Joseph D. Warner

Design and development of ferroelectric tunable microwave components for Kuand K-band satellite communication systems

Integration of a high-temperature superconductor with a nonlinear dielectric ferroelectric such as strontium titanate, i.e., SrTiO/sub 2/ (STO), has created a new class of electrically tunable low-loss microwave components. We have designed and fabricated frequency and phase agile components using a conductor/ferroelectric/dielectric two-layered microstrip configuration. Some examples of these components are: microstrip ring resonators, local oscillators, edge coupled filters, and phase-shifter circuits. These structures have been fabricated using YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// or gold conductor-based microstrip lines fabricated on lanthanum aluminate (LaAlO/sub 3/) or magnesium oxide (MgO) substrates coated with an STO thin film. Frequency and phase agility are achieved using the nonlinear dc electric-field dependence of the relative dielectric constant of STO ferroelectric thin him (E/sub rSTO/). In this paper, we will present an assessment of the progress that our group has achieved thus far toward integration of this technology into wireless and satellite communication systems.

YBCO superconducting ring resonators at millimeter-wave frequencies

Superconducting microstrip ring resonators operating at 35 GHz have been fabricated from laser ablated YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) films on lanthanum aluminate substrates. The circuits consisted of superconducting strips over normal metal ground planes. The circuits are measured from 20 K to 90 K and with microwave input powers ranging from 0.25 mW to 10 mW. The superconducting resonators show significant improvement in Q over identical gold resonators at 20 K, but only marginal improvement at 77 K. No variation in the superconductor performance is observed with varying input power. The lowest microwave surface resistance of the superconductors at 77 K is 9 m Omega . The change in the resonant frequency with temperature is analyzed and a value for the penetration depth computed. Double resonances were observed in some superconducting ring resonators and an explanation is advanced. Factors limiting millimeter-wave high-temperature superconductor circuits are explored and potential performance levels calculated based on current reported values for high-temperature superconductor surface resistances. >

Growth of 2H‐SiC on 6H‐SiC by pulsed laser ablation

A 2H‐SiC thin film has been grown on a 6H‐SiC substrate by laser ablation using an excimer laser. The deposition of 2H‐SiC film occurred in a high vacuum system (≊10−6 Torr) with the substrate temperature near 1200 °C. Plan‐view and cross‐sectional transmission electron microscopy (TEM) were used to measure the lattice parameters and to identify the polytype. Cross‐sectional TEM images clearly show the symmetry of the film as c‐axis oriented 2H‐SiC containing columnar grains with an average diameter of 20 nm and a length of 100 nm.

Microwave properties of YBa2Cu3O7−δ high‐transition‐temperature superconducting thin films measured by the power transmission method

The microwave response of YBa2Cu3O7−δ superconducting thin films has been studied by performing power transmission measurements. The measurements were made at frequencies within the 26.5–40.0‐GHz frequency range, and at temperatures from 20 to 300 K. The films were deposited on LaAlO3, MgO, yttria‐stabilized zirconia, and LaGaO3 substrates by laser ablation and dc off‐axis magnetron sputtering. From these measurements the complex conductivity σ* = σ1 − jσ2, the magnetic penetration depth λ, and the surface resistance Rs of the films have been determined. It was observed that both σ1 and σ2 increased when cooling the films below their transition temperature. This behavior disagreed with that expected from the two‐fluid model. In addition, it was observed that the temperature behavior of σ1 deviates from the predictions of the Bardeen–Cooper–Schrieffer theory. Values of λ have been obtained that are in good agreement with the best reported values for high quality c‐axis‐oriented thin films and single crysta...

Lunar Communication Terminals for NASA Exploration Missions: Needs, Operations Concepts and Architectures

NASA is conducting architecture studies prior to deploying a series of short- and long-duration human and robotic missions for the exploration of the Moon and Mars under the Vision for Space Exploration Initiative. A key objective of these missions is to establish and expand, through a series of launches, a system of systems approach to exploration capabilities and science return. The systems identified were Crew Exploration Vehicles, crew and cargo launch vehicles, crew EVA suits, crew and cargo landers, habitats, mobility carriers, and small, pressurized rovers. Multiple space communication networks and systems, deployed over time, will support these space exploration systems of systems. Each deployment phase will support interoperability of components and provide 20 years of legacy systems. In this paper, we describe the modular lunar communications terminals needed for the emerging lunar mission operational scenarios. These lunar communication terminals require flexibility for use in stationary, integrated, and mobile environments. They will support links directly to Earth, to lunar relay satellites, to astronauts and to fixed and mobile lunar surface systems. The operating concepts and traffic models are presented for these terminals within variety of lunar scenarios. A preliminary architecture is outlined, providing for suitable long-duration operations in the harsh lunar environment.

Analysis and Optimization of Thin-Film Ferroelectric Phase Shifters

Microwave phase shifters have been fabricated from (YBa2Cu3O(7-delta) or Au)/SrTiO3 and Au/Ba(x)Sr(1-x)TiO3 films on LaAlO3 and MgO substrates. These coupled microstrip devices rival the performance of their semiconductor counter-parts parts at Ku- and K-band frequencies. Typical insertion loss for room temperature ferroelectric phase shifters at K-band is approximately equal 5 dB. An experimental and theoretical investigation of these novel devices explains the role of the ferroelectric film in overall device performance. A roadmap to the development of a 3 dB insertion loss phase shifter that would enable a new type of phased array antenna is discussed.

Performance and modeling of superconducting ring resonators at millimeter-wave frequencies

Microstrip ring resonators operating at 35 GHz have been fabricated from laser-ablated YBCO thin films deposited on lanthanum aluminate substrates. They were measured over a range of temperatures, and their performance was compared to that of identical resonators made of evaporated gold. Below 60 K the superconducting strip performed better than the gold, reaching an unloaded Q approximately 1.5 times that of gold at 25 K. A shift in the resonant frequency follows the form predicted by the London equations. The phenomenological loss equivalence method is applied to the ring resonator, and the theoretically calculated Q values are compared to the experimental results.<<ETX>>

Ferroelectric thin-film based electrically tunable Ku-band coplanar waveguide components

Barium strontium titanate Ba/sub 0.6/Sr/sub 0.4/TiO/sub 3/ thin-film based tunable coplanar waveguide (CPW) components were studied in this research. The CPW components modeled and experimentally verified include CPW transmission lines, resonators and 2-pole filters. The resonators and filters fabricated and tested exhibited a frequency tunability of approximately 3% for a bipolar bias voltage of /spl plusmn/100 V, corresponding to a peak biasing field of 40 kV/cm.

Plasma deposition of amorphous hydrogenated carbon films on III-V semiconductors

Abstract Amorphous hydrogenated carbon films were grown on GaAs, InP and fused silica substrates using plasmas generated from hydrocarbon gases. Methane and n -butane sources were utilized. The effects of flow rate and power density on film growth were investigated. Carbon was the major constituent in the films. The degree of asymmetry at the carbon-semiconductor interface was approximately independent of the power density. Different HC bonding configurations were detected by the technique of secondary ion mass spectrometry. Band gaps up to 3 eV were obtained from optical absorption studies. Breakdown strengths as high as 6 × 10 8 V m −1 were measured.

Evaluation of Chemical Solution Deposited Ba x Sr 1−x TiO 3 Thin Films on LaAlO 3 in Tunable Microwave Devices

Epitaxial Ba x Sr 1 m x TiO 3 (BST) films grown on LaAlO 3 by several deposition methods have been tested in coupled microstrip phase shifters (CMPS) at frequencies from 10 to 24 GHz. To date the best performance for the devices has been achieved using Pulsed Laser Deposition (PLD). However, recently chemical solution deposition (CSD) methods such as sol-gel and Metal-Organic Chemical Liquid Deposition (MOCLD) have shown advances in fabricating BST films for tunable microwave applications. CSD processes promise improvements in cost, speed and area covered during BST film deposition. This paper compares over 35 BST films used in identical CMPS circuits. In this study, the highest measured figures of merit of phase shift per dB of loss for PLD, MOCLD and sol-gel CMPS are 49, 47 and 41°/dB respectively. While other phase shifter designs using BST films have surpassed these values, these data base of identical circuits allows us to compare the BST films. X-ray diffraction characterization for many of the BST films is also given.