Processing and electromechanical properties of lead zirconate titanate thick films by electrophoretic deposition

Electrophoretic deposition (EPD) was used for the fabrication of piezoelectric [lead zirconate titanate (PZT)] thick films on alumina substrates. The EPD was performed in constant current mode from an ethanol based suspension consisting of PZT and PbO particles. The influence of addition of ethyl cellulose (EC) and sintering temperature on the thickness, density, homogeneity and functional response of PZT thick films is studied. Results show that the highest electromechanical performance is obtained for the PZT thick films sintered at 900 or 950°C, with a thickness coupling factor k_t of 50%. The addition of EC influenced the thickness of the PZT thick films but had only minor effect on the porosity content for sintering temperatures over 900°C. Moreover, elastic constants of the thick films based on the suspension with EC were lower, which leads to lower acoustic impedance (15?MRa) while maintaining high (k_t) value. In this last case, a better acoustic matching can be expected with propagation media such as water or biological tissues for ultrasound medical imaging applications.     

Electrophoretic Deposition of Lead Zirconate Titanate Ceramics

Electrophoretic deposition (EPD) of submicrometer lead zirconate titanate (PZT) powders in ethanol was conducted to form thick green PZT films up to 160 μm thick. The PZT colloid stability, as a function of pH, was studied by zeta-potential measurement. The electrical condition of the suspension was quantified by conductivity measurement at various pH values. The effect of different applied current densities on the deposition mass was investigated. A kinetic model for the constant-current-density EPD process, taking into account the particle concentration variation, was also examined, based on the experimental results obtained in the present work. An empirical relationship between the kinetic constant and the applied current density has been proposed.     

Fabrication and Electrical Properties of Lead Zirconate Titanate Thick Films on Si Substrate by Using Lanthanum Nickelate Buffer Layer

Lead zirconate titanate PbZr_0.53Ti_0.47O₃ (PZT) thick films have been deposited on silicon substrate by modified metallorganic decomposition process. Crack-free PZT films of 8 μm thickness can be obtained by using lanthanum nickelate LaNiO₃ (LNO) as buffer layer. The greater LNO thickness, the greater thickness of crack-free PZT can be obtained. The X-ray diffraction measurements show the films exhibit a single perovskite phase with (110) preferred orientation. SEM measurements showed the PZT thick films have a columnar structure with grain size about 60–200 nm. The thickness dependence of ferroelectric, dielectric, and piezoelectric properties of PZT thick films have been characterized over the thickness range of 1–8 μm. For PZT with thickness of 8 μm, P _r and E _c are 30 μC/cm² and 35 kV/cm, and dielectric constant and dielectric loss are 1030 and 0.031, respectively. The piezoelectric coefficient ( d ₃₃) of PZT with 8 μm thickness is obtained to be 77 pm/V. PZT thick films on LNO-coated Si substrate are potential for MEMS applications.     

Synthesis and Electrical Characterization of Thin Films of PT and PZT Made from a Diol-Based Sol-Gel Route

Lead titanate (PT) sols were prepared using propanediol, butanediol, or pentanediol solutions of lead acetate trihydrate and titanium diisopropoxide bis(acetylacetonate). Precursor sols for PbZr_0.53Ti_0.47O₃ (PZT) films were prepared from propanediol solutions, with zirconium tetrapropoxide being used as the zirconium source. Films were formed by spin-coating the sols onto silicon and platinized silicon substrates; the resulting gel layers were converted to ceramic films by adopting a two-stage heating schedule with final firing temperatures of 600–700°C. Information on film crystallization, microstructure development, and electrical properties is presented for both compositions. The limiting thickness of surface-smooth crack-free single-layer films was ∼1 μm. The PT films exhibited a "linear" polarization-electric field ( P-E ) response, while the PZT films gave rise to characteristic ferroelectric P-E hysteresis loops. A 0.5 μm thick single-layer PZT film exhibited remanent polarization (P_r) values of ∼34 μC·Cm⁻², with a coercive field ( E _c) of ∼45 kV·Cm⁻²; the relative permittivity (ɛ_r) and the dissipation factor ( D ) were ∼1250 and 0.07. For a 1 μm single-layer PZT film, the respective values were P _r∼19 μC∼Cm⁻², E _c∼40 kV∼Cm⁻², ɛ_r∼750, and D = 0.03.     

Synthesis of 10-μm-Thick Lead Zirconate Titanate Films on 2-in. Si Substrates for Piezoelectric Film Devices

To achieve micro-machined piezoelectric film devices, crack-free and dense 10-μm-thick lead zirconate titanate (PZT) films were successfully deposited onto 2-in. Pt/Ti/SiO₂/Si substrates using an automatic coating system, and disk-shaped structures with a diameter from 20 to 100 μm were fabricated by an RIE process. The prepared PZT thick film disks showed well-saturated P–E hysteresis curves and butterfly-shaped longitudinal displacement curves. The AFM-measured piezoelectric constant of the 30-μm-diameter PZT thick film disk after poling at 100 V for 10 min was AFM d ₃₃=290 pm/V. The resonant and anti-resonant frequencies of the thickness oscillation mode were observed at 180 MHz. The calculated thickness mode effective coupling factor was ( k _eff)²=0.1 for the poled 30-μm-diameter PZT thick film disks. These results suggest that the prepared PZT thick film disks are applicable for piezoelectric micro devices such as micro-machined ultrasonic transducers.     

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.     

Electrophoretic deposition and sintering of thin/Thick PZT films

Electrophoretic deposition (EPD) is a simple, rapid, and low cost method for forming dense lead zirconate titanate (PZT) films down to 5 μm from particulate precursors. The three main steps of this process are: (1) formation of a charged suspension of the starting PZT powder; (2) deposition of the powder particles on an electrode under the influence of a dc electric field; and (3) fluxing and constrained sintering of the resulting particulate deposit at 900°C to form a dense continuous film. A 10 μm film formed using this process exhibited a polarization hysteresis equivalent to that of a bulk sample formed from the same starting powder, with a remnant polarization of 33 μC cm⁻².     

Dielectric and Piezoelectric Properties of PZT Composite Thick Films with Variable Solution to Powder Ratios

The use of PZT films in sliver-mode high-frequency ultrasonic transducers applications requires thick, dense, and crack-free films with excellent piezoelectric and dielectric properties. In this work, PZT composite solutions were used to deposit PZT films >10 μm in thickness. It was found that the functional properties depend strongly on the mass ratio of PZT sol–gel solution to PZT powder in the composite solution. Both the remanent polarization, P _r, and transverse piezoelectric coefficient, e _{31, f} , increase with increasing proportion of the sol–gel solution in the precursor. Films prepared using a solution-to-powder mass ratio of 0.5 have a remanent polarization of 8 μC/cm², a dielectric constant of 450 (at 1 kHz), and e _{31, f} =−2.8 C/m². Increasing the solution-to-powder mass ratio to 6, the films were found to have remanent polarizations as large as 37 μC/cm², a dielectric constant of 1250 (at 1 kHz) and e _{31, f} =−5.8 C/m².     

Fabrication and Electrical Properties of Lead Zirconate Titanate Thick Films

Thick films of lead zirconate titanate of the morphotropic phase boundary composition, Pb(Zr_0.52Ti_0.48)O₃, have been fabricated on platinum-buffered silicon using a modified sol–gel spin-coating technique. Crack-free films of 12-μm thickness can be uniformly deposited on 3-in.-diameter wafers with high yield and properties comparable to those of bulk ceramics. The thickness dependence of film structure and the dielectric, ferroelectric, and piezoelectric properties have been characterized over the thickness range of 1–12 μm. A strong (100) texture develops as film thickness increases above 5 μm; the films were marked by saturation values of longitudinal piezoelectric coefficient d ₃₃, 340 pC/N; remanent polarization, 27 μC/cm²; and dielectric permittivity, 1450. PZT films in this thickness range are extremely well-suited to application as electromechanical transduction media in silicon-based microelectromechanical systems (MEMS).     

Electrophoretic Deposition and Characterization of Micrometer-Scale BaTiO3 Based X7R Dielectric Thick Films

Uniform and relatively dense BaTiO₃ thick films of 1–5 μm were prepared by an electrophoretic deposition process using submicrometer BaTiO₃ powders (mean particle size: ∼0.2 μm). Two different BaTiO₃ powders and solvent media were used to investigate the film quality and thickness control. The surface charge mechanism of BaTiO₃ particles was explained according to the observed results. The microstructures were examined by means of SEM. The experimental results show that the thickness could be controlled independently of suspension concentration by keeping a constant applied voltage and a constant current drop in a given suspension. BaTiO₃ thick films have good insulation resistance and dielectric properties such as a dielectric constant and a dissipation factor that are compatible with the data from conventional tape-cast BaTiO₃ thin layers.     

Effects of a Conducting LaNiO3 Thick Film as a Buffer Layer of a Pb(Zr,Ti)O3 Film on Titanium Substrates

A conducting 8-μm-thick LaNiO₃ (LNO) film was deposited on a Ti substrate by aerosol deposition for use as a diffusion barrier between a lead zirconate titanate (PZT) and a Ti substrate during postannealing. The deposited 20-μm-thick PZT films were annealed at 800°C. The PZT film deposited without LNO was cracked and partially detached from the substrate after postannealing, presumably due to a severe reaction with the Ti substrate, while no significant reactions were observed when the LNO buffer layer was used. The remnant polarization and relative dielectric constant of the 20-μm-thick annealed PZT films deposited on the LNO-buffered Ti substrate were 43 μC/cm² and 1010, respectively.     

Electrophoretic Deposition of Y2O3-Stabilized ZrO2 Electrolyte Films in Solid Oxide Fuel Cells

An electrophoretic deposition (EPD) method was applied for the preparation of yttria-stabilized zirconia (YSZ) films for solid oxide fuel cell (SOFC) applications. Dense YSZ films with uniform thickness can be readily prepared with the EPD method by using acetylacetone or acetone as a solvent. The open-circuit voltages of SOFC, for which the YSZ films were prepared by the EPD method, increased with increasing repetitions of deposition and sintering. It was found that the open-circuit voltage exceeded 1.0 V after five repetitions. When the planar SOFC was fabricated using La_0.6Sr_0.4MnO₃ as a cathode, and electroless plating Pt as an anode, the open-circuit voltage and the maximum power density attained were 1.03 V and 1.84 W·cm⁻², respectively. Consequently, it became evident that the electrophoretic deposition was a suitable processing route for the formation of gas-tight YSZ films with thickness less than 10 μm.     

Fabrication of Perovskite-Based High-Value Integrated Capacitors by Chemical Solution Deposition

Projected trends for capacitors include increasing capacitance density and decreasing operating voltages, dielectric thickness and process cost. Advances in the fabrication and processing of barium strontium titanate (BST) and lead zirconate titanate (PZT)-based thin films are presented toward attaining these goals in next-generation high-value integrated capacitors. Increasing capacitance density has been demonstrated through the use of large-area electrodes, multilayer structures, and decreased dielectric layer thickness. Capacitance values as high as 10 μF were obtained in a single-layer, 10 cm² film, and layer thicknesses as small as 9 nm have been achieved using chemical solution deposition. Base metal integration results for BST and PZT films are discussed in terms of additional cost and volume reduction; such films have achieved capacitance densities as high as 1.5 μF/cm² and electric fields of 25 V/μm.     

Preparation of Highly Dense PZN–PZT Thick Films by the Aerosol Deposition Method Using Excess-PbO Powder

Lead zinc niobate–lead zirconate titanate thick films with a thickness of 50–100 μm were deposited on silicon and alumina substrates using the aerosol deposition method. The effects of excess lead oxide (PbO) on stress relaxation during postannealing were studied. Excess PbO content was varied from 0 to 5 mol%. The as-deposited film had a fairly dense microstructure with nanosized grains. The films deposited on silicon were annealed at temperatures of 700°C, and the films deposited on sapphire were annealed at 900°C in an electrical furnace. The annealed film was detached and cracks were generated due to the high residual compressive stress and thermal stress induced by thermal expansion coefficient mismatch. However, the film deposited using powder containing 2% of excess PbO showed no cracking or detachment from the substrate after the postannealing process. The PbO evaporation at elevated temperature during the postannealing process seemed to have reduced the residual compressive stress. The remanent polarization and relative dielectric constant of the 50 μm thick films annealed at 900°C were 43.1 μC/cm² and 1400, respectively, which were comparable with the values of a bulk specimen prepared by a powder sintering process.     

Highly Oriented, Chemically Prepared Pb(Zr, Ti)O3 Thin Films

We have fabricated highly oriented, chemically prepared thin films of Pb(Zr_0.04Tio._0.60)O₃ (PZT 40/60) on both insulating and conducting substrates. While (100) MgO single crystals were used as the insulating substrates, the conducting substrates. were fabricated by RF magnetron sputter deposition of 100-nm-thick (100) Pt films onto (100) MgO substrates. For comparison, we also fabricated PZT 40/60 films that had no significant preferential orientation on platinized MgO substrates. Sputter deposition of an underlying amorphous Pt film was used to fabricate randomly oriented PZT 40/60 films. Highly (001) oriented PZT 40/60 films had higher remanent polarization (61 μC/cm² compared to 41 μC/cm²) and lower relative dielectric constant (368 compared to 466) than PZT 40/60 films that were randomly oriented.     

0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 thick films prepared by electrophoretic deposition from an ethanol-based suspension

We have investigated the processing of 0.65Pb(Mg_1/3Nb_2/3)O₃–0.35PbTiO₃ (denoted PMN–PT) thick films using an electrophoretic deposition process (denoted EPD), with the PMN–PT particles suspended in an ethanol-based suspension. The zeta-potential and the viscosity were measured to identify the conditions for the preparation of a stable suspension suitable for the EPD. The applied voltage, the deposition time, the chemical composition of the suspension and the concentration of the powder were investigated in order to obtain a high-quality PMN–PT deposit with a target thickness of about 50 μm. The PMN–PT thick films prepared from stoichiometric and PbO-excess suspensions by sintering at 950 and 1100 °C were examined by X-ray powder-diffraction analysis and scanning electron microscopy. The highest functional response was obtained for a homogeneous, dense, crack-free PMN–PT thick film prepared from a PMN–PT suspension with excess PbO. The film was deposited at a constant voltage of 10 V and for a time of 120 s, followed by sintering at 1100 °C in a PbO-rich atmosphere. The film's properties were as follows: a dielectric permittivity ? of 20,250 at a T_m of 172 °C, a remanent polarization of 17 μC/cm² and a coercive field of 5 kV/cm.     

Thickness effects on structures and electrical properties of lead zirconate titanate thick films

PbZr_0.52Ti_0.48O₃ thick films with thickness of 1–6 μm have been prepared by a polymer-assisted MOD process. The polymer, poly(vinyl acetate) (PVAc) was introduced into PZT precursor solutions. The grain size increased from 30 nm to 100 nm with an increase of the additive amount of PVAc. Meanwhile, the grains grew larger (in a range of 100–500 nm) and the surface of the films became rougher with increasing film thickness. This promotes the structural relaxation and prevents cracking formation. The critical thickness at which the film begins to crack increases significantly. The dielectric constant and remanent polarization (P_r) increased from 1070 to 1490 and from 36.1 μC/cm² to 52.4 μC/cm², respectively, and the coercive field (E_c) decreased from 57.3 kV/cm to 41.3 kV/cm as the film thickness increased from 0.95 μm to 6.02 μm. PZT thick films prepared in this study are promising materials for MEMS applications.     

Sol–Gel Preparation of Thick PZN–PZT Film Using a Diol-Based Solution Containing Polyvinylpyrrolidone for Piezoelectric Applications

Dense and crack-free lead zinc niobate–lead zirconate titanate (PZN–PZT) films were deposited on silicon and glass substrates by spin coating using a sol containing propanediol and polyvinylpyrrolidone. Single-layer PZN–PZT films as thick as 0.80 μm were deposited by a single spin coating with successive heat treatments at 250° and 700°C. After heat treatment, the films were dense, crack free, and optically transparent. In addition, the crystallographic orientation of the thick film was controllable by adjusting the heat-treatment conditions. The ferroelectric properties of the (111)-oriented film were superior to those of the (100)-oriented film. On the other hand, the piezoelectric and dielectric properties of the (100)-oriented film were better than those of the (111)-oriented film. The piezoelectric coefficients ( d ₃₃) of the PZN–PZT films of 4.0-μm-thickness were 192 and 110 pC/N for the (100)-and (111)-oriented films, respectively.     

Dielectric Properties of Electrophoretically Deposited and Isothermally Pressed BaTiO3 Thick Films

Thick BaTiO₃ films were prepared on platinum metallic foils by the electrophoretic deposition (EPD) technique using BaTiO₃ nanoparticles. In order to increase the density of the thick film, the green film was pressed under an isostatic pressure of 200 MPa before high-temperature sintering. The microstructures of deposited films were examined using X-ray diffraction and scanning electron microscopy techniques. Dielectric properties of the thick films were investigated. As the films grow thicker, the dielectric constant increases gradually and the dielectric loss decreases slightly. The experimental results indicate that isostatic pressing is an effective method to process thick films with dense microstructure and better dielectric properties.     

Room temperature deposition of functional ceramic films on low-cost metal substrate

In various practical applications, such as high power actuators, high sensitivity sensors, and energy harvesting devices, polycrystalline piezoelectric films of 1–100?µm thickness and sizes ranging from several µm² to several cm² are required. With conventional film deposition processes, such as sol-gel, sputtering, chemical vapor deposition, or pulsed laser deposition, it is difficult to fabricate films with higher thickness due to their low deposition rate and high interfacial stress. The aerosol deposition method (AD), a relatively new deposition technique, can be used to fabricate highly dense thick films at room temperature by the consolidation of submicrometer-sized ceramic particles on various ceramic, metal, glass, and polymer substrates. Ferroelectric BaTiO₃ ceramic films of different thicknesses ranging from 1 to 30?µm were fabricated on a low-cost metallic substrate at room temperature using the AD method. Surface morphology and adhesion of the film were analyzed. Analysis of internal residual stresses revealed an equibiaxial compressive stress state in the as-processed film. Electrical characterization of films annealed at 500?°C shows an enhanced polarization value of ~?14?µC/cm² over that of the as-processed film. This improved property is related to the decreasing internal residual stress. In addition, the BT films prepared in this work were found to withstand electric fields greater than 100?kV/mm, which is possibly related to the inherent relatively defect-free structure of AD films.