Ferroelectric lead iron-chromium-nickel niobate films

Abstract

The fabrication of ferroelectric films of modified lead iron niobate by a multiple magnetron sputtering technique with a subsequent rapid thermal annealing at 800°C for 5 seconds is reported. Since the magnetic properties of pure iron preclude its use in magnetron sputtering, a non-magnetic stainless steel was used as one of the target materials resulting in a ferroelectric of composition Pb[(Fe_0.7Cr_0.2Ni_0.1)_0.5Nb_0.5]O₃. The reaction sequence involved in the formation of the ferroelectric perovskite phase has been identified. The films exhibit unsaturated ferroelectric hysteresis loops with a remanent polarization of 15 μC/cm² and a coercive field of 100 kV/cm. The room temperature dielectric constant and dielectric loss at 1 kHz were 640 and 0.1, respectively. The dielectric constant showed a dielectric anomaly as a function of temperature in the form of a broad maximum around 90°C confirming the ferro-para electric phase transition. The films were highly insulating with a room temperature conductivity of ≈1 X^?12 Ω^?1 cm^?1, and an activation energy of 0.8 eV.     

Ferroelectric thin films prepared by sol-gel processing

Ferroelectric thin films are playing a growing role as key elements in variety of devices. For various techniques of ferroelectric thin film preparation, the sol-gel processing is one of the most promising. In comparison with different deposition techniques, we survey the intrinsic advantages and the recent improvements of the sol-gel processing. In this review paper, several interesting topics, including epitaxial growth and grain-orientation, symmetric and asymmetric P-E hysteresis loops, heterojunction effect of the interface between film and substrate, to attest pyroelectricity of the films, electrooptic coefficients in poled and unpoled films, possibility of amorphous ferroelectrics, etc., are introduced.     

Ferroelectric ceramics and thin films for pyroelectric applications

Abstract

The extensive work carried out at Caswell in recent years on ferroelectric ceramics for pyroelectric applications is reviewed briefly. With the ultimate aim of fully CMOS compatible integrated thermal detectors and imagers, pure and lanthanum doped lead titanate thin films have been deposited using the emerging PVD technique of dual ion beam sputtering (DIBS). The DIBS process produces high quality orientated perovskite films. Films have been formed at 500–600°C onto sapphire, MgO and silicon substrates by sputtering from an adjustable composite PLZT ceramic/Ti and Pb metallic target. Some substrates were coated with platinum/titanium prior to deposition to allow longitudinal electrical measurements to be made on the films. On silicon, the platinum/titanium electrodes were found to blister during the PLZT thin film deposition process. Pure and 7% lanthanum doped lead titanate films have shown pyroelectric effects with coefficients in the range 0.5–4.0 × 10^?4 Cm^?2 K^?1 and a figure of merit of 2.6 × 10^?5 Pa^?0.5 These results are encouraging with respect to the goal of integrated pyroelectric IR detector arrays on silicon. Further improvements should be possible since the process and substrate/electrode preparation have not yet been fully optimised.     

Ferroelectric polymer Langmuir-Blodgett films for nonvolatile memory applications

We review the potential for integrating ferroelectric polymer Langmuir-Blodgett (LB) films with semiconductor technology to produce nonvolatile ferroelectric random-access memory (NV-FRAM or NV-FeRAM) and data-storage devices. The prototype material is a copolymer consisting of 70% vinylidene fluoride (VDF) and 30% trifluoroethylene (TrFE), or P(VDF-TrFE 70:30). Recent work with LB films and more conventional solvent-formed films shows that the VDF copolymers are promising materials for nonvolatile memory applications. The prototype device is the metal-ferroelectric-insulator-semiconductor (MFIS) capacitance memory. Field-effect transistor (FET)-based devices are also discussed. The LB films afford devices with low-voltage operation, but there are two important technical hurdles that must be surmounted. First, an appropriate method must be found to control switching dynamics in the LB copolymer films. Second, the LB technology must be scaled up and incorporated into the semiconductor-manufacturing process, but since there is no precedent for mass production of LB films, it is difficult to project how long this will take.     

Ferroelectric electrode interactions in BaTiO3 and PZT thin films

Abstract

We have studied ferroelectric thin films deposited by sol-gel processing onto non-noble metal substrates. The results obtained indicate that by careful control of processing conditions, ferroelectric materials can be deposited onto these substrates, although interdiffusion between the metal and the ferroelectric can significantly degrade the ferroelectric properties of the materials. The effects of this interdiffusion are demonstrated and possible implications of ferroelectric-electrode interactions for fatigue in ferroelectric materials are discussed.     

Ferroelectric properties of heterolayered lead zirconate titanate thin films

Heterolayered Pb(Zr_{1 − x} Ti _x )O₃ thin films consisting of alternating PbZr_0.7Ti_0.3O₃ and PbZr_0.3Ti_0.7O₃ layers were successfully deposited via a multistep sol-gel route assisted by spin-coating. These heterolayered PZT films, when annealed at a temperature in the range of 600–700^∘C show (001)/(100) preferred orientation, demonstrate desired ferroelectric and dielectric properties. The most interesting ferroelectric and dielectric properties were obtained from the six-layered PZT thin film annealed at 650^∘C, which exhibits a remanent polarization of 47.7 μC/cm² and a dielectric permittivity of 1002 at 100 Hz. Reversible polarization constituents a considerably high contribution towards the ferroelectric hysteresis of the heterolayered PZT films, as shown by studies obtained from C-V and AC measurement.     

Ferroelectric thin films for Smart Spatial Light Modulator applications

Abstract

System, device and material issues for the use of ferroelectric ceramic thin films in the realization of Smart Spatial Light Modulators are considered. Results show that ferroelectric thin films such as PLZT PBN, KTN, and SBN are particularly attractive.     

Ferroelectric properties of plzt thin films prepared by mocvd

Abstract

Lanthanum-modified lead zirconate titanate (PLZT) thin films have been grown on Pt/SiO₂/Si substrate at 650[ddot]C by metalorganic chemical vapor deposition. The relative dielectric constant increased as the La content was increased up to about 5 atomic percent (at%). The remanent polarization and coercive field decreased from 30 to 20 μC/cm² and from 53 to 30 kV/cm, respectively, with increasing La content in the range of 0–13 at%. The leakage current of PLZT film was 3 × 10^?9 A/cm² at an applied voltage of 3 V. The degradation of switched charge density of PLZT film was not observed even at 2 × 10¹¹ cycles.     

Ferroelectric films at high microwave power of ka-band frequency

Abstract

This paper presents the experimental and modeling results on microwave (～37 GHz) investigations of SrTiO₃ and (Ba,Sr)TiO₃ ferroelectric films at high levels of microwave power. The ferroelectric film planar varactors were incorporated into the fin-line. The threshold microwave power leading to the appreciable variation in the microwave response of the tunable structure was determined. Thermal conditions of the varactors under test were analyzed. Thermal time constant and overheating of the ferroelectric films were estimated. The dependence of the varactor overheating on geometry was studied. Design optimization possibilities for the varactors in high microwave power applications are discussed.     

Ferroelectric films of lead germanate prepared by modified chemical deposition techniques

Abstract

The high adhesive, single crystal lead germanate films of 5–105 μm in thick were fabricated on platinum substrates by in situ sol-gel technique. The stoichiometry of the films was closed to 5:3:11 without any oxygen deficiency. The microstructure of better films consisted of closed packed hexagonal crystals of 200–300 μm in size. Ferroelectric transition was sharp with Curie point 170–180°C, ε₂₀=30–40, tgδ₂₀?0.02, ε_max?200, P_s=3.2 μC/cm², E_c=16 kV/cm, ρ=10⁸–10⁹ Ωcm. All these parameters (with the exception of ε_max) were in a good agreement with bulk single crystals ones.     

Ferroelectric effect in spin coated Ba0.9Sr0.1TiO3 thin films

Abstract

The achievement of excellent growth of lead zirconium titanate (PZT) films by various techniques for use as ferroelectric memories has generated an extensive research interest in the synthesis of various other perovskite and layered oxides. Ba_xSr_1?xTiO₃ thin films have also been deposited by various methods to study their dielectric behavior. We report the synthesis of Ba_xSr_1?xTiO₃ (where x ' 0.9, 0.1) by a solution method using hydroxides, acetates, and nitrate salts as precursors for barium and strontium, and titanium isopropoxide for titanium. The films deposited by spin coating on ITO coated glass substrates showed ferroelectric behavior.     

Ferroelectric PbZr0.2Ti0.8O3 thin films on epitaxial Y-Ba-Cu-O

Abstract

Using a combination of pulsed laser deposition and sol-gel processing, we have fabricated epitaxial PbZr_0.2Ti_0.8O₃/YBa₂Cu₃O₇-x heterostructures on single crystalline [001] LaAlO₃. Rutherford back-scattering studies show the composition to be the same as the nominal starting composition. Transmission electron microscopy shows the existence of a randomly oriented polycrystalline microstructure in the PZT layer with a grain size of about 500–1000Å. Microscopic pores were also observed in the PZT layer. The PZT film exhibits ferroelectric hysteresis with a saturation polarization of 22–25μC/cm² (at 7.5V, 1kHz), a remanence of 5–6μC/cm² and a coercive field of about 40kV/cm.     

Ferroelectric Na0.5K0.5NbO3 thin films by pulsed laser deposition

Abstract

Highly c-axis oriented single phase Na_0.5K_0.5NbO₃ (NKN) thin films have been deposited onto polycrystalline Pt₈₀lr₂₀ substrates and SiO₂/Si(001) wafers using pulsed laser ablation of stoichiometric ceramic target. Strong self-assembling of NKN films along the [001] direction has been observed. Properties of NKN/Pt thin film structures have been successfully tailored by oxygen pressure control from the ferroelectric state, characterized by the remnant polarization of 12 uC/cm², dielectric constant ? ～ 520 and tan δ ～ 0.024 @ 100 kHz, to superparaelectric state with tan δ as low as 0.003 and ? = 210 with very small 1.7% dispersion in the frequency domain 0.4–100 kHz and less than 10% variation in the temperature range 77–415 K. NKN films grown onto SiO₂/Si(001) substrates show quadrupled super-lattice structure along c-axis, loss tan δ less than 0.01, and ? ～ 110 @ 1 MHz. C-V measurements for Au/NKN (270nm)/SiO₂/Si MFIS-diode structure yield memory window of 3.26 V at the programmable voltage of 8 V.     

Ferroelectric and dielectric properties of sol-gel and excimer-laser-deposited lead zirconate titanate and barium titanate films

Abstract

Switched remanent polarization was measured as a function of accumulated switching cycles for a variety of ferroelectric films using sinusoidally driven hysteresis loops. Switched remanent polarization and dielectric constant and loss were also obtained as a function of the cycling frequency. PZT films with niobium additives appeared to lose switched remanent polarization with accumulated cycles at a lesser rate than films without niobium. The switched remanent polarization was found to decrease with increasing frequency, which we attribute to the effect of grain size. Also, a decrease of dielectric constant with increasing frequency and an increase of dielectric constant with increased applied voltage are attributed to the effects of domain wall motion contributions to dielectric constant.     

Ferroelectric memory programs in Canada

Abstract

Thin film PZT ferroelectrics have been fabricated in Canada since 1976 by magnetron sputtering and more recently by acetate-based sol gel processing and are now being considered for implementation into commercial communications systems. Processing based on rapid thermal annealing has shown marked advantages for crystallization into the required perovskite phase. Applications based on the piezoelectric properties of PZT films are shown to have an interesting potential for a range of devices.     

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.     

Ferroelectric thin film research in france

Abstract

After a review of the research made on thin film deposition in France, this work presents the comparison between two chemical deposition methods for PZT films: sol-gel method based on low molecular weight precursors and solvent, and MOD (Metallo-Organic Deposition) process based on a hydrophobic solvent. The influence of the viscosity of the solvent and of the solubility of water is shown with regard to stability and drying properties. The final electrical properties of the ferroelectric films are also compared such as the hysteresis loop which characterizes the most important properties for memory application: coercive voltage and rectangularity.     

Competing Instabilities in Ferroelectric Aurivillius Compounds

The stability of SrBi₂Ta₂O₉ has been studied by means of ab-initio calculations. The main instability of the tetragonal configuration concerns a non-polar mode at the Brillouin zone border. It can be related through Brillouin zone folding to the well-known soft rigid-unit mode R₂₅ in perovskites. This implies a complex scenario for the whole Aurivillius family with two competing order parameters, which can result in a sequence of two continuous phase transitions or a single discontinuous one. A third hard-mode is shown to play an essential role in the stabilization of the ferroelectric phase.     

Diffuse Dielectric Anomaly in Ferroelectric Materials

It has not been clear whether the diffuse dielectric anomaly by Debye-type dielectric relaxation is extrinsic or intrinsic in origin although it has been frequently found in ferroelectric materials regardless of their structures and ferroelectric properties. We experimentally investigated the extrinsic nature of the diffuse dielectric anomaly in ferroelectric oxides and sulfide such as BaTiO₃, Pb_0.9La_0.1TiO₃, and SnP₂S₆. The advanced fitting method using the modified Debye relaxation equation was introduced in order to explain the temperature dependent behavior of the diffuse dielectric anomaly. It was confirmed that the diffuse dielectric anomaly was a competitive phenomenon between the dielectric relaxation and the electrical conduction of the relaxing species. It was also proved that the activation energy of the dielectric relaxation should be always higher than the conductivity activation energy of the relaxing species in the diffuse dielectric anomaly.     

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.