Properties Of Lead Zirconate Titanate Thin Films Research Articles

Effect of neodymium substitution on crystalline orientation, microstructure and electric properties of sol-gel derived PZT thin films

Pb(NdxZr0.52Ti0.48)O3 (PNZT) (x = 0%, 1%, 2%, 3%, 4%, 5%) thin films were prepared by sol-gel process to investigate the effects of neodymium substitution on crystalline orientation, microstructure and electric properties of lead zirconate titanate (PZT) films. X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis showed that PNZT films with Nd doping concentration below 3% exhibited dense perovskite structure with (100) preferred orientation. The average grain size of PNZT films decreased as the Nd substitution increased. The maximum dielectric constant, remnant polarization and minimum coercive field were obtained in 2% Nd-doped PZT films. Fatigue resistance was also improved significantly with 2% Nd dopant.

Lanthanide-Assisted Deposition of Strongly Electro-optic PZT Thin Films on Silicon: Toward Integrated Active Nanophotonic Devices.

The electro-optical properties of lead zirconate titanate (PZT) thin films depend strongly on the quality and crystallographic orientation of the thin films. We demonstrate a novel method to grow highly textured PZT thin films on silicon using the chemical solution deposition (CSD) process. We report the use of ultrathin (5-15 nm) lanthanide (La, Pr, Nd, Sm) based intermediate layers for obtaining preferentially (100) oriented PZT thin films. X-ray diffraction measurements indicate preferentially oriented intermediate Ln2O2CO3 layers providing an excellent lattice match with the PZT thin films grown on top. The XRD and scanning electron microscopy measurements reveal that the annealed layers are dense, uniform, crack-free and highly oriented (>99.8%) without apparent defects or secondary phases. The EDX and HRTEM characterization confirm that the template layers act as an efficient diffusion barrier and form a sharp interface between the substrate and the PZT. The electrical measurements indicate a dielectric constant of ∼650, low dielectric loss of ∼0.02, coercive field of 70 kV/cm, remnant polarization of 25 μC/cm(2), and large breakdown electric field of 1000 kV/cm. Finally, the effective electro-optic coefficients of the films are estimated with a spectroscopic ellipsometer measurement, considering the electric field induced variations in the phase reflectance ratio. The electro-optic measurements reveal excellent linear effective pockels coefficients of 110 to 240 pm/V, which makes the CSD deposited PZT thin film an ideal candidate for Si-based active integrated nanophotonic devices.

Ferroelectric Properties of Lead Zirconate Titanate Thin Film on Glass Substrate Crystallized by Continuous-Wave Green Laser Annealing

The ferroelectric properties of lead zirconate titanate (PZT) films crystallized by a continuous-wave (CW) green laser are discussed in this paper. After CW green laser annealing, two kinds of typical crystallization modes of the PZT thin films were observed: island crystallization and lateral crystallization. In the island crystallization region, the PZT film was crystallized uniformly over the thin films. However, poor surface roughness was found in lateral crystallization region. Significant improvements of ferroelectric characteristics have been achieved in the island crystallization region after optimizing with a low energy density. By varying energy density from 4.5 to 7.1 kW/cm2 and fixing annealing time at 42.5 ms, significant features were found at an energy density of 5.3 kW/cm2. A maximum remanent polarization of 27 µC/cm2 was obtained.

Structural, ferroelectric and optical properties of PZT thin films

We report on the structural, ferroelectric and optical properties of lead zirconate titanate (PZT) thin films (with a molar ratio of Zr:Ti::65:35) deposited by sol–gel technique on ITO-coated corning 7059 glass substrates. A seed layer of PbTiO 3 (0.1 μm) was coated by sol–gel on the substrates before depositing PZT. A metal/ferroelectric/metal (MFM) structure was used for electrical property measurements, formed by depositing gold electrodes on top of the film. The films were characterized for C– V, I– V, P– E and optical transmission. Relatively low remnant polarization ( P r = 3.6 μ C / c m 2 ) was observed for the films. Value of optical band gap was found to be 3.4 eV. The results are discussed.

Stress Control and Ferroelectric Properties of Lead Zirconate Titanate (PZT) Thin Film on Si Substrate with Buffer Layers

Lead zirconate titanate (PZT) thin films were grown on a Si substrate with an epitaxial relationship by introducing yttria-stabilized zirconia (YSZ), CeO2, and (La,Sr)CoO3 (LSCO) buffer layers. The buffer layers, which facilitated the growth of the epitaxial PZT thin film and controlled the residual stress, were deposited by pulsed laser deposition (PLD). The PZT thin films were fabricated on [A]: LSCO*/CeO2/YSZ/Si and [B]: LSCO*/PZT*/LSCO/CeO2/YSZ/Si by pulsed metalorganic chemical vapor deposition. The respective thicknesses of the LSCO* and PZT* layers were changed to control the residual stress in the PZT thin films. The relationship between residual stress and the ferroelectric properties of the PZT thin films was investigated. Residual tensile stresses in the PZT thin films were maximum in [A] as LSCO* thickness changed. Increasing the PZT* layer thickness at a fixed thickness of LSCO* of 188 nm changed the residual tensile stress in the PZT thin films from 2.92 GPa to 2.67 GPa. Consequently, remanent polarization (2Pr) was increased from 15 µC/cm2 to 27 µC/cm2, suggesting that residual stress may be controlled by introducing buffer layers and that ferroelectric properties may be improved.

Electrical properties of PZT thin films by photochemical deposition

The electrical properties of lead zirconate titanate (PZT) thin film prepared by photochemical metal–organic deposition (PMOD) using photosensitive starting precursors were characterized. Unlike sol–gel procedure based on the chemical reaction including hydrolysis and condensation, by PMOD, metallic state is obtained through the removal of organic ligand by exposure to UV. This metallic state usually turns to oxide state through oxidation reaction with atmospheric oxygen during exposure to UV. Fourier transform infra-red spectroscopic observation showed that a complete removal of organic group was possibly obtained by exposure of spin-coated PZT precursor film to UV at room temperature. After anneal treatment of the UV-exposed PZT precursor film to crystallize, a highly preferred growth orientation was found in PZT film according to the orientation of substrate Pt. The characteristics of ferroelectric properties (remnant polarization and coercive field) and leakage current behavior were almost the same as those of conventional PZT film prepared by sol–gel processing. However, a slight shift of hysteresis curve and more leaky behavior with negative direction of bias were found and it seemed to be due to the presence of micro-defects formed during PMOD reaction.

Electrical properties of PZT thin films by photochemical deposition

The electrical properties of lead zirconate titanate (PZT) thin film prepared by photochemical metal–organic deposition (PMOD) using photosensitive starting precursors were characterized. Unlike sol–gel procedure based on the chemical reaction including hydrolysis and condensation, by PMOD, metallic state is obtained through the removal of organic ligand by exposure to UV. This metallic state usually turns to oxide state through oxidation reaction with atmospheric oxygen during exposure to UV. Fourier transform infra-red spectroscopic observation showed that a complete removal of organic group was possibly obtained by exposure of spin-coated PZT precursor film to UV at room temperature. After anneal treatment of the UV-exposed PZT precursor film to crystallize, a highly preferred growth orientation was found in PZT film according to the orientation of substrate Pt. The characteristics of ferroelectric properties (remnant polarization and coercive field) and leakage current behavior were almost the same as those of conventional PZT film prepared by sol–gel processing. However, a slight shift of hysteresis curve and more leaky behavior with negative direction of bias were found and it seemed to be due to the presence of micro-defects formed during PMOD reaction.

Effects of crystallization conditions on dielectric and ferroelectric properties of PZT thin films

This paper reports studies on dielectric and ferroelectric properties of lead zirconate titanate (PZT) thin films crystallized by conventional thermal annealing (CTA) and rapid thermal annealing (RTA) in air, oxygen and nitrogen atmospheres to better understand, control and optimize these properties. The dielectric constant (ε) and dissipation factor (tan δ) values, at a frequency of 100 kHz, for film crystallized in air by CTA process, were 358 and 0.039, respectively. Considering the same frequency for film crystallized in air by RTA, these values were 611 and 0.026, respectively. The different dielectric values were justified by a space-charge or interfacial polarization in films, often characterized as Maxwell–Wagner type. This effect was also responsible to dispersion at frequencies above 1 MHz in film crystallized in air by CTA process and film crystallized by RTA in oxygen atmosphere. The film crystallized by RTA under nitrogen atmosphere presented an evident dispersion at frequencies around 100 Hz, characterized by an increase in both ε and tan δ. This dispersion was attributed to conductivity effects. The remanent polarization (Pr) and coercive field (Ec) were also obtained for all films. Films obtained from RTA in air presented higher Pr (17.8 μC cm−2) than film crystallized from CTA (7.8 μC cm−2). As a function of the crystallization atmospheres, films crystallized by RTA in air and nitrogen presented essentially the same Pr values (around 18 μC cm−2) but the Pr (3.9 μC cm−2) obtained from film crystallized under oxygen atmosphere was profoundly influenced.

Nanomechanical properties of lead zirconate titanate thin films bynanoindentation

The nanomechanical properties of lead zirconate titanate (PZT) thin films weresubjected to nanoindentation evaluation. A PZT thin film was created on a siliconsubstrate by radio frequency magnetron sputtering. The structure andsurface morphology were analysed by x-ray diffraction and atomic forcemicroscopy. Results show that PZT thin films were well ordered with a high(110) orientation and presented a pure perovskite-type structure and thatthe average roughness was reduced as the annealing temperature wasincreased. The Young’s modulus and hardness increased as the rapidannealing temperature increased from 600 to 800 °C,with the best results being obtained at 800 °C.

Fabrication and properties of silicon-based PZT thin films for MFSFET applications

Fabrication and properties of lead zirconate titanate (PZT) thin films have been studied for metal-ferroelectric-semiconductor FET (MFSFET) devices. PZT-based MFS capacitors using lead titanate (PT) as seeding layers have been prepared, respectively, on p-type 〈111〉 and n-type 〈100〉 silicon wafers directly by a sol–gel method. PZT/PT films are finally annealed at 650 °C for 1 min in oxygen ambient using rapid thermal annealing (RTA). The measured memory windows of the MFS capacitors are about 1.8 and 5 V under the polarization voltages of ±5 and ±10 V correspondingly. The MFS structure can be valuable for MFSFET applications.

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.

The effects of solvent on the properties of sol-gel derived PZT thin films

The effects of various solvents on the material properties of lead zirconate titanate (PZT) thin films were investigated. PZT films have been made from alkoxide precursor by sol-gel method using four kinds of solvent (2-methoxyethanol, iso-propyl alcohol, ethanol, and methanol). It was found that phase formation temperature decreases as molecular weight of solvent decreases. And the stock solution using light alcohol such as ethanol or methanol induced decrease of grain size and increase of (111) preferred orientation in PZT films. Furthermore, remnant polarization value was also decreased.

Ultrasonic Properties of Lead Zirconate Titanate Thin Films in UHF-SHF Range

We describe the ultrasonic properties of lead zirconate titanate (PZT) thin films prepared by the sol-gel method. It is shown that the PZT thin film exhibits efficient transduction of bulk and surface acoustic waves in UHF-SHF range. A conversion loss of less than 4 dB is achieved for bulk wave excitation and detection at 1.7 GHz, where the electromechanical coupling factor k t reaches 30%. This indicates that the PZT thin film is promising for use in the development of large-bandwidth resonators and filters in modern communication systems as well as for high-frequency ultrasonic transducer applications.

Correlations Among Degradations in Lead Zirconate Titanate thin Film Capacitors

AbstractMany attempts have been made to reduce degradation properties of Lead Zirconate Titanate (PZT) thin film capacitors. Although each degradation property has been studied extensively for the sake of material improvement, it is desired that they be understood in a unified manner in order to reduce degradation properties simultaneously. This can be achieved if a common source(s) of degradations is identified and controlled. In the past it was noticed that oxygen vacancies play a key role in fatigue, leakage current, and electrical degradation/breakdown of PZT films. It is now known that space charges (oxygen vacancies, mainly) affect ageing, too. Therefore, a quantitative ageing mechanism is proposed based on oxygen vacancy migration under internal field generated by either remanent polarization or spontaneous polarization. Fatigue, leakage current, electrical degradation, and polarization reversal mechanisms are correlated with the ageing mechanism in order to establish guidelines for simultaneous degradation control of PZT thin film capacitors. In addition, the current pitfalls in the ferroelectric test circuit is discussed, which may cause false retention, imprint, and ageing.

Modeling of Hysteresis Properties of Lead Zirconate Titanate Thin Films

AbstractIt is proposed that the polarization reversal mechanism in ferroelectric ceramics such as titanates is controlled by nucleation, growth, merging and shrinkage of ferroelectric domains. These domain phenomena are in turn determined by the nature of Barkhausen jumps, internal electric field, and dielectric relaxation times of the dipoles. Based on the proposed polarization reversal mechanism, a quantitative model was developed for simulating the hysteresis properties of lead zirconate titanate (PZT) thin films. The simulated hysteresis loops are in good agreement with the experimental results.It was observed that dielectric viscosity, which is very useful in understanding fatigue and aging behavior of PZT thin films, is one of the key parameters that controls the hysteresis properties.