Improved dielectric properties of lead lanthanum zirconate titanate thin films on copper substrates

Thin films of lead lanthanum zirconate titanate (PLZT) were directly deposited on copper substrates by chemical solution deposition and crystallized at temperatures of ~ 650 °C under low oxygen partial pressure (pO₂) to create film-on-foil capacitor sheets. The dielectric properties of the capacitors formed have much improved dielectric properties compared to those reported previously. The key to the enhanced properties is a reduction in the time that the film is exposed to lower pO₂ by employing a direct insertion strategy to crystallize the films together with the solution chemistry employed. Films exhibited well-saturated hysteresis loops with remanent polarization of ~ 20 μC/cm², dielectric constant of > 1100, and dielectric loss of < 0.07. Energy densities of ~ 32 J/cm³ were obtained at a field of ~ 1.9 MV/cm on a ~ 1 μm thick film with 250 μm Pt electrodes.     

Corona poling of highly (001)/(100)-oriented lead zirconate titanate thin films

Corona poling is an interesting non-contact poling process for ferroelectric materials which, has in the past, been extensively applied to ferroelectric polymers, but not to other types of ferroelectric materials. Here, it has been investigated as an alternative technique to the conventional direct-contact poling of ferroelectric thin films.

Contact-poling and corona poling techniques were applied to highly (001)/(100) oriented lead zirconate titanate thin films of composition 52% Zr, 48% Ti (PZT52/48). Different poling voltages and durations were used to pole the samples, and the effects on the piezoelectric coefficients e_31,f and d_33,f were explored. From the magnitudes of piezoelectric coefficients and suppression of e_31,f relative to d_33,f, it was concluded that corona poling is a more suitable technique for poling PZT52/48 thin films than direct poling, since piezoelectric coefficients were higher and sample damage was less for corona poling when compared with contact-poling.     

不锈钢衬底上锆钛酸铅膜的制备

以改性二氧化锆为过渡层,用溶胶－凝胶法在不锈钢衬底上成功制备了锆钛比为52／48的锆钛酸铅膜,扫描电镜分析表明,膜的表面平整,无裂纹,X射线分析结果说明,经650℃退火30min后,膜为纯的钙钛矿相,以衬底为下电极、直径为0.32mm的金上电极,测量了0.8μm膜的电滞回线及其它性能,膜的剩余极化为18μC/cm^2。     

Role of precursors in the formation of lead zirconate titanate thin films

Thin ferroelectric Pb(Zr_0.48Ti_0.52)O₃ lead zirconate titanate films have been prepared on platinized silicon substrates via chemical solution deposition. The starting film-forming solutions were prepared by reacting lead acetate with Ti and Zr alkoxides in 2-methoxyethanol. The electrical properties of the films were shown to depend on the Ti and Zr alkoxide precursors used in synthesis. The nature of the zirconium alkoxide had the strongest effect on the properties of the films. The best properties were obtained with zirconium n-propoxide.     

Studies on the dielectric and relaxor behavior of sol-gel derived barium strontium zirconate titanate thin films

The dielectric behavior of sol-gel derived Ba_0.80Sr_0.20(Zr_xTi_1−x)O₃ (0.0 ≤ x ≤ 0.50) thin films is studied. A relaxor behavior is observed for x ≥ 0.35. The degree of relaxation increases with Zr content. The frequency dependence of the polar regions follows Vogel-Fulcher relation with a characteristic cooperative freezing at freezing temperature (T_f). Below T_f, a long range polarization ordering is likely to take place. The plausible mechanism of the relaxor behavior of BSZT thin films with Zr contents ≥ 0.35 has been proposed based on the measured temperature as well as frequency dependent dielectric data. The solid solution system is visualized as a mixture of Ti^+ 4 rich polar regions and Zr^+ 4 rich regions; with the increase in Zr content the volume fraction of the polar regions is progressively reduced. At and above 35.0 at.% Zr substitution the polar regions exhibit typical relaxor behavior.     

Characterization on pulsed laser deposited nanocrystalline ZnO thin films

Nanocrystalline zinc oxide thin films were deposited on glass and silicon substrates by using pulsed laser deposition at different laser energy densities (1.5, 2, and 3 J/cm²). The film thickness, surface roughness, composition, optical and structural properties of the deposited films were studied using an α-step surface profilometer, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), optical transmittance, and X-ray diffraction (XRD), respectively. The film thickness was calculated as 244 nm. AFM analysis shows that the root-mean-square roughness increases with increasing laser energy density. XPS analysis shows that the interaction of zinc with oxygen atoms is greatly increased at high laser energy density. In the optical transmittance spectra, a shift of the absorption edge towards higher wavelength region confirms that the optical band gap increases with an increase in laser energy density. The particle size of the deposited films was measured by XRD, it is found to be in the range from 7.87 to 11.81 nm. It reveals that the particle size increases with an increase in laser energy density.     

Interfacial mechanisms controlling phase formation in sol-gel derived lead zirconate titanate thin films

An RBS study has been carried out to study the relative extent of Pb diffusion in the substrate from PZT films. It is found that extensive diffusion of Pb occurs into the quartz substrate making the film severely deficient in Pb. No such diffusion occurs in the case of PZT films on sapphire and the concentration of Pb is near stoichiometric, except for a small loss due to volatilization. Excessive Pb deficiency, rather than any epitaxial effect, has earlier been proposed by us to be the crucial factor responsible for the existence of the pyrochlore phase in PZT thin films on substrates such as Si, glass, quartz etc. The present results confirm this. The effects of other process variables such as thickness and chemical composition (Zr/Ti ratio) of the film can also be understood in terms of the same phenomenon.     

Phase stabilization and microstructural studies of lead lanthanum titanate thin films

Thin ferroelectric films of PLTx (Pb_1−xLa_xTi_1−x/4O₃) have been prepared by a sol-gel spin coating process. As deposited films were thermally treated for crystallization and formation of perovskite structure. Characterization of these films by X-ray diffraction (XRD) have been carried out for various concentrations of La (x = 0.04, 0.08 and 0.12) on ITO coated corning glass substrates. For a better understanding of the crystallization mechanism, the investigations were carried out on films annealed at temperatures (350, 450, 550 and 650 °C). Characterization of these films by X-ray diffraction shows that the films annealed at 650 °C exhibit tetragonal phase with perovskite structure. Atomic force microscope (AFM) images are characterized by slight surface roughness with a uniform crack free, densely packed structure. Fourier transform infrared spectra (FTIR) studies of PLTx thin films (x = 0.08) deposited on Si substrates have been carried out to get more information about the phase stabilization.     

Effect of microwave annealing temperatures on lead zirconate titanate thin films

Lead zirconate titanate (Pb(1.1)(Zr(0.52)Ti(0.48))O(3)) thin films of thickness 260?nm on Pt/Ti/SiO(2)/Si substrates were densified by 2.45?GHz microwave annealing. The PZT thin films were annealed at various annealing temperatures from 400 to 700?°C for 30?min. X-ray diffraction showed that the pyrochlore phase was transformed to the perovskite phase at 450?°C and the film was fully crystallized. The secondary (again pyrochlore) phase was observed in the PZT thin films, which were annealed above 550?°C. The surface morphologies were changed above 550?°C of the PZT thin films due to the secondary phase. Higher dielectric constant (ε(r)) and lower dielectric loss coercive field (E(c)) were achieved for the 450?°C film than for the other annealed films.     

Thickness and erbium doping effects on the electrical properties of lead zirconate titanate thin films

Thin films of erbium doped lead zirconate titanate (PZT) of different thickness were deposited by sol–gel technique on Pt/TiO₂/SiO₂/Si substrates. Capacitance–voltage measurements show that the dielectric constant continuously increases with the thickness. This is interpreted in terms of effects due to a low permittivity interfacial layer in series with the ferroelectric bulk. The linear fit of the reciprocal of capacitance vs. thickness leads to a true dielectric constant of the ferroelectric of 774 and interfacial capacitance of 14.6 nF. The leakage current properties also depend on thickness and temperature. The calculated interfacial potential barrier height amounts to 0.81 and 0.74 eV, respectively for erbium doped and pure PZT thin films.     

Effects of sol infiltration on the screen-printed lead zirconate titanate thick films

Ferroelectric PZT(60/40) thick films were fabricated by the screen-printing method and the PZT precursor solution was spin-coated on the thick films to obtain a densification. Structural and electrical properties of the thick films with the treatment of sol coating were investigated. The lattice constant of PZT thick films was 0.4073 nm and there is no dependence on the number of sol coatings. The thickness of PZT films obtained by one screen-printing was approximately 16 μm. The relative dielectric constant increased and dielectric loss decreased with the increase in the number of sol coatings, and the values of the 15-coated PZT-15 film were 369 and 2.16% at 1 kHz, respectively. The remanent polarization, coercive field, and breakdown strength of the PZT-15 thick film were 23.2 μC/cm², 18.03 kV/cm and 78 kV/cm, respectively.     

On the annealing temperature, penetration depth of oxygen and film thickness on the DC and AC electrical properties and nano-structure of Ti thin films

Ti films of different thickness ranging from 12.3 to 246.2 nm were deposited, using resistive heat method and post-annealed at different temperatures with a flow of 5 cm³ s⁻¹ oxygen. The nano-structures of the films were obtained using X-ray diffraction (XRD) and atomic force microscopy (AFM). The results showed an initial reduction of the grain size at 373 K annealing temperature and increase of the grain size at higher temperatures. The cause of this was due to the reaction of oxygen with Ti atoms which breaks up the Ti grains and hence needle-like features form. The enhancement of activation processes at higher temperatures results in larger grains. The analysis of XRD in conjunction with AFM images showed that those films containing (004) line of anatase phase and sub-oxide phases of titanium oxide also show two types of grains in the AFM images. The resistivity of the film increased with annealing temperature, which is due to competition between increased diffusion rate and the increased reaction rate of oxygen with Ti atoms. The Hall coefficient R_H and the mobility μ decreased with increasing film thickness at all annealing temperatures, while R_H increases and μ decreases with increasing the annealing temperature. The carrier concentration increased with film thickness and decreased with annealing temperature. The impedance spectroscopy showed that all films have a pure RC behaviour, where the magnitude of R depends on the annealing temperature and film thickness. The apparent activation energies E_a, obtained from three different methods, namely σ, R_H and grain size showed good agreement within 0.30-0.46 eV for the range of film thickness examined in this work. It was found that films with thickness less than 70 nm can be recognized as Ti-oxide films while thicker films are only surface-oxidised Ti films.     

Application of the X-ray combined analysis to the study of lead titanate based ferroelectric thin films

Lead titanate based ferroelectric thin films are well known for their excellent piezo and pyroelectric properties. In order to obtain a complete characterisation of the structural, micro structural and texture parameters of these films, a recently developed combined analysis of the X-ray diffraction data is carried out. The advantages of this approach reside in the fact that we obtain simultaneously quantitative and more reliable information of these parameters than with more conventional methods. Results obtained for ferroelectric thin films are analysed and compared with those obtained with other methods of analysis. The conclusions show that the texture of the films obtained with the combined method is able to separate the contributions of close texture components, like 〈100〉 and 〈001〉, or to study components with low contribution to the texture of the film.     

Structural and ferroelectric properties of europium doped lead zirconate titanate thin films by a sol-gel method

Using a sol-gel method, rare earth element europium doped lead zirconate titanate thin films with a pure perovskite structure were obtained. The effects of excess lead and pyrolyzing temperature on the crystalline structure of the thin films were investigated using X-ray diffraction. Their ferroelectric and dielectric properties were determined by P-E loop and impedance measurements. The remnant polarization is 23.5 μC/cm² and the coercive electric field strength is 5.5 kV/mm. The dielectric constant and the dissipation factor is approximately 950 and 0.07, respectively.     

Dielectric properties of lead zirconate titanate thin films seeded with barium strontium titanate nanoparticles

A low temperature synthetic method recently proposed by the authors was applied to the fabrication of lead zirconate titanate (PZT) thin films containing crystalline seeds of barium strontium titanate (BST) nanoparticles. PZT precursor and the BST particles were prepared with complex alkoxide methods. Precursor solution suspending the BST particles was spin-coated on Pt/Ti/SiO₂/Si substrate to film thickness of 500–800 nm at particle concentrations of 0–25.1 mol%, and annealed at various temperatures. Seeding of BST particles prevented the formation of pyrochlore phases, which appeared at temperatures above 400 °C in unseeded PZT films, and induced crystallization of PZT into perovskite structures at 420 °C, which was more than 100 °C below the crystallization temperature of the unseeded PZT films. Measurement of dielectric properties at 1 kHz showed that the 25.1 mol% BST-seeded PZT films annealed at 450 °C had a dielectric constant as high as 300 with a dissipation factor of 0.05. Leakage current density of the film was less than 1×10⁻⁶ A/cm² at applied electric field from 0 to 64 kV/cm.     

Densification and electrical properties of solution coated lead zirconate titanate thick films

Ferroelectric Pb(Zr_0.7Ti_0.3)O₃ (PZT(70/30)) powder was prepared by a sol-gel method and PZT thick films were fabricated by the screen-printing method on the alumina substrates. A concentration of a coating solution was 0.5, 1.0 mol/L and the number of coating was repeated from 0-6. The thickness of the all PZT thick films was about 60 μm. All PZT multilayered thick films showed the XRD patterns of typical peroveskite polycrystalline structure. The relative dielectric constant of the 0.5 M coated PZT-6 (6-number of sol coatings) and 1.0 M coated PZT-6 thick films were 540 and 656.2, respectively. The dielectric loss of the 0.5 M coated PZT-6 and 1.0 M coated PZT-6 thick films were 3.2% and 2.7%, respectively.     

DC electrical conduction of zinc telluride thin films

Zinc telluride (ZnTe) thin films were deposited by thermal evaporation onto glass substrates kept at room temperature. X-ray diffraction studies showed that the films were polycrystalline and of cubic structure. The current-voltage (I-V) characteristics of the Au/ZnTe/Au thin film sandwich system at different temperatures were studied. The DC conduction was explained using the Schottky or Jonscher-Ansari modified Pool-Frenkel mechanism.     

Al浓度对AZO薄膜结构和光电性能的影响

采用射频溅射方法在Si基片上制备出AZO掺杂薄膜,对薄膜进行了XRD和AFM分析,并对其电性能作了研究.结果表明,掺杂量低于15%(原子分数)时,AZO薄膜结构为纤锌矿结构,呈c轴方向择优生长,没有Al2O3相出现.薄膜的可见光透过率均在80%以上,其最高电阻率出现在掺杂量为30%(原子分数),为1.3×107 Ω·cm.     

Performance characteristics of smart-materials based on lead zirconate titanate

This paper deals with the characterization of smart-material combinations based on the principle of phase transformation; that may provide drastic change in resistance with a small change in pressure. Lead zirconate titanate (PZT) has been selected as a base material for the development of smart-material combinations and pressure-sensitive devices were fabricated using the same. The devices have been characterized with change in pressure. Both dynamic and static pressures were used for characterization of the devices. Fast switching action i.e. large change in resistance with pressure has been observed and discussed. The reliability tests on the devices have also been performed to establish their long-term stability.