Preparation of Zr-rich PZT and La-doped PbTiO3 thin films by RF magnetron sputtering and their properties for pyroelectric applications

Abstract

Zr-rich PZT and La-doped PT films were fabricated on a PLT/Pt/Ti/SiO₂/Si or Pt/Ti/SiO₂/Si substrate by an RF planar magnetron sputtering equipment using powder targets with compositions of PbZr_{0 94}Ti_0.06O₃, PbZr_0.92Ti_0.08O₃ and Pb_0.85La_0.15 Ti_0.96O₃ with excess PbO of 20 mol%. The dielectric constants of PZT and PLT films showed anomalies at the transition temperatures of around 246 and 300°C, and their dielectric constants at room temperature were 350 and 1070, respectively. Significant pytroelectric currents were observed in both as-grown PZT and PLT films even without a poling treatment. The pyroelectric coefficients of those films were 10 and 30 nC/cm²K, respectively. Therefore, Zr-rich PZT and [111]-oriented PLT films sputtered on Pt/Ti/SiO₂/Si substrates possess desirable properties for potential applications to pyroelectric devices.     

In situ formation of sol-gel derived PbTiO3/NiFe2O4 biphase thin film

In this article, magnetoelectric (ME) biphase composite thin films consisted of PbTiO₃ as ferroelectric phase and NiFe₂O₄ as ferromagnetic phase which were successfully formed in situ by sol-gel process. The phase structure, morphology and dielectric properties of the films were measured by X-ray diffraction (XRD), scanning electron microscope (SEM) and LCR precision impedance analyzer. It is concluded that the thin films were capable of being controlled to form the biphase composite of PbTiO₃ and NiFe₂O₄ at the heat-treatment temperature between 600 and 850 °C. The phases coexisting in the composite thin film are in forms of solid solutions doped with Ni²⁺ and Fe³⁺ and with Ti⁴⁺, respectively. Their lattice constants vary with their doping contents. The capacitance of the composite thin film depends on the content of perovskite phase and the doping addition of Ni²⁺ and Fe³⁺ in crystalline phase of PbTiO₃.     

Electrical properties of TiO2 thin films prepared by the sol-gel method

A TiO₂ thin film was prepared by the sol-gel method using a metal alkoxide [Ti(O-i-Pr)₄ tetrasopropoxy titanium: TIPT]. The crystalline form of the film depends on the preparation conditions and the heat treatment temperature. When the ratio (γ) of H₂O to TIPT is 7, the crystalline phase is formed at 400°C; when γ = 2 it is formed at 500°C. The anatase crystal structure was obtained for both γ = 2 and γ = 7. The electrical conductivity of the TiO₂ film increased with the heat treatment temperature.     

Preparation and properties of sol-gel derived PZT thin films for decoupling capacitor applications

Abstract

The use of ceramic thin films as decoupling capacitors offers the possibility of capacitor integration within the integrated circuit (IC) package, and potentially, directly onto the IC itself. Since these configurations minimize series inductance, higher operational speeds are possible. In the present study we have investigated the dielectric and leakage characteristics of sol-gel PZT films. For compositions near the morphotropic phase boundary, dielectric constants of 1000, and loss tangents of about 0.02, were observed. The current-voltage behavior of the capacitors was characterized by a non-linear response, and significant asymmetry in both the leakage and breakdown characteristics as a function of bias sign was observed. Breakdown fields for PZT 53/47 thin films were typically ～800 kV/cm at 25°C. We have also studied the effects of La and Nb dopant additions and alternate firing strategies on film leakage characteristics. Donor doping at 2–5 mol% lowered leakage currents by a factor of 10³ For films prepared by a multilayering approach, firing each layer to crystallization resulted in leakage currents that were a factor of 10² lower than films prepared by the standard process.     

Electrical and optical properties of PZT ferroelectric films fabricated by the PVP-assisted sol-gel method

Lead zirconate titanate (PZT) films were deposited on platinized silicon substrates by spin coating using organic macromolecule polyvinylpyrrolidone (PVP) as an additive, which has the hybrid effects, was dispersed uniformly into the sol-gel precursor solution of PZT. The films were coated by spin-coating and then annealed at a proper temperature by repaid thermal processing. PZT ferroelectric films were polycrystalline and perovskite phase structure. The Coercive Field and remnant polarization of the PZT films annealed at 600 °C were 91 kV/cm and 19 μC/cm² respectively. The fatigue resistance properties were improved and the polarization value decreased only 8% of the initial polarization at 10⁸ cycles. The optical properties were measured by spectrophotometer and the band energy was calculated about 3.59eV.     

Pyroelectric properties of sol-gel derived PZT thin films with various Zr/Ti ratios

Abstract

Integrated pyroelectric arrays are receiving serious attention for the next generation of room temperature uncooled IR cameras. Such pyroelectric arrays are based on monolithic ferroelectric(FE) thin films. FE films with large values of reported pyroelectric coefficients include PbTiO₃, Ca-doped PbTiO₃, La-doped PbTiO₃, PZT 53/47 and Pb(Sc_0.5Ta_0.5)O₃. The present paper reports a systematic study of the compositional dependence of PZT thin films on their pyroelectric properties. A series of sol-gel derived PZT (lead zirconate titanate) thin films with various Zr/Ti ratios, namely, PbTiO₃, PZT 20/80, PZT 35/65, PZT 53/47, PZT 65/35, PZT 92/8 and PbZrO₃, were prepared on platinized Si substrates. The films were fired to 650 – 700°C to crystallize them into single-phase perovskite. The degree of preferred orientation, grain size and firing temperature affect the pyroelectric responses. Pyroelectric coefficients as large as 2.5 × 10^?8 C/cm²-K were obtained, making such PZT thin films attractive in pyroelectric arrays.     

Electrical properties of BaPb1+x−y Sb y O3 ceramics derived from a modified sol-gel method

BaPbO₃ ceramics has attracted considerable interest due to the promising electrical applications. For the best control of the microstructure and phase, Sb-doped BaPbO₃ ceramics were prepared by a sol-gel route. Inorganic compounds were used as starting chemicals, citric acid and Ethylene diamine tetra-acetic acid (EDTA) as complex chelate agent, and distilled water as solvent. Experimental results demonstrate that the Sb-doped BaPbO₃ ceramics with homogeneous composition could be prepared by the method mentioned above. Influence of Pb/Ba ratio and Sb concentration on the room-temperature resistivity and the PTCR behavior of BaPb_1+x−y Sb _y O₃ (x = 0.0, 0.1, 0.2 and 0 ≤ y ≤ 0.2) compositions was investigated. The PTCR behavior was related to the Pb/Ba ratio and major compensating defect in BaPbO₃. The lowest electrical resistivity of Sb-doped BaPbO₃ was calculated to be 2.69 × 10⁻⁴ Ω·cm when the Sb concentration y = 12–13 mol%. The 0.5 mol% Sb-doped BaPbO₃ showed the best PTCR behavior, and its Curie temperature is about 850 °C.     

Influence of anatase-rutile phase transformation on dielectric properties of sol-gel derived TiO2 thin films

The phase transformation behavior and resulting dielectric properties of sol-gel derived TiO₂ thin films were investigated. Thin films showed a typical behavior of mixture systems during the phase transformation; a kinetic investigation on the isothermal curve of pre-crystallized thin films revealed that the phase transformation was a first-order reaction with an Avrami time component of 1. Dielectric constants of TiO₂ thin films increased with the increasing amount of the rutile phase while the dielectric losses showed the opposite relationship. From a fitting process using the parallel mixing rule, dielectric constants of two end members of the mixture system were calculated to be 41.4 and 145.2 for the pure anatase and rutile phase thin films, respectively.     

Fabrication of MFIS diodes using sol-gel derived SBT films and LaAlO3 buffer layers

Abstract

We demonstrate the ferroelectric behavior of Sr_0.8Bi_2.2Ta₂O₉ (SBT) films grown on Si(100) substrates by using lanthanum aluminate (LaAlO₃) buffer layers. LaAlO₃ films were prepared by vacuum evaporation method. Then, they were subjected to ex situ dry N₂ annealing in a rapid thermal annealing (RTA) furnace. From the capacitance-voltage (C-V) measurement, the dielectric constant of LaAlO₃ was estimated to be 20～25. On these substrates, SBT films (210nm) were deposited by sol-gel method and they were characterized by XRD analysis after annealing under various conditions. It was found from C-V characteristics that the memory window of an SBT film annealed at 750°C for 30min in O₂ atmosphere was about 3.0V for the voltage sweep of ±10V. It was also found from the retention measurement that the capacitance values of the SBT film annealed at 750°C did not change over 12hours. It is concluded from these results that the SBT/LaAlO₃/Si(100) structure is one of the most promising structures for realizing MFISFETs (metal-ferroelectric-insulator-semiconductor field-effect-transistors).     

Effect of preheating process on crystallization and optical properties of sol-gel derived ZnO semiconductor thin films

Highly transparent ZnO semiconductor thin films were deposited onto alkali-free glass substrates by a sol-gel spin coating process. This research investigated the effects of different preheating rates (4 or 10°C/min) on the various surface morphologies, crystallization characteristics, and optical properties of these thin films. The ZnO sol was synthesized by dissolving the zinc acetate dihydrate in isopropanol (IPA), and then adding monoethanolamine (MEA). These as-coated films were preheated at 300°C for 10 min and annealed in an air ambiance at 500°C for 1 h. Experimental results revealed that the as-prepared films had a hexagonal wurtzite structure, and that the heating rates of the preheating process obviously affected the surface morphologies, crystallization qualities, and transparency levels of the thin films. A ZnO thin film preheated at 10°C/min exhibited preferential orientation along the (002) plane, a flat surface, and also achieved a high transmittance value, 92.5%, for light with a wavelength of 550 nm.     

Influence of deposition parameters on physico-chemical and optical properties of sputtered PbTiO3 thin films

Abstract

Stoichiometric thin films of lead titanate (PbTiO₃) have been grown “in situ” without postannealing on (0001) sapphire substrates by rf magnetron sputtering technique. X-ray diffraction scans have revealed that as-grown films consist of the perovskite phase and are polycrystalline with a high (111) orientation. The structure, the microstructure and the optical properties have been studied as a function of the process parameters i.e., substrate temperature, gas pressure and the target composition, in particular the lead content. We report the dependence of the deposition conditions on the optical constants. The optimum experimental conditions (100m Torr and 600°C) to produce thin films with high transparency and refractive indices (n = 2.61 at 633 nm), similar to values for bulk materials, are given in this paper.     

Texturing and electrical characteristics of sol-gel derived ferroelectric thin films

Abstract

Highly oriented PZT, PLZT and PMN thin films were fabricated on various substrates using sol-gel method. The thin films having different orientation were fabricated by different drying conditions for pyrolysis. The preferred orientations of the PZT, PLZT and PMN thin films were observed using XRD(X-ray diffraction). The hysteresis loops, capacitance-voltage, and fatigue characteristics of the films were investigated using an RT66A standardized ferroelectric test system. The dielectric constant and current-voltage characteristics of the films were investigated using impedance analyzer and pA meter, respectively. The films oriented in particular direction showed better electrical characteristics to the randomly oriented films.     

Preparation of PbTiO3 thin films by laser ablation

Abstract

PbTiO₃ thin films have been deposited on Si or Pt substrates by laser ablation method using ArF excimer or YAG laser. Species evaporated in the vacuum have been studied by mass analysis, and the measured Pb and Ti are not oxidized. Spacial distributions of the deposition rates on the substrate have been studied as a parameter of laser fluence. The excimer laser gives better films than the YAG. Perovskite films have been obtained at substrate temperature ～ 400 °C and appropriate ambient O₂ gas pressure.     

Effects of thickness of the thermal insulation layer on the properties of PbTiO3 thin films

A multilayer pyroelectric thin film structure (MPTFS) is one of promising candidates for applications on uncooled IR focal plane array detectors. In the MLPTFS, a porous silica film is used as a thermal insulation layer, and the thermal insulation is improved with increasing thickness of a porous silica film. On the other hand, the effects of thickness of the porous silica films on the electrical properties of pyroelectric thin films need to be addressed. The research results have shown: the thickness of the porous silica films can not be increase unboundedly. With increasing thickness of porous silica films, the coercive field increase, the dielectric constant and the breakdown field decrease respectively. When the thickness of the porous silica films is lower than 3 μm, the effects of the porous silica films on the properties of PT thin films are acceptable. The optimized thickness of the porous silica films is determined according to the results of the electrical properties.     

Growth and microstructures of sputtered ferroelectric PbTiO3 thin films

Abstract

PbTiO₃ thin films, 5–200 nm in thickness, were epitaxially growth on miscut (001) SrTiO₃ substrates by planar magnetron sputtering for understanding of film growth mechanism and their ferroelectricity. The surface of the miscut substrates with miscut angle of 1.7 degree contains periodic step lines and terraces; the step height is 0.4 nm and terrace width is 14 nm. The surface structures of PbTiO₃ films comprised periodic striped patterns which was reflected in the initial surface of the substrate. It was found that under a stoichiometric film composition the film growth was governed by Frank-van der Merwe type and resultant epitaxial films showed extremely smooth surface. Deposition on a miscut substrate under a stoichiometric condition is essential to making the uniform ferroelectric thin films.     

Structural and electrical properties of sol-gel synthesized PLZTthin films

Thin films of PLZT with PbTiO₃ interlayers have been fabricated by using a sol-gel spin-on process. Three compositions of PLZT, namely 8/65/35, 15/40/60 and 18/30/70, have been deposited on platinum and quartz substrates and heat treated at 650°C. All three compositions have crystallized in the perovskite phase. The 8/65/35 composition, which has been investigated in greater detail exhibits a low value of leakage current. It also exhibits polarization hysteresis, with E_c=20 kV/cm and P_r=25 μC/cm²     

Ferroelectric properties of Al and Nb doped PbTiO3 thin films prepared by chemical solution deposition process

Abstract

Thin films of pure and acceptor (Al) as well as donor (Nb) doped PbTiO₃ were prepared using a chemical solution deposition method. The nominal compositions of the solutions were equivalent to those of PbTiO₃, Pb(Ti_0.95Al_0.95)O₃ and Pb(Ti_0.95Nb_0.05)O₃, respectively. In the case of PbTiO₃, the remanent polarization amounted to 43 μC/cm², but the shape of the hysteresis curve was round. On the other hand, Al and Nb doped PbTiO₃ thin films exhibited well-saturated P-Ehysteresis curves. The shape of these curves was slim compared to that of PbTiO₃. The remanent polarization of the Pb(Ti_0.95Al_0.05)O₃ and Pb(Ti_0.95Al_0.05)O₃ thin films amounted to 18 and 15 μC/cm², respectively, and the coercive field decreased in comparison with that of PbTiO₃. The leakage currents of the PbTiO₃, Pb(Ti_0.95Al_0.05)O₃ and Pb(Ti_0.95Al_0.05)O₃ thin films were 7.68x10^?3, 3.21x10^?6 and 6.58x10^?4 A/cm², respectively, at+10V.     

Electrical properties of 3-component piezoelectric thick films by screen printing method

Abstract

PZT(52/48) thick films with Pb-based complex oxide (PCW) additive were prepared on Pt/TiO₂/YSZ/SiO₂/Si substrate by screen printing method. PCW addition and PZT sol application are performed to fabricate high density PZT thick film and to lower sintering temperature. With the increase of sintering temperature, electrical properties of screen-printed films were improved. Further, for the sol-gel treated thick films, the electrical properties were improved as compared to only screen-printed films. For the PZT-0.12PCW thick films with sol-treated and sintered at 900°C, the remanent polarization (P_r) was about 23.8 μC/cm² at the applied filed of 150 kV/cm², the dielectric permittivity (Ω_r) was 1024 at the frequency of 100 kHz, and the piezoelectric coefficient (d₃₃) was 339 pC/N at the applied pressure of 1 atm. Finally, the application of these PZT thick films to piezoelectric actuator is described.     

Structure and properties of sol-gel processed (Pb,La)TiO3 ferroelectric thin films

Abstract

The influence of heat treatment and substrate materials on PLT thin films by sol-gel processing has been researched. Epitaxial growth PLT thin films with perovskite-type structure on sapphire, SrTiO₃ and MgO single crystal substrates have been prepared. The epitaxial relations are (100)PLT28/(100)SrTiO₃, (111)PLT28//(0001)sapphire and (100)PLT14//(100)MgO. The PLT polycrystal thin films with perovskite-type structure on Si single crystal and quartz glass substrates have been prepared. The remanent polarization Pr and the coercive field Ec of PLT15 ceramic thin films are 7.7 μc/cm² and 34 kv/cm at 4 KHz respectively. The optical transmittance of PLT28 ceramic thin films within the wavelength range of λ = 500–1000 nm is approximately 80%.