LNO Films Research Articles

Influence of LaNiO 3 bottom electrode on the structural and physical properties of ferroelectric capacitors

Techniques such as high energy electron diffraction (RHEED), atomic force microscope (AFM) are used to characterize LNO film prepared by rf sputtering. It is found that LNO films are epitaxially grown on the SrTiO 3 (STO) substrates. Root mean square roughness (RMS) of LNO film increases with increasing growth temperature, and then becomes somewhat saturated when deposition temperature is higher than 350 °C. Meanwhile, resistivity of LNO film decreases with increasing growth temperature, and becomes relatively stable when deposition temperature is higher than 200 °C. It is found that ferroelectric properties of LaNiO 3/Pb(Zr,Ti)O 3/LaNiO 3 (LNO/PZT/LNO) capacitors prepared on STO substrate strongly depend on the deposition temperature of LNO bottom electrode. The higher the deposition temperature of LNO bottom electrode, the larger is the switchable polarization of LNO/PZT/LNO capacitor.

Investigation of room temperature electrical resistivities of LaNiO3−δ thin films deposited by rf magnetron sputtering and high oxygen-pressure processing

Highly (100)-oriented electrically conductive LaNiO3−δ (LNO) thin film with perovskite-type structure was deposited on Si(100) substrates by rf magnetron sputtering at substrate temperatures of 200, 300, 450, and 600°C with a series of 0%, 20%, 40%, and 60% oxygen partial pressures, respectively. The room temperature (RT) resistivity of LNO films decreases with decreasing substrate temperature at a fixed oxygen partial pressure and with increasing oxygen partial pressure at a fixed substrate temperature. The lowest RT resistivity of as-sputtered LNO thin films was about 5.3×10−4Ωcm. This value could be as low as ∼1.55×10−4Ωcm by postprocessing called high oxygen-pressure processing at 8MPa and is comparable to the lowest one, 1.5×10−4Ωcm, of epitaxial LNO thin film deposited on lattice-matched SrTiO3, LaAlO3, or sapphire single-crystal substrates.

Fabrication of epitaxial conductive LaNiO 3 films on different substrates by pulsed laser ablation

LaNiO 3 (LNO) thin films were deposited on (1 0 0) MgO, SrTiO 3 (STO) and LaAlO 3 (LAO) crystal substrates by pulsed laser deposition (PLD) under 20 Pa oxygen pressure at different substrate temperatures from 450 to 750 °C. X-ray diffraction (XRD), ex situ reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM) were employed to characterize the crystal structure of LNO films. LNO films deposited on STO and LAO at a temperature range from 450 to 700 °C exhibit high (0 0 l) orientation. XRD ψ scans and RHEED observations indicate that LNO films could be epitaxially grown on these two substrates with cubic-on-cubic arrangement at a wide temperature range. LNO films deposited at 700 °C on MgO (1 0 0) substrate have the ( l l 0) orientation, which was identified to be bicrystalline epitaxial growth. La 2NiO 4 phase appears in LNO films deposited at 750 °C on three substrates. The epitaxial LNO films were tested to be good metallic conductive layers by four-probe method.

Orientation control and electrical properties of PZT/LNO capacitor through chemical solution deposition

This paper describes the deposition of PZT/lanthanum nickel oxide (LNO) electrode thin-film capacitor on a Si(1 0 0) substrate with a chemical solution deposition (CSD). Highly (1 0 0)-oriented LNO film with a perovskite structure was deposited by annealing at 700 °C from a precursor solution of La(NO 3) 3 and Ni(CH 3COO) 2. In addition, highly (1 0 0)&(0 0 1)-oriented PZT/LNO capacitor was deposited on LNO/Si substrate by annealing at 600 °C, showing P r = 18 μC/cm 2 and E c = 36 kV/cm. Furthermore, the resultant PZT/LNO thin-film capacitor exhibited no fatigue up to 10 8 switching cycles.

Growth and electrical properties of highly (0 0 1)-oriented Pb(Zr 0.52Ti 0.48)O 3 thin films on amorphous TiN buffered Si(1 0 0)

Pb(Zr 0.52Ti 0.48)O 3 (PZT) ferroelectric thin films with LaNiO 3 (LNO) as bottom electrodes have been grown on amorphous TiN buffered Si(1 0 0) substrates by pulsed laser deposition. It was found that highly (0 0 1)-oriented LNO films could be obtained even if TiN underlayers were amorphous. XRD analyses showed that the subsequently deposited PZT films were also preferentially (0 0 1)-oriented due to the template effect of the perovskite structured LNO films. Dielectric constant of the PZT thin films remained almost constant with frequency in the range from 10 3 to 10 6 Hz, and tangent loss was as small as 0.02 at high frequencies. The remnant polarization and coercive field of an Au/PZT/LNO capacitor were typically 20 μC/cm 2 and 30 kV/cm, respectively. C– V and I– V characteristics revealed the capacitance and leakage current variations with applied voltage were asymmetric when the bottom electrode was negatively as well as positively biased, indicating that ferroelectric/electrode interfaces and space charges play an important role in the electrical properties of ferroelectric capacitors.

Preparation of highly (1 0 0)-oriented LaNiO 3 nanocrystalline films by metalorganic chemical liquid deposition

Lanthanum nickelate LaNiO 3 (LNO) nanocrystalline films have been grown by the metalorganic chemical liquid deposition (MOCLD) technique using lanthanum acetate and nickel acetate as the starting materials. The technique simplified the process of preparation for LNO thin films by chemical solution routes. XRD measurements showed that the LNO films deposited on Si, SiO 2/Si and Pt/Ti/SiO 2/Si substrates exhibit preferential (1 0 0) orientation. The effects of pyrolysis temperature and thickness on (1 0 0)-orientation parameters of LNO films were investigated. The lowest resistivity film was obtained by annealing at 750 °C. The effects of thickness and annealing temperature on resistivity of the LNO films have been discussed. PbZr 0.4Ti 0.6O 3 (PZT) films deposited onto LNO films displayed a good P–E hysteresis characteristic and fatigue free to 10 8 fatigue cycles.

Ferroelectric properties of PZT films on LaNiO 3 bottom electrode deposited under different oxygen partial pressure

LaNiO 3 (LNO) films were deposited on by RF magnetron sputtering of Ni metal target and La metal chips on top of it under Ar and O 2 atmosphere at different oxygen partial pressures (20, 25, 30, 35, and 40% oxygen). The resistivity of the LNO films increased with the increasing oxygen partial pressure. This is attributed to the reduction of oxygen vacancy concentration. About 150 nm thick Pb(Zr 0.35Ti 0.65)O 3 (PZT) ferroelectric thin films were spin coated on the LNO films with subsequent post annealing. To find out the relationship, the electrical properties of the PZT/LNO thin film capacitors and the oxygen partial pressure, the P– E curve, X-ray diffraction, microstructure, leakage current density, and fatigue property were investigated as a function of oxygen partial pressure. An optimal remanent polarization and lowest leakage current density of the PZT capacitor has been obtained when its LNO thin film bottom electrode was deposited at 30% oxygen partial pressure. The microstructure of the LNO film deposited at 30% oxygen partial pressure had columnar structure, while the ones deposited under other conditions had granular structure. The ferroelectric properties of the PZT/LNO capacitor are critically affected by the structure of LNO bottom electrode, and they are excellent when optimally processed as discussed above.

Effect of heat-treatment on LaNiO3film electrode of PZT thin films derived by a sol–gel method

Lanthanum nickel oxide (LaNiO3 or LNO) conducting thin films that could be used as electrodes for improving fatigue and aging properties of ferroelectric thin films were investigated. In this paper, LNO films were directly spin-coated onto SiO2/Si(1 0 0) substrates followed by thermal treatment in air and in oxygen. It was found that crack-free dense and uniform films with good crystallinity and medium grains were obtained, preferentially (1 0 0)-oriented LNO thin films could be formed at a lower annealing temperature of 550 °C and that with the increase in thermal annealing temperature the LNO thin film possessed better electrical properties especially at 750 °C. However, the LNO film displayed a structure transformation above 850 °C. A phenomenon was found that the first heat-treatment temperature and time played a key role to determine the crystallite size of LNO films. A subsequent deposition of a sol–gel derived Pb(Zr0.53Ti0.47)O3 (PZT53/47) thin film on the LNO-coated SiO2/Si(1 0 0) substrates was also found to have a (1 0 0)-oriented texture. Moreover, the Au/PZT/LNO capacitor was found to significantly improve the fatigue and the effects of the LNO electrodes to the fatigue were discussed.

Microstructure and electrical properties of Pb(Zr 0.52Ti 0.48)O 3 ferroelectric films on different bottom electrodes

The crystalline quality, dielectric and ferroelectricity of the Pb(Zr 0.52Ti 0.48)O 3 (PZT) films deposited on the LaNiO 3 (LNO), LNO/Pt and Pt bottom electrodes were comparatively analyzed to investigate the possibility for their application. LNO thin films were successfully prepared on Si (100) and Pt(111)/Ti/SiO 2/Si substrates by modified metallorganic decomposition (MOD). The PZT thin films were spin-coated onto the LNO, LNO/Pt and Pt bottom electrodes by sol–gel method. The crystallographic orientation and the microstructure of the resulting LNO films and PZT thin films on the different bottom electrodes were characterized by X-ray diffraction analysis. The dielectric and ferroelectric properties of PZT films on the different bottom electrodes are discussed. The PZT films deposited onto Pt/Ti/SiO 2/Si and LNO/Si substrates show strong (110) and (100) preferred orientation, respectively, while the films deposited onto LNO/Pt/Ti/SiO 2/Si substrates show the peaks of mixed orientations. PZT films on LNO and LNO/Pt bottom electrodes have larger dielectric constant and remnant polarizations compared with those grown on the Pt electrode.

Sol–gel derived LaNiO 3 thin films on ZrO 2-buffered (1 0 0) Si substrates

Perovskite LaNiO 3 (LNO) thin films with a strong (1 0 0)-orientation were fabricated on yttrium-stabilized-zirconia (YSZ)-buffered silicon substrates using a sol–gel method. The YSZ buffer layer showed a stable tetragonal phase, and proved to be effective to suppress inter-diffusion between the Si substrates and the LNO films. Our obtained LNO films on the YSZ buffer layer exhibited a homogenous and smooth surface, with an average grain size below 0.1 μm. The resistivity of the LNO films was in the magnitude order of 10 −4 Ω cm. The crystallographic orientation and low resistivity make the sol–gel derived LNO films very attractive as the bottom electrode layer for perovskite oxide ceramic thin films.

Growth and characterization of (001)-oriented Pb(Zr0.52Ti0.48)O3/LaNiO3/LaAlO3 heterostructures prepared by pulsed laser deposition

Completely (001)-oriented ferroelectric Pb(Zr0.52Ti0.48)O3/LaNiO3 heterostructures on single-crystal LaAlO3(001) substrates have been successfully grown by pulsed laser deposition. X-ray-diffraction analyses (θ–2θ scan, ω scan and φ scan) indicate that good out-of-plane orientation and in-plane alignment have been obtained with the epitaxial relationship of PZT(001)//LNO(001)//LAO(001) and PZT〈001〉//LNO〈001〉//LAO〈001〉. Scanning electron and atomic force microscopic images reveal very smooth LNO surfaces with roughness of about 0.4–0.6 nm. Based on a microstructural study of the LNO and PZT films, a layer-by-layer growth mode for the LNO growth is proposed, while island growth is dominant for the PZT films. Secondary ion mass spectroscopy analyses show that no distinct interdiffusion can be found between the PZT and LNO layers. P–E hysteresis loop measurements of the PZT films with LNO as bottom electrodes and Au as top electrodes were carried out at an applied voltage of 5 V. The best remanent polarization Pr and coercive field Ec were found to be 28 μC/cm2 and 74.5 kV/cm, respectively.

Preparation and evaluation of LaNiO 3 thin film electrode with chemical solution deposition

LaNiO 3 (LNO) thin films were prepared onto Si substrate by chemical solution deposition. The orientation of the LNO films was controlled by changing concentration of precursor solution. The resistivity of the resultant LNO films was 1.82 – 2.57×10 −3Ωcm. The obtained 0.3 M-LNO film was flat surface, highly (100) orientation, and had a low resistivity of 1.85×10 −3Ωcm. PbZr 0.53Ti 0.47O 3 was fabricated onto the resultant 0.3 M-LNO electrode, and the sample showed a good ferroelectric property.

Completely (001)-textured growth and electrical properties of Bi 4Ti 3O 12/LaNiO 3 heterostructures prepared by pulsed laser deposition on LaAlO 3 single crystal substrates

Heterostructures of Bi 4Ti 3O 12(BTO)/LaNiO 3(LNO) have been prepared on (001) LaAlO 3 single crystal substrates by pulsed laser deposition (PLD). Analyses of X-ray diffraction (XRD), (including θ–2 θ scan, rocking curve), atomic force microscopy (AFM) and scanning electron microscopy (SEM) reveal that the high quality LNO and BTO films are completely c-axis oriented. With Pt top electrodes, the BTO films exhibit a highly insulative characteristic of low leakage current (∼10 −7 A/cm 2 at an applied voltage of 6 V) and excellent dielectric properties. At 100 kHz, the dielectric constant and dielectric loss are 238 and 0.033, respectively. Also a well symmetric ferroelectric hysteresis loop is observed with remnant polarization P r of 4.5 μC/cm 2 and coercive field E c of 72.5 kV/cm. Our experiments confirm that the use of the LNO as an electrode material can reduce the amount of the interfacial charges, and thus remove the imprint failure due to thermal processes.

Comparative analysis for the crystalline and ferroelectric properties of Pb(Zr,Ti)O 3 thin films deposited on metallic LaNiO 3 and Pt electrodes

The crystalline quality and ferroelectricity of the Pb(Zr,Ti)O 3 (PZT) films deposited on the metallic LaNiO 3 (LNO) and Pt electrodes were comparatively analyzed to investigate the possibility for their application to non-volatile memory devices. LNO thin films were successfully deposited on various substrates by using r.f. magnetron sputtering even at a low temperature ranging from 250 to 500 °C, and the ferroelectric PZT thin films were spin-coated onto the LNO and Pt bottom electrodes. Metallic LNO thin films exhibited [100] orientation irrespective of the substrate species and PZT films coated onto LNO films had highly a- and c-axis orientations, while those with Pt bottom electrode were polycrystalline. PZT films with LNO bottom electrode had smaller grain size and larger dielectric constant compared to those grown on the Pt electrode. The ferroelectric thin films fabricated on LNO bottom electrode displayed an asymmetric D–E hysteresis loop, which was explained by the defect effects formed at the interface. Especially, the LNO/PZT/LNO capacitor was found to significantly improve the polarization fatigue and the effects of the LNO electrodes to the fatigue were discussed.

Low-temperature epitaxial growth of conductive LaNiO 3 thin films by RF magnetron sputtering

Epitaxial growth of LaNiO 3 (LNO) thin films was successful on CeO 2/YSZ/Si(100), MgO(100) and SrTiO 3 (STO)(100) substrates by RF magnetron sputtering at 300 °C, although pulsed laser deposition requires 600 °C to prepare epitaxial LNO films according to the literature. Epitaxial LNO films deposited on CeO 2/YSZ/Si(100) and STO(100) had single orientation of LNO[100]//CeO 2[110]//YSZ[110]//Si[110]) and LNO[100]//STO[100], respectively. On the other hand, epitaxial LNO films deposited on MgO(100) had mixed orientations of LNO[100]//MgO[100] and LNO[100]//MgO[110]. The lattice parameter, composition and resistivity of the LNO thin films were strongly dependent on the substrate temperature. The minimum resistivity of LNO films was approximately 5×10 −6 Ω m, which value almost agrees with the resistivity in the literature. It was found that the temperature to achieve minimum resistivity was 200 °C, irrespective of the type of substrate. The surface of the LNO films was smooth and flat.

Microstructures of LaNiO 3 films grown on Si(001) by pulsed laser deposition

Conductive LaNiO 3 (LNO) thin films were prepared on Si(001) by pulsed laser deposition and their microstructures were investigated using synchrotron X-ray scattering and atomic force microscopy. We observed that the surface morphology of the LNO thin films was extremely smooth with typically a 1.0-nm root-mean-squared roughness for films up to 360 nm in thickness and the film strain increased monotonically with the film thickness, suggesting that the LNO/Si(001) films be grown with a layer-like growth mode. Grown with the (00 l) preferred orientation, the LNO films showed a significant anisotropic structural order; the coherence length of the out-of-plane stacking order was one order of magnitude larger than that of the in-plane atomic order.

Oxygen diffusion in La2/3Ga1/3MnO3 and Sr2FeMoO6 thin films

Thin films of colossal magnetoresistance La 0.67 Ca 0.33 MnO 3 (LCMO) (d=200+300 nm), highly conductive LaNiO 3 (LNO) (150+200 nm), double perovskite Sr 2 FeMoO 6 (SFMO) (( 70 nm) as well as LCMO/LNO bilayers were grown heteroepitaxially by dc magnetron sputtering and pulsed laser deposition on lattice-matched NdGaO 3 (100) and SrTiO 3 (100) to investigate oxygen diffusion in LCMO, LNO and SFMO. In-situ electrical resistance measurements were performed at (78÷1000) K in vacuum (P(10-4 Pa) and oxygen gas (p(10 5 Pa) by varying temperature of the films linearly with time: T(t)=T 0 ±β t. The activation energy of oxygen ion diffusion, E D , of 1.3 eV and 1.2 eV have been estimated for the LCMO and LNO films, respectively, by fitting numerical and experimental data. Unusual resistance changes of the Sr 2 FeMoO 6 thin films during their annealing in oxygen at T>500K had showed formation of high resistance regions in the vicinity of grain boundaries.

Pulsed laser deposition of epitaxial LaNiO 3 thin films on buffered Si(100)

Epitaxial LaNiO 3(LNO) thin films were deposited on Si(100) substrates by pulsed laser deposition. (100)-oriented films, without any other orientations, were obtained by using an intermediate double layer of CeO 2/YSZ. We studied the influence of substrate temperature and oxygen pressure on the crystal structure and room temperature electrical resistivity of LNO films. Optimal processing conditions allow the growth of LNO films with surface morphology, crystal structure and electrical properties suitable for the use of the conductive layer as an electrode in ferroelectric capacitors.

Growth of (1 0 0)-oriented LaNiO 3 thin films directly on Si substrates by a simple metalorganic decomposition technique for the highly oriented PZT thin films

LaNiO 3 (LNO) thin films directly on Si (1 0 0) substrates were prepared by a simple metalorganic decomposition (MOD) technique at annealing temperatures ranging from 450°C to 650°C using a rapid thermal annealing (RTA) method. Highly (1 0 0)-oriented LNO thin films were obtained at low annealing temperature of 550°C. The results indicate the LNO film annealed at 600°C exhibits good metallic property, which is comparable with the LNO films derived from physical techniques. A subsequent deposition of sol–gel derived Pb(Zr 0.52Ti 0.48)O 3 (PZT52/48) thin film on the LNO-coated Si substrate was also found to have a (1 0 0)-oriented texture. The ferroelectric capacitor derived from these films displayed a good P– E hysteresis characteristic.

Conducting lanthanum nickel oxide as electrodes for lead zirconate titanate films

Lanthanum nickel oxide (LaNiO 3 or LNO) is a conducting ceramic which has good potential for use as electrodes in multilayer actuators. In this work, lead zirconate titanate (PZT) films were prepared by a modified sol–gel process on stainless steel substrates. A LNO film prepared by a metal–organic deposition method was spin-coated onto the PZT film and the LNO/PZT film was cofired by rapid thermal processing at various temperatures. A transition layer consisting of a mixture of PZT and LNO was introduced between the LNO and PZT layer in order to enhance adhesion. The electrical resistivity of the LNO films was measured as a function of the sintering temperature and 750°C was found to be the optimum sintering temperature. The microstructures of the LNO/PZT films were studied in a scanning electron microscope (SEM).