Effects of Ar post-annealing on the electrical properties of Pt/YMnO3/p-Si and Pt/YMnO3/Y2O3/p-Si

Abstract

YMnO₃ thin films were prepared on p-Si(111) and Y₂O₃/p-Si(111) substrates by chemical solution deposition and annealed at 800°C for 1 hour under the oxygen pressure of 2 Torr. The YMnO₃ thin films showed good crystallinity and c-axis preferred orientation. Effects of Ar post-annealing on electrical properties were examined in Pt/YMnO₃/p-Si and Pt/YMnO₃/Y₂O₃/p-Si structures. Leakage current densities decreased considerably by Ar post-annealing. The Pt/YMnO₃/p-Si and Pt/YMnO₃/Y₂O₃/p-Si showed clockwise C-V hysteresis induced by ferroelectric polarization after Ar post-annealing and memory windows of MFS and MFIS structure were 1.1V and 0.6V, respectively.     

Self-Organized (100)-/(001)-Preferred Orientation in Pb(Zr,Ti)O3 Films Grown on Polycrystalline Substrates by Metalorganic Chemical Vapor Deposition

Lead zirconate titanate [Pb(Zr _x Ti_{1 ? x} )O₃, PZT] films were grown on (100), (110) and (111)SrRuO₃//SrTiO₃ substrates at 600°C by metalorganic chemical vapor deposition (MOCVD). The crystal orientation dependence of the growth rate was investigated for these films. The growth rate of (100)-/(001)-oriented epitaxial films was approximately 1.7 and 2.0 times higher than that of (110)-/(101)- and (111)-/(11&1macr;)-oriented epitaxial films, respectively. On the other hand, the growth rate of (100)-/(001)-preferred oriented PZT films grown on (111)Pt/TiO₂/SiO₂/(100)Si substrates was almost the same with that of (100)-/(001)-oriented epitaxial films. The deposition rate of these films was approximately 1.5 μm/h. High growth rate of (100)-/(001)-oriented PZT grains makes (100)-/(001)-preferred orientation on (111)Pt/TiO₂/SiO₂/(100)Si substrate. From transmission electron microscopy observation, (100)-/(001)-oriented grains were found to be directly grown on (111)-oriented Pt grains without obvious another oriented grains. As a result, orientation-controlled PZT films were successfully grown on (100)Si substrates having (111)-oriented Pt bottom electrodes.     

Preparation of BaPbO3 Electrode Thin Films by RF Magnetron Sputtering

For electrode materials of Pb(Zr,Ti)O₃ (PZT) thin films in ferroelectric random access memory (FeRAM), various materials have been studied. As new electrode material with which the polarization and fatigue properties are improved, we take notice of barium metaplumbate BaPbO₃ (BPO). Because the BPO contained lead (Pb) and oxygen is conductor that adopted same perovskite structure as PZT. BPO thin films were prepared by rf magnetron sputtering on various substrates. (SiO₂/Si, MgO, Al₂O₃ and Pt-coated substrates), and influence of growth conditions (sputtering gas, rf power, the substrate-heating temperature and post anneals) on crystallization and conductivity were investigated. In case of post anneal after sputtering at room temperature, perovskite single phase was obtained above 400°C. In case of substrate heating while sputtering, without post anneal, perovskite single phase was obtained at 350–500°C on SiO₂/Si substrates (110) preferred orientation BPO films obtained at low temperature, and resistivity of the films decreased at decreasing sputtering temperature. Resistivity of the film at substrate temperature 350°C was 3 × 10^?3 Ω cm. In the case of single crystal substrate, the BPO films were epitaxially grown. Orientation of the films was varied with the sputtering condition. The epitaxial PZT thin films were also grown on the BPO, revealing that PZT(111)[011] //BPO(111)[011] //Pt(100)[011] //MgO(100)[011] and PZT(111)[011] //BPO(111)[011] //Pt(111)[011] //Al₂O₃(001)[100] structures were obtained, and their ferroelectric properties were also evaluated.     

PREPARATION AND PROPERTIES OF LITHIUM-DOPED K0.5Na0.5NbO3 THIN FILMS BY CHEMICAL SOLUTION DEPOSITION

ABSTRACT

Lithium-doped K_0.5Na_0.5NbO₃ (KLNN) films were fabricated by chemical solution deposition on Pt/TiO₂/SiO₂/Si substrates. Homogeneous and stable precursor solutions were prepared by controlling the reaction of starting metal alkoxides. Perovskite KLNN single-phase thin films were successfully synthesized on Pt/TiO _x /SiO₂/Si substrates. The 0.75-μ m-thick KLNN film annealed at 650°C exhibited ferroelectric polarization hysteresis loops at ?250°C. The loop at room temperature was round, indicating the film contained leakage components. The dielectric constant under zero bias was 490 at room temperature. A typical upside-down butterfly DC bias-capacitance curve was obtained in the KLNN film capacitors at room temperature, indicating that polarization reversal occurred in the obtained KLNN films.     

Film Thickness Dependence of Electrical Properties for Pb(Zr,Ti)O3 Thin Films Prepared on (111)Ir/TiO2/SiO2/Si and (111)Pt/TiO2/SiO2/Si Substrates by Pulsed-Metalorganic Chemical Vapor Deposition

Polycrystalline Pb(Zr,Ti)O₃ (PZT) films with various film thicknesses were deposited on (111)Ir/TiO₂/SiO₂/Si and (111)Pt/TiO₂/SiO₂/Si substrates at 540°C by source-gas-pulsed metalorganic chemical vapor deposition (pulsed-MOCVD). PZT films deposited on (111)Ir/TiO₂/SiO₂/Si substrates showed good surface flatness and lower leakage current density. The rate of the decrease of remanent polarization (P _r ) and the rate of increase of coercive field (E _c ) for the films with decreasing the film thickness smaller on (111)Ir/TiO₂/SiO₂/Si substrates than those of (111)Pt/TiO₂/SiO₂/Si substrates. In addition, P _r and E _c values saturated at low voltage when the film thickness was the same. As a result, good ferroelectricity with P _r and E _c values of 40 μC/cm² and 140 kV/cm were obtained for 35 nm-thick films prepared on (111)Ir/TiO₂/SiO₂/Si substrates by pulsed-MOCVD.     

Low-Temperature Process of Ferroelectric (Y0.95,Bi0.05)MnO3 Thin Films and Their Structural and Electrical Properties

[(Y_0.95,Bi_0.05)MnO₃] (YBM) films have been grown on Y₂O₃ buffered Si (001) by pulsed-laser deposition (PLD). We have compared the structural and dielectric properties of YBM films with those of typical YMnO₃ films from the viewpoint of lowering the process temperature. The highly c-axis oriented YBM film have been obtained on Y₂O₃/Si (001) at 700°C, which is a significantly reduced growth temperature from that of typical YMnO₃ films (850°C). The Bi modification was effective for the low temperature processing of YBM films. These highly c-axis oriented YBM films was obtained only at high ambient oxygen pressures, for example above 100 mTorr, contrary to YMnO₃ films which requires low ambient oxygen pressure for the growth of c-axis preferred orientation. The dielectric constant and dissipation factor was 29 and 0.017 at 1 MHz, respectively. The memory window due to ferroelectric polarization switching was found in a capacitance-voltage (C-V) characteristic. The YBM/Y₂O₃/Si structure with above characteristics of YBM films exhibited the C-V memory window of 1.2 V at a sweep voltage of 5 V. The flat-band voltage shifted symmetrically with increasing the sweep voltage up to 8 V due to little charge injection from Si. As a result, the memory window increased progressively with increasing the sweep voltage and amounted to 2 V at a sweep voltage of 8 V. The leakage current density was below 5 × 10^?7 A/cm² at a bias voltage of 8 V.     

Fabrication and Characterization of Ba(Ti,Zr)O3 Thin Films Through the Chemical Solution Deposition Process

Lead- and bismuth-free Ba(Ti_{1 ? x} Zr _x )O₃ (BTZ) thin films were fabricated on Pt(111)/Ti/SiO₂/Si(100) substrates by the chemical solution deposition (CSD) process. The single phase BTZ thin films were obtained at 650°C by conventional process and the control of lattice parameter a was possible by Zr substitution. As the D-E hysteresis loops and J-V characteristics depended on the precipitates on film surface, the fabrication process was reexamined by 2-step sintering process. Consequently the decreasing of first sintering time was able to prevent the precipitates, and the larger grain of about 40–50 nm were obtained by additional sintering for 2 hour.     

Improvement of Capacitive Behavior on Gradient-Free PZT Thin Films

PbZr_0,52Ti_0,48O₃ thin films were synthetized by sol-gel techniques on large scale Pt(111)/TiO_x/SiO₂/Si substrates (200 mm in diameter). The Zr/Ti ratio gradient – that appears through the thickness of the layer with standard processing – can be reduced using an optimized “gradient-compensated” approach. Capacitance measurements revealed an augmentation of the effective permittivity from 5 to 15% using “gradient-free” PZT (reaching 1700 for 2μm). Large scale breakdown voltage analysis revealed an increase of 20% for the breakdown field for low thicknesses (1.25MV/cm for 240 nm-thick layer) suitable for capacitor integration.     

Glycolate tantalum based solutions for the sol-gel spin-coating deposition of SrBi2Ta2O9 thin films

Abstract

The reaction of tantalum ethoxide with a glycol solvent produces the interchange of the ethoxide groups with the glycol. As a result, a polymeric derivative is formed with a high resistance towards hydrolysis. Compounds of Sr(II) and Bi(II) can be added to this Ta-glycol sol, leading to strontium bismuth tantalate (SBT) precursor solutions stable in air. These solutions were spin-coated onto two substrates: Pt/TiO₂/SiO₂/(100)Si and Ti/Pt/Ti/SiO₂/(100)Si. Crystallisation of the SBT phase was carried out by a first formation of a fluorite phase that evolves to the layered perovskite at temperatures over 600°C. During crystallisation, a larger tendency to the formation of a substrate/film interface was observed in the films deposited onto Ti/Pt/Ti/SiO₂/(100)Si than onto Pt/TiO₂/SiO₂/(100)Si. A remanent polarisation of P_r5 μC/cm² and a coercive field of E_c <100 kV/cm were measured in the films on Pt/TiO₂/SiO₂/(100)Si. These films retain its remanent polarisation, P_r, up to 10⁵seconds and are fatigue-free up to 10⁹ cycles.     

Preparation of Textured Growth Pb(Zr,Ti)O3 Thin Films on Si Substrate Using SrTiO3 as Buffer Layers

PZT thin films are deposited on SiO₂/Si substrate by metallo-organic decomposition (MOD) process, using SrTiO₃ (STO) as buffer layer for textured growth. The STO layers deposited on SiO₂/Si substrate by pulsed laser deposition process show (100)/(200) preferred orientation, whereas the STO buffer layer deposited on silica substrate using spin-coating technique show random orientation behavior. The use of STO as buffer layers enhanced the crystallization and the preferred orientations of the PZT films. The PZT on STO buffered SiO₂/Si substrates thus obtained possess high refractive index, (n)_PZT/STO = 2.1159, and are of good enough quality for optical waveguide applications.     

The influence of microstructure on the electronic properties of thin films of barium strontium titanium oxide composites

Abstract

Microstructural and electrical properties were investigated for barium strontium titanium oxide (BSTO) magnesium oxide doped (0 to 10 wt.%) thin films deposited by the pulsed laser deposition (PLD) method on Pt/TiO_x/SiO₂/Si substrates. The dielectric properties were found to be strongly dependent on composition and microstructure. In cross-section, all films exhibited a columnar polycrystalline microstructure with vertical orientation deviations dictated by the surface roughness of the Pt electrode. A uniform granular microstructure was observed for all films in plan view. The dielectric constant, loss tangent and grain size decreased with increasing MgO concentration.     

Properties of (001)-textured Pb(Mg1/3Nb2/3)O3–PbTiO3 thin films

Relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PMN–PT) thin films with [001] preferential orientation were deposited on platinized silicon wafers by a sol–gel method, in which a PbO seeding layer was involved. The influences of annealing temperature on the crystal phase, microstructure, and electrical properties of the PMN–PT films were investigated. Pyrochlore-free perovskite PMN–PT films could be formed on PbO-seeded Pt(111)/Ti/SiO₂/Si wafers at 800 °C, which was also the optimal annealing temperature for endowing the film with the best ferroelectric and dielectric properties. The enhanced properties were attributed to the improved crystallinity and microstructure. The leakage behaviors of the PMN–PT films annealed at different temperatures were also measured and discussed.     

Structure and properties of Zn-doped CoFe2O4 thin films via a sol–gel method

Zn-doped cobalt ferrite Co_0.9Zn_0.1Fe₂O₄ (CZFO) films with the spinel structure were fabricated on Pt(111)/Ti/SiO₂/Si(100) using a sol-gel method, and the effect of annealing temperature and time on structure and magnetic properties of the CZFO thin films were investigated. The coercivity and saturation magnetization of the films are not sensitive to annealing time, and increase with a rise in the annealing temperature below 800 °C. The CZFO thin films annealed at 800 °C show the best crystallization and the highest coercivity (3.5 kOe), and above 800 °C, the coercivities of the films decrease as a result of formation of multi-domains, while the saturation magnetization comes to stable.     

Novel diffusion control process using ultra thin buffer layer for MFIS memory

Abstract

MFIS structures having excellent clear interfaces and well-crystallized ferroelectric layer were successfully fabricated by a newly developed ultra thin metal buffer layer process on SiO₂/Si. We examined the effect of sputtered Zr or ZrO₂ ultra thin films as a buffer layer for Pb_xLa_1?xTiO₃ (PLT) growth. TEM observation revealed that the buffer layer formation process in which Zr oxidized after the metal deposition had advantages to produce MFIS structures. This method is also superior for the crystallization and the control of the orientation of PLT thin film on amorphous SiO₂. Especially, for buffer layer thicknesses below 10 nm, preferred c-axis oriented PLT thin films were grown. The I-V characteristics of MFIS-FET fabricated by the proposed method showed a clear memory window due to the remanent polarization of the ferroelectric thin film. This process is the most attractive candidate for realizing MFIS structure memory.     

Growth of MgTiO3 thin films by pulsed laser deposition and their electrical properties

Abstract

MgTiO₃ thin films have been grown on various substrates by pulsed laser deposition (PLD) to investigate the application for microwave dielectrics and optical devices. Highly oriented MgTiO₃ thin films were obtained on sapphire (c-plane Al₂O₃). MgTiO₃ thin films deposited on SiO₂/Si and platinized silicon (Pt/Ti/SiO₂/Si) substrates were polycrystalline nature. MgTiO₃thin films grown on sapphire were transparent in the visible and had a sharp absorption edge at 280 nm. These MgTiO₃ thin films had extremely fine feature of surface morphology, i.e., rms roughness of 0.87 nm. Dielectric constant and loss of MgTiO₃ thin films deposited by PLD were about 24 and 1.5% at 1MHz, respectively. These MgTiO₃ thin films also exhibited little dielectric dispersion.     

Structure and dielectric properties of Ba(Sn0.2Ti0.8)O3 thin films grown on different substrates by a sol-gel process

Ba(Sn_0.2Ti_0.8)O₃ (BTS) thin films were deposited on Pt/Ti/SiO₂/Si and LaNiO₃/Pt/Ti/SiO₂/Si substrates by a sol-gel processing technique, respectively. The influences of substrates on the phase and microstructure of the thin films were examined. Dielectric properties of the thin films were investigated as a function of frequency and direct current electric field. The results showed that the substrates strongly influenced the microstructure and the dielectric properties of the films. The properties of BTS thin films on LaNiO₃/Pt/Ti/SiO₂/Si substrates were superior to that of the films grown on Pt/Ti/SiO₂/Si substrates.     

The <00l>-oriented growth of Cu2S films and its switching properties

Cu₂S films have been deposited on Pt/TiO₂/SiO₂/Si(111) substrates, and annealed at different temperatures in a vacuum chamber. They were characterized by using X-ray diffraction and scanning electron microscopy. It was observed that the Cu₂S films deposited at room temperature are well crystallized and the grains are oriented along different directions. With the increase of the annealing temperature, the grains of Cu₂S films prefer the <00l>-orientations, and the average size of Cu₂S films decreases. After annealed at 400°C, the films are completely <00l>-oriented, and the grain boundaries of Cu₂S films become undistinguishable due to the possible movements of the ions at high temperature. The resistive ratio of the ‘off’ state to the ‘on’ state is about 10⁷ for the memory unit of Cu/Cu₂S/Pt structure with the Cu₂S films annealed at 400°C, about 6 orders of magnitude higher than that for the memory unit with the Cu₂S films deposited at room temperature.     

Lateral Epitaxial Growth of Ba0.6Sr0.4TiO3 Thin Films

We report a novel growth technique for epitaxial thin films by combination of selective heteroepitaxial growth and lateral homoepitaxial growth. Ba_0.6Sr_0.4TiO₃ (BST) thin films were deposited on the substrates having patterned SiO_x layers at 450°C using pulsed laser deposition. Post annealing was carried out thereafter for lateral epitaxial growth. The difference in the crystallization temperature of BST thin film on the amorphous masking layers and lattice-matched single crystalline substrate enables selective nucleation and heteroepitaxial growth from the regions of single crystalline substrates during the film deposition. Lateral homoepitaxial growth is expected from the crystallized BST thin film toward the amorphous BST on SiO_x during the post annealing process. In this paper, a study on the difference in nucleation and growth behavior of BST thin films on the amorphous masking layers and lattice-matched single crystal substrates is presented.     

Investigation on various insulator layers for MFIS capacitors

Abstract

Effects of insulator layers of Metal(Au)/Ferroelectrics(PZT)/Insulator/Si (MFIS) structure capacitors are investigated for non-destructive type non-volatile memory device applications. Various high dielectric oxide layers such as Al₂O₃, Ta₂O₅, TiO₂ and ZrO₂ were fabricated by reactive sputtering as insulating layers. The oxide insulators give significant impacts on the morphologies of PZT layer and the properties of capacitors. It is noted that the oxide layers with small thermal expansions (<6x10^–6/°C) coefficient caused cracks on PZT films during PZT crystallization annealing. The effects of insulators as a diffusion barrier are also comparatively studied using Auger electron spectroscopy. In addition, the characteristics of high dielectric solid solution, such as titanium oxide-zirconium oxide, are also studied.     

(Zr/Ti) ratio effect on RF magnetron sputtered lead titanate zirconate films

Abstract

Sputtered Pb(Zr_xTi_1?x)O₃ thin films with various (Zr/Ti) compositions ranging from 15/85 to 70/30 were grown and characterised in terms of structural and electrical properties. PZT thin films, with 0.7–0.8μm thickness, were deposited on Si/SiO₂/Ti/Pt by sputtering followed by conventional annealing. The sputtering conditions were the same for all the compositions. There were no apparent differences in crystallographic orientation as a function of Zr/Ti and the films a-lattice constant evolution is not exactly identical to the one of bulk ceramics. The permittivity increases when the Zr concentration increases and decreases just after the mor-photropic composition i.e. Zr-rich films. The ferroelectric properties are very sensitive to the Zr/Ti ratio. For example, the coercive field increases when the Ti concentration in the film increases.