Lead Strontium Titanate Thin Films Research Articles

Polymer‐based route to ferroelectric lead strontium titanate thin films

ABSTRACTCeramic films with high values of ferroelectricity, piezoelectricity, and dielectricity with perovskite structure, like lead zirconate titanate (PZT, PbZrxTi1‐xO3), lead strontium titanate (PST, PbxSr1‐xTiO3), and barium strontium titanate (BST, BaxSr1−xTiO3), are subjects of intensive research due to their use in sensors, energy harvesters, capacitors, and FeRAMs. Here a novel, simple way to produce micropatterned perovskite PST thin films on silicon substrates by a polymer‐based direct UV‐lithography process is presented. By acrylic acid modification of PST precursor sols it is possible to generate photosensitive metal organic PST precursor xerogel films by spin‐coating and subsequently drying on silicon wafers. These films can be patterned by UV‐lithography and developed with organic solvents. The resulting patterned gel films can be crystallized in air via rapid thermal annealing. The obtained perovskite thin ceramic films are polycrystalline and fine grained. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40901.

Crystallographic orientation dependence of dielectric response in lead strontium titanate thin films

This investigation presents the growth of (100), (110) and preferential (111)-oriented Pb0.6Sr0.4TiO3 thin films prepared on different orientations LaNiO3 buffered silicon substrates via radio-frequency magnetron sputtering method. The effects of the orientation on microstructure and dielectric response were systematically investigated. The capacitance–voltage property versus the crystallographic orientation analysis revealed that preferential (111)-orientation film possesses the largest relative permittivity and tunability of 1180 and 84% (at 400kV/cm) respectively, which are much higher than those of (100)- and (110)-oriented thin films. These results suggest preferential (111)-orientation films as promising candidates for microwave tunable devices.

Low Temperature Deposition of High Performance Lead Strontium Titanate Thin Films by in situ RF Magnetron Sputtering

Highly (100) oriented lead strontium titanate (Pb0.4Sr0.6TiO3) thin films were deposited on LaNiO3 ‐coated Si substrate via radio‐frequency magnetron sputtering method with substrate temperature ranging from 300 to 500°C. The PST thin films were crystallized at a temperature as low as 300°C, which may result from the well‐controlled stoichiometry and the in situ crystallization on seed layer. At an electric field of 400 kV/cm, high tunability of 43% and 57% can be achieved for PST films deposited at 300°C and 500°C, respectively. Moreover, the dielectric response shows weak frequency dependence and the loss factor stays relatively low. The results suggest that such films should be promising candidate for the microwave tunable devices compatible with the current Si technology.

Effects of Fast Neutrons on the Electromechanical Properties of Materials Used in Microsystems

Microelectromechanical systems (MEMS) technology is expected to play a significant role in avionics and in future space missions provided that the effect of radiation on the reliability of MEMS devices is well understood. Most tests, to date, have been performed on MEMS that operate based on electrostatic principles, and radiation-induced dielectric charging has been identified as a mechanism which can potentially limit the reliability of such devices. Experiments with piezoresistive and piezoelectrically actuated MEMS have also revealed changes in the operation of devices after exposure to different types of ionizing radiation. However, not many reports on the damage effects in MEMS due to fast neutrons exist. In this paper, we present results from mechanical and electrical tests on different materials which are typically used in microsystems, before and after exposure to fast neutrons. Changes were detected in the residual stress and in the resonant frequencies of silicon nitride microbeams. There was also evidence of radiation-induced charge trapping in metal-insulator-semiconductor capacitors fabricated from thermal oxide, silicon nitride, and aluminum oxide deposited by atomic layer deposition. Finally, we observed that the electrical properties of ferroelectric capacitors fabricated from lead zirconate titanate and lead strontium titanate thin films do not degrade after exposure to fast neutrons.

Effect of biphase on dielectric properties of Bi-doped lead strontium titanate thin films

Pb 0.4Sr 0.6TiO 3 (PST) thin films doped with various concentration of Bi were prepared by a sol–gel method. The phase status, surface morphology and dielectric properties of these thin films were measured by X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance analyzer, respectively. Results showed that the thin films with the maximum dielectric constant and minimum dielectric loss were obtained for x=0.15. For x<0.15, only pure PST perovskite phase were in the thin films. For 0.2< x<0.4, the PST/Bi 2Ti 2O 7 biphase were obtained. The thin films with pure Bi 2Ti 2O 7 pyrochlore phase were obtained for x=0.67. The biphase thin films had high tunability and high figure of merit (FOM). The FOM of PST/Bi 2Ti 2O 7 biphase thin film was about 6 times higher than that thin films formed with pure perovskite phase or pure pyrochlore phase.

High tunability of lead strontium titanate thin films using a conductive LaNiO3 as electrodes

Highly tunable films of dielectric PbxSr1−xTiO3 (with x=0.3 and 0.4) have been deposited on conductive LaNiO3 coated LaAlO3 substrates using a sol-gel technique. The processing condition was found to greatly influence the microstructure as well as the dielectric and electrical properties of the films. At room temperature, dielectric tunability values as high as 70% and 78.6% at an applied electric field of 223kV∕cm were achieved for the Pb0.3Sr0.7TiO3 and Pb0.4Sr0.6TiO3 films, respectively.

Structural and Electrical Investigations of Ferroelectric Lead Strontium Titanate Thin Films and Ceramics

ABSTRACTLead strontium titanate (PbxSr1-xTiO3) (x=0.3–1.0) ceramic targets were prepared by the conventional powder-processing method. Thin films of these compositions were deposited on platinized silicon substrates by pulsed laser deposition technique. X-ray diffraction studies of the ceramic targets showed that the lattice structure changes from tetragonal to cubic phase with the increase of Sr content in PbTiO3. Raman spectroscopic studies of PbxSr1-xTiO3(PST) ceramics and thin films showed that the soft mode decreases to lower frequency and finally disappear at around 60–70 at% Sr content, which confirms the tetragonal to cubic phase transition at room temperature. Dielectric constant measured for PST thin films was in the range of 900–1500 at 1 MHz, with maximum value obtained for PST30 thin film. The loss tangents at room temperature were in the range of 0.07–0.1 for PST thin films with different compositions.

Synthesis and characterization of lead strontium titanate thin films by sol–gel technique

A series of strontium doped lead titanate (Pb x Sr 1− x TiO 3) thin films were deposited on platinized silicon substrates by sol–gel technique and were characterized for their phase purity, surface morphology, dielectric and leakage current characteristics. The grain size of lead titanate thin films was systematically reduced with the increase in strontium content. With the addition of 50 at.% strontium doping, at room temperature, cubic perovskite phase was stabilized in lead titanate thin film. The measured dielectric constant decreased with the increase of strontium content of Pb x Sr 1− x TiO 3 thin films. The leakage current densities of PT thin films were systematically reduced with the increase in strontium content. The high dielectric constant, low loss tangent and leakage current densities of cubic PST thin films could be attractive combinations for these films to be used in dynamic random access memories (DRAM).