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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]

SrTiO3 (STO) thin films were grown onto Pt/Ti/TiO2/SiO2/Si and bare Si substrates via metallo-organic solution deposition (MOSD). X ray diffraction, scanning electron microscopy, atomic force microscopy, spectroscopic ellipsometry (SE), and dielectric/insulating measurements were utilized to characterize the STO thin films. By optimizing the solution molarity, it is shown that it is possible to obtain low-frequency dielectric properties in STO thin films on Si substrates that approach those of bulk STO: a dielectric permittivity of 325 at 100 kHz with a tunability of ∼28% at ∼650 kV/cm, a low loss (<2%), and a leakage current density of 1.0 × 10-6 A/cm2 at 100 kV/cm. The bulk-like dielectric response of these films is attributed to the elimination of the relatively large in-plane tensile thermal stresses, which arise due to the thermal expansion mismatch between the STO film and the Si substrate. These tensile thermal stresses may be relaxed or completely eliminated through modification of the post-coalescence compressive growth stresses by precursor solution optimization. The SE data indicates that the STO thin films have a refractive index of ∼2.04 at 633 nm wavelength, which is lower than that of bulk STO. The dielectric, physical, and optical characterization results above the bandgap are consistent, but below the bandgap, the optical-frequency results demonstrate a ∼25% reduced dielectric response as compared to the bulk, which may be due to the different polarization mechanisms at work at high frequencies. These findings demonstrate that high-quality, electronic-grade, thin film STO films can be grown on Si substrates via the affordable, simple, and industry-standard MOSD technique by carefully adjusting the deposition parameters. [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]

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]

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]

A theoretical study of the rotational dynamics of H[sub 2] molecules trapped in the interstitial channels of a carbon nanotube bundle is presented. The potential used in this study is modeled as a sum of atom–atom (C–H) van der Waals interactions and electrostatic interactions of the molecule with the surrounding nanotubes. The rotational energy spectra is calculated using a product wave function, where the coupling between translational and rotational modes is treated in a mean-field manner. A molecular dynamics simulation study was performed for estimating the hydrogen rotational barrier. Both theoretical calculations and simulation results reveal the existence of a large rotational barrier (∼40 meV). The consequences of this rotational barrier for the rotational energy levels are worked out in detail. © 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.

Presents information on a study which analyzed the line shape reflectance spectroscopy from gallium arsenic/aluminum arsenic multiple-quantum-well structures. Description of the model; Factors that affect the detail of line shape; Characteristics of the gallium arsenic/aluminum arsenic structure.