Search

SrTiO3 (STO) thin films were grown simultaneously via the metal organic chemical vapor deposition (MOCVD) technique on two different substrates: platinized sapphire and platinized TiO2/SiO2/Si. The thin films were analyzed for stoichiometry, crystallinity, surface roughness, and average grain size. Dielectric properties of the thin films such as dielectric constant, loss, and leakage current characteristics were measured and compared. We demonstrate that the MOCVD technique is an appropriate method for fabrication of STO thin films with excellent structural, microstructural, dielectric, and insulation properties. Comparative analysis of the films yielded an unexpected result that the thin film with a higher mismatch in thermal expansion coefficient between the substrate (Si) and the deposited STO film yielded a higher dielectric constant with respect to that of STO/sapphire. The dielectric loss for both films were similar (tan δ = 0.005 at 100 kHz), however, the leakage current for the film with a higher dielectric constant was three orders of magnitude higher. An explanation of these results is presented and discussed. [ABSTRACT FROM AUTHOR]

There has been significant progress on the fundamental science and technological applications of complex oxides and multiferroics. Among complex oxide thin films, barium strontium titanate (BST) has become the material of choice for room-temperature-based voltage-tunable dielectric thin films, due to its large dielectric tunability and low microwave loss at room temperature. BST thin film varactor technology based reconfigurable radio frequency (RF)/microwave components have been demonstrated with the potential to lower the size, weight, and power needs of a future generation of communication and radar systems. Low-power multiferroic devices have also been recently demonstrated. Strong magneto-electric coupling has also been demonstrated in different multiferroic heterostructures, which show giant voltage control of the ferromagnetic resonance frequency of more than two octaves. This manuscript reviews recent advances in the processing, and application development for the complex oxides and multiferroics, with the focus on voltage tunable RF/microwave components. The over-arching goal of this review is to provide a synopsis of the current state-of the-art of complex oxide and multiferroic thin film materials and devices, identify technical issues and technical challenges that need to be overcome for successful insertion of the technology for both military and commercial applications, and provide mitigation strategies to address these technical challenges. [ABSTRACT FROM AUTHOR]

Isothermal (700 °C) ultraviolet annealing (UVA) processing of crystallized Ba0.60Sr0.40TiO3 (BST) thin films for exposure times up to 225 min films has been studied. The BST films, grown on PtSi wafers via the metalorganic solution deposition (MOSD) technique, were crystallized via conventional furnace annealing (CFA) prior to UVA treatment, and the effects of UV annealing time on the structural, dielectric, and insulation properties were evaluated. The experimental results demonstrated significantly improved structural, dielectric, and insulation properties for the UVA films. Specifically, lattice parameter contraction (toward that of bulk BST60/40) and a 20% reduction in loss were observed for the UVA treated films with respect to the CFA/control film. Leakage current characteristics were found to be the most sensitive characterization technique to access material property modification as a result of UVA exposure time. Specifically, the 225 min UVA exposure time resulted in a three-order of magnitude reduction in leakage current density compared to the CFA film, and the lowest value observed was 1.06 × 10-7 A/cm2 at E = 300 kV/cm. The useable tunability (tunability value at the maximum acceptable leakage current, 500 pA) was found to be elevated by a factor of two with respect to that of the CFA/control BST film (52.31%/UVA film vs. 18.5%/control film). It is suggested that the improved material properties are due to the mitigation of unwanted oxygen vacancies within the film after UV-annealing. A mechanistic model is presented and discussed. [ABSTRACT FROM AUTHOR]

A nonlinear thermodynamic model is used to investigate the influence of thermal stresses on the room temperature (RT) pyroelectric properties of (001)-textured polycrystalline barium strontium titanate (BaxSr1-xTiO3, BST) films with four different compositions on three integrated circuit-friendly substrates: Si, (0001) and (1120) sapphire. It is found that the in-plane tensile thermal strain in BST increases with increasing deposition/processing temperature TG due to the difference of thermal expansion coefficients between the BST film and the selected substrate materials. Considering the variations in the ferroelectric phase transformation due to thermal strains, our findings show that relatively lower processing temperatures would result in better pyroelectric response. For BST 60/40 and 70/30 on all the substrates, the film is in the paraelectric state for TG=25-800 °C and the pyroelectric response is due to the interplay of the electric field and thermal strain dependence of the dielectric constant and the TG-dependence of the thermal strains. While the RT pyroelectric response of these films is expected to be relatively low (0.02-0.05 μC/cm2 K at ∼200 kV/cm), at high applied fields the pyroelectric properties do not display a significant dependence on the temperature at which the material was treated. On the other hand, BST 80/20 and BST 90/10 films may be in the ferroelectric state at RT depending on TG. If TG can be adjusted such that the ferroelectric phase transformation is near RT, a relatively high bulklike pyroelectric response (>0.5-1.0 μC/cm2 K) can be realized. However, the pyroelectric coefficient decreases sharply above and below these 'critical' TG, and thus a precise temperature control during processing would be required. [ABSTRACT FROM AUTHOR]

A thermodynamic model was developed to analyze the effect of the difference in the thermal expansion coefficient (TEC) of a multilayered barium strontium titanate Ba1-ySryTiO3 (BST) ferroelectric heterostructure and a passive substrate on the dielectric properties by taking into account electrostatic and electromechanical interactions between the ferroelectric layers. Results show that the dielectric constant and tunability can be maximized by minimizing the TEC mismatch. Furthermore, lower processing temperatures lead to lower thermal strains and thus to better dielectric properties. We also provide a numerical analysis describing the effect of thermal strains on dielectric properties of a compositionally graded trilayer consisting of BST 60/40, BST 75/25, and BST 90/10 on a variety of substrates including Si, sapphire (α-Al2O3), SrTiO3, MgO, and LaAlO3. The multilayer BST heterostructure on Si is expected to experience high in-plane tensile strains due to the large TEC mismatch, resulting in dielectric permittivities and tunabilities lower compared to the same multilayer on SrTiO3 or LaAlO3 for which there is a better TEC match. For BST multilayers on MgO, SrTiO3, Si, and sapphire, higher processing temperatures lead to lower dielectric response and tunability. [ABSTRACT FROM AUTHOR]

Compositionally layered BaxSr1-xTiO3 (Ba0.60Sr0.40TiO3–Ba0.75Sr0.25TiO3–Ba0.90Sr0.10TiO3) 220 nm thin film heterostructures were fabricated on Pt coated high resistivity Si substrates via the metal organic solution deposition technique (MOSD). Optimization of the material design was achieved by evaluating two integration schemes, namely, the single- and multianneal process protocols. Materials characterization demonstrated that both film process protocols resulted in smooth, dense, crack-free films with a single phase perovskite structure. Rutherford backscattering spectroscopy revealed compositionally distinct layers and severe elemental interdiffusion for the films fabricated via the multianneal and single-anneal process protocols, respectively. The retention of the compositional layering subsequent to film crystallization deemed the multianneal processed BaxSr1-xTiO3 (BST) film suitable for evaluation of dielectric properties. The dielectric properties were compared to both paraelectric uniform composition BST and to the relevant compositionally graded BST films reported in the technical literature. Our results made evident that the multiannealed compositionally layered BST films possessed higher permittivity ([variant_greek_epsilon]r=360) and lower dissipation factor (tan δ=0.012) with respect to both uniform composition paraelectric Ba0.60Sr0.40TiO3 film fabricated via the same MOSD processing method and the relevant literature values for compositionally graded BST films. The multilayered BST material design exhibited minimal dielectric dispersion in the range of 90 to -10 °C, showing a 6.4% decrease in permittivity (corresponding to a temperature coefficient of capacitance TCC20–90=-0.921) as the temperature was elevated from 20 to 90 °C and only a 2.1 increase in permittivity (TCC20–(-10)=-0.716) as the temperature was lowered from 20 to -10 °C. Additionally, the dielectric tunability of the multilayered BST structures over the temperature range of -10–90 °C was temperature independent. Our results show that the multilayered BST design has excellent dielectric properties and the enhanced tunability and dielectric loss are stable over a relatively broad temperature range (-10–90 °C), thereby making them excellent candidates for the next generation of enhanced performance temperature stable tunable devices. [ABSTRACT FROM AUTHOR]

Integration of Ba1-xSrxTiO3- (BST) based thin films with affordable Si substrates has a potentially significant commercial impact as the demand for high-frequency tunable devices intensifies. Utilizing a coplanar device design we have monolithically integrated, optimized, and fabricated a high-performance composite bilayer heterostructure, Si/Ta2O5/BST, whereby the base layer film Ta2O5 serves as a passive buffer layer to allow integration of BST active thin films with affordable Si substrates. Optimization of this design configuration was achieved by evaluating two heterostructure processing protocols: (1) a single-anneal and (2) a dual-anneal process protocol. The reliability susceptibility, i.e., the nonabrupt defect-laden bilayer film interface, of the single-anneal protocol deemed it inappropriate for the fabrication of this monolithic heterostructure design. In contrast, the defect-free, structurally abrupt bilayer and buffer layer film-substrate interfaces suggest the dual anneal process to be an excellent method for realizing monolithic integration of BST with affordable Si substrates. This work suggests that the coefficient of thermal expansion mismatch between the Ta2O5 buffer and the BST thin films in the coplanar device design serves to enhance the dielectric tunability of the device. Realization of this materials integration technology serves to promote broadscale implementation of affordable tunable microwave devices across a variety of advanced communications platforms. [ABSTRACT FROM AUTHOR]

Low dielectric loss in conjunction with high tunability are simultaneous requirements for tunable device applications which have proved problematic to achieve. In this work, material compositional design and optimized film processing methods were employed to simultaneously lower the dielectric loss and enhance the dielectric tunability of Ba[sub 0.6]Sr[sub 0.4]TiO[sub 3] (BST) based thin films without compromising the device impedance matching ([variant_greek_epsilon][sub r]<500) and control voltage (<10 V) requirements. The films compositional design was achieved by Mg doping BST from 3 to 10 mol %. The Mg doped thin films were fabricated via the metalorganic solution deposition technique using carboxylate-alkoxide precursors and postdeposition annealing in an oxygen ambience at 750 °C for 60 min. The films dielectric loss at these doping levels was identical, tan δ∼0.007. In contrast, the films permittivity (339–220), leakage current density (2.55×10[sup -8]–2.43×10[sup -9] A/cm[sup 2]), tunability (21.3%–5.7%), and grain size (75.2–61.55 nm) were observed to decrease with increasing Mg concentration levels from 3 to 10 mol %, respectively. Device quality values of tunability, 40% and 32%, for the 3 and 7 mol % doped BST films, respectively, were achieved by elevating the applied bias from 237 to 474 kV/cm. This device quality tuning is compatible with voltage requirements of current semiconductor based systems. Our results suggest that the low level acceptor doping from 3 to 7 mol %, optimized precursor solution concentration (0.43 M), and oxygenated postdeposition thermal processing were found to work in concert to lower dielectric loss, limit defect density concentration, optimize film microstructure, and eliminate undesirable film/electrode interfacial phases. As a result, high quality BST thin films, with their resultant high breakdown fields, were realized. It is the excellent film quality... [ABSTRACT FROM AUTHOR]

Successful integration of Ba[sub 1-x]Sr[sub x]TiO[sub 3] (BST) based thin films with affordable Si substrates has a potential significant commercial impact as the demand for high-frequency tunable devices intensifies. This work evaluates the material properties of postdeposition annealed Ta[sub 2]O[sub 5] thin films fabricated via the metalorganic solution technique for use as a passive buffer layer between BST and Si. The microstructure, surface morphology, and interfacial properties of the Ta[sub 2]O[sub 5] film deposited on n [sup +]-Si and PtSi substrates was evaluated via field-emission scanning electron microscopy, Rutherford backscattering spectrometry, Auger electron spectroscopy, and atomic force microscopy. The presence of a transition interaction zone between the Ta[sub 2]O[sub 5] film and Si substrate was detected after annealing at temperatures >600 °C. The width of the interaction zone increased with increasing annealing temperature reaching a maximum of 29 nm at 750 °C. The width of the interaction zone was also found to be dependent on the Ta[sub 2]O[sub 5] film microstructure. The Ta[sub 2]O[sub 5] film was typified by a smooth; fine grain, crack/pinhole free surface morphology. The presence of the interfacial layer had no appreciable effect on the microstructure of the film or surface morphology. The narrowness of the interaction zone with respect to the overall film thickness combined with the fact that the interfacial layer did not seriously deteriorate the dielectric properties of the Ta[sub 2]O[sub 5] film suggests Ta[sub 2]O[sub 5] to be a favorable candidate buffer layer enabling the integration of BST with Si substrates. [ABSTRACT FROM AUTHOR]

The influence of low concentration (1 mol %) Mg doping on the structural, microstructural, surface morphological, and dielectric properties of Ba[sub 1-χ]Sr[sub χ]TiO[sub 3] (BST) thin films has been measured and analyzed. The films were fabricated on MgO and Pt-Si substrates via the metalorganic solution deposition technique using carboxylate-alkoxide precursors and postdeposition annealed at 800 °C (film/MgO substrates) and 750 °C (film/Pt-Si substrates). The structure, microstructure, surface morphology, and film/substrate compositional quality were analyzed by glancing angle x-ray diffraction, field emission scanning microscopy, atomic force microscopy, and Auger electron spectroscopy studies. Dielectric properties of unpatterned films were measured at 10 GHz using a coupled, tuned split dielectric resonator system, and at 100 kHz using metal-insulator-metal capacitors. The Mg-doped BST films exhibited improved dielectric and insulating properties compared to the undoped Ba[sub 0.6]Sr[sub 0.4]TiO[sub 3] thin films. The improved dielectric properties, low leakage current, and good dielectric tunability of the low level Mg-doped BST thin films merits strong potential for utilization in tunable microwave devices. [ABSTRACT FROM AUTHOR]

Pt/Ti/WSi/Ni ohmic contacts to n-SiC, initially annealed at 950 and 1000 °C for 30 s, were evaluated for thermal stability via pulsed/cyclic thermal fatigue and aging experiments at 650 °C. Modifications of material properties in response to cyclic thermal fatigue and aging tests were quantitatively assessed via current–voltage measurements, field emission scanning microscopy, atomic force microscopy, and Rutherford backscattering spectrometry. Negligible changes in the electrical properties, microstructure, and surface morphology/roughness were observed for both annealed ohmic contacts in response to 100 cycles of acute cyclic thermal fatigue. Aging of the 950 °C annealed contact for 75 h at 650 °C resulted in electrical failure and chemical interdiffusion/reaction between the contact and SiC substrate. The 1000 °C annealed contact retained ohmicity after 100 h of aging and was found to be chemically and microstructurally stable. These findings indicate that the 1000 °C annealed Pt/Ti/WSi/Ni ohmic contact to n-SiC is thermally stable and merits strong potential for utilization in high temperature and pulsed power devices. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Pure and La doped Ba[sub 0.6]Sr[sub 0.4]TiO[sub 3] thin (BST) films were fabricated via the metalorganic solution deposition technique using carboxylate-alkoxide precursors on Pt-Si substrates. The La doping concentration, from 0 to 10 mol %, was found to have a strong influence on the 750 °C postdeposition annealed films material properties. All Reviews the book ' ontextured polycrystalline microstructure with no evidence of secondary phase formation. The pure and 1 mol % La doped films exhibited a uniform microstructure suggestive of a fully developed film at this annealing temperature. Improved dielectric and insulating properties were achieved for the 1 mol % La doped BST thin films with respect to that of undoped BST films. The 1 mol % La doped BST film exhibited a lower dielectric constant, (283 vs 450) and enhanced resistivity (31.4x10[sup 13] Ω cm vs 0.04x10[sup 13] Ω cm) with respect to that of undoped BST films. The loss tangent and tunability ! (at 100 kHz) of the 1 mol % La doped BST films were 0.019% and 21% (at E=300 kV/cm), respectively. Films doped at concentrations between 5 and 10 mol % possessed under developed microstructures suggesting that higher annealing temperatures and/or longer annealing times are required. The single phase structure of the 5-10 mol % La doped BST films, combined with the beneficial influence of the 1 mol % La doping on the BST films dielectric and insulating properties, suggest potential for further enhancement of the films material properties after optimization of the thermal treatments for the 5-10 mol % La doped BST thin films. Pure and La doped Ba[sub 0.6]Sr[sub 0.4]TiO[sub 3] thin (BST) films were fabricated via the metalorganic solution deposition technique using carboxylate-alkoxide precursors on Pt-Si substrates. The La doping concentration, from 0 to 10 mol %, was found to have a strong influence on the 750 °C postdeposition annealed films material properties. All film! s possessed a... [ABSTRACT FROM AUTHOR]

Presents the results of a surface modification study of InGaP etched with an electron cyclotron resonance source at variable microwave powers. Background to the study; Experimental details; Results and discussion.

Features a study that examined the residual damage incurred to gallium arsenide via etching with a chlorine/argon plasma generated by an electron cyclotron resonance source. Discussion on plasma based etching tools which are critical to the fabrication of submicron scale devices; Information on dry etching techniques; Details of a diagram showing the influence of ion energy on unannealed contact resistance and etch induced damage.

Presents a study which examined the elemental diffusion, interfacial microstructure and phase composition of platinum-titanium-germanium-palladium ohmic contacts. Details on the experiment; Information on the Auger electron spectroscopy depth profile for the as-deposited contact; AES depth profile for the annealed contact.

Presents information on a study which determined the thickness and composition of molecular beam epitaxy grown in a superlattice structure with nominal indium concentrations by transmission electron microscopy. Background of the study; Methodology of the study; Results and discussion.

Deals with a study which examined the microstructure and electrical properties of nonalloyed epitaxial gold-germanium contacts. Information on ohmic contacts; Methodology of the study; Results and discussion.

A review of the temperature stability issues associated with BaxSr1−xTiO3(BST) thin films and a summary of innovative materials designs, and novel process science solutions which serve to help mitigate this temperature sensitivity is presented. The experimental results from the literature and from our own work are reviewed; the correspondence between the theoretical results and the measured properties of tunable materials is critically analyzed; and reasons for discrepancy between literature results are discussed. Particular emphasis is concentrated on tunable phase shifters and filters to enable phased array antennas, radars and other advanced communications devices. This critical review provides the foundation to spawn new materials research solutions to further enable the development of BST films for microwave device applications. [ABSTRACT FROM PUBLISHER]

We develop a nonlinear thermodynamic model for multilayer ferroelectric heterostructures that takes into account electrostatic and electromechanical interactions between layers. We concentrate on the effect of relative layer fractions and in-plane thermal stresses on dielectric properties of Ba0.6Sr0.4TiO3-, BaTiO3-, and PbZr0.2Ti0.8O3 (PZT)-SrTiO3 (STO) multilayers on Si and c-sapphire. We show that dielectric properties of such multilayers can be significantly enhanced by tailoring the growth/processing temperature and the STO layer fraction. Our computations show that large tunabilities (∼90% at 400 kV/cm) are possible in carefully designed barium strontium titanate-STO and PZT-STO even on Si for which there exist substantially large in-plane strains. [ABSTRACT FROM AUTHOR]

Using microwave reflection spectroscopy, the complex permittivities of etch defined, 240 nm thick, (Ba0.6Sr0.4)TiO3, thin films have been measured over the frequency range of (1 to 4) GHz. Anomalous electric-field-induced electro-acoustic resonances were observed and characterized as a function of extrinsic electric field magnitude, ambient temperature, and sample diameter. The real and imaginary parts of the measured permittivities were fit to frequency-dependent functions derived from the Lorentz oscillator model. From these functions, extracted static dielectric constants were found to display excellent agreement with a closed-form expression derived by calculating third-order nonlinear susceptibility from the Landau-Devonshire-Ginzberg model. [ABSTRACT FROM AUTHOR]

We report the growth of a compositionally stratified BaxSr1-xTiO3 (BST) thin film on MgO by metal organic chemical vapor deposition (MOCVD). Real-time control of the precursor flux based on UV absorption spectroscopy was used to systematically vary the ratio of Ba:Sr during deposition. The composition of the film with depth was measured by Rutherford backscattering spectroscopy, and x was found to decrease from 0.87 at the film-air interface to 0.43 near the film-MgO interface. [ABSTRACT FROM AUTHOR]

This paper describes an MOCVD technique for producing both monolithic and compositionally graded BaxSr1-xTiO3 (BST) thin films for tunable RF device applications. Specifically, we describe a 'multiple injection flash evaporation' technique, which can easily produce BST thin films with a wide variety of compositional grading and dopant profiles. Preliminary results show the films to have excellent voltage standoff properties and tunability of dielectric permittivity. These materials are presently being used in the development of tunable RF filters for communication and radar applications. [ABSTRACT FROM AUTHOR]

SrTiO3 films were deposited using metallo-organic solution deposition with different precursor solution molarities. The films were characterized via X-Ray diffraction and field emission scanning electron microscopy. The dielectric constant, loss tangent, tunability, and leakage current were measured as a function of electric field, frequency, and temperature. The film deposited with a lower precursor solution molarity solution had a larger permittivity and tunability, but it also had higher loss tangent and leakage current density. The internal stresses in the films are almost completely relaxed, and this is the main reason for the large, bulk-like dielectric constant in these films. [ABSTRACT FROM AUTHOR]

We report on an innovative isothermal post-growth/crystallization process that utilizes ultraviolet (UV)-photon irradiation. We fabricated Ba1-xSrxTiO3 (BST) thin films using metalorganic solution deposition (MOSD) and UV-photon irradiation isothermal treatment via two protocols: in situ crystallized UV-photon irradiated films, and post-crystallization UV-photon irradiated films. Isothermal UV-photon irradiation treatment improves the structural quality of the BST films, and the irradiated films possessed lattice parameters close to the bulk values, which is evidence for a reduction in oxygen vacancies. MOSD fabricated BST films crystallized via conventionally furnace annealing and subsequently exposed to UV-photon irradiation possessed improved structural, dielectric, and electrical quality. [ABSTRACT FROM AUTHOR]

We present the correlation between film fabrication conditions (crystallization temperatures), microstructure, and dielectric phase shift of Ba1-xSrxTiO3 (BST) thin films synthesized by metal organic solution deposition (MOSD) on sapphire substrates. The structure, microstructure, surface morphology, and composition of the films were assessed by glancing angle X-ray diffraction (GAXRD), atomic force microscopy (AFM), and Rutherford backscattering spectroscopy (RBS). The dielectric phase shift measurements were carried out using coplanar waveguide (CPW) test circuits over a frequency range of 2-18 GHz. Our results indicate that BST processed at 950°C achieved large relative phase shift response with low attenuation of the microwave signal. [ABSTRACT FROM AUTHOR]

The residual stress and morphology of Pt electrodes were investigated using Ti and titanium oxide (TiOx) adhesion layers. Conventional or rapid thermal annealing (RTA) was used to compare the morphologies. The morphology depended on the substrate, adhesion layer, and annealing conditions, with large hillocks formed for electrodes incorporating Ti on Si. Electrode stacks utilizing TiOx adhesion layers resulted in residual stresses that were ∼50% less than those with Ti. Ba0.60Sr0.40TiO3 (BST) thin films were deposited onto several electrodes to investigate the integrity of the electrode/film heterostructures. Delamination or roughening of the film was observed depending on the adhesion layer. [ABSTRACT FROM AUTHOR]

The premier candidate active material for tunable microwave phase shifter devices is single composition, paraelectric BaSrTiO3 (BST). However, there is concern that in practical applications the device performance will be compromised due to the temperature dependence of the BST based device capacitance. We report a device design which controls the magnitude and the sign of the temperature coefficient of capacitance (TCC) via a multilayer paraelectric BST/buffer layer/ferroelectric BST coplanar device structure. To realize this multilayer device structure we have designed, fabricated, and optimized a 10 mol% Al doped Ta2O5 barrier layer with low loss (tan δ = 0.004), moderate permittivity (εr = 42.8), low TCC (-20 ppm/°C), and a low bias stability of capacitance (0.4%). The thin film integration of the barrier layer with the BST layers was optimized for structure, microstructure, interfacial/surface morphology, and dielectric properties as a function of Al doping concentration, annealing temperature, material growth and integration process parameters. [ABSTRACT FROM AUTHOR]

The Army's Future Force (FF) antennas require increased bandwidth for multimission communications; increased antenna gain for robust communications and range extension; increased mobility for high data rate on-the-move (OTM) communications; and undetectable antenna visual signatures for low probably of mission detection and increased survivability. Electronic scanning antennas (ESA's) are the key components for such advanced communication systems. ESA's provide rapid scanning capability, which enables modes such as multiple target tracking, track while scan, and sensor fusion operation. One of the major challenges, which must be overcome before such advanced ESA systems can be realized, is the development of affordable, low loss, high tunability, low power, lightweight, and high performance microwave frequency phase shifters. The enabling technology for such phase shifters is centered on the development of single-phase nanometer-scale constituent perovskite oxide thin films with enhanced dielectric, insulating, and microstructural properties. The Army Research Laboratory (ARL) has successfully designed, fabricated, characterized, and optimized, novel pure and acceptor doped Ba0.6Sr0.4TiO3 (BST) based thin films on MgO substrates with excellent microwave material properties. Pure and 1-mol% Mg doped BST thin films were fabricated by the metalorganic solution deposition (MOSD) technique and the film's dielectric properties were characterized at microwave frequency via a tuned coupled-split dielectric resonator technique developed at NIST. Using this measurement technique, for first time ever, has allowed the true “singular” dielectric loss (tan δ) and permittivity (εr) of the BST-based films to be assessed and optimized without the influence of device design (radiative losses) and electrode metallization (conductor losses). [ABSTRACT FROM AUTHOR]

The US Army Workshop on “Advanced Active Thin Films for the Next Generation of Meso-Micro Scale Army Applications” was held at the Hilton Sandestin Beach Golf Resort in Destin FL May 10–12 2005. This workshop was dedicated to the memory of Dr. Bruce Fink of the U.S. Army Research Laboratory. Dr. Fink was a strong leader, a visionary, and a proponent of novel research that supported the survivability of the soldier in the field. Dr. Fink's selfless attitude, encouragement, and unconditional support for the solider provided the motivation for organizing this topical workshop on “Advanced Active Thin Films for the Next Generation of Meso-Micro Scale Army Applications”. This workshop consisted of 35 invited oral presentations, spread over a three day duration. Each presentation was focused on a particular aspect, issue, or research facet associated with the current state-of-the-art and/or future thrust areas for active thin films technology. Approximately 120 scientists, engineers and technology applications specialists attended and participated in this workshop and this journal volume, Integrated ferroelectrics, serves to disseminate the science and engineering brought fourth in this workshop. [ABSTRACT FROM AUTHOR]

BaSrTiO3 (BST) thin films with a nominal composition of Ba0.60Sr0.40TiO3 and BST thin films doped with magnesium, aluminum, lanthanum and tantalum (0-20.0 mol% for Mg and 1.0 mol% for the Al, La and Ta dopants) were synthesized via the metalorganic solution deposition (MOSD) technique in order to investigate their potential for use as the active material in uncooled infrared (IR) detector applications. The films were characterized for structural, microstructural, compositional, surface morphological, dielectric and insulating properties. The Materials Detectivity Figure of Merit (FOM), D*, [D* = pi/(CV(ε0εrtan δ)1/2] was used to evaluate the film's detectivity response. Our results suggest that undoped Ba60Sr40TiO3, with a value of D* = 0.08 (cm3/J)1/2, appears to out perform Pb based pyroelectric thin films, thus making it a viable candidate for IR pyroelectric detector applications. In addition the preliminary dielectric response studies of the 5 mol% Mg doped BST and 1 mol% La doped BST thin films indicate that these two materials are also excellent potential IR material candidates. [ABSTRACT FROM AUTHOR]

Residual stress plays an important role in the determination of properties and lifetime of thin film dielectric films. While residual stress can be caused by a variety of factors, grain growth is of particular importance. Using theoretical approaches the stress due to grain growth and coalescence are predicted for magnesium doped barium strontium titanate thin films on magnesium oxide single crystal substrates. Grain growth leads to large compressive stresses for larger grains, while grain coalescence yields extremely high tensile stresses in very thin films. How stress affects defect incorporation, stress relaxation pathways, and their impact on film properties are examined. [ABSTRACT FROM AUTHOR]

In order to fully understand the performance envelope of Stress-biased piezoelectric actuators, which offer an alternative to electromechanical motors, experimental work was conducted to assess the effects of operational conditions on device performance and fatigue during device lifetime, including tests at five loads, two actuator widths, and two substrate thicknesses and related to the displacement, dielectric, resonance, and impedance properties. Applied load increased the displacement, contributed to substantially decreased lifetime and determined the fatigue mechanism. Highly loaded samples experienced domain pinning, while lightly loaded samples suffered from micro-cracking. Lateral and longitudinal stresses had a similar effect. [ABSTRACT FROM AUTHOR]

The dielectric, impedance, and displacement characteristics for stress-biased Thunder TM actuators with varying degrees of lateral stress were measured under applied load. The steady-state displacement was larger for devices with higher lateral stress and devices under low external loading, than devices with less applied stress. Devices with higher lateral stress had significantly lower initial displacement due to stress induced domain pinning. Displacement resonances were shifted to lower applied masses for devices with higher internal stress. The impedance showed a sharp increase at low loading for Thunders TM , indicating an increased absorption of input energy under applied load, though the dielectric constant decreased. [ABSTRACT FROM AUTHOR]

Utilizing a BaSrTiO 3 /NiTi hybrid composite thin film design on a silicon substrate we have successfully fabricated, characterized, and optimized a high performance vibration control pedestal for passive damping of die level MEMS components. The thin film fabrication and integration protocols were accomplished via semiconductor industry standard processing methods and procedures. The ferroelectric tetragonal phase of BaSrTiO 3 was deposited by metalorganic solution deposition (MOSD) technique followed by annealing in flowing oxygen. Thin film NiTi was sputter deposited utilizing a TiNi target in an ultrahigh vacuum chamber, followed by in situ vacuum annealing. Comparison of a variety of designs and integration processing protocols demonstrated that the sequential deposition of the BaSrTiO 3 and NiTi thin films, followed by their respective optimized crystallization anneals at 750 and 500°C, achieved successful materials compatible monolithic integration of the composite bi-layer stack with the Si support wafer. The impact of this materials integration technology, based on foundry friendly film deposition techniques and integration procedures, serves to promote wide-scale implementation of vibration control passive damping for a variety of device/die level structures. [ABSTRACT FROM AUTHOR]

Utilizing a co-planar device design we have successfully designed, faricated, characterized, and optimized a high performance Ta 2 O 5 thin film passive uffer layer on Si sustrates, which will allow the integration of Ba 1 - x Sr x TiO 3 (BST) films with large area affordale Si sustrates. This passive uffer layer thin film was faricated via the industry standard metalorganic solution deposition technique. The anneal optimized Ta 2 O 5 ased thin film possessed an enhanced dielectric constant (ε r = 45.6), low dielectric loss (tan δ = 0.006), high film resistivity (ρ = 10 12 Ω -cm at be = 1 MV/cm), excellent temperature staility (temperature coefficient of capacitance of 52 ppm/°C), and excellent ias staility of capacitance (&nvsim; 1.41% at 1 MV/cm). Additionally, the permittivity and dissipation factor exhiited minimal dielectric dispersion with frequency. The dielectric passive uffer layer film was typified by a uniform dense microstructure with minimal defects, and a smooth, nano-scale fine grain, crack/pinhole free surface morphology. Optimization of the integration design configuration was achieved by evaluating two heterostructure processing protocols; (1) a single anneal and (2) a dual anneal process protocol. Our results demonstrated the dual anneal process, to be an excellent method for realizing the successful monolithic integration of BST with affordale Si sustrates. This work also demonstrated that the coefficient of thermal expansion (CTE) mismatch etween the Ta 2 O 5 uffer and BST active thin films in the coplanar device design serves to enhance the dielectric tunaility of the device. The impact of this materials integration technology will promote road scale implementation of affordale On-The-Move (OTM) phased array antenna systems across a variety of advanced communications platforms. [ABSTRACT FROM AUTHOR]

Comments on a symposium on ferroelectricity and piezoelectricity that part of the 13th International Materials Research Congress in Mexico in August 2004. Range of issues and subject matter discussed during the symposium; Keynote speakers; Implications on studies of integrated ferroelectrics.

In order to enhance the permittivity and tunability of the dielectric component, a thin film dielectric composite consisting of a radio frequency sputtered SrTiO3 (STO) buffer layer and metalorganic solution deposited Mg-doped BaxSr1-xTiO3 (Mg-BST) thin film overgrowth was developed using affordable industry standard processes and materials. The effect of the STO buffer layer thickness on the dielectric response of the heterostructure was investigated. Our results demonstrate that the composite film heterostructure, evaluated in the metal-insulator-metal configuration Pt/STO/Mg-BST/Pt on sapphire substrate, with the thinner (9-17 nm) STO buffer layers possessed enhanced permittivity ([variant_greek_epsilon]r ∼ 491) with respect to the thicker 41 nm buffer layer ([variant_greek_epsilon]r ∼ 360) and that of a control Mg-BST film without a STO buffer layer ([variant_greek_epsilon]r ∼ 380). Additionally, the composite film with the thinner buffer layers were shown to have low losses (tan δ ∼ 0.02), low leakage characteristics (J = 7.0 × 10-9 A/cm2), high breakdown voltage (VBR > 10 V), a large grain microstructure (∼125 nm), and smooth pin-hole free surfaces. The enhanced permittivity of the composite dielectric film resulted from three major factors: (i) the template-effect of the thin STO buffer layer on the thicker Mg-BST over-layer film to achieve a large grain microstructure, (ii) the low viscosity of the metallo-organic solution deposition (MOSD) solution, which ensured heterogeneous nucleation of the Mg-BST overgrowth film on the surface of the STO buffer layer, and (iii) minimization of the low permittivity grain boundary phase (TiO2-x phase). The dielectric response of the BST can be explained using a thermodynamic model taking into account interlayer electrostatic and electromechanical interactions. Additionally, Mg doping of the BST enabled low loss and low leakage characteristics of the heterostructure. The large permittivity, low loss, low leakage characteristics, and defect free surfaces of the composite dielectric heterostructure promote tunable device miniaturization and hold the potential to enable enhanced electromagnetic coupling in ferromagnetic/high permittivity dielectric heterostructures, which in turn would facilitate the realization of integrated charge mediated voltage controlled magnetic radio frequency/microwave communication devices. [ABSTRACT FROM AUTHOR]

Information about the XV International Materials Research Congress which was held on August 20-24, 2006 in Cancun, Mexico is presented. The symposia were focused on a variety of research areas under the umbrella of material science, including nanotechnology, material design, and materials modeling. It aims to cover a wide spectrum of research activities, from the basic science of ferropiezoelectricity to technological applications in diverse fields.

The effect of ultraviolet (UV) photon assisted annealing on the structural, dielectric, and insulating properties of barium strontium titanate (BST) thin films was investigated. Isothermal-temporal annealing experiments revealed that the films annealed utilizing UV assist possessed enhanced crystallization and lattice parameters closer to bulk values with respect to conventional thermal annealed films. The leakage current density and dielectric loss of the films was significantly reduced by employing UV-assisted annealing without degradation of film tunability. Mitigation of oxygen vacancies, associated with the UV-assisted annealing, is deemed responsible for the improvement of the dielectric and electrical properties of the BST thin films. [ABSTRACT FROM AUTHOR]

Compositionally graded barium strontium titanate (BaxSr1-xTiO3 or BST) multilayers (5 mol % MgO doped and undoped) were prepared via metallo-organic solution deposition on Pt–Si substrates and characterized electrically at 0.5, 5, and 10 GHz. For the undoped BST multilayers, the small-signal dielectric response, tunability, and the loss tangent at 10 GHz were 261, 25% at 1778 kV/cm, and 0.078, respectively. On the other hand, the Mg-doped BST multilayers displayed a significant improvement in the loss characteristics at 10 GHz (0.039) but the dielectric response and its tunability were lower (189 and 15%, respectively, at 1778 kV/cm). [ABSTRACT FROM AUTHOR]

We have grown 5 mol % MgO-doped multilayered Ba1-xSrxTiO3 (BST) films having a nominal thickness of 220 nm with compositions of each layer as BST60/40, BST75/25, and BST90/10 (upgraded). We also fabricated undoped upgraded BST and uniform BST60/40 films for comparison. Results show that Mg-doping improves dielectric loss (tan δ=0.008) and yields better surface roughness (∼3.1 nm) compared to undoped upgraded BST. Mg-doped films displayed excellent temperature stability with temperature coefficient of capacitances of -0.94 and 1.14 ppt/°C from 20 to 90 °C and 20 to -10 °C, respectively. Mg doping resulted in a moderate dielectric tunability (29%) compared to undoped BST (65.5%) at 444 kV/cm. [ABSTRACT FROM AUTHOR]

The article discusses the proceedings of an August 2005 materials research conference focused on ferroelectricity and piezoelectricity, in Cancun, Mexico. The commercialization of ferroelectric and piezoelectric materials is advancing at a rapid pace. Subjects of presentations include magnetoelectric properties, theory and computer simulation, and thin film growth.

Ni[sub 2]Si Ohmic contacts were fabricated via pulsed laser deposition on n-SiC. The contacts electrical, structural, compositional, and surface morphological properties were investigated as a function of annealing temperatures ranging from 700 to 950 °C. The as-deposited and 700 °C annealed contacts were non-Ohmic. Annealing at 950 °C yielded excellent Ohmic behavior, an abrupt void free interface, and a smooth surface morphology. No residual carbon was present within the contact metallization or at the contact-SiC interface and the contact showed no appreciable thickness increase as a result of the annealing process. Our results demonstrate that aside from maintaining the desirable electrical integrity associated with Ni and Ni/Si Ohmic contacts, the Ni[sub 2]Si Ohmic contacts possessed improved interfacial, compositional, microstructural, and surface properties which are required for reliable high temperature and high power device operation. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Ba0.6Sr0.4TiO3 films with a thickness of 200 nm were deposited on Pt–Si substrates at 400 and 700 °C. Room-temperature tunability was measured and found to improve with deposition temperature, but losses also increased. The dielectric constant, tunability, and loss tangent are found to be 350, 52%, and 0.07 at 300 kV/cm for the 700 °C deposition. The film grown at 700 °C has a larger grain size, leading to approximately 5% higher tunability compared to the film deposited at 400 °C. Supporting theoretical calculations were carried out using a modified Landau-Devonshire thermodynamic formalism that takes into account the internal stresses that arise from the differences of coefficients of thermal expansion between the film and the substrate. [ABSTRACT FROM AUTHOR]

We study the capillary condensation of liquid 4He films inside narrow slit pores with a density functional model and compare the result to the predictions of the Kelvin equation. Our investigation, in the wetting situation, indicates that pores with sizes up to 100 Å are still too small for the macroscopic thermodynamic arguments used to derive the Kelvin equation to be successful. The discrepancy is tentatively attributed to the use of a slab-density model and bulk parameters in the region of very thin films. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the guest editors discuss regarding ferroelectric and piezoelectric materials, their integration in devices and their technological applications.

The article presents the authors' comments on the symposium on Ferroelectricity and Piezoelectricity: Materials, Devices, and Applications, which was held at the International Materials Research Congress (IMRC) held in Cancun, Mexico, during August 16-21, 2009. According to the authors, the symposium focused on topics including nanotechnology, material design, and surface engineering of thin films. The authors say that the symposium has helped in the establishment of new collaborations.

Presents a study which determined the residual damage of gallium arsenide samples etched in a magnetron reactive ion etcher. Indication of the aligned yields from ion channeling measurements; Process of transmission electron microscopy; Capability of magnetron reactive ion etching.

Tunability of ferroelectric complex oxides is achieved by applied bias voltage. Many applications require usage of relatively low voltage which is achievable by using a ferroelectric thin-film. Recently developed dielectric metamaterials were implemented in bulk and in thick films. Metamaterials are resonant structures. The frequency range of 0.1–1.5 THz is of special interest for such applications as non-destructive evaluation of materials and detection of chemical and biological hazards. This paper numerically investigates the possibility of a resonant effect in a thin-film ferroelectric metamaterial and the effects of increased dielectric constant and thickness on the thin-film's resonance frequency. [ABSTRACT FROM AUTHOR]

Monolayer films on graphite, remarkably diverse examples of two-dimensional matter, are now well understood in terms of semiempirical interactions. We explore the phase behavior of helium films on two variants of graphene: graphane (graphene coated with H, denoted GH) and graphene fluoride (GF). The behaviors predicted with quantum Monte Carlo differ qualitatively from those on graphite because of the different surface composition, symmetry, and spacing of the adsorption sites. On both substrates we find that the analog of the standard √3 x √3 R30° commensurate state on graphite is unstable. Results include a superfluid ground state for 4He and a fluid ground state for 3He, neither of which has been found for the monolayer film on any substrate; these two-dimensional fluids are anisotropic because of the symmetry imposed by the honeycomb lattice of adsorption sites. In the case of 4He on GF the anisotropy is as large as if the superfluid were restricted to move in a multiconnected space, along the bonds of a honeycomb lattice. The superfluid transition temperature at the ground-state density of 4He on GF (GH) is of order 0.25 (1.1) K. At higher coverages both an incommensurate triangular solid and a commensurate state at filling factor 2/7 are found. [ABSTRACT FROM AUTHOR]