The influence of chemical passivation on the PZT/Pt electrode interface

It has been recognized that the interdiffusion of atomic species between a PZT film and the Pt bottom electrode leads to the gradual degradation of a PZT capacitor. In order to prevent this interdiffusion, experimental studies on chemical passivation to the bottom electrode surface were carried out by the sulfurization method. It was observed that a sulfur layer was built up on the Pt substrate with small grains, which resulted in a structural change at the Pt surface. Atomic force microscopy (AFM) showed that the film roughness of the Pt surface was increased by sulfur treatment. Pb(Zr_0.5Ti_0.5)O₃(PZT) thin films were prepared on a Pt/Ti/SiO₂Si bottom electrode by spin-coating techniques. The microstructure and the preferred orientation of the PZT films were shown to depend on the sulfur-treated electrode. The PZT capacitor on a clean Pt electrode was confirmed to be ferroelectric with Pr=17.7 μC/cm² and Ec=65 kV/cm from the P-E hysteresis curves. The fatigue behavior of a PZT film capacitor prepared on a sulfur-treated one was observed to be relaxed, but the absolute value of Pr was paid off.     

Phase and Texture Evolution in Chemically Derived PZT Thin Films on Pt Substrates

The crystallization of lead zirconate titanate (PZT) thin films was evaluated on two different platinum‐coated Si substrates. One substrate consisted of a Pt coating on a Ti adhesion layer, whereas the other consisted of a Pt coating on a TiO₂ adhesion layer. The Pt deposited on TiO₂ exhibited a higher degree of preferred orientation than the Pt deposited on Ti (as measured by the Full Width at Half Maximum of the 111 peak about the sample normal). PZT thin films with a nominal Zr/Ti ratio of 52/48 were deposited on the substrates using the inverted mixing order (IMO) route. Phase and texture evolution of the thin films were monitored during crystallization using in situ X‐ray diffraction at a synchrotron source. The intensity of the Pt₃Pb phase indicated that deposition on a highly oriented Pt/TiO₂ substrate resulted in less diffusion of Pb into the substrate relative to films deposited on Pt/Ti. There was also no evidence of the pyrochlore phase influencing texture evolution. The results suggest that PZT nucleates directly on Pt, which explains the observation of a more highly oriented 111 texture of PZT on the Pt/TiO₂ substrate than on the Pt/Ti substrate.     

底电极原位退火与沉积温度对PZT薄膜性能影响研究

采用磁控溅射工艺,在Pt/Ti底电极上沉积锆钛酸铅(PZT)薄膜,研究了原位退火温度与底电极沉积温度对溅射PZT薄膜结晶取向、微观结构、介电性能、铁电性能及疲劳性能的影响。X射线衍射(XRD)和扫描电子显微镜(SEM)分析结果表明,随着电极沉积温度升高,Pt晶粒尺寸增大,随着退火温度升高,PZT薄膜致密性变差。对室温制备的Pt/Ti底电极进行200 ℃原位退火30 min后,易于促进PZT薄膜沿(100)择优取向,而高温制备或经高温退火处理的Pt/Ti底电极更有利于PZT薄膜的(111)晶向生长。电学性能分析表明,室温制备的Pt/Ti底电极在经200 ℃原位退火30 min后,其PZT薄膜介电性能最优,同时展现较高的剩余极化强度和最小的矫顽场强,经历10⁸次极化翻转后,初始极化下降仅为11％。     

Bottom electrode crystallization of PZT thin films for ferroelectric capacitors

The bottom electrode crystallization (BEC) method was applied to the crystallization of PZT thin films deposited by laser ablation over Si/SiO₂/Ti(Zr)/Pt structures, with the platinum films being deposited at two different temperatures. The results were compared with those obtained by rapid annealing with halogen lamps and furnace annealing. PZT films crystallized over Pt made at lower temperature with Ti adhesion layers tend to have a (1 1 1) preferential orientation, while those deposited on platinum made at higher temperature tend to have a (1 0 0)/(1 1 1) mixed orientation. When Zr adhesion layers are used, the PZT films crystallized over Pt have a preferential (1 0 0) orientation, except for films deposited over Pt made at 500 °C and crystallized with a high heating rate. The ferroelectric properties of the films crystallized with the BEC method are good, being similar to those obtained with the other crystallization methods using the same parameters.     

Hysteretic properties of Mn-doped Pb(Zr,Ti)O3 thin films

Pb(Zr,Ti)O₃ (PZT 30/70) and Mn-doped Pb(Zr,Ti)O₃ (PMZT 30/70) thin films have been fabricated on Pt/Ti/SiO₂/Si substrates by a chemical solution deposition technique. The experiments found that the addition of Mn in PZT thin films greatly improves the ferroelectric properties of thin films. It is demonstrated that the Mn-doped (1 mol%) PZT showed fatigue-free characteristics at least up to 10¹⁰ switching bipolar pulse cycles under 10 V and excellent retention properties. The Mn-doped PZT thin films also exhibited well-defined hysteresis loops with a remnant polarization (Pr) of 34 μC/cm² and a coercive field (Ec) of 100 kV/cm for the thickness of 300 nm. Dielectric constant and loss (tanδ) for Mn doped PZT thin films are 214 and 0.008, respectively. These figures compare well with or exceed the values reported previously. In this paper, the mechanism by which Mn influences on the ferroelectric properties of PZT thin films has also been discussed.     

Effect of electrode and substrate on the fatigue behavior of PZT thick films fabricated by aerosol deposition

10 μm-thick lead zirconate titanate (PZT) films with identical LaNiO₃ (LNO) top and bottom electrodes were fabricated on silicon and yttria-stabilized zirconia (YSZ) substrates by aerosol deposition (AD). A Pt electrode was also made for comparison. The dielectric, ferroelectric and fatigue behaviors at different fields were investigated. The PZT films on YSZ/LNO showed the highest dielectric and ferroelectric properties and good fatigue behavior under various fields. PZT films with a Pt electrode also showed good fatigue behavior up to 10⁸ cycles as thicker film can minimize the effect of defect entrapment near the interface.     

Film thickness dependence of the dielectric properties of SrTiO3/BaTiO3 multilayer thin films deposited by double target RF magnetron sputtering

Four-layer SrTiO₃/BaTiO₃ thin films ((ST/BT)₄) with various thicknesses deposited on Pt/Ti/SiO₂/Si substrates at 500 °C by double target RF magnetron sputtering have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), profilometry, capacitance-voltage and current-voltage measurements. The XRD patterns reveal the frame formation of the sputter deposited (ST/BT)₄ with controlled modulation. The adhesion between the Pt bottom electrode layer and the BT layer is excellent. The dielectric constant of the (ST/BT)₄ multilayer thin film increases with increasing film thickness. The effects of temperature, frequency, and bias voltage on the dielectric constant of the (ST/BT)₄ multilayer thin films are discussed in detail. The leakage current density of the (ST/BT)₄ multilayer with a thickness of 450.0 nm is lower than 1.0 × 10⁻⁸ A/cm² for the applied voltage of less than 5 V, showing that the multilayer thin films with such a characteristic could be applied for use in dynamic random access memory (DRAMs) capacitors.     

Micro-patterning of PZT thick film by lift-off using ZnO as a sacrificial layer

Micro-pattern of 8.2-μm-thick PZT films was prepared on Pt/Ti/SiO₂/Si (1 0 0) substrate wafer by combining composite sol–gel and a novel lift-off using ZnO as a sacrificial layer. The processes include ZnO sacrificial layer deposition and patterning, PZT film preparation, and final lift-off. The results reveal the micro-pattern was better than that formed by wet etching, the PZT thick films patterned by lift-off possessed similar dielectric characters, better ferroelectric properties, and higher breakdown voltage than those of films patterned by wet etching. The lift-off is suitable for micro-patterning of PZT thick films.     

Effects of Thermal Annealing on the Structure of Ferroelectric Thin Films

The effects of thermal annealing on the structure of polycrystalline Pb(Zr_0.3Ti_0.7)O₃ (PZT) ferroelectric thin films prepared by chemical solution deposition on Pt/TiO _x electrode stacks were studied using scanning electron microscopy, transmission electron microscopy (TEM), and grazing incidence X-ray specular and diffuse reflectivity of synchrotron radiation. The stratified multilayered structure and element diffusions in the sample were characterized by TEM. Global statistical structural parameters including the density, surface or interface roughness and thickness of each layer in the samples were obtained from fitting the X-ray specular reflectivity using a homogeneous stratified multilayer model of PZT/Pt/TiO _x /SiO₂. The results showed that the PZT surface and PZT/Pt interface roughness changed slightly during thermal annealing in oxygen at 700°C. By contrast, the density increase of the PZT ceramic and density decrease of the Pt-bottom electrode during annealing were observed. A high density value of the PZT ceramic film after the annealing was found, up to 99.8% of the theoretical value of the corresponding bulk ceramics. The density changes of the PZT and Pt layers were further confirmed by X-ray diffuse reflectivity. The influences of the annealing treatment on the density changes of the PZT and Pt layers were attributed to the further densification of the PZT ceramic and incorporation of light elements such as Zr, Ti and O from the neighboring layers into the Pt layer, respectively, as discussed in correlation with the TEM analyses.     

Improvement of reliability and dielectric breakdown strength of Nb-doped lead zirconate titanate films via microstructure control of seed

A Pb(Zr,Ti)O₃ (PZT) seed layer without Pb-deficient defective areas was developed to improve the dielectric breakdown strength and lifetime of thin film piezoelectric actuators. The proportion of defective area in the seed layers was reduced by adjusting the amount of Pb excess in the solution, combined with implementation of a dense, large-grained (>200 nm) Pt bottom electrode. The optimal Pb excess amount in the solution was about 20 at%; seeding was improved when a slightly Ti-rich composition (relative to the morphotropic phase boundary) was utilized. It was found that the dielectric breakdown strength and lifetime of PZT films improved as the proportion of visible defective area on the PZT seed layer decreased. Dielectric breakdown strength increased from approximately 300 kV/cm to about 1 MV/cm. The lifetime, characterized by highly accelerated lifetime testing, was increased 60 times by reducing the fraction of defective area. The activation energy (E_a) and voltage acceleration factor (N) for failure of devices (eg, patterned PZT films) were 1.12 ± 0.03 eV and 4.24 ± 0.07 respectively.     

Fine-patterning of sol-gel derived PZT film by a novel lift-off process using solution-processed metal oxide as a sacrificial layer

Sub-5 µm pattern of sol-gel derived lead-zirconium-titanate (PZT) film with a thickness of 80–390 nm was successfully prepared on Pt(111)/TiO_x/SiO₂/Si (100) substrate by a novel lift-off process using solution-processed metal oxides as a sacrificial layer. The process is simply divided into three steps: In-Zn-O (IZO) sacrificial layer spin-coating and patterning, PZT film formation followed by lift-off process. The results suggested that the IZO layer is effective in preventing PZT crystallization because of its thermal stability during PZT post-annealing, and its barrier-effects between the spin-coated PZT precursor and the Pt/TiO_x substrate. Consequently, the micro-pattern of lift-off PZT exhibited better properties than that formed by wet-etching. In particular, the lift-off PZT films possessed better ferroelectric properties, higher break-down voltage, and more well-defined shape than those of films patterned by conventional wet-etching. This lift-off process shows great promise for highly integrated devices due to its fine pattern-ability.     

High Piezoelectric Longitudinal Coefficients in Sol–gel PZT Thin Film Multilayers

A five‐layer stack of lead zirconate titanate (PZT) thin films with Pt electrodes was fabricated for potential applications in nanoactuator systems. The 1 μm thick PZT films were deposited by a sol–gel technique, the platinum electrodes by sputtering. The PZT films were crack‐free, in spite of the use of silicon as a substrate, suggesting an increased toughness of the metal–ceramic composite. For piezoelectric characterization, the intermediate electrodes were liberated by successive etching of the PZT and Pt layers, obtaining a functional three‐ layer stack. A total thickness change of 5.2 nm was achieved with 10 V, measured by double beam laser interferometry. The small signal response was obtained as 0.49 nm/V. Finite element simulations were made to account for the thickness change in the substrate due to the transverse piezoelectric effect. The average response corresponds to an average d_33,f of 120 pm/V. The multiple annealed buried layers show clearly a better performance with up to 175 pm/V. It is concluded that the electrode interfaces in the interior exhibit higher qualities, as supported by transmission electron microscopy, and that the multiple anneals were beneficial for PZT thin film quality.     

Electrophoretic deposition of Pb(Ni1/3Nb2/3)O3–Pb(Zr,Ti)O3 thick film on Pt wire

0.2PbNi_1/3Nb_2/3–0.8Pb(Zr,Ti)O₃ (PNN–PZT) thick films were deposited on Pt wire with the diameter of 50 μm by electrophoretic deposition (EPD) method. The EPD deposition times on the microstructures of PNN–PZT thick films were investigated. By optimizing the EPD process, the Pt wire can be uniformly wrapped with the PNN–PZT powders. During the sintering process, the as-deposited PNN–PZT/Pt wires were buried in the mixed powders of PbCO₃ and ZrO₂, and then sintered in the optimal temperature to get a dense microstructure. The piezoelectric properties of the thick films were characterized by scanning force microscopy (SFM) method. The results show that the PNN–PZT thick films prepared by EPD method have good piezoelectricity.     

The preparation and properties of PZT thin film by sputering method

The ferroelectric PZT thin films were prepared on Pt/Ti/SiO₂/Si substrate by RF sputtering method followed by the rapid thermal annealing. The preparation of the Pt and Ti thin films as bottom electrode, and their influences on the PZT thin films were studied in details. The substrate temperature during sputtering was room temperature; the rapid thermal annealing temperature was 500°C-750°C and the annealing time was 30-70s. The influences of different preparation parameters on the structure and electric properties were studied with X-ray diffraction technique and RT66A Standardized Ferroelectric Test System. The electric properties of the prepared PZT thin film was: P_a=39μc/cm₂, P_r = 9.3 μc/cm², E_c=28KV/mm, ε=300, p=10⁹ω⋅cm.     

Solution Chemistry,Substrate, and Processing Effects on Chemical Homogeneity in Lead Zirconate Titanate Thin Films

The effects of chemistry, substrate, and processing conditions on through‐thickness cation distributions are explored in solution‐derived morphotropic composition lead zirconate titanate (PZT) films. Films prepared from chelate‐based and conventional sol–gel chemistries were spin cast onto Pt/ZnO/SiO₂/Si and Pt/Ti/SiO₂/Si substrates and pyrolyzed at 300°C, 350°C, and 400°C prior to crystallization at 700°C either in a preheated furnace or via rapid thermal processing. For films crystallized within a conventional furnace on Pt/ZnO/SiO₂/Si substrates no chemical gradients were observed. All films prepared on Pt/Ti/SiO₂/Si substrates had increased titanium concentrations near the PZT/Pt interfaces, and the source is shown to be titanium diffusing from the substrate metallization stack. The effect of heating method and rate was explored in films prepared on Pt/ZnO/SiO₂/Si substrates with 15°C, 50°C, and 100°C/s heating rates within a rapid thermal annealer. Only one solution chemistry‐heating rate combination resulted in the formation of a chemical gradient: a conventional sol–gel chemistry and a 50°C/s heating rate. Infrared spectroscopy of pyrolyzed gel films showed absorption spectra differences in the bonding structure between the two chemistries with the conventional sol–gel‐derived films exhibiting a signature more similar to that of a PbTiO₃ gel, suggestive of a gel‐structure source of gradient formation during crystallization.     

Thermal treatment effect on the magnetoelectric properties of (Ni0.5Zn0.5)Fe2O4/Pt/Pb(Zr0.3Ti0.7)O3 heterostructured thin films

Magnetoelectric (ME) property modulation in heterostructured (Ni_0.5Zn_0.5)Fe₂O₄/Pt/Pb(Zr_0.3Ti_0.7)O₃ (NZFO/Pt/PZT) thin films on platinized Si substrate by thermal annealing condition variation was studied. In an attempt to prevent interfacial reaction between NZFO and PZT layers during high temperature annealing, thin Pt layer was deposited which can serve as inter-diffusion barrier as well as electrode. The ferroelectric, magnetic, and ME properties of the heterostructured film were noticeably modulated due to microstructural evolution and clamping relaxation developed during thermal annealing process. Room temperature ME voltage coefficient of the heterostructured thin films was enhanced with increasing annealing temperature and reached to 29 mV/cm·Oe when annealed at 650 °C.     

Rapid Microwave Annealing of Amorphous Lead Zirconate Titanate Thin Films Deposited by Sol‐Gel Method on LaNiO3/SiO2/Si Substrates

The heating behavior of LaNiO₃ (LNO) films on SiO₂/Si substrate heated by 2.45 GHz microwave irradiation in the microwave magnetic field was first investigated, and then amorphous Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films were deposited on LNO‐coated SiO₂/Si substrates by a sol‐gel method and crystallized in the microwave magnetic field. The crystalline phases and microstructures as well as the electrical properties of the PZT films were investigated as a function of the elevated temperature generated by microwave irradiation. The perovskite PZT films with a highly (100)‐preferred orientation can be obtained by microwave annealing at 700°C for only 180 s of total processing time, and have good electrical properties. The results demonstrated that conductive metal oxide LNO as a bottom electrode layer is an advantage for the crystallization of PZT thin films by microwave irradiation in the microwave magnetic field.     

Preparation of ferroelectric Pb(Zr0.52 Ti0.48)O3 thin films by sol-gel processing

Ferroelectric Pb(Zr_0.52 Ti_0.48)O₃ thin films were prepared by sol-gel processing on the Pt/Ti/SiO₂/Si(100) substrates. Effects of the concentration (0.2–0.8 M) of the starting solution (Pb/Zr/Ti= 1.1/0.52/0.48) and the sintering temperature (500–700 ‡C) on crystallinity, microstructure and electrical properties of PZT thin films were investigated. For the thin film prepared at 0.4 M starting solution, the highest crystallinity appeared at a sintering temperature of 650 ‡C. The average grain size of the PZT thin films was about 0.17 Μm. The film thickness was about 0.2 Μm. The relative dielectric constant and the dissipation factor of the film measured at 1 kHz were about 750 and 4.3%, respectively. The remnant polarization (Pr) and coercive field (Ec) of the film measured at the applied voltage of 5 V were about 49 ΜC/cm² and 134 kV/cm, respectively.     

Dielectric behavior and magnetical response for porous BFO thin films with various thicknesses over Pt/Ti/SiO2/Si substrate

A novel sol–gel method has been developed to deposit multiferroic nanocrystalline bismuth ferrite (BFO) thin films over Pt/Ti/SiO₂/Si substrate by spin-coating technique with various thicknesses. It is found that the deposition parameters significantly influence the quality and the thickness of BiFeO₃ films. The films are all uniform and adherent to Pt/Ti/SiO₂/Si substrate. The spin-coated films are characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM), Atomic force microscope (AFM), photoluminescence spectroscopy (PL) and Fourier transform infrared spectroscopy (FTIR). Rhombohedral structure of BFO is confirmed from the XRD and FT-IR studies. The SEM image shows a porous structure formation of BFO over Pt/Ti/SiO₂/Si substrate. The surface outgrowth for the films at various thicknesses is measured from root mean square (RMS) and surface roughness through AFM. The step height and the RMS are found to be high for the film at 500 nm in comparison with thickness of 200 nm. The influence of the dielectric properties of the porous BFO at different thicknesses is studied using LCRQ meter. Finally, the magnetic behavior of film is compared with M–H hysteresis loop and Magnetoresistance (MR) studies.     

Platinum-coated nanostructured oxides for active catalytic electrodes

In this work we propose the use of platinum-coated nanostructured oxides for improving the redox rate of active electrodes for applications in catalysts for water splitting, fuel cells, organic depollution, etc. In order to test this concept, CaCu₃Ti₄O₁₂ nanorods were grown by magnetron sputtering over Si/SiO₂/Ti/Pt substrates and coated with a platinum layer using the same technique. The performance of this active electrode was studied by cyclic voltammetry and electrochemical impedance spectroscopy. Other Pt films (both dense and porous) deposited on oxidized silicon, and platinum-coated FTO-glass, when tested under the same conditions, were less efficient. The charge transfer resistance and the capacitance of one dimensional platinum-coated nanostructured electrodes were at least one order of magnitude better than those measured for platinum-coated FTO-glass.