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.     

Damping properties of epoxy-based composite embedded with sol–gel-derived Pb(Zr<Subscript>0.53</Subscript>Ti<Subscript>0.47</Subscript>)O<Subscript>3</Subscript> thin film annealed at different temperatures

Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films were prepared on Pt/Ti/SiO₂/Si substrate by sol–gel method. The effect of annealing temperature on microstructure, ferroelectric and dielectric properties of PZT films was investigated. When the films were annealed at 550–850 °C, the single-phase PZT films were obtained. PZT films annealed at 650–750 °C had better dielectric and ferroelectric properties. The sandwich composites with epoxy resin/PZT film with substrate/epoxy resin were prepared. The annealing temperature of PZT films influenced their damping properties, and the epoxy-based composites embedded with PZT film annealed at 700 °C had the largest damping loss factor of 0.923.     

Peculiarities of crystallization of thin ferroelectric films of lead zirconate titanate

The thermodynamics of processes involved in the growth and annealing of ferroelectric films of lead zirconate titanate Pb(Ti,Zr)O₃ (PZT) has been studied using the method of synchronous thermal analysis (STA). Thin PZT films were grown by the RF magnetron sputtering and then annealed in air or in an inert gas (argon) at atmospheric pressure and various temperatures within 20–600°C. It was found that the annealing in an oxygen-containing medium (air) is accompanied by changes in the enthalpy and mass of the system, which is due to the interaction with oxygen, while the heat treatment in an inert medium did not lead to any changes in the PZT film. It is established that the observed changes are related to the conversion of lead monoxide into orthoplumbate in the PZT film volume. STA experiments demonstrate that this transformation leads to a significant change in the structure of the ferroelectric film. Based on these data, a mechanism is proposed that accounts for the structural changes involved in the annealing of PZT films.     

Preparation of lead zirconate titanate thin films with a combination of self-assembly and spin-coating techniques

A low-temperature synthetic method for preparing lead zirconate titanate (PZT) perovskite film on a Pt substrate is proposed. The method consists of the self-assembly of PZT particles on a substrate and successive spin coating with a precursor of PZT. The PZT particles that had sub-micron sizes and perovskite structures were prepared by annealing amorphous PZT particles formed from a complex alkoxide precursor. The PZT particles were deposited on a Pt substrate that was surface-modified with (3-mercaptopropyl) trimethoxysilane to chemically fix the particles on the substrate. Another PZT precursor solution was used for the spin-coating on the PZT-deposited substrate, and then the spin-coated film was annealed at 350 °C to remove organic residues left in the film. The spin-coated PZT film prepared at 350 °C had a dielectric constant of 118 at a frequency of 1000 Hz.     

Low-temperature crystallization of sol-gel-derived lead zirconate titanate thin films using 2.45 GHz microwaves

Lead zirconate titanate (PZT) thin films of thickness 420 nm were deposited on Pt/Ti/SiO₂/Si substrate using a spin coating sol-gel precursor solution, and then annealed using 2.45 GHz microwaves at a temperature of 450 °C for 30 min. The film has a high perovskite content and high crystallinity with a full width at half maximum of 0.35°. The surface roughness of the PZT thin film was 1.63 nm. Well-saturated ferroelectric properties were obtained with a remanent polarization of 46.86 μC/cm² and coercive field of 86.25 kV/cm. The film also exhibited excellent dielectric properties with a dielectric constant of 1140 and a dissipation factor of 0.03. These properties are superior to those obtained by conventional annealing at a temperature of 700 °C for 30 min.     

Micropore formation in lead zirconate titanate films

This paper presents an experimental study of the pyrochlore-to-perovskite phase transition in ferroelectric lead zirconate titanate (PZT) films grown on silicon substrates by rf magnetron sputtering and annealed in air or in an inert (argon) atmosphere at temperatures of up to 600°C and atmospheric pressure. Simultaneous thermal analysis results demonstrate that annealing in air leads to release of the latent heat of the phase transition, which is due to the conversion of lead oxide to lead orthoplumbate in the bulk of the PZT film. This transition is accompanied by changes in the densities of the perovskite phase and parent (pyrochlore) phase. In this case, the possibility of phase transformation should be ensured by changes in the volume of the system. The change in the volume of the film leads to the formation of micropores in the bulk of thin PZT films. The micropore size has been determined by scanning electron microscopy, and the phase composition of the films has been assessed by X-ray diffraction. We present experimental evidence that micropore nucleation and growth at the interface between the new and old phases in thin PZT films is due to the difference in density between these phases.     

Phase formation and characteristics of r.f.-sputtered barium-strontium titanate thin films on various bottom layers

(Ba_0.7Sr_0.3)TiO₃ thin films were deposited by r.f.-magnetron sputtering on Pt/Ti/Si, Pt/TiSi₂/Si and Pt/Ti/SiO₂/Si substrates, respectively, and annealed at 650 C for 30s by Rapid Thermal Annealing (RTA). XRD (X-ray diffraction) patterns revealed that the BST films had perovskite structure without preferred orientation. Auger depth profiles of barium-strontium titanate (BST) films on various substrates were performed. In the Pt/Ti/Si and Pt/TiSi₂/Si structures, Si diffused into the BST film, but in the Pt/Ti/SiO₂/Si structure, the diffusion of Si into the BST film was prevented and the interface between the BST film and the electrode was stable. The dielectric constants were about 310–260 (100 kHz–1 MHz).     

The electrical and interface properties of metal-ferroelectric (lanthanum substituted bismuth titanate: BLT)-insulator-semiconductor (MFIS) structures with various insulators

We have investigated metal-ferroelectric-insulator semiconductor (MFIS) structures with lanthanum substituted bismuth titanate (BLT) as a ferroelectric layer and lanthanum oxide (LO) or zirconium silicate (ZSO) as an insulating buffer layer between BLT and Si substrate. The morphology of BLT films deposited on LO or ZSO oxide was not changed due to the good thermal stability of LO and ZSO films. But an interface reaction between BLT and buffer layer started at high annealing temperature (750 °C), which was confirmed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The maximum memory window was 3.59 V at a sweep voltage of 7 V with the LO film annealed at 650 °C and a thickness of 5 nm. With BLT/LO annealed at 750 °C, the window was decreased due to the reaction between the BLT film and LO. The memory window was about 1 V lower with a ZSO film because ZSO film has a lower dielectric constant than LO film. The MFIS structure annealed at 750 °C had a lower leakage current density because the electrical properties of the buffer layer (La oxide or Zr silicate) were improved by the thermal process.     

Investigation of the drying temperature dependence of the orientation in sol–gel processed PZT thin films

The crystal orientations of lead zirconate titanate (PZT) thin films have been investigated by using various drying temperatures in the sol–gel process. The films were dried at different temperatures between 310 and 350°C for pyrolysis and then were heat treated at 650°C using rapid thermal annealing (RTA). TG/DTA and FTIR spectroscopy were used to detect the remnants of organic materials in the thin films prior to the final heat treatment. In order to examine the relationship between the film orientation and the remaining organic materials for the prior and final heat treatment, the films were fabricated with different coating cycles and dried for different holding times and then annealed at 650°C. The preferred orientations were investigated using X-ray diffraction. This revised version was published online in November 2006 with corrections to the Cover Date.     

Lead zirconate titanate thin films on GaAs substrates

Thin films of the piezoceramic lead zirconate titanate (PZT) of composition Pb(Zr0.53Ti0.47)O3 have been prepared on a platinized GaAs substrate system using a propanediol based sol-gel technique. A Si3N4 buffer layer was deposited onto the GaAs by plasma-enhanced chemical vapour deposition so as to minimize Ga and As diffusion during film fabrication. Rapid thermal processing (RTP) techniques were used to thermally decompose the sol-gel layer to PZT in a further effort to avoid problems of Ga and As diffusion. Adhesion between the electrode and substrate was found to improve when an intermediate Ti layer deposited between the Pt and Si3N4 was oxidized prior to depositing the Pt layer. A crystalline PZT film was produced on the Pt/TiO2/Si3N4/GaAs by firing the sol-gel coating at 350°C for 1 min and then at 650°C for 10 s using RTP. A single deposition of precursor sol resulted in a film 0.5 μm thick. Measured average values of remanant polarization and coercive field were 14 μC cm-2 and 47 kV cm-1, respectively. The polarization value is rather low, as conventionally fired films on silicon have remanent polarization values of 20–30 μC cm-2; the lower values may be due to incomplete crystallization during RTP, but a degradation of properties due to Ga-As diffusion, despite the precautions, cannot be ruled out at this stage. This revised version was published online in November 2006 with corrections to the Cover Date.     

Preparation and characterization of Mn-doped BaTiO<Subscript>3</Subscript> thin films by magnetron sputtering

Barium titanate (BaTiO₃) thin films doped with Mn (0.1–1.0 at%) were prepared by r.f. magnetron sputtering technique. Oxygen/argon (O₂/Ar) gas ratio is found to influence the sputtering rate of the films. The effects of Mn doping on the structural, microstructural and electrical properties of BaTiO₃ thin films are studied. Mn-doped thin films annealed at high temperatures (700 °C) exhibited cubic perovskite structure. Mn doping is found to reduce the crystallization temperature and inhibit the grain growth in barium titanate thin films. The dielectric constant increases with Mn content and the dielectric loss (tan δ) reveals a minimum value of 0.0054 for 0.5% Mn-doped BaTiO₃ films measured at 1 MHz. The leakage current density decreases with Mn doping and is 10⁻¹¹ A/cm⁻² at 6 kV/cm for 1% Mn-doped thin films.     

Hydrothermal processing of barium strontium titanate sol-gel composite thin films

Stoichiometric barium strontium titanate (BST) films of composition with thickness >2 μm have been fabricated on Si/SiO₂/Pt substrates by hydrothermal sol-gel composite processing. This film deposition technique involves the treatment of a spun-on sol-gel composite film, formed from a suspension of a powder in an aqueous BST sol-gel, at temperatures from 100–200°C at a pressure of 1–15 atm. An initial hydrolysis procedure eliminates dissolution of the dried sol-gel during the hydrothermal treatment. Glancing angle X-ray diffraction shows excellent crystallinity and stoichiometry in the BST films with no evidence of new phases created during processing. Scanning electron micrography and atomic force microscopy show densification of the film structure and the development of a bridging microstructure. Transmission electron micrography indicates that while much of the sol-gel derived matrix phase is amorphous a more crystalline interface occurs with the powder particles. The relative permittivity and loss tangent of the films are measured using a parallel plate capacitor technique in the frequency range 1–100 kHz. At 100 kHz relative permittivities of the films range from ɛ_r = 400–1200 and loss tangents lie in the range 0.05 < tan δ < 0.10, depending on the parameters of film preparation. The film structure and morphology and the electrical studies suggest that the microstructure of the films evolves by deposition of the sol-gel derived BST on the underlying powder, resulting in an electrically interconnected microstructure in which the sol-gel derived material bridges between the high permittivity powder particles.     

Improvement electrical properties of sol–gel derived lead zirconate titanate thick films for ultrasonic transducer application

In this work, a fabrication process of piezoelectric PZT [Pb(Zr_0.52Ti_0.48)O₃] thick films up to 60 μm deposited on silicon and aluminum substrates is reported. Crystalline spherical modified PZT powder about 300 nm in diameter was used as filler. PZT polymeric precursor produced by Chemat Inc. was used as the matrix material. Spinning films were annealed at 700 °C for one hour in the furnace in air. The thickness of the thick films was measured using a scanning electron microscope (SEM). Compared with previous piezoelectric PZT composite films, the modified piezoelectric thick films exhibit better dielectric properties. The dielectric constant is over 780 and dielectric loss is 0.04 at 1 KHz. Using a PiezoCAD model, the high frequency transducer was designed and fabricated. It showed a bandwidth of 75% at 40 MHz.     

Characterization of poly(vinylidene fluoride-trifluoroethylene) 50/50 copolymer films as a gate dielectric

Thin films of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) 50/50 copolymer were prepared by spin coating on p-Si substrate. Thermal behavior of the film was observed by measuring the film thickness with ellipsometry as a function of the temperature and abrupt volume expansion was observed at 130–150 °C. Capacitance-voltage (C-V) and current-voltage (I-V) behavior of the aluminum/P(VDF-TrFE)/p-Si MIS (metal-insulator-semiconductor) structures were studied and dielectric constant of the P(VDF-TrFE) film was measured to be about 15.3 at optimum condition. No hysteresis was observed in the C-V curve for films as deposited and annealed (70–200 °C). Films annealed at temperatures higher than the volume expansion temperature showed substantial surface roughness due to the crystallization. Flat band voltage (V_FB) of the MIS structure with as deposited films was about −0.3 V and increased up to −2.0 V with annealing. This suggested that positive charges were generated in the film. Electronic properties of the annealed P(VDF-TrFE) film at above melting temperature were degraded substantially with larger shift in flat band voltage, low dielectric constant and low breakdown voltage. Organic thin film transistor with pentacene active layer and P(VDF-TrFE) as a gate dielectric layer showed a mobility of 0.31 cm²/V·s and threshold voltage of −0.45 V.     

Sol-solvothermal synthesis and characterization of fine lead zirconate titanate particles

We present a novel low-temperature sol-solvothermal method to synthesize fine lead zirconate titanate (PZT) particles. This sol-solvothermal method combines the advantages of conventional sol–gel process and the solvothermal method, and isopropyl alcohol (IPA) was used as the solvent. The effects of different parameters including KOH concentration, IPA/(IPA + water) ratio and reaction temperature, on the microstructures of the PZT powder were studied. With increasing KOH concentration and reaction temperature, the crystalline structure of as-synthesized PZT transformed from tetragonal to rhombohedral phase. More IPA added in the solvent can effectively reduce agglomeration of the PZT powder and decrease the crystallization temperature, but impurity phase was also detected at high IPA/(IPA + water) ratio. As a result, the synthesis parameters are optimized, and well-crystallized 700 nm PZT particles were successfully synthesized in 2.0 M KOH and 50 % IPA/(IPA + water) ratio at temperatures as low as 120 °C.     

Synthesis and characterization of nanocrystalline barium strontium titanate powders prepared by citrate precursor method

Nanocrystalline and well dispersed barium strontium titanate (BST) powders were prepared by a novel and simple citrate precursor method. This method involved direct crystallization of a white precursor from a stable solution in the citric acid (CA)–ethylene glycol (EG)–tetrabutyl titanate–M²⁺ (M = Ba, Sr) system under a specific pH value range. Subsequent heat treatment of the precursor at 850 °C led to a pure phase BST powder. TG/DTA was used to examine the decomposition behaviour of the precursor. The crystalline phase and morphology of the BST powders were investigated by XRD and TEM. It was found that the BST powders synthesized by citrate precursor process were more homogeneous and uniform than that obtained by the citrate gel method.     

Wafer scale lead zirconate titanate film preparation by sol-gel method using stress balance layer

In this paper, platinum/titanium (Pt/Ti) film was introduced as a residual stress balance layer into wafer scale thick lead zirconate titanate (PZT) film fabrication by sol-gel method. The stress developing in PZT film's bottom electrode as well as in PZT film itself during deposition were analyzed; the wafer curvatures, PZT crystallizations and PZT electric properties before and after using Pt/Ti stress balance layer were studied and compared. It was found that this layer is effective to balance the residual stress in PZT film's bottom electrode induced by thermal expansion coefficient mismatch and Ti diffusion, thus can notably reduce the curvature of 4-in. wafer from − 40.5 μm to − 12.9 μm after PZT film deposition. This stress balance layer was also found effective to avoid the PZT film cracking even when annealed by rapid thermal annealing with heating-rate up to 10.5 °C/s. According to X-ray diffraction analysis and electric properties characterization, crack-free uniform 1-μm-thick PZT film with preferred pervoskite (001) orientation, excellent dielectric constant, as high as 1310, and excellent remanent polarization, as high as 39.8 μC/cm², can be obtained on 4-in. wafer.     

Sandwich-type composite multilayer films of strontium titanate and barium strontium titanate and their controllable dielectric properties

It is a challenge to reduce the dielectric loss and increase the tunability of pure barium strontium titanate(BST)films for microwave tunable application because these two properties change simultaneously.Herein,a novel composite of strontium titanate(ST)and potassium-doped BST(KBST)has been designed as ST/KBST/ST sandwich-type film with various ST and KBST layers.X-ray diffraction patterns show that the film exhibits cubic perovskite polycrystalline structure composed of BST and ST phase,mainly grow along(110)crystal plane with average grain size of less than 20 nm and decreasing BST phase/ST phase ratio with increasing film thickness.Scanning electron microscope shows that no interfacial layer can be observed,indicating that ST and KBST are fully compounded.Low dielectric loss and high tunability at-10-10V and stable and excellent dielectric properties at 1 GHz are achieved,meeting the needs of microwave tunable application at high frequency.The surface structures are also studied by other analysis methods,and ST/MgBST/ST sandwich-type film is compared.     

Characterization of lead zirconate titanate thin film deposition onto Pt/Ti/SiO2/Si substrates

Lead zirconate titanate, (Pb(Zr_0.52Ti_0.48)O₃PZT) thin films were deposited onto a Pt/Ti/SiO_2/Si substrate using radio frequency (r.f.) planar magnetron sputtering in this study. The deposited PZT thin films were almost amorphous before the annealing processes and developed a perovskite structure after the annealing process. If the annealing temperature was too low or annealing time too short, pyrochlore would form. However, if the annealing temperature was too high or annealing time too long, the thin film structure would degrade due to the volatilization of PbO. The significant finding in this experiment is that high quality perovskite PZT thin films on Pt/Ti/SiO_2/Si substrates can be obtained by adjusting the annealing temperature to a range of 650 °C to 850 °C and annealing time to a range from 5 to 80 min. In this experiment, the optimal annealing condition was an annealing temperature of 650 °C and time of 20 min. The properties of PZT thin film annealed at 650 °C for 20 min were dielectric constant _r = 869 free dielectric constant ^T ₃₃ = 893 piezoelectric constant d₃₃ = 2.03p m V^-1 piezoelectric constant g₃₃ = 2.57 x 10^-4 V m N^-1, remanent polarization P₁ = 112.5 nC cm^-2 and coercive field E_c= 0.061 kV cm^-1.     

Structural evaluation of sol-gel derived lead strontium titanate diffusion barrier for integration in lead zirconate titanate transducer design

Sol-gel derived Pb₄₀Sr₆₀TiO₃ (PST) thin film has been investigated as a diffusion barrier for integrating in PbZr₃₀Ti₇₀O₃ (PZT) device structures on Si substrates. PST film was deposited on SiO₂/Si substrate and annealed at a relatively low temperature range of 550-600 °C producing a crack-free, smooth and textured surface. Following deposition on PST/SiO₂/Si template PZT thin film was crystallised exhibiting random grain orientations and an insertion of the bottom Pt/Ti electrode forming PZT/Pt/Ti/PST/SiO₂/Si stacks promoted the preferred PZT (111) perovskite phase. PZT (111) peak intensity gradually decreased along with slight increase of the PZT (110) peak with increasing annealing temperature of the buffer PST film. The dielectric and ferroelectric properties of the PZT with barrier PST deposited at 550 °C were assessed. The dielectric constant and loss factor were estimated as 390 and 0.034 at 100 kHz respectively and the remnant polarisation was 28 µC/cm² at 19 V. The performance of the PZT/PST device structures was compared to similar PZT transducer stacks having widely used barrier TiO₂ layer.