M. Ivill

Enhanced dielectric properties from barium strontium titanate films with strontium titanate buffer layers

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 (er ∼ 491) with respect to the thicker 41 nm buffer layer (er ∼ 360) and that of a control Mg-BST film without a STO buffer layer (er ∼ 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 (...

Ultraviolet assisted processing: A unique approach to mitigate oxygen vacancies and attain low loss highly tunable Ba0.60Sr0.40TiO3 thin films

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 re...

Ba0.60Sr0.40TiO3 THIN FILMS FOR MICROWAVE PHASE SHIFTER DEVICES: THE INFLUENCE OF CRYSTALLIZATION TEMPERATURE ON THE ELECTRIC FIELD DEPENDENT PHASE SHIFT RESPONSE

ABSTRACT 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.

Radio Frequency Carbon Nanotube Thin-Film Bolometer

A radio frequency bolometer was realized using a thermistor fabricated from a carbon nanotube thin-film deposited on a sapphire substrate. Power detection performance was characterized at room and liquid nitrogen temperatures. With the thermistor held at a temperature of 15 °C, the bolometer’s sensitivity of 915-MHz test signals was found to be 0.36 mV/mW, and power levels as low as −45 dBm could be detected with a 20-s integration time constant. The sensitivity increased to 2.3 mV/mW when the thermistor was cooled to −193 °C. Experiments over the temperature range of 15 °C–240 °C indicate that internanotube mechanisms dominate power detection at temperatures below a value of approximately 200 °C and that intrananotube mechanisms (primarily Joule-heating) dominate at higher temperatures.

An Elegant Post-Growth Process Science Protocol to Improve the Material Properties of Complex Oxide Thin Films for Tunable Device Applications

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.

RESIDUAL STRESS OF Pt FILMS WITH Ti AND TiOx ADHESION LAYERS ON Si AND SAPPHIRE SUBSTRATES

ABSTRACT 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.

Microwave power detection from an anharmonic dipolar resonance

Electric-field-induced, anharmonic dipolar resonances of room-temperature, barium strontium titanate (BST) thin film varactors have been used to rectify and detect microwave signals with frequencies ranging from 2GHz to 3GHz. The resonant frequency was shown to have strong dependence on film thickness with some amount of voltage-controlled tunability. Our experiments involved lock-in detection of a 100% amplitude modulated microwave signal with power levels ranging from -20 dBm to +10 dBm. An on-resonant sensitivity of 0.6 mV/mW was observed. This power detection sensitivity was shown to have built-in bandpass filtering arising from resonant line shape.

Fabrication of self-aligned, nanoscale, complex oxide varactors

Abstract. Applications in ferroelectric random access memory and superparaelectric devices require the fabrication of ferroelectric capacitors at the nanoscale that exhibit extremely small leakage currents. To systematically study the material-size dependence of ferroelectric varactor performance, arrays of parallel-plate structures have been fabricated with nanoscale dielectric diameters. Electron beam lithography and inductively coupled plasma dry etching have been used to fabricate arrays of ferroelectric varactors using top electrodes as a self-aligned etch mask. Parallel-plate test structures using RF-sputtered Ba0.6Sr0.4TiO3 thin-films were used to optimize the fabrication process. Varactors with diameters down to 20 nm were successfully fabricated. Current-voltage (I-V) characteristics were measured to evaluate the significance of etch-damage and fabrication quality by ensuring low leakage currents through the structures.