellite features on both sides of the substrate feature about the (002) STO Bragg peak indicate the high quality of the BFO/LNO artificial superlattice structure formed on a STO substrate at all deposition temperatures. X-ray measurements show that these superlattice films become subject to greater compressive strain in the in-plane direction, and possess increased crystalline quality when increasing the deposition temperature to 660 degrees C. The measurement of hysteresis loops shows that the largest remanent polarization (P-r) occurs at 660 degrees C. (C) 2011 Elsevier B.V. All rights reserved.
Strain enhanced ferroelectric properties of multiferroic BiFeO3/SrTiO3 superlattice structure prepared by radio frequency magnetron sputtering
(2013-07-31)
Chiu, Shang-Jui
;
Liu, Yen-Ting
;
Lee, Hsin-Yi
;
Yu, Ge-Ping
;
Huang, Jia-Hong
Asymmetric superlattice structures consisting of SrTiO3 (STO) and multiferroic BiFeO3 (BFO) sublayers were deposited on a Nb-doped STO (001) substrate with a radio frequency magnetron sputtering system. For an investigation of the effect of strain on the microstructures, ferroelectric properties and piezoelectric properties resulting from a difference of lattice parameters of the BFO sublayer, varying the thickness of the STO sublayer in a range 1-2.5 nm introduced interfacial strain into the superlattice. The epitaxial relation and strain state of films were clearly observed with a synchrotron as a source of radiation. The results of X-ray diffraction measurements clearly showed that the decrease of strain was related to the thickness of the STO substrate. A separate diffraction signal of the superlattice structure with thickness >= 1.75 nm of the STO sublayer was found, indicating a large strain relaxation in these superlattice films. The remnant polarization values P-r, piezoelectric coefficient d(33) and leakage properties of the BFO/STO superlattice thin films that improved with increasing in-plane strain provide strong evidence of a strain-enhancement effect. The BFO/STO superlattice with a well defined crystal structure and a large strain state showed a large P-r, greater than a BFO single layer of the same thickness. (C) 2013 Elsevier B.V. All rights reserved.
The structure and ferroelectric property of La-doped BiFeO3/SrTiO3 artificial superlattice structure by rf sputtering: Effect of deposition temperature
(2013-02-01)
Chiu, Shang-Jui
;
Liu, Yen-Ting
;
Yu, Ge-Ping
;
Lee, Hsin-Yi
;
Huang, Jia-Hong
Improvement of ferroelectric property by Lanthanum (La)-doping of BiFeO3 (BFO) and strain effect of high quality superlattice films deposited at temperature. >= 700 degrees C was shown in this study. The in-pane (200) radial scans showed that films at deposition temperature above 700 degrees C behaved high strained similar to-1.4% and showed epitaxity properties. The La-doped BFO superlattice structure also behaved higher polarization value similar to 197 mu C/cm(2) and lower leakage current density comparing with BFO superlattice structure shown in our previous study. The ferroelectric properties of superlattice structures are enhanced by lattice strain and strongly correlated with the defect state of films. (C) 2012 Elsevier B.V. All rights reserved.
Ultrathin Oriented BiFeO3 Films from Deposition of Atomic Layers with Greatly Improved Leakage and Ferroelectric Properties
(2014-01-08)
Liu, Yen-Ting
;
Ku, Ching-Shun
;
Chiu, Shang-Jui
;
Lee, Hsin-Yi
;
Chen, San-Yuan
Highly (001)-oriented BiFeO3 ultrathin films of total thickness of less than 10 nm were deposited on Si(001) substrates via deposition of atomic layers (ALD) with a LaNiO3 buffer. A radio-frequency (RF)-sputtered sample of the same thickness was prepared for comparison. The ALD combined with interrupted flow and an exchange reaction between Bi and Fe precursors provides a superior method to grow ternary compounds. According to X-ray diffraction, upon deposition at a temperature of less than 550 degrees C, the only phase in the film was BiFeO3. Anomalous fine structure from synchrotron X-ray diffraction certified the valence bonding through the BiFeO3 (001) diffraction signal. The stoichiometric ratio of BiFeO3 obtained from X-ray photoelectron spectroscopy indicated that ALD has a proportion much improved over the RF preparation, and this is also in agreement with the results for diffraction anomalous fine structure. The use of high-resolution transmission electron and atomic force microscopes showed that the layer structure and morphology from ALD presented a satisfactory coverage, more conformal than that with the RF method. The BiFeO3 thin film deposited with ALD shows excellent leakage, improved at least 1000 times with respect to the RF preparation, making this method suitable for the fabrication of ferroelectric random-access memory devices. From the hysteresis loop, the largest remanent polarization was observed as 2P(r) = 2.0 mu C cm(-2).