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 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 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.     

Electrical switching in lithium niobate thin films

The ferroelectric switching properties of thin films of lithium niobate (LiNbO3) on silicon have been investigated. The polarization is shown to be partially reversible with an applied electric field at room temperature. The samples were films of LiNbO3 which were magnetron sputter deposited on silicon substrates. A double pulse method was used to investigate the ferroelectric switching properties of the films. Evidence for partial stable switching of the LiNbO3 film was observed at a field of roughly 500 kV/cm.     

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.     

Temperature dependent Raman scattering study of order-disorder lead zinc niobate

Abstract

Raman spectra have been measured in lead zinc niobate (PZN)- lead titanate (PT) solid solution single crystals (facets undefined) as functions of temperature (70K–580K) and composition (x ' 0.02, 0.085, and 0.11) into its parallel and perpendicular configurations. The presence of complex multiband Raman spectra is inconsistent with Pm3m space group symmetry and is an indication of short-range ordering on the B-site. Raman bandwidths are substantially large and nearly independent of temperature indicating a static structural disorder rather than a dynamic dipolar disorder. No soft mode like behavior is observed in the measured frequency range. Abrupt change in wavenumber (frequency) and width of certain bending mode (270 cm_?1) at 410 K (140°C) is interpreted as an evidence for a reversible structural phase transition (C-R) at this temperature. The sequence of structural phase transition of C-T-R was also observed in one of the compositions (x ' 0.085), though diffuse and less obvious. In addition, the spectroscopic properties are found to be dependent on the substitution of titanium ion reflecting in the temperature of phase transition.     

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 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 hysteresis in simultaneously stretched andcorona-poled PVDF films

SSCP (simultaneous stretching and corona poling) of PVDF (polyvinylidene fluoride) films has enhanced the ferroelectric properties. D-E hysteresis loops of these films were observed by using the Sawyer-Tower method in the field range 35 to 80 MV/m. The dependence of ferroelectric hysteresis on poling field has also been studied. The average value of remanent polarization ≈82 mC/m² was observed for the SSCP (simultaneous stretching and corona poling) films, which is significantly higher than the value P≈62 mC/m² observed for the STCP (stretched and then corona poled) films. Coercive fields of E_c≈61 and 50 MV/m were obtained for the SSCP and the STCP films respectively. A comparison of the IR spectra of the SSCP and the STCP films in perpendicularly polarized light E_⊥ indicates that the dipolar orientation is better in the SSCP films     

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 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 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 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.     

Focussing and defocussing regimes in the multistable optical response of single-crystal lead magnesium niobate

Abstract

Experimental observation of the static and dynamic response of monocrystalline lead magnesium niobate, Pb(Mg_1/3Nb_2/3)O₃ (PMN), at moderate power c. w. laser irradiation shows five distinct regimes depending on the beamwidth and wavefront curvature of the incident Gaussian laser beam. In one of these regimes, the system exhibits multistability and transient aperiodic regenerative oscillations similar to those observed previously in ceramic PMN. In the other four regimes, thermal focussing and/or defocussing combine with nonlinear Fabry-Perot resonances to produce qualitatively different responses. The thermal relaxation time is calculated theoretically as 1 - 500 s, about 10³ longer than earlier estimates and in agreement with experiment. Damage thresholds are also discussed.     

Structural evolution and dopant occupancy preference of yttrium-doped potassium sodium niobate thin films

Sodium potassium niobate (KNN) is the most promising candidate for lead-free piezoelectric material, owing to its high Curie temperature and piezoelectric coefficients among the non-lead piezoelectric. Numerous studies have been carried out to enhance piezoelectric properties of KNN through composition design. This research studied the effects of yttrium concentrations and lattice site occupancy preference in KNN films. For this research, the yttrium-doped KNN thin films (mol% = 0, 0.1, 0.3, 0.5, 0.7 and 0.9) were fabricated using the sol-gel spin coating technique and had revealed the orthorhombic perovskite structures. Based on the replacement of Y³⁺ ions for K⁺/ Na⁺ ions, it was found that the films doped with 0.1 to 0.5 mol% of yttrium had less lattice strain, while films with more than 0.5 mol% of Y³⁺ ions had increased strain due to the tendency of Y³⁺ to occupy the B-site in the perovskite lattice. Furthermore, by analysing the vibrational attributes of octahedron bonding, the dopant occupancy at A-site and B-site lattices could be identified. O-Nb-O bonding was asymmetric and became distorted due to the B-site occupancy of yttrium dopants at high dopant concentrations of >0.5 mol%. Extra conduction electrons had resulted in better resistivity of 2.153× 10⁶ Ω at 0.5 mol%, while higher resistivity was recorded for films prepared with higher concentration of more than 0.5 mol%. The introduction of Y³⁺ improved the grain distribution of KNN structure. Further investigations indicated that yttrium enhances the surface smoothness of the films. However, at high concentrations (0.9 mol%), the yttrium increases the roughness of the surface. Within the studied range of Y³⁺ _, the film with 0.5 mol% Y³⁺ represented a relatively desirable improvement in dielectric loss, tan δ and quality factor, Q_m.     

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 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.     

Ultra-thin lead titanate films prepared by tripole magnetron sputtering

Abstract

Ultra-thin lead titanate (PbTiO₃) films of 6 to 80 nm in thickness were deposited on single crystal MgO (100) substrate by employing tripole magnetron sputtering system, which was deviced to make the erosion area on the co-axial targets movable, and hence make a layer-by-layer process realized. Thin films of PbTiO₃ with highly-oriented perovskite single phase were obtained at substrate temperature of 550°C. In the films thicker than 20 nm, the X-ray diffraction showed clearly the separated (100) and (001) peaks, while in those thinner than 10 nm, two peaks seemed to be superimposed onto a single peak, suggesting a gradual transition into pseudocubic. Far-infrared spectroscopy indicated a thickness-dependent absorption at wavenumber of 85 cm^?1, which may be attributed to the phonon related to the Pb-TiO₆ vibration.     

Antiferroelectric lead zirconate thin films by excimer laser ablation

Abstract

Utilization of antiferroelectric thin films was proposed for high charge storage capacitors and transducer applications. The volume changes that are associated with the AFE? FE and FE ? AFE phases are high enough to use them in MEMs device technology. Lead zirconate was the first identified antiferroelectric compound with a reported dielectric phase transition temperature of ～ 230°C. In this article, deposition of lead zirconate thin films by a pulsed excimer laser ablation technique is reported. The antiferroelectric nature of the lead zirconate thin films were confirmed by the presence of double hysteresis loop in polarization vs. applied electric field response as well as double butterfly behavior in capacitance vs. voltage characteristics. The variations in the polarization hysteresis with temperature were elucidated in detail. The switching times between the field induced FE and AFE phases (backward switching) were studied at various applied electric fields.