Pt-coated Si Substrates Research Articles

Radio-frequency magnetron sputter-deposited barium hexaferrite films on Pt-coated Si substrates suitable for microwave applications

Hexagonal barium ferrite films were deposited on Si (1 1 1) substrates by radio-frequency magnetron sputter deposition. The films exhibited strong c- axis perpendicular orientation benefiting from a Pt buffer layer. The results include measurements of crystallographic structure, magnetic domain structure, and magnetic and microwave properties for barium hexaferrite films with different thicknesses of Pt underlayers, revealing ferromagnetic resonance linewidths, Δ H = 400–600 Oe at 40–60 GHz. These results provide a viable pathway to realizing miniaturized microwave devices integrated with semiconductor device platforms.

Enhancement of crystallographic and electrical properties in 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 thin films grown on Pb(Zr,Ti)O3-buffered platinized silicon substrates by sol-gel process

We present here a comparative study of sol-gel-derived 0.9Pb(Mg1/3Nb2/3)O3−0.1PbTiO3 (PMNT) thin films about 120 nm in thickness that were, respectively, deposited directly on a platinized Si substrate and on a Pb(Zr,Ti)O3 (PZT)-buffered one, but were both annealed at 750 °C in ambient air. It was found that the PZT buffer layer plays an important role in the enhancement of crystallographic and electrical properties of PMNT thin films. The PMNT film grown on PZT-buffered platinized Si substrate showed a nearly pure perovskite structure, while the film without buffer layer contained a big amount of pyrochlore phase. Also, the PZT buffer layer changed the preferred orientation of PMNT thin films from (111) to mainly (110) orientation, and helped to improve the films' densification and microstructural evolution. Coherent with what was observed comparatively in structural characterization, enhanced dielectric and leakage current characteristics were observed in the film with buffer layer. For the PMNT film grown directly on Pt-coated Si substrate, the dielectric permittivity is as low as 570, whereas the value is enhanced to 1200 for the PMNT film with PZT buffer layer. Moreover, the leakage current density of PMNT thin films is reduced remarkably, roughly 4-5 orders of magnitude lower, by introducing the PZT buffer layer.

Formation of PbTiO3 films from multilayered structures of primitive oxides

The possibility of the formation of PbTiO3 from a multilayer structure of PbO and TiO2 layers on Pt-coated Si substrates prepared by rapid thermal metal organic chemical vapor deposition (RTMOCVD) followed by an appropriate annealing process was examined. The metal organic precursors of PbO and TiO2 were Pb(C2H5)4 and Ti(Oi-C3H7)4, respectively. The composition of the PbTiO3 thin film was adjusted by control of the thickness of each binary oxide layer of PbO and TiO2. The multilayer structure was converted into crystalline PbTiO3 by rapid thermal annealing under O2 ambient at temperature greater than 550 °C. As the annealing temperature was increased from 550 to 750 °C, the peaks related to perovskite PbTiO3 in the XRD patterns became stronger and sharper. From this study, it was confirmed that the crystalline PbTiO3 thin films could be prepared from the interdiffusion reaction of multilayer structure composed of primitive binary oxides through the appropriate post annealing process.

Fabrication of a Highly Sensitive Chemical Sensor Based on ZnO Nanorod Arrays

We report a novel method for fabricating a highly sensitive chemical sensor based on a ZnO nanorod array that is epitaxially grown on a Pt-coated Si substrate, with a top–top electrode configuration. To practically test the device, its O2 and NO2 sensing properties were investigated. The gas sensing properties of this type of device suggest that the approach is promising for the fabrication of sensitive and reliable nanorod chemical sensors.

Process and properties of the carbon nanotube assisted LiCoO2 thin-film battery electrode by pulsed laser deposition

In this study, a pulsed laser deposition process was developed to deposit a carbon nanotube (CNT) assisted LiCoO2 electrode to improve its power density. The electrodes were deposited on Pt-coated Si substrates with Ar and O2 as sputtering gases and LiCoO2+C as the target. The results indicate that the working pressure is the most important parameter to control the composition of the electrode. Therefore, electrodes with a three-layer structure (i.e., LiCoO2-rich/CNT-rich/LiCoO2-rich) were fabricated by a three-step deposition process by varying the pressures from 13 to 1.3×104 Pa and then 13 Pa again, and it was found that the charge/discharge capacity became approximately 1.5 times greater than that in the corresponding electrode without a CNT-rich layer. The results also indicate that a higher substrate temperature is favorable for improving the crystallinity of the electrode to approach LiCoO2 crystals.

The Effects of Growth Temperature on the Field-Emission Properties of ZnO Nanoneedle Arrays

Field-emission properties of ZnO nanoneedle arrays (NNAs) grown on Pt-coated Si (001) substrates by metalorganic chemical vapor deposition at various growth temperatures were investigated. Growth temperature determines the morphology and alignment of NNAs and hence their field-emission properties. The ZnO NNAs grown at 550°C demonstrated better emission properties compared with ones grown at higher temperatures. ZnO NNAs grown at higher temperatures had sharper tips but were relatively less aligned, resulted in inferior field-emission properties. Optimization of the shape and alignment of ZnO nanoneedles is important to obtain better emission properties.

The influence of A-site rare-earth for barium substitution on the chemical structure and ferroelectric properties of BZT thin films

Rare-earth ( RE) doped Ba(Zr,Ti)O 3 (BZT) thin films were prepared by rf-magnetron sputtering from a Ba 0.90 Ln 0.067Zr 0.09Ti 0.91O 3 ( Ln=La, Nd) target. The films were deposited at a substrate temperature of 600 °C in a high oxygen pressure atmosphere. X-ray diffraction (XRD) patterns of RE-BZT films revealed a 〈001〉 epitaxial crystal growth on Nb-doped SrTiO 3, 〈001〉 and 〈011〉 growth on single-crystal Si, and a 〈111〉-preferred orientation on Pt-coated Si substrates. Scanning electron microscopy (SEM) showed uniform growth of the films deposited, along with the presence of crystals of about half-micron size on the film's surface. Transmission electron microscopy (TEM) evidenced high crystalline films with thicknesses of about 100 nm for 30 min of sputtering. Electron-probe microanalysis (EPMA) corroborated the growth rate (3.0–3.5 nm/min) of films deposited on Pt-coated Si substrates. X-ray photoelectron spectroscopy (XPS), in depth profile mode, showed variations in photoelectron Ti 2 p doublet positions at lower energies with spin-orbital distances characteristic of BaTiO 3-based compounds. The XPS analysis revealed that lanthanide ions positioned onto the A-site of the BZT-perovskite structure increasing the MO 6-octahedra distortion ( M=Ti, Zr) and, thereby, modifying the Ti–O binding length. Polarization-electric field hysteresis loops on Ag/ RE-doped BZT/Pt capacitor showed good ferroelectric behavior and higher remanent polarization values than corresponding non-doped system.

Piezoelectric, ferroelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 thin films with compositions around the morphotropic phase boundary prepared by a sol-gel process of reduced thermal budget

Single perovskite polycrystalline Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) thin films with PMN to PT ratios around the morphotropic phase boundary composition (070PMN-0.30PT, 0.65PMN-0.35PT, and 0.60PMN-0.40PT) have been prepared by chemical solution deposition (CSD). Air-stable and precipitate-free PMN and PT precursor sols were separately synthesized, and PMN-PT sols were obtained by the simple mixture in air of the former. The PMN-PT sols were deposited onto Pt-coated Si substrates and dried on a hot-plate. Crystallization of the films was carried out by rapid thermal processing (RTP) in oxygen, using different temperatures, soaking times, and heating rates. Single perovskite PMN-PT thin films were obtained at low temperatures (650 °C) with short soaking times (6s) and rapid heating rates (200 °C/s). The films show a columnar growth and a uniform thickness. Both the evolution of the perovskite distortion and the electrical properties with the PMN to PT ratio indicate the correct formation of the solid solution. The temperature and frequency dependences of the permittivity and the ferroelectric loops also indicate an increase of the relaxor characteristic of the films as compared with bulk materials. Piezoelectric coefficients were measured across the ferroelectric loop by optical interferometry, and an enhancement of piezoelectricity at the MPB composition was found. A piezoelectric d33 coefficient of ∼55 pC/N was measured in ∼300-nm-thick films of this composition with a saturation polarisation of Ps ∼25 μC/cm2.

Switching spectroscopy piezoresponse force microscopy of polycrystalline capacitor structures

Polarization switching in polycrystalline PbZr0.52Ti0.48O3 films on Pt-coated Si substrates was studied by switching spectroscopy piezoresponse force microscopy (SSPFM). Acquisition of multiple hysteresis loops allows polarization switching parameters, including nucleation, coercive biases, and switchable response to be mapped in real space. In contrast to measurements made on the free surface, those on the metal-ferroelectric-metal capacitor structures show the evolution of correlated switching of 102–103 grain clusters with well-defined imprint and nucleation biases. The role of substrate bending on clustering and SSPFM detection mechanisms are discussed. These studies demonstrate real-space imaging of mesoscopic polarization reversal in real-world devices.

Ferroelectric and dielectric properties of SrBi4Ti4O15 thin films grown on Bi4Ti3O12 film layer

Ferroelectric and dielectric properties of bilayered ferroelectric thin films, SrBi4Ti4O15 grown on Bi4Ti3O12, were investigated. The thin films were annealed at 700°C under oxygen atmosphere. The bilayered thin films were prepared on a Pt(111)/Ti/SiO2/Si substrate by a chemical solution deposition method. The dielectric constant and dielectric loss of the bilayered thin films were 645 and 0.09, respectively, at 100 kHz. The value of remnant polarization (2Pr) measured from the ferroelectric thin film capacitors was 60.5 μC/cm2 at electric field of 200 kV/cm. The remnant polarization was reduced by 22% of the initial value after 1010 switching cycles. The results showed that the ferroelectric and dielectric properties of the SrBi4Ti4O15 on Bi4Ti3O12 ferroelectric thin films were better than those of the SrBi4Ti4O15 grown on a Pt-coated Si substrate suggesting that the improved properties may be due to the different nucleation and growth kinetics of SrBi4Ti4O15 on the c-axis-oriented Bi4Ti3O12 layer or on the Pt-coated Si substrate.

Growth and characterization of BLZT–CFO composite thin films

Composite Ba 0.90La 0.067Zr 0.09Ti 0.91O 3–CoFe 2O 4 (BLZT–CFO) thin films were prepared by rf-magnetron sputtering from a 0.68 BLZT–0.32 CFO mixed target at a substrate temperature of 1033 K in a high oxygen pressure atmosphere. Single-crystal conducting Nb-doped (1%) SrTiO 3 and Pt-coated Si substrates were used. X-ray diffraction (XRD) patterns revealed that the films had both BLZT and CFO phases. Scanning electron microscopy (SEM) showed that the CFO phase was intermixed into a BLZT matrix. X-ray photoelectron spectroscopy (XPS) data in depth profile mode showed that all constituent elements were present and confirmed the favourable TiO 6-octahedron distortion in the BLZT-perovskite structure. The Au/BLZT–CFO/substrate capacitors were ferroelectric and magnetic at room temperature. The magnetoelectric nature of the composite thin films was demonstrated through the reduction of measured ferroelectric polarization with the application of an external magnetic field.

Patterned Array of Nanoparticles on Substrates via Contact Printing Method with CNTs/AAO Stamp

Patterned arrays of Fe oxide nanoparticles were transferred via contact printing method on a substrate surface using carbon nanotubes embedded in anodic aluminum oxide (CNTs/AAO) as a stamp, in which vertically aligned CNTs in hexagonally patterned array was first fabricated by chemical vapor deposition into the AAO, followed by a partial chemical etching to expose the CNTs from the AAO. Fe precursor inked CNTs stamp was contact-printed on a Pt-coated Si substrate, and after heat treatment at 200 degrees C, patterned array of Fe oxide nanoparticles with ca. 80 nm of diameter and ca. 120 nm of inter-distance between the nanoparticles was consequently obtained.

An approach to fabricating chemical sensors based on ZnO nanorod arrays

Vertically and laterally aligned ZnO nanorod arrays were synthesized on Pt-coated Sisubstrates by catalyst-free metal organic chemical vapor deposition. An approach tofabricating chemical sensors based on the nanorod arrays using a coating-and-etchingprocess with a photo-resist is reported. Tests of the devices as oxygen gas sensors have beenperformed. Our results demonstrate that the approach holds promise for the realization ofsensitive and reliable nanorod array chemical sensors.

Enhanced piezoelectric response from barium strontium titanate multilayer films

Multilayered and homogeneous thin films of BaxSr1−xTiO3 (BST) were grown on Pt-coated Si substrates via metal-organic solution deposition. The multilayer 220nm thick BST heterostructure consisted of Ba0.60Sr0.40TiO3, Ba0.75Sr0.25TiO3, and Ba0.90Sr0.10TiO3. A single composition 220nm thick Ba0.60Sr0.40TiO3 was also grown for comparison. The piezoelectric properties were measured using piezoresponse force microscopy. There is approximately a 50% improvement in the piezoelectric response of the multilayered heterostructure compared to the homogeneous sample, with some spatial inhomogeneity. This enhancement can be attributed to the internal potential that arises from the polarization gradient and the commensurate built-in strain in the multilayer sample.

Optical properties of Pb(Zr xTi 1− x)O 3 ( x = 0.4, 0.6) thin films on Pt-coated Si substrates studied by spectroscopic ellipsometry

Lead zirconate titanate Pb(Zr x Ti 1− x )O 3 thin films with Zr/Ti ratio 40/60 (PZT40/60) and 60/40 (PZT60/40) were grown on Pt/Ti/SiO 2/Si(1 0 0) substrates by a sol–gel process. Structure, surface morphologies and root mean square (rms) roughness of the thin films were studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). On the surface images of the thin films, many clusters are found, which are composed by grains in size of about 0.5–1 and 0.15–0.2 μm, respectively for the PZT40/60 and PZT60/40 thin films. The rms roughnesses of the PZT40/60 and PZT60/40 thin films are 2.1 and 6.7 nm, respectively. The refractive index n, the extinction coefficient k and thickness of PZT40/60 and PZT60/40 thin films annealed at 600 °C were obtained by spectroscopic ellipsometry as a function of the wavelength in rang from 270 to 1700 nm.

Structural and electrical characterization of xBiScO3–(1−x)BaTiO3 thin films

Using a tolerance factor approach, it was predicted that xBiScO3–(1−x)BaTiO3 will have a morphotropic phase boundary that should enhance both the polarizability and permittivity, relative to the BiScO3 end member, near a composition of x=0.4. To verify this prediction, pulsed laser deposition was used to grow xBiScO3–(1−x)BaTiO3 thin films on (100) SrRuO3∕LaAlO3 and Pt-coated Si substrates. Typical growth conditions were 700°C and 100mTorr O2∕O3. The perovskite structure was found to be stable for compositions of x=0.2–0.6 in epitaxial films, with reduced stability in polycrystalline films. The temperature where the maximum permittivity occurs rises as BiScO3 is added to BaTiO3, and increasingly relaxorlike behavior is observed with increasing BiScO3 content. Room temperature permittivity values ranged from 200 to 400, with loss tangents of ∼0.1 at 10kHz. The experimental morphotropic phase boundary occurs near x=0.4. 0.4BiScO3–0.6BaTiO3 showed a broad permittivity maximum near 800 from 150–275°C. Films with x=0.4 show a coercive field of about 200kV∕cm with a modest room temperature remanent polarization near 8μC∕cm2. The films exhibit a dielectric tunability of greater than 25% at fields of ∼500kV∕cm. The combination of high polarizability and high transition temperature makes this family an interesting base composition for lead-free piezoelectrics, especially if the degree of relaxor character could be reduced.

Strains in BaTiO3 thin film deposited onto Pt-coated Si substrate

The ferroelectric-paraelectric phase transition was investigated in BaTiO3 100nm thick film deposited on platinized Si substrate by measuring the lattice parameters as a function of temperature and the hysteresis loop at room temperature. The transition from paraelectric to ferroelectric phase takes place at ∼420K (instead of 400K for unconstrained single crystals), whereas the film is under high tensile elastic in-plane strain (0.34%) and high inhomogeneous strain (0.69%) along the growth direction. Comparison of the experimental results with recent theoretical calculations suggests a monoclinic ferroelectric phase at room temperature, where interface “dead layer” plays a key role.

Optical properties of Pb(Zr 0.53Ti 0.47)O 3 thin films on Pt-coated Si substrates measured by spectroscopic ellipsometry in the UV–vis–NIR region

Pb(Zr 0.53Ti 0.47)O 3 (PZT) thin films grown on Pt-coated Si substrates were prepared by a sol–gel process. Crystalline structure characterisation and optical constants (refractive index n, extinction coefficient k) and bandgaps E g of PZT thin films annealed at 550, 600 and 650 °C were obtained by X-ray diffraction (XRD) and spectroscopic ellipsometry (SE) in the UV–vis and near-infrared range of 235–1700 nm. A four-phase fitting model was employed to describe the optical properties of the PZT thin films; the spectra of their optical constants and the bandgap energy E g were determined by means of optimisation. The refractive index n, absorption coefficient α and bandgaps E g of crystalline PZT thin films on Pt-coated Si substrates annealed at 550–650 °C are lager than that of pure PbZrO 3 and PbTiO 3 thin films. In addition, the refractive index dispersion data related to the structure of the films agreed well with Cauchy dispersion relationship. The dependencies of the refractive index, the extinction coefficient and the optical bandgap energy on annealing temperature were analysed.

Chemical solution deposited silver tantalate niobate, Ag x (Ta0.5Nb0.5)O3−y , thin films on (111)Pt/Ti/SiO2/(100)Si substrates

Silver tantalate niobate films are candidates for temperature stable microwave dielectrics. In this work, a chemical solution deposition synthesis method was developed for Ag x (Ta0.5Nb0.5)O3−y films on Pt-coated Si substrates. Stable solutions with a range of silver stoichiometries were prepared using 2-methoxyethanol and pyridine as solvents, from AgNO3 and Nb and Ta ethoxide precursors. It was extremely difficult to prepare phase-pure perovskite films of Ag(Ta0.5Nb0.5)O3 on Pt-coated Si subtrates; instead a mixture of perovskite and natrotantite phases was identified. Such mixed phase films had dielectric constant ɛ r and dielectric loss tanδ values ranging from 200±20 to 270±25 and 0.006±0.002 to 0.002±0.001 at 100 kHz, respectively, depending on the firing temperature. For Ag2(Ta0.5Nb0.5)4O11, Ag0.8(Ta0.5Nb0.5)O2.9, Ag0.85(Ta0.5Nb0.5)O2.925 and Ag0.9(Ta0.5Nb0.5)O2.95 films, mainly the natrotantite phase was observed. The ɛ r values of these films were between 70±10 and 130±15 with tan δ values of 0.008±0.002 at 100 kHz.

Barium titanate nanocrystals and nanocrystal thin films: Synthesis, ferroelectricity, and dielectric properties

Advanced applications for high k dielectric and ferroelectric materials in the electronics industry continues to demand an understanding of the underlying physics in decreasing dimensions into the nanoscale. We report the synthesis, processing, and electrical characterization of thin (<100nm thick) nanostructured thin films of barium titanate (BaTiO3) built from uniform nanoparticles (<20nm in diameter). We introduce a form of processing as a step toward the ability to prepare textured films based on assembly of nanoparticles. Essential to this approach is an understanding of the nanoparticle as a building block, combined with an ability to integrate them into thin films that have uniform and characteristic electrical properties. Our method offers a versatile means of preparing BaTiO3 nanocrystals, which can be used as a basis for micropatterned or continuous BaTiO3 nanocrystal thin films. We observe the BaTiO3 nanocrystals crystallize with evidence of tetragonality. We investigated the preparation of well-isolated BaTiO3 nanocrystals smaller than 10nm with control over aggregation and crystal densities on various substrates such as Si, Si∕SiO2, Si3N4∕Si, and Pt-coated Si substrates. BaTiO3 nanocrystal thin films were then prepared, resulting in films with a uniform nanocrystalline grain texture. Electric field dependent polarization measurements show spontaneous polarization and hysteresis, indicating ferroelectric behavior for the BaTiO3 nanocrystalline films with grain sizes in the range of 10–30nm. Dielectric measurements of the films show dielectic constants in the range of 85–90 over the 1KHz–100KHz, with low loss. We present nanocrystals as initial building blocks for the preparation of thin films which exhibit highly uniform nanostructured texture and grain sizes.