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We report on the effects of Ag impurities at interfaces of parallel-plate Pt/Ba0.6Sr0.4TiO3/Pt thin film ferroelectric varactors. Ag impurities occur at the interfaces due to diffusion of Ag from colloidal silver paint used to attach the varactor samples with their back side to the plate heated at 600-750 °C during deposition of Ba0.6Sr0.4TiO3. X-ray photoelectron spectroscopy and secondary ion mass spectrometry suggest that amount and distribution of Ag adsorbed at the interfaces depend strongly on the adsorbent surface layer. In particular, Ag preferentially accumulates on top of the Pt bottom electrode. The presence of Ag significantly reduces the barrier height between Pt and Ba0.6Sr0.4TiO3/ leading to an increased leakage current density and, thus, to a severe degradation of the varactor performance. [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]

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]

Structural and optical properties of zinc oxide thin films deposited on glass substrates were studied before and after plasma and laser treatment. It was shown that the polycrystalline ZnO structure was destroyed by modifying laser radiation, while in the center of the spot amorphous zinc oxide was formed. Plasma treatment performed a transformation of the surface morphology of ZnO layers without deterioration of their optical and electrical properties. Longer treatment times result in over flattening of the surface followed by observable reduction of light scattering along with degradation of electronic properties. [ABSTRACT FROM PUBLISHER]

We present preliminary results of metal organic chemical vapor deposition (MOCVD) growth of BaxSr1-xTiO3 (BST) thin films. Films were deposited on MgO, sapphire, Si, and Si/Pt/Ti substrates. Real-time monitoring of the precursor flux by UV absorption spectroscopy was used to control the composition of the films over the range 30 ≤ x ≤ 80. The films were characterized for a number of attributes including composition, crystalline structure, and morphology. [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]

Residual stress in thin film barium strontium titanate is thought to be preferentially distributed within the thickness of the film, such that a high degree of residual stress is manifested at the film-substrate interface, and the level of residual stress gradually decreases towards the free surface. To investigate this phenomena, a series of very thin films of barium strontium titanate with both cubic (30-70 Ba-Sr ratio) and tetragonal (80-20 Ba-Sr ratio) lattice structures were fabricated on platinized silicon and magnesium oxide. The thickness of these films was varied from 4-25 nm and the level of residual stress was investigated. The results highlighted within this paper, indicate that the cubic and tetragonal films manifest stress via different mechanisms, and that the substrate affected the magnitude of the residual stress but not the mechanism of stress relief. [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]

Structural health monitoring is a means for drastically decreasing the maintenance and logistical cost associated with vehicular platforms especially aircraft. A system of small piezoelectric sensors distributed throughout the vehicle will be capable of acting passively or actively to monitor the changes within a structure that presage a component failure, and they will be able to detect and localize all impacts on the structure and evaluate any damage. Piezoelectric thin films were directly integrated with structural titanium utilizing a metal-organic chemical solution approach. The optimum integration strategy yielded a process easily performed without a cleanroom and semiconductor fabrication tools. [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 (∼⃒ 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]

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]

Tunable complex oxide thin films have generated a lot of interest in recent years due to their potential to become a core technology in the new generation of multiple communications devices. These films are grown via different deposition methods and frequently postprocessed in order to enhance their dielectric properties. This paper discusses an alternative postprocessing technique where complex oxide thin films grown by radio frequency (RF) magnetron sputtering have been treated with an external microwave field instead of a conventional furnace. The treated films and untreated reference film were characterized for their microstructure and dielectric properties. The obtained results indicate a significant reduction in dielectric losses and leakage current in the microwave processed films as opposed to the untreated reference. The results are discussed together with potential additional benefits of the proposed approach. [ABSTRACT FROM AUTHOR]