Zirconate Titanate Thin Films Research Articles

Structural and Electrical Properties of Pb(Zr,Ti)O3 Thin Films on GaN/Sapphire, Ru/Sapphire and Ru/GaN/Sapphire Substrates

Lead zirconate titanate or Pb(Zr0.3Ti0.7)O3 thin films were deposited on GaN, Ru/Sapphire and Ru/GaN/Sapphire substrates by the sol-gel technique. The Ru films, with a (002) preferred orientation, were deposited by metalorganic chemical vapor deposition (MOCVD) on Sapphire (0001) and GaN/Sapphire substrates. The properties of PZT on Ru films, rapid thermal annealed under different conditions, are investigated. The P-E hysteresis curves and C-V data for PZT films on Ru/GaN and Ru/Sapphire substrates were measured as a function of voltage and frequency. The Metal-Ferroelectric-Semiconductor (MFS or Pt/PZT/GaN) structures, prepared by depositing PZT thin films on n-type (Si doping ∼1×1018 cm−3) and (0001)-GaN/Sapphire, were characterized for their dielectric properties. The PZT films on as-deposited Ru, as opposed to annealed Ru, exhibit improved properties; remnant polarization of 37 μC/cm2, dielectric permittivity of 425 at 100 KHz, and leakage current density ∼1×10−7 A/cm2 at 1.5 V.

Predicted Frequency Response of Integrated Pyroelectric PNZT Infrared Detectors

Numerous studies have been carried out on the fabrication of ferroelectric lead titanate (PT) and lead zirconate titanate (PZT) thin films and their applications to pyroelectric sensors [1–3]. Not many efforts have been made to integrate the films with silicon technology. In this article, we report on the growth of lead-zirconium-titanates films doped with niobium (PNZT) by a sol-gel method on platinized Si substrates along with its characteristics for use in infrared sensor applications.

Piezoelectric thin films formed by MOD on cantilever beams for micro sensors and actuators

Novel piezoelectric cantilever beams for micro sensors and actuators based on PZT thin films have been batch fabricated by surface micromachining. Lead zirconate titanate (PZT) thin film is formed by metalorganic deposition (MOD) on Pt/Ti/SiO2/Si (1 0 0) substrates and Pt/Ti/LTO/Si3N4 cantilever beams and then annealed at 700 °C in air. The PZT thin film is 0.5 μm thick and has dielectric permittivity of 1698, remanent polarization of 13.66 μC/cm2, and coercive field of 44.5 kV/cm. The influence of deposition temperatures on PZT thin film stress has been investigated. When continuously controlling the deposition temperatures, the stress of the thin film is reduced from 0.313 × 108 to 0.269 × 108 N/m, that is 16.4% decrease. With the total 120 designed devices on 4-inch wafers, the number of functional devices is increased from 82 to 97, that is 12.47%.

Fabrication of Isolated Ferroelectric Domains in Nano-Scale

Lead zirconate titanate (PZT) thin films were prepared by a sol-gel method on platinized Si. Their microstructure and surface morphology were characterized by XRD and AFM. Phase transformations of the prepared PZT films from pyrochlore to ferroelectric were observed at 550 and 600°C for furnace and RTP annealing, respectively. Smaller scattering angle (2°) XRD results showed more pyrochlore phases in the near surfaces and PZT (100) nucleated in Pt substrate and transformed to the surfaces in FA annealing PZT films. Isolated ferroelectric phases in the surroundings of pyrochlore phases were fabricated in order to study size effect of laterally confined ferroelectric domains. The isolated ferroelectric phases in the diameter of about 400 nm were found in FA PZT films at 450°C. Piezoresponse mode of AFM shows complex ferroelectric domains in the isolated phase, not from the surroundings.

Infrared spectra and second-harmonic generation in barium strontium titanate and lead zirconate-titanate thin films: “Polaron” artifacts

We report infrared absorption spectroscopy and second-harmonic generation data for barium strontium titanate (BST) and lead zirconate-titanate (PZT) ceramic films in the 3000−5500 cm−1 region. Second-harmonic generation experiments give temperature dependences in accord with oxygen vacancy cluster theory [S. A. Prosandeev, Sov. Phys. JETP 83, 747 (1996); S. A. Prosandeev, V. S. Vikhnin, and S. Kapphan, Integr. Ferroelectr. 32, 1047 (2001); J. Phys. Condens. Matter 14, 4407 (2002)]. A percolation model of vacancy ordering is discussed. The present work shows that earlier data interpreted as polaron spectra in these films were actually artifacts due to interference in the optical apparatus used [B. Guettler, U. Bismayer, P. Groves, and E. Salje, Semicond. Sci. Technol. 10, 245 (1950]; more recent “polaron” spectra in WO3 films may also be artifacts [L. Berggren, A. Azens, and G. A. Niklassson, J. Appl. Phys. 90, 1860 (2001)]. Numerical estimates of the polaron mass m**=16 me in SrTiO3 and BST help prove that dielectric data in strontium titanate interpreted as bipolarons [A. Levstik et al., Appl. Phys. Lett. 81, 4046 (2002)] are also artifacts.

Design of a Triaxial Piezoelectric Accelerometer

A monolithic MEMS triaxial accelerometer based on piezoelectric lead zirconate titanate (PZT) thin films with highly symmetric quad-beams and a seismic mass, has been designed and simulated. Theoretical and numerical models for this structure are presented. The dynamic response and the trade-off between several design considerations are discussed. Static and modal simulations with FEM (Finite Element Method) simulator have been performed to analyze the mechanical response. It shows that the sensitivities of the three axes (X, Y, Z) are respectively 27, 27, and 29 mv/g, and there is almost no transverse sensitivity for the accelerometer. Also, the device is expected to have good temperature performance.

Micropatterned lead zirconium titanate thin films

Micropatterning of Pb(Zr0.52Ti0.48)O3 (PZT) thin films with line features as small as 350 nm was demonstrated through capillary molding of organometallic solutions within the continuous channels of an elastomeric mold. Despite the large stresses that develop during the evaporation of the solvent, pyrolysis of the organics, and the densification and crystallization of the inorganic gel, the patterned crystalline PZT films were crack-free and mechanically robust. Flawless regions as large as 1 cm2 were obtained. The cross-sectional shape of the patterned PZT lines was trapezoidlike. Single perovskite PZT grains that formed during annealing at 600–700 °C completely filled the cross-sectional area of the patterned lines. Lead acetate, zirconium propoxide, and titanium isopropoxide were used as the starting materials. Substrates used included silver tape, stainless steel plate, silicon wafer, and platinum-coated silicon wafer.

Influence of substrate temperature on the chemical and microstructural properties of MO-CVD ZrTiO 4 thin films

In the last few years, intensive research activity has been focused on the development of suitable synthesis methods for high-permittivity materials, used for the realization of next-generation microdevices able to fulfil the previsions of the Technology Roadmap of Semiconductors. The use of high-permittivity materials can overcome the difficulties concerning the production of SiO2-based ultra-thin dielectrics, such as the generation of pinholes and the non-uniformity of the film, which may result in a malfunction in high-density systems. Recently, zirconium titanate thin films were discovered to have very interesting dielectric properties, which suggests a use for them in microwave integrated systems, such as receivers or DRAMs, since they are monophasic, have little dissipation and show a good thermal stability and a high value for the dielectric constant, independent of frequency in the range from kilohertz to a few gigahertz. Real application is possible only in strict connection with the development of a suitable preparation method which allows production with controlled and reproducible characteristics. In this work, the synthesis and characterization of ZrxTi1-xO4 (ZT) thin films grown via MO-CVD is described, studying the influence of growth parameters on their structural, chemical and physical properties.

Non-Linear Imprint Behavior of PZT Thin Films

Ferroelectric thin film capacitors are promising candidates for non-volatile ferroelectric Random Access Memories (FeRAM's) as they exhibit a switchable polarization. There are three important failure-mechanisms influencing the performance of these capacitors and disturbing the long-term stability and reliability under operation conditions fatigue, retention, and imprint. The imprint effect of lead zirconate titanate (PZT) thin films was investigated in this paper. Establishing and maintaining a polarization state leads to a shift of the hysteresis loop on the voltage axis and also to a loss of polarization. The voltage shift as well as the loss of polarization can cause a failure of the ferroelectric memory cell (read and write failure). The experimental results obtained on PZT films are discussed in view of the predictions of imprint models proposed in the literature.

Conducting Strontium Ruthenium Oxide Interface Layers for Application to PZT/SrRuO3/Metal Thin Film Capacitors

Ferroelectric lead zirconate titanate (PZT) thin films have been prepared by chemical solution deposition (CSD) and were spin-coated onto stainless steel substrates. In order to improve the ferroelectric properties, the influence of an additional layer of strontium ruthenium oxide (SrRuO3) at the interface between the perovskite type PZT and the metal substrate has been studied. The elaboration route of the SrRuO3 thin films by CSD and spin-coating is presented. The influence from the annealing temperature on the PZT crystallization behavior has been analyzed by X-ray diffraction, and the PZT coercive field and remanent polarization were investigated as a function of the SrRuO3 process parameters. The results are compared with those obtained for PZT/RuO2/metal thin film capacitors.

Miniature Microphone with Silicon-Based Ferroelectric Thin Films

A miniature microphone with silicon-based lead zirconate titanate (PZT) thin films has been fabricated and tested. The main structure of the device is composed of Al/Pt/PZT/Pt/Ti/SiO2/Si3N4/SiO2/Si multi-layer diaphragm. The PZT thin films have been prepared using an improved sol-gel method. Optimized fabrication process of the device has been developed, especially, RIE (reactive ion etching) and IBE (ion beam etching) processes have been used to etch the PZT thin film and electrode metal successfully. The sensitivity of microphone is 16 mV/Pa at 1 KHz and 158 mV/Pa at the resonant frequency of 17.3 KHz. The electrical and thermal reliability of the microphone is satisfactory. This miniature microphone can be widely used in hearing aids, mobile phones, and many other applications.

Growth and electrical characterization of laser ablated highly oriented zirconium titanate thin films in a metal–oxide semiconductor configuration

Highly oriented zirconium titanate (ZrTiO4) thin films were deposited along the (020) direction on a p-type Si substrate using the pulsed excimer laser ablation technique. X-ray diffraction and energy dispersive analysis of ZrTiO4 thin films reveal that they exhibit excellent phase and stoichiometry, respectively. Secondary ion mass spectrometer analysis has revealed that the presence of less thick native oxide is unavoidable and that a nearly sharper interface exists at the semiconductor–insulator interface. Electrical characterization was carried out on the highly oriented ZrTiO4 thin films. The density of interface states and fixed oxide charges were calculated using capacitance–voltage (C–V) analysis and the obtained dielectric constant was greater than 19. The annealed films exhibited higher dielectric constant and lower fixed oxide charges than the as-grown thin films. The influence of temperature on the response of the C–V characteristics has been studied and the recombination–generation of charge carriers was found to be responsible for the transition of the C–V curve from high frequency to low frequency. The conduction mechanism was examined using dc leakage current characteristics, revealing the bulk limited Poole–Frenkel conduction mechanism as the dominant mechanism in the ZrTiO4 thin films in a metal–oxide semiconductor capacitor.

Investigations of concentration effects of La on the infrared optical properties of PLZT thin films

Lead lanthanum zirconate titanate (PLZT) thin films with different La concentrations (x), whose composition is x/40/60, have been grown directly on Pt/Ti/SiO2/Si substrates by a modified sol-gel method. x-ray diffraction analysis shows that the PLZT thin films are polycrystalline with a single perovskite p hase. The infrared optical properties of the PLZT thin films are investigated us ing the infrared spectroscopic ellipsometry in the spectral range of 2.5—12.6μ m. By fitting the measured ellipsometric parameters, and a classical dispers ion relation for the thin films, the optical constants and thickness of the thin films have been obtained. The refractive index of the PLZT thin films decreases with increasing La concentration; however, the extinction coefficient increases with increasing La concentration except for the PLZT (4%) thin films. It is bel ieved that the decrease in the refractive index for the PLZT thin films with inc reasing La concentration is mainly due to the crystallinity and the electronic b and structure of the PLZT thin films. The absorption coefficient of the PLZT thi n films is larger than that of the PZT thin films. The values of the effective s tatic charge in the PLZT thin films, which are smaller than those of the purely ionic materials for the PLZT thin films, decrease with increasing La concentrati on. This indicates that PLZT belongs to a mixed ionic-covalent compound.

Perovskite crystallization of sol-gel processed (Pb,La0.06,Gd0.02)(Zr0.65,Ti0.35)O3 thin films: Dielectric, ferroelectric and optical properties

Ferroelectric lead lanthanum gadolinium zirconium titanate (PLGZT) thin films were prepared by the sol-gel spin coating technique. Three-step preannealing heat treatment was employed to prepare crack-free films. Various types of substrates, and the effects of the seed layer and annealing temperature on the perovskite crystallization were studied. Phase-pure perovskite crystallization was obtained by annealing the films on PbTiO3/Pt/Ti/Si substrates at 700 °C for 30 min. The Auger electron spectroscopy depth profile showed uniform elemental distribution along the thickness except the surface and interface regions. Dielectric constant and loss tangent at 10 kHz were 1000 and 0.06, respectively. Remanent polarization (Pr) and coercive field (Ec) were 11.8 μC/cm2 and 71 kV/cm, respectively. The direct band gap energy was 3.55 eV for the amorphous films. The refractive index and extinction coefficient at 610 nm for amorphous PLGZT films were 2.14 and 0.0028, respectively. The dispersion of the refractive index was interpreted in terms of a single electronic oscillator at 6.06 eV.

Investigations on the sol–gel-derived barium zirconium titanate thin films

Barium zirconium titanate thin films are attractive candidates for dynamic random access memories and tunable microwave devices. In the present work, a wide range of Zr-doped BaTiO 3 thin films has been prepared by sol–gel technique. X-ray diffraction and micro-Raman scattering studies confirmed the structural phases in the powder and films of BZT and various structural transitions of BaTiO 3, as a function of different Zr content, and compared well with the published result on ceramics and single crystalline BZT. The deposited films were smooth, crack-free and have homogeneous microstructure, and Zr content strongly influences the evolution of the microstructures of the films. Some selected compositions of these films are characterized in terms of their dielectric properties and phase transition behavior. BZT films with 20 at.% Zr have shown a ferroelectric to paraelectric transition in the vicinity of room temperature. Efforts are underway to optimize the annealing conditions and to grow epitaxial BZT films with various Zr contents on suitable single-crystalline substrates.

Zirconium Titanate Thin FIlm Prepared by Surface Sol-Gel Process and Effects of Thickness on Dielectric Property

【Single phase of multicomponent oxide ZrTiO4 film could be prepared through surface sol-gel route simply by coating the mixture of 100 mM zirconium butoxide and titanium butoxide on $Pt/Ti/SiO_2Si(100)$ substrate, following pyro lysis at $450^{\circ}C$ , and annealing it at 770 $^{\circ}C.$ The dielectric constant of the film was reduced as the film thickness decreased due to of the interfacial effects caused by layer/electrode and a few voids inside the multilayer. However, the dielectric property was independent of applied dc bias sweeps voltage (-2 to +2 V).The dielectric constant of bulk film, 31.9, estimated using series-connected capacitor model was independent of film thickness and frequency in the measurement range, but theoretical interfacial thickness, ti, was dependent on the frequency. It reached a saturated ti value, $6.9{\AA}$ , at high frequency by extraction of some capacitance component formed at low frequency range. The dielectric constant of bulk ZrTiO4 pellet-shaped material was 33.7 and very stable with frequency promising as good applicable devices.】

Influence of growth parameters on properties of electroceramic thin films grown via MO-CVD

In the last years, zirconium titanate thin films Zr x Ti 1− x O 4 (ZT) turned out to have very interesting dielectric properties, which suggests a use in microwave integrated systems. In this work, the synthesis and characterization of Zr x Ti 1− x O 4 (ZT) thin films grown via MOCVD are described, giving emphasis to the study of their structural, chemical and physical properties, with relation to the different process parameters applied. All samples analysed by XRD, AFM, SEM and EDS, show a great dependence on substrate temperature and reactor pressure on the kinetic of growth as well as on the chemical, crystallographic, morphological and microstructural features.

Synthesis and Structural Characterization of Sol-Gel Derived Barium Zirconium Titanate Thin Films

AbstractBarium zirconium titanate (BZT) thin films are attractive candidates for dynamic random access memories and tunable microwave devices. In the present work a wide range of Zr doped BaTiO3 thin films have been prepared by sol-gel technique. X-ray diffraction and micro-Raman scattering studies confirmed the structural phases in the powder and film of BZT and various structural transitions of BaTiO3 as a function of different Zr content compared well with the published result on ceramics and single crystalline BZT. The deposited films had smooth, crackfree and homogeneous microstructure and Zr content has strong influence on the evolution of the microstructures of the films. Some selected compositions of these films were characterized in terms of their dielectric properties and phase transition behavior. BZT film with 20 at % Zr had a ferroelectric to paraelectric transition in the vicinity of room temperature. Efforts are underway to optimize the annealing condition and grow epitaxial BZT films, with various Zr contents, on a suitable single-crystalline substrate.

Nanoscale Phenomena in Ferroelectric Thin Films

This paper reviews recent progress in our group in the area of thin film ferroelectrics. Specific focus is on nanoscale phenomena and relaxation dyanmics in model thin films using voltage modulated scanning force microscopy. Using this technique we show the 3 dimensional reconstruction of the polarization vector in lead zirconate titanate(PZT) thin films. Secondly the time dependent relaxation of remanant polarization in epitaxial PZT ferroelectric thin films, containing a uniform 2-dimensional grid of 90° domains ( c -axis in the plane of the film), has been investigated extensively. The 90° domain walls preferentially nucleate the 180° reverse domains during relaxation. Relaxation occurs through the nucleation and growth of reverse 180° domains, which subsequently coalesce and consume the entire region as a function of relaxation time. The kinetics of relaxation is modeled through the Johnson-Mehl-Avrami-Kolmogorov approach with a decreasing driving force. In addition we also present results on investigation of the relaxation phenomenon on a very local scale, where pinning and bowing of domain walls has been observed.

Comparison of the Electrical Characteristics of PZT and SBT Thin Films

The electrical properties of lead zirconate titanate (PZT) and strontium bismuth tantalate (SBT) thin films are compared for nonvolatile random access memory applications. PZT thin films have high switchable polarization with poor fatigue resistance and higher leakage current densities as compared to SBT thin films deposited on platinized silicon substrates. Characterization of these films in terms of their domain dynamics under application of sub-switchable and switchable electric fields give valuable insight about the observed differences in the electrical behavior. In the present work the dielectric behaviors of SBT and PZT thin films at sub-switchable electric field were analyzed in terms of Rayleigh law. The reversible and irreversible polarization component of switchable polarization was separated by the measurement of capacitance-voltage (C-V) and polarization hysteresis loops. The conduction mechanisms in these films were evaluated by measuring field dependence of leakage current densities at various temperatures. The observed differences in electrical properties are explained in terms of the intrinsic defects and defect-domain interaction of these two materials.