Study of pulsed laser deposition of RuO2 and SrRuO3 thin films

In this study, the pulsed laser ablation of RuO₂ and SrRuO₃ (SRO) is investigated by observing the fluorescence from excited atoms in the plume by using a framing streak camera. Vaporization, phase explosion and boiling are suggested to play the main roles in the processes for the interaction between the laser beam and target. Collisions and adiabatic expansion are also suggested before particles move forward with shifted Maxwellian spatial distribution. In O₂ pressure, numerous collisions between fast and slow atoms occur and result in the exchange of speeds. The structural and electrical (conductivity and work-function) properties of RuO₂ and SRO thin films are measured. Epitaxial SRO growth was obtained at growth temperatures down to 350 °C. Ferroelectric and high- dielectric thin-film capacitors with RuO₂ or SRO thin film electrode are also studied.     

Band Gap Energies and Refractive Indices of Epitaxial Pb1-xSrxTe Thin Films

Pb1-x Srx Te thin films with different strontium （St） compositions axe grown on BaF2 （111） substrates by molecular beam epitaxy （MBE）. Using high resolution x-ray diffraction （HPLXRD）, we obtain Pb1-xSrxTe lattice constants, which vary in the range 6.462-6.492 A. According to the Vegard law and HRXRD data, Sr compositions in Pb1-xSrxTe thin films range from 0.0-8.0%. The Pb1-xSrxTe refractive index dispersions are attained from infrared transmission spectrum characterized by Fourier transform infrared （FTIR） transmission spectroscopy. It is found that refractive index decreases while Sr content increases in Pb1-xSrx Te. We also simulate the Pb1-xSrxTe transmission spectra theoretically to obtain the optical band gap energies which range between 0.320 e V and 0.449 e V. The simulated results are in good agreement with the FTIR data. Finally, we determine the relation between Pb1-xSrx Te band gap energies and Sr compositions （Eg = 0.320＋0.510x-0.930x^2 ＋184x^3 （eV））.     

Preferential orientation of modified SrBi2Nb2O9 ferroelectric thin films prepared by pulsed laser deposition

We report on the deposition of SrBi₂Nb₂O₉ and Sr_1-xNa_xBi_2-xTe_xNb₂O₉ ferroelectric thin films on Pt/TiO₂/SiO₂/(100)Si substrates using the pulsed laser deposition technique. Deposition on substrates heated to 600-700 °C produces {11l} film texture and dense films with grain sizes up to about 500 nm. The recrystallization at 700 °C of amorphous films deposited at lower temperatures enhances the contribution of the {100} and {010} orientations. These films show smaller grain size, namely 50-100 nm. {11l}-oriented Sr_1-xNa_xBi_2-xTe_xNb₂O₉ films have remnant polarization P_rۆ 7C/cm², a coercive field E_c䏐 kV/cm and dielectric constant, )𪓴. The low value of P_r is probably related to the low fraction of grains with the ferroelectric axis in the direction of the applied field, E. The recrystallized films have more grains with the ferroelectric axis parallel to E; however, they have a low resistivity which so far has prevented electrical characterization.     

Quantitative ferroelectric characterization of single submicron grains in Bi-layered perovskite thin films

The local polarization state and the electromechanical properties of ferroelectric thin films can be probed via the converse piezoelectric effect using scanning force microscopy (SFM) combined with a lock-in technique. This method, denominated as piezoresponse SFM, was used to characterize at the nanoscale level ferroelectric SrBi₂Ta₂O₉ and Bi₄Ti₃O₁₂ thin films, grown by pulsed laser deposition. Two types of samples were studied: polycrystalline films, with grains having random orientations, and epitaxial films, consisting of (100)_orth- or (110)_orth-oriented crystallites, 100 nm to 2 7m in lateral size, which are embedded into a (001)-oriented matrix. The ferroelectric domain structure was imaged and the piezoelectric response under different external conditions was locally measured for each type of sample. Different investigation procedures are described in order to study the ferroelectric properties via the electromechanical response. A distinct ferroelectric behavior was found for single grains of SrBi₂Ta₂O₉ as small as 200 nm in lateral size, as well as for 1.2 7m쏿 nm crystallites of Bi₄Ti₃O₁₂. By probing separately the crystallites and the matrix the investigations have demonstrated at the nanoscale level that SrBi₂Ta₂O₉ has no spontaneous polarization along its crystallographic c-axis, whereas Bi₄Ti₃O₁₂ exhibits a piezoelectric behavior along both the a- and c-directions. The electrostriction coefficients were estimated to be 3᎒^-2 m⁴/C² for polycrystalline SrBi₂Ta₂O₉ and 7.7᎒^-3 m⁴/C² for c-orientedBi₄Ti₃O₁₂. Quantitative measurements at the nanoscale level, within the experimental errors give the same values for remanent polarization and coercive field as macroscopic ferroelectric measurements performed on the same samples.     

Role of bismuth precursor in crystallization of SrBi2Ta2O9 thin films

Crystallization of SrBi₂Ta₂O₉ (SBT) thin films was studied as a function of viscosity of bismuth precursor and baking temperature, in order to fabricate capacitors with improved ferroelectric properties. SBT thin films were deposited on to Pt substrates using a chemical solution deposition (CSD) technique. Post-deposition anneal at 750 °C for 1 h in oxygen atmosphere revealed a significant influence of baking temperature and the viscosity of bismuth precursor on the microstructure and the ferroelectric properties of SBT thin films. A high baking temperature (350 °C) and a low viscosity of bismuth precursor (8 cp) yielded larger amounts of Bi₂O₃ secondary phase, smaller SBT grains (104 nm), and lower remanent polarization (P_r=2.0 7c/cm²). Additionally, these films exhibited a very high rate of ageing (>45% reduction in P_r after 7 days). A modified CSD process is suggested, which could suppress the formation of Bi₂O₃ secondary phase. Films fabricated using modified CSD technique exhibited a much larger grain size of 165 nm, higher P_r of 7.2 7c/cm², and significantly improved ageing characteristics (<1% reduction in P_r after 7 days). A qualitative model to describe the ageing in SBT-based capacitors is also suggested.     

Low-temperature preparation of SrxBi2+yTa2O9 ferroelectric thin film by pulsed laser deposition and its application to a metal–ferroelectric–nitride–oxide–semiconductor structure

Preferentially (105)-oriented Sr_xBi_2+yTa₂O₉ (SBT) thin films on SiN/SiO₂/p-Si(100) prepared by the pulsed laser deposition (PLD) method at a temperature as low as 400 °C, which is the lowest process temperature for growing SBT ferroelectric thin films on a silicon nitride film. Excess Bi promotes crystallization of the SBT film. A metal-ferroelectric-nitride-oxide-semiconductor (MFNOS) structure, which is very important in ferroelectric gate memory FET, has been fabricated by depositing the SBT film on silicon nitride-oxide-silicon. The MFNOS structures show capacitance-voltage (C-V) hysteresis corresponding to ferroelectric hysteresis. A memory window of the C-V hysteresis is improved, to be as high as 3.5 V in the SBT(400 nm)/SiN_x(7 nm)/SiO₂(18 nm)/Si compared with the window of 2.7 V in the SBT(400 nm)/SiO₂(27 nm)/Si (MFOS), where the thicknesses of their insulator layers are nearly the same. Little degradation is induced in the C-V characteristics of the SiN_x/SiO₂/p-Si structure when depositing the SBT film by PLD at low temperature. It is also found that the SiN_x layer acts as a diffusion barrier against component atoms in the SBT film during its deposition. Finally, the MFNOS structure prepared at the low temperature is very promising for a next-generation ferroelectric gate memory FET.     

Room-Temperature Ferromagnetism in Zn1-xMnxO Thin Films Deposited by Pulsed Laser Deposition

Zn1-xMnxO （x = O.Olq3.1） thin films with a Curie temperature above 300K are deposited on Al2O3 （0001） substrates by pulsed laser deposition. X-ray diffraction （XRD）, ultraviolet （UV）-visible transmission and Raman spectroscopy are employed to characterize the microstructural properties of these films. Room temperature ferromagnetism is observed by superconducting quantum interference device （SQUID）. The results indicate that Mn doping introduces the incorporation of Mn^2＋ ions into the ZnO host matrix and the insertion of Mn^2＋ ions increases the lattice defects, which is correlated with the ferromagnetism of the obtained films. The doping concentration is also proven to be a crucial factor for obtaining highly ferromagnetic Zn1-xMnxO films.     

Pulsed-laser deposition of Ta-doped PZT ferroelectric films for memory applications using conductive oxide La0.25Sr0.75CoO3 and SrRuO3 electrodes

New methods for fabricating highly 𘚡¢-oriented and complete 𘜏¢-textured Pb(Ta_0.05Zr_0.48Ti_0.47)O₃ (PTZT) films on Pt/TiO₂/SiO₂/Si(001) substrates by pulsed-laser deposition have been developed using conductive oxide La_0.25Sr_0.75CoO₃ and SrRuO₃ electrodes. The 𘚡¢-preferred orientated PTZT ferroelectric capacitor was not subjected to loss of its polarization after 1᎒¹⁰ switching cycles at an applied voltage of 5 V and a frequency of 1 MHz, and the 𘜏¢-textured PTZT film capacitor retains 94.7% of its polarization after 1.5᎒¹⁰ switching cycles at 5 V and 50 kHz. The PTZT capacitors using these conductive oxide electrodes have low leakage current dominated by Schottky field emission mechanism.     

Electrical Characterization of Deep Trap Properties in High-k Thin-Film HfO2 Dielectric

Deep-trap properties of high-dielectric-constant （k） HfO2 thin films are investigated by deep-level transient spectroscopy and capacitance-voltage methods. The hole traps of the HfO2 dielectric deposited on a p-type Si substrate by sputtering are investigated in a metal-oxide-semiconductor structure over a temperature range of 300-500K. The potential depth, cross section and concentration of hole traps are estimated to be about 2.5eV, 1.8 ×10^-16 cm^2 and 1.0 × 10^16 cm^-3, respectively.     

Artificial Modulation of Ferroelectric Thin Films into Antiferroelectric through H+ Implantation for High-Density Charge Storage

Hydrogen ions are implanted into Pb（Zro.3Tio.7）03 1014 ions/cm^2. Pseudo-antiferroelectric behaviour in thin films at the energy of 40keV with a flux of 5 x the implanted thin films is observed, as confirmed by the measurements of polarization versus electric hysteresis loops and capacitance versus voltage curves. X-ray diffrac- tion patterns show the film structures before and after H＋ implantation both to be perovskite of a tetragonal symmetry. These findings indicate that hydrogen ions exist as stable dopants within the films. It is believed that the dopants change domain-switching behaviour via the boundary charge compensation. Meanwhile, time dependence of leakage current density after time longer than lOs indicates the enhancement of the leakage cur- rent nearly in one order for the implanted film, but the current at time shorter than i s is mostly the same as that of the original film without the ionic implantation. The artificial tailoring of the antiferroelectric behaviour through H＋ implantation in ferroelectric thin films is finally proven to be achievable for the device application of high-density charge storage.     

Role of electrodes materials in determining the interfacial and magnetoelectric properties in BaTiO<Subscript>3</Subscript>-based multiferroic tunnel junctions

Using the first-principles calculations based on density functional theory, the important role of electrode materials in determining the interfacial, ferroelectric stability and magnetoelectric properties in BaTiO₃-based multiferroic tunnel junctions (MFTJs) have been investigated comparatively. It is found that the SrO–TiO₂ interface of MFTJs with oxide electrode SrRuO₃ is the most favorable interfacial structure. The average ferroelectric polarizations of MFTJs with electrode Co, FeCo and SrRuO₃ are 25, 36 and 0 μC/cm², respectively. The using of alloy electrode FeCo is more contributed to ferroelectric stability and the enhancement of magnetoelectric coupling of BaTiO₃-based MFTJs. We expect our findings can provide an essential evaluation for the selection of electrode materials in spintronic storage devices.     

Size effect on SrRuO3/BaTiO3/SrRuO3 ferroelectric ultrathin film capacitor

We have carried out a detailed investigation on the size effect on SrRuO₃/BaTiO₃/SrRuO₃ ferroelectric ultrathin film capacitors with film thickness fully strained with a SrTiO₃ substrate. We employ the transverse field Ising model, taking into account the incomplete charge compensation of the realistic SrRuO₃ electrode and the misfit strain imposed by the SrTiO₃ substrate in the Hamiltonian, to quantitatively explain the experimental observation in the literature. It is found that BaTiO₃ ultrathin films between two metallic electrodes lose their ferroelectric properties below a critical thickness of about 4.17 nm due to the enhancement of the quantum effect under the influence of the incomplete charge compensation of the electrode.     

Epitaxial growth of non-c-oriented ferroelectric SrBi2Ta2O9 thin films on Si(100) substrates

Epitaxial SrBi₂Ta₂O₉ (SBT) thin films with well-defined (116) orientation have been grown by pulsed laser deposition on Si(100) substrates covered with an yttria-stabilized ZrO₂ (YSZ) buffer layer and an epitaxial layer of electrically conductive SrRuO₃. Studies on the in-plane crystallographic relations between SrRuO₃ and YSZ revealed a rectangle-on-cube epitaxy with respect to the substrate. X-ray diffraction pole figure measurements revealed well-defined orientation relations, viz. SBT(116)SrRuO₃(110)YSZ(100)Si(100), SBT[110]SrRuO₃[001], and SrRuO₃[111]YSZ[110]Si[110].     

Off-axis pulsed laser deposition system for epitaxial oxide growth on substrates up to 2 inches in diameter

A novel off-axis pulsed-laser deposition (PLD) system for ferroelectric oxide thin films has been developed. The substrates are mounted "upside-down" and are rotating. The maximum substrate size is 2 inches in diameter. The optical and structural properties of the grown BaTiO₃ films are compared to the films produced by an on-axis PLD system. The stoichiometry and thickness were checked with Rutherford backscattering spectrometry (RBS). The crystalline quality and orientation were investigated with X-ray diffraction (XRD) and Rutherford backscattering spectrometry in channeling configuration (RBS/C). Using atomic force microscopy, the rms surface roughness was measured. The BaTiO₃ films grown on MgO form a planar optical waveguide. The optical losses and the refractive indices of these waveguides were determined with a prism coupling setup. Films grown on 10᎒ mm² MgO (100) substrates in on-axis geometry show optical waveguide losses less than 3 dB/cm.     

Simultaneous Generation of Multi-Wavelength Laser from Nd:YAG Crystals in a Cruciform Cavity

A cruciform cavity is presented for multi-wavelength laser generation. On the basis of considering the optimal power ratio and good spatial overlap of the two fundamental beams, the maximum output power of 589 nm laser reaches 3.5 W when the pumping power of Nd：YAG A and Nd：YAG B are 311.5 W and 261.8 W, respectively. At the same time, the other wavelength lasers are also obtained with the output power distribution of 2.5 W at 66Onto, 15 W at 532nm, lOOmW at 1319nm and 240mW at 1064nm. The corresponding beam quality factors are M^2 x = 4.93, M^2 y = 5.01 at 589nm, M^2z = 4.51, M^2 y = 4.85 at 660hm, and M^2 x = 4.12, M^2 y = 3.96 at 532nm, respectively. The instabilities of the three visible lights are measured, which are also less than 2% within three hours.     

Effects of strontium and calcium simultaneous substitution on electrical and structural properties of Pb1?x?yCaxSryTiO3 thin films

Ferroelectric Pb_1−x−y Ca _x Sr _y TiO₃ thin films (denoted by PCST90, PCST70, and PCST30) were deposited on the Pt/Ti/SiO₂/Si substrates by a chemical solution deposition method. Their properties were investigated from the viewpoint of crystal structure, microstructure, dielectric, and ferroelectric properties. X-ray diffraction patterns revealed the formation of PCST90, PCST70, and PCST30 thin films without any secondary phases. Infrared and Raman spectroscopy results show that a gradual phase transition from tetragonal to pseudocubic or cubic perovskite structure may occur in PCST thin films with the simultaneous increase of Ca²⁺ and Sr²⁺ contents. Both substitution of isovalent Ca²⁺ and Sr²⁺ at Pb²⁺-site enhanced the dielectric constant and reduced the remnant polarization. In addition, ferroelectric test analyses show that the PCST thin films undergo a ferroelectric-to-paraelectric phase transformation with an amount of Pb²⁺, Ca²⁺, and Sr²⁺ at 30%, 35%, and 35% mol, respectively. Hence, the absence of ferroelectric property may be attributed to a decreasing of the octahedron distortion in the perovskite structure accompanied by a weakening of long-range ferroelectric order.     

Single Particle Schr dinger Fluid and Moments of Inertia of Deformed Nuclei

We have applied the theory of the single-particle Schrodinger fluid to the nuclear collective motion of axially deformed nuclei. A counter example of an arbitrary number of independent nucleons in the anisotropic harmonic oscillator potential at the equilibrium deformation has been also given. Moreover, the ground states of the doubly even nuclei in the s-d shell ²⁰Ne,²⁴Mg,²⁸Si,³²S and ³⁶Ar are constructed by filling the single particle states corresponding to the possible values of the number of quanta of excitations n_x,n_y, and n_z. Accordingly, the cranking-model, the rigid-body model and the equilibrium-model moments of inertia of these nuclei are calculated as functions of the oscillator parameters ω_x,ω_yand ω_z which are given in terms of the non deformed value ω00 , depending on the mass number A, the number of neutrons N, the number of protons Z, and the deformation parameter β. The calculated values of the cranking-model moments of inertia of these nuclei are in good agreement with the corresponding experimental values and show that the considered axially deformed nuclei may have oblate as well as prolate shapes and that the nucleus ²⁴Mg is the only one which is highly deformed. The rigid body model and the equilibrium model moments of inertia of the two nuclei ²⁰Ne and ²⁴Mg are also in good agreement with the corresponding experimental values.     

Effect of Pretreatment of TaN Substrates on Atomic Layer Deposition Growth of Ru Thin Films

The polycrystalline ruthenium films are grown on TaN substrates by atomic layer deposition （ALD） using bis（cyclopentadienyl） ruthenium [RuCp2] and oxygen as ruthenium precursor and reactant respectively at a deposition temperature of 330℃. The low-energy Ar ion bombardment and Ru pre-deposition are performed to the underlying TaN substrates before ALD process in order to improve the Ru nucleation. X-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy and atomic force microscopy are carried out to characterize the properties of ALD Ru films. The results show that the nucleation density of Ru films with Ar^＋ bombardment to the underlying TaN substrates is much higher than that of the ones without any pretreatment. The possible reasons are discussed.     

Ferroelectric domain structures and polarization switching characteristics of polycrystalline BiFeO3 thin films on glass substrates

We investigated ferroelectric characteristics of BiFeO₃ (BFO) thin films on SrRuO₃ (SRO)/yttria-stabilized zirconia (YSZ)/glass substrates grown by pulsed laser deposition. YSZ buffer layers were employed to grow highly crystallized BFO thin films as well as SRO bottom electrodes on glass substrates. The BFO thin films exhibited good ferroelectric properties with a remanent polarization of 2P_r = 59.6 μC/cm² and fast switching behavior within about 125 ns. Piezoelectric force microscopy (PFM) study revealed that the BFO thin films have much smaller mosaic ferroelectric domain patterns than epitaxial BFO thin films on Nb:SrTiO₃ substrates. Presumably these small domain widths which originated from smaller domain energy give rise to the faster electrical switching behavior in comparison with the epitaxial BFO thin films on Nb:SrTiO₃ substrates.