The Study of Ferroelectric La-Doped PbTiO3 Thin Films Prepared by RF Magnetron Sputtering

Ferroelectric La-modified lead titanate (PLT) thin film were grown on Pt/Ti/SiO2/Si by sputtering the Pb_0.93La_0.07TiO₃ targets containing an amounts of excess 8% PbO. The effects of sputtering and annealing conditions on the crystalline structures and the surface morphologies of the PLT thin films have been investigated. The remanent polarization (Pr) and the coercive field of the PLT film through rapid thermal annealing (RTA) was 10.2 μC/cm² and 45 kV/cm respectively. The maximum pyroelectric coefficient reached 19 nC/cm².K at 20°C.     

Characterization of the CeO2 thin films for insulation layer and Pt/SrBi2Ta2O9/CeO2/Si MFISFET structure

Abstract

CeO₂ and SrBi₂Ta₂O₉ (SBT) thin films for MFISFET (metal-fcrroelectrics-insulator-semiconductor field effect transistor) were deposited by rf sputtering and pulsed laser deposition method, respectively. The effects of oxygen partial pressure during deposition for CeO₂ films were investigated. The oxygen partial pressure significantly affected the preferred orientation, grain size and electrical properties of CeO₂ films. The CeO₂ thin films with a (200) preferred orientation were deposited on Si(100) substrates at 600°C. The films deposited under the oxygen partial pressure of 50 % showed the best C-V characteristics among those under various conditions. The leakage current density of films showed order of the 10^?7～10^?8 A/cm² at 100 kV/cm. The SBT thin films on CeO₂/Si substrate showed dense microstructure of polycrystalline phase. From the C-V characteristics of MFIS structure composed of the SBT film annealed at 800°C, the memory window width was 0.9 V at ±5 V. The leakage current density of Pt/SBT/CeO₂/Si structure annealed at 800°C was 4×10^?7 A/cm² at 5 V.     

Ferroelectric SrBi2Ta2O9 thin films deposited by liquid injection MOCVD using novel bimetallic alkoxide precursor

Abstract

The ferroelectric SBT films were deposited on Pt/Ti/SiO₂/Si substrates by liquid injection metalorganic chemical vapor deposition (MOCVD) with single-mixture solution of Sr[Ta(OEt)₅(dmae)]₂ and Bi(C₆H₅)₃. The Sr/Ta and Bi/Ta ratio in SBT films depended on deposition temperature and mol ratio of precursor in the single-mixture solution. At the substrate temperature of 400°C, Sr/Ta and Bi/Ta ratio were close to 0.4 and 1 at precursor mol ratio of 0.5～1.0. As-deposited film was amorphous. However, after annealing at 750°C for 30 min in oxygen atmosphere, the diffraction patterns indicated polycrystalline SBT phase. The remanent polarization (Pr) and coercive field (Ec) of SBT film annealed at 750°C were 4.7 μC/cm²and 115.7 kV/cm at an applied voltage of 5 V, respectively. The SBT films annealed at 750°C showed practically no polarization fatigue up to 10¹⁰ switching cycles.     

EFFECTS OF PZT BUFFER LAYERS ON PZFNT FERROELECTRIC THIN FILMS

ABSTRACT

PZFNT thin films were fabricated on 5-inch Pt/Ti/SiO₂/Si and PZT/Pt/Ti/SiO₂/Si substrates by RF magnetron sputtering method and rapid thermal annealing process. By investigating the two thin films at various annealing temperatures, the results show that the annealing temperature of PZFNT thin films without PZT buffer layers is about 730°C, which is higher than that of PZFNT films with PZT buffer layers. By use of PZT buffer layers, the annealing temperature of PZFNT films is decreased greatly, and the dielectric and ferroelectric properties are improved. In the optimum process, the thin films with PZT buffer layers have a dielectric constant of 1199 and dielectric loss of 3.0% at 1 KHz. The remanent polarization and coercive field of the thin films are 21.1 μC/cm² and 53.5 KV/cm respectively. The films have the significant potential for FRAM and pyroelectric infrared detectors.     

Preparation and characterization of SrBi2Ta2O9 thin films by low-oxygen-concentration annealing technique

SrBi₂Ta₂O₉ thin films were successfully prepared at a low annealing temperature using a low-oxygen-concentration annealing technique. It was possible to obtain a single perovskite phase at 600 °C in 0.7% oxygen concentration and fluorite phase was observed at 600 °C in 100% oxygen. In addition, the SrBi₂Ta₂O₉ thin films annealed at 650 °C in 0.7% oxygen were well crystallized and composed of dense crystal grains with a size of 70 nm. The remanent polarization and leakage current density of the SrBi₂Ta₂O₉ thin film obtained using this new technique were 7 μC/cm² and 3 × 10⁻⁹ A/cm² (at 5 V), respectively. The final remanent polarization after 10⁹ switching cycles was nearly constant. © 1999 Scripta Technica, Electr Eng Jpn, 129(4): 1–6, 1999     

Influence of Post-Annealing on the Characteristics of Pb(Zr,Ti)O3 Thin Films Deposited by Liquid Delivery MOCVD Using a Cocktail Solution

Ferroelectric PZT thin films were deposited by liquid delivery MOCVD using a cocktail solution. The cocktail solution consisted of Pb(METHD)₂, Zr(METHD)₄ and Ti(MPD)(METHD)₂ diluted with ethylcyclohexane. The films deposited on Pt/Ti/SiO₂/Si at a substrate temperature of 500°C consisted of PZT, PbO and PbPt_x, and showed poor properties. However, after annealing at 450°C in air for thirty minutes, the PbPt_x phase disappeared while the volume of the PbO phase increased. The hysteresis properties were also improved by annealing at 450°C. After annealing at 600°C in air for thirty minutes, the PbPt_x and the PbO phases disappeared perfectly and the PZT thin films showed good hysteresis properties with the remanent polarization of 30 μC/cm² and the coercive field of 88 kV/cm.     

Effects of transition metal (Ni, Mn, Cu) doping on ferroelectric properties of Bi0.9Nd0.1FeO3 thin films prepared by chemical solution deposition method

Transition metal (Ni, Mn, Cu) doped Bi_0.9Nd_0.1FeO₃ thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Compared to pure BiFeO₃ (BFO) thin film, improved ferroelectric and leakage current properties were observed in the transition metal doped thin films. The values of remnant polarization (2P _r ) and coercive electric field (2E _c ) of the transition metal doped thin films were 59 μC/cm² and 690 kV/cm at 700 kV/cm for the Ni-doped Bi_0.9Nd_0.1FeO₃ thin film, 57 μC/cm² and 523 kV/cm at 670 kV/cm for the Mn-doped thin film, and 85 μC/cm² and 729 kV/cm at 700 kV/cm for the Cu-doped thin film, respectively. The 2P _r values observed in the transition metal doped thin films were much larger than that of the BFO thin film, 21 μC/cm² at 660 kV/cm. Also the 2E _c values of in the transition metal doped thin films were lower than that of the BFO thin film, 749 kV/cm at 660 kV/cm. The reduced leakage current density was observed in the transition metal doped thin films, which is approximately two orders of magnitude lower than the BFO thin film, 2.6?×?10^?3 A/cm² at 100 kV/cm.     

Improvement in the electrical properties of ferroelectric SrBi2Ta2O9 capacitors by electron beam irradiation on precursor films

Abstract

Ferroelectric SrBi₂Ta₂O₉ (SBT) capacitors were fabricated by the Electron-Beam-Induced Patterning process and their electrical properties were evaluated in detail. In this process, the dose of an electron beam irradiated on precursor films had a great influence on the electrical properties of the SBT capacitors. The appropriate electron dose significantly improved the electrical properties of the SBT capacitors although the excess electron dose made severe deterioration in the properties. The SBT capacitors fabricated with the optimum electron dose, 1.5 mC/cm² for Sr:Bi:Ta = 0.8:2.2:2.0 solutions, exhibited excellent ferroelectric properties: a remanent polarization of 11.5 μC/cm², a coercive field of 40 kV/cm, a leakage current of 8×10^?8 A/cm²@ 1V and fatigue-free up to 1010 cycles. It seems that such improvements were caused by the adjustment of Bi contents in the films and the modification or the decompositon of precursors before heat treatment by electron beam irradiation.     

Dielectric and Ferroelectric Properties of Ba(Zr0.35Ti0.65)O3 Thin Films Grown by a Sol-Gel Process

The Ba(Zr_0.35Ti_0.65)O₃ (BZT) thin films were deposited via sol-gel process on LaNiO₃-coated silicon substrates. XRD showed that the crystallinity of BZT film grown on LaNiO₃ coated silicon substrates is better than that of BZT film grown on Pt. Both films showed perovskite phase and polycrystalline structure. The temperature dependent dielectric measurements revealed that the thin films had the relaxor behavior and diffuse phase transition characteristics. The capacitor tuning was about 44% for each BZT film grown on LaNiO₃/Pt and Pt electrodes at 1 MHz. Especially, the values of dielectric loss at 1 MHz ranged from 0.02 to 0.009 in the bias range of 0 to 514 kV/cm, respectively. The leakage currents density of thin films grown on LaNiO₃/Pt and Pt electrodes at 300 kV/cm was about 8.5 × 10^–7 and 1.1 × 10^–5 A/cm², respectively. This work demonstrates a potential use of BZT films for application in tunable microwave devices.     

Recent progress in sputtering PZT thin films for ferroelectric memories

Abstract

This paper describes amorphous Pb(Zr, Ti)O₃ (PZT) thin films deposited by cosputtering Pb(Zr_0.5 Ti_0.5)O₃ and PbO targets. By optimizing the amount of the excess Pb and the deposition temperature, PZT thin films with a single perovskite phase were obtained successfully on Ir substrates and Pt substrates at 520°C. 250-nm-thick PZT films crystallized by rapid thermal annealing (RTA) at 600°C for 20 s exhibited excellent ferroelectric properties: a coercive voltage of 1.0 V, a remanent polarization density of about 40 μC/cm², and a polarization switching endurance over 1x109 cycles. Although a heat treatment in a reductive ambient causes degradation of ferroelectric properties of PZT thin films, their degraded ferroelectric properties can be easily recovered from by a 1-min RTA in an oxygen at 400°C.     

Structural and improved electrical properties of rare earth (Sm, Tb and Ho) doped BiFe0.975Mn0.025O3 thin films

Pure BiFeO₃ (BFO) and rare earth (RE) ion co-doped (Bi_0.9RE_0.1)(Fe_0.975Mn_0.025)O₃ (RE?=?Sm, Tb and Ho, denoted by BSFM, BTFM and BHFM) thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Formations of distorted rhombohedral perovskite structure for the thin films were confirmed by using an X-ray diffraction and a Raman scattering analysis. Microstructural features for the thin films were examined by using a scanning electron microscopic analysis. Among the thin films, the lowest leakage current density of 1.22?×?10^?6 A/cm² (at 100 kV/cm), large remnant polarization (2Pr) of 72.4 μC/cm² and low coercive field (2E _c ) of 689 kV/cm (at 980 kV/cm) were measured for the BTFM thin film.     

Laser ablation preparation and property of bismuth-layer-structured SrBi2Ta2Ta2O9 and Bi4Ti3O12 ferroelectric thin films

Abstract

Bismuth-layer-structured ferroelectric thin films, SrBi₂Ta₂O₉ and Bi₄Ti₃O₁₂, have been prepared by laser ablation method on both Pt sheets and Si wafers at low temperatures of 400 ～ 500°C. These thin films have been characterized by XRD, XPS, AFM, C-V, D-E hysteresis and J-V measurement. SrBi₂Ta₂O₉ thin films have a good (105) preferential orientation, and Bi₄Ti₃O₁₂ thin films have (117) and c-axis orientation on these substrates. Ferroelectric film-SiO₂-Si structures show good C-V hysteresis curve owing to Si surface potential controlled by the D-E hysteresis. D-E hysteresis is obtained in Bi₄Ti₃O₁₂ thin film prepared on Pt sheet, and the remnant polarization and the coercive force are 7.5 μC/cm² and 72 kV/cm, respectively.     

Enhancement of ferroelectricity in gadolinium (Gd) and transition metal (Ni, Co, Cr) Co-doped BiFeO3 thin films via a chemical solution deposition technique

The BiFeO₃ (BFO) and the gadolinium and transition metal ions co-doped (Bi_0.9Gd_0.1)(Fe_0.975 TM _0.025)O_3-δ (TM?=?Ni, Co and Cr, BGFNi, BGFCo and BGFCr) thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Compared to the pure BFO, improved electrical and ferroelectric properties were observed in the co-doped (Bi_0.9Gd_0.1)(Fe_0.975 TM _0.025)O_3-δ thin films. Among the thin films, the BGFCr thin film exhibited large remnant polarization (2P _r ), low coercive field (2E _c ), and reduced leakage current density, which are 136 μC/cm², 1360 kV/cm at 1470 kV/cm, and 5.14?×?10^-6 A/cm² at 100 kV/cm, respectively.     

Effect of excess-PB and prenucleation layer on properties of Pb(ZryTi1-y)O3 thin films prepared by mod process

Abstract

A modified metal-organic decomposition process, MOD has been successfully utilized to improve the ferroelectric properties of Pb(Zr_0.52Ti_0.48)O₃, PZT, thin films. Multilayer PZT/Pt(Si) films, which contain 0.12 μm layer of spin coated PbO-excess (10 mol%) precursors on top of 0.12 μm layer of stoichiometric PZT precursors, exhibit superior ferroelectric properties (P_r=14.2 μC/cm²; E_c=62 kV/cm) to the single layer PZT/Pt(Si) films of the same thickness (0.24 μm), which are either stoichiometric or 10 mol% Pb-enriched. The ferroelectric properties are further improved when the PZT films were synthesized using a thin pulsed laser deposited (PLD) prenucleation layer (0.06 μm). The subsequently MOD-prepared PZT films posses high remanent polarization (P_r=23.2–26.6 μC/cm²) and low coercive field (E_c=62.9–69.0 kV/cm).     

Ferroelectric Properties of Mo-Doped Bi4-XLaXTi3O12 Films

Mo-doped Bi_3.35La_0.75Ti₃O₁₂ (BLTM) films were deposited on Pt/Ti bottom electrodes by using a sol-gel method and crystallized at 700°C for 30 min in O₂ atmosphere. The ferroelectric properties were greatly improved by substituting B-site ions with Mo ions and the BLTM films showed strong preferred (117) orientation. Typical remanent polarization (2Pr) and coercive field (2Ec) values were 32.0 μC?cm^?2 and 158 kV?cm^?1, respectively. It was also found that the leakage current densities in the BLTM films were lower than those in Bi_3.35La_0.75Ti₃O₁₂ (BLT) films.     

Advances in processing and properties of perovskite thin-films for FRAMs,DRAMs, and decoupling capacitors

Abstract

Highly oriented, dense, and crack-free ferroelectric and paraelectric thin-films on three inch diameter Pt/Ti/Si₃N₄/Si (100) substrates were obtained by polymeric sol-gel processing. Ferroelectric PZT thin-films were fabricated at temperatures as low as 550°C within 15 minutes by rapid thermal annealing. The films heat treated at 700°C for 5 minutes were single grain thick and exhibited P_r, P_sp, and E_c in the ranges of 29–32 μC/cm², 44–53 μC/cm², and 50–60 kV/cm, respectively, and high speed switching times below 5 ns on 30×30 μm² electrodes. A switching time of 2.7 ns was observed on 19×19 μm² area electrodes at a field of 200 kV/cm. Results of low and high field characterization on paraelectric PLT thin-films which were conventionally heat treated indicated that it has an excellent potential for use in ULSI DRAMs and as decoupling capacitors. These films showed a high charge storage density (15 μC/cm²) and a low leakage current (0.5 μA/cm²) at a field of 200 kV/cm. Also, the charging time for a capacitor area of 1 μm² at 200 kV/cm was estimated to be 0.10 ns.     

Preparation and characterization of PZT ferroelectric thin films by plasma enhanced metalorganic chemical vapor deposition

Abstract

PZT thin films with a uniform distribution of components were prepared by plasma enhanced chemical vapor deposition (PECVD) using Pb(C₂H₅)₄, Z (O-i-C₄H₉)₄, Ti(O-i-C₃H₇)₄, and oxygen. The crystallization of films was occure after annealing in the temperature range between 450 and 550°C under O₂ ambient for 1 hr. The significant change of Pb concentration in PECVD PZT thin films was not observed in the relation to annealing temperature and time. The dielectric constant PECVD PZT thin films increased with the Ti content, showed the maximum value in the vicinity of morphotropic phase boundary (MPB) composition of PZT material, and decreased with the Ti content. The leakage current density of PZT (65/35) thin film of 180 nm in thickness was 3·37 × 10^?7 A/cm² at the applied voltage of 3 V. Remanent polarization increased with increasing of Zr content in the film and coercive field was nearly independent of the composition. The typical values of electrical properties were ε_r = 570, E_c = 90 kV/cm, and P_r = 19 μC/cm² in the PECVD PZT (54/46) thin film of 220 nm in thickness.     

Electrical properties of paraelectric PLT(28) thin films deposited by dc magnetron sputtering

Abstract

Paraelectric [Pb, La]TiO₃ (PLT, La = 28 mol%) thin films were prepared by dc magnetron sputtering using a multi-element metal target. In order to crystallize the as-deposited PLT thin films into the cubic perovskite structure, a heat treatment was applied at annealing temperatures ranging between 450 and 750°C. The electrical measurements such as dielectric properties, polarization-electric field (P-E), and current-voltage (I–V) were investigated with the change of annealing temperature. The dielectric constant and dissipation factor of paraelectric PLT film annealed at 750°C were 1216 and 0.018, respectively. The charge storage density was approximately 12.5 μC/cm². The leakage current density in PLT film annealed at 650°C was around 0.1 μA/cm² at the electric field of 0.25 MV/cm.     

Single-grained PZT thin films for high level FRAM integration—fabrication and characterization

Abstract

A new method for formation of large single grains as large as 40 μm in length of the sputter-deposited PZT(65/35) thin films has been developed in this research group. Crystallized PZT dots were used as a seed and the grains were laterally grown to form a square pattern on the Pt substrate. It turned out that the electrical characteristics of the single grained PZT thin films were much superior to those of the poly-grained PZT thin films. The leakage current was measured to be less than 8x10^?8 A/cm², the breakdown field more than 1,240 kV/cm, the value of saturation polarization and remanent polarization as high as 42 μC/cm², 30 μC/cm², respectively. No degradation of the polarization properties was observed even after the 2×10¹¹ cycles at 1 MHz using a ± 10 V wave form in Pt/PZT/Pt structure. The accelerated retention test revealed that it takes more than 6×10⁷ years for the remanent polarization to be reduced down to 80% of the original value.     

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.