Richard G. Geyer

National Institute of Standards and Technology, Maryland, United States

Are you Richard G. Geyer?

Claim your profile

Publications (65)51.94 Total impact

  • M. W. Cole · R. G. Geyer · W. D. Nothwang
    [Show abstract] [Hide abstract]
    ABSTRACT: 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 Ba 0.6 Sr 0.4 TiO 3 (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 (ϵ r ) of the BST-based films to be assessed and optimized without the influence of device design (radiative losses) and electrode metallization (conductor losses).
    No preview · Article · Mar 2011 · Ferroelectrics
  • [Show abstract] [Hide abstract]
    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    No preview · Article · Oct 2010 · ChemInform
  • [Show abstract] [Hide abstract]
    ABSTRACT: A review of the most common methods for nondestructive permittivity and permeability measurements is presented. Transmission-line techniques, coaxial apertures, open resonators, surface-waves, and dielectric resonator methods are examined. Measurements on bulk, thin materials, and thin films are addressed. Measurement fixtures that can be used as sensors are highlighted. The frequency range of applicability and typical uncertainties associated with each method are addressed.
    No preview · Article · Apr 2009 · Research in Nondestructive Evaluation
  • M.W. Cole · W.D. Nothwang · R.G. Geyer
    [Show abstract] [Hide abstract]
    ABSTRACT: This study demonstrates that large area affordable silicon substrates can be utilized in phase shifter devices if a "microwave friendly" passive buffer layer is sandwiched between the silicon substrate and the low loss active Ba 1-xSr xTiO 3 (BST) based thin film. In this heterostructure configuration there will be negligible attenuation of the microwave energy by the substrate. In our approach, metalorganic solution deposition (MOSD) fabricated Ta 2O 5 was employed as a buffer layer film to promote the integration of BST with affordable large area silicon substrates. In addition, the buffer layer material was designed to promote a tensile stress in the active thin film, such that the tunability of the BST-based coplanar device was enhanced to levels comparable to that of a varactor device design. The optimized Ta 2O 5 based thin film possessed excellent material properties, namely, an enhanced dielectric constant (ε r =45.6), low dielectric loss (tan δ=0.006), high film resistivity (ρ=10 12 Ω-cm at E=l MV/cm), excellent temperature stability (TCK of 52 ppm/°C), and excellent bias stability of capacitance (∼ 1.41% at 1 MV/cm). The integration of the BST/Ta 2O 5 bilayer heterostructure on silicon substrates was demonstrated via a dual anneal process protocol. The defect free, structurally abrupt BST/Ta 2O 5 and Ta 2O 5-silicon substrate interfaces; combined with the smooth, uniform and defect free surface morphology of the dual anneal fabricated heterostructure suggests this process protocol to be an excellent method for achieving successful monolithic integration of BST with affordable silicon substrates in a coplanar device design.
    No preview · Article · Jan 2006
  • M.W. Cole · W.D. Nothwang · S. Hirsch · E. Ngo · C. Hubbard · R.G. Geyer
    [Show abstract] [Hide abstract]
    ABSTRACT: Ba( 1-x)Sr xTiO 3 (BST) thin films appear to be excellent candidates for microwave phase shifters. However, the major issue impeding the utilization of BST films in beam steering devices is the simultaneous achievement of the required performance properties. These properties, at frequencies ≥10 GHz, include a dielectric permittivity ≤500, low dielectric loss (<2%), high tunability (∼2:1), low leakage current characteristics, and low operating control voltages (<10V). Additionally, these properties must be obtained via an industry standard growth and processing methods. Our approach to satisfy the above mentioned dielectric properties of BST based films is focused on material compositional design and optimized film processing parameters. A systematic study was employed to examine the influence of low concentration Mg acceptor doping and optimized post-deposition annealing conditions on the structure and microwave dielectric properties of BST based thin films fabricated via the metalorganic solution deposition technique. The Mg doping was found to have a strong Influence on the material properties of the BST films whereby the films permittivity, dissipation factor, and leakage characteristics were significantly reduced with respect to that of undoped BST. Optimum material properties were achieved for the 5-7 mol% Mg doped BST films. At these doping concentrations the dissipation factor (10 GHz) for both films was less than 1.7%. The leakage characteristics were 5.78×10 -8 and 7.97×10 .9, respectively, and the tunability was ∼40%. Our results suggest that Mg doping and optimized post-deposition annealing served to mitigate the oxygen vacancies thereby lowering the films dielectric loss. Furthermore, the acceptor doping maintained the dielectric permittivity well below 500. Our results suggest the 5-7 mol% Mg doped BST thin films to be commercially viable for microwave phase shifter devices.
    No preview · Article · Jan 2006
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, different densities within a ceramic are used to provide a wide continuous range of dielectric constants for high-frequency applications. Cofiring different ceramic materials together to make a single unified structure to obtain different dielectric constant combinations is quite difficult due to phase stability issues and shrinkage mismatches. However, using various levels of porosity in order to alter the effective dielectric constant in the same material allows patterning different dielectric constants into a single unit. Since the structure is made from a single material, the varying porosity regions can be made compatible. Glassy-carbon-assisted and microcellular-structure-based porous titania allow for an extremely wide range of dielectric constants, ranging from 12 to 90, while maintaining a low loss tangent. Highly anisotropic materials are demonstrated herein to achieve a dielectric constant contrast of 90/9.6 using large-range aligned microcellular structure. Dielectric-resonator antennas are shown as an application of adjusting the bandwidth between 0.5% and 2.5% by tailoring the ceramic dielectric constant. A stratified-medium-loaded cavity resonator and a buried dielectric ring resonator internal to a microcellular substrate are used to demonstrate both the cofiring and variable dielectric constant capabilities of structured porosity.
    Full-text · Article · Dec 2005 · IEEE Transactions on Microwave Theory and Techniques
  • Source
    Richard G. Geyer · Bill Riddle · Jerzy Krupka · Lynn A. Boatner
    [Show abstract] [Hide abstract]
    ABSTRACT: Microwave dielectric properties of single-crystal incipient quantum ferroelectrics, KTaO3 and SrTiO3, have been measured at cryogenic temperatures. Cylindrical specimens were used as TE0n1-mode and quasi-TE011-mode dielectric resonators at temperatures ranging from 4 to 300 K. Conductive losses of the measurement resonant structures were taken into account, both as a function of frequency and temperature, so that uncertainties in the evaluated dielectric losses were ±5%. The real permittivity was measured with an accuracy of ±0.5%. The evaluated real permittivities of KTaO3 and SrTiO3 exhibit no ferroelectric transition, and remain paraelectric down to 5 K, consistent with soft-mode stabilization. Dielectric loss tangent values of KTaO3 at 3 GHz were 4.2×10−5 at 5.4 K, 8.9×10−5 at 77 K, and 1.4×10−4 at 300 K, while those of SrTiO3 were 3.4×10−3 at 5.4 K, 2.4×10−4 at 77 K, and 3.8×10−4 at 300 K. Results of the complex permittivity measurements are compared with theoretical predictions from a modified Devonshire phenomenological model.
    Full-text · Article · May 2005 · Journal of Applied Physics
  • R.G. Geyer · J. Baker-Jarvis · J. Krupka
    [Show abstract] [Hide abstract]
    ABSTRACT: The microwave dielectric properties of single-crystal LiF, CaF<sub>2</sub>, MgF<sub>2</sub>, BaF<sub>2</sub>, and SrF<sub>2</sub>, synthesized by Stockbarger melt-growth techniques, are measured using cylindrical specimens as TE<sub>01δ</sub> dielectric resonators enclosed in a cylindrical cavity. Single-crystal permittivity and dielectric loss tangent were evaluated at fixed frequencies between 7 and 9 GHz and over a temperature range from -75 to 150°C. The real permittivities of the measured fluorides increase quasi-linearly with temperature, permitting evaluation of the thermal coefficients of permittivity. The dielectric loss tangents increase approximately linearly with frequency, so that Qf (GHz) products at room temperature for BaF<sub>2</sub>, SrF<sub>2</sub>, CaF<sub>2</sub>, LiF, and MgF<sub>2</sub> (normal to c-axis) are 57600, 73000, 92000, 192400, and 458600, respectively. The dielectric data supports existing ion polarizabilities that are used with molar volumes and molecular additivity rules to estimate the permittivities of more complex fluorides whose values have not been experimentally determined.
    No preview · Conference Paper · Nov 2004
  • M.W. Cole · R.G. Geyer
    [Show abstract] [Hide abstract]
    ABSTRACT: The materials properties of undoped and low concentration Mg doped Ba0.6Sr0.4TiO3 (BST) thin films are reported. The films were fabricated on single crystal (1 0 0) MgO and Pt coated Si substrates via the metalorganic solution deposition (MOSD) technique using carboxylate-alkoxide precursors and post-deposition annealed at 800 °C (film/MgO substrates) and 750 °C (film/Pt–Si substrates). The dielectric properties were measured at 10 GHz using unpatterned/non-metallized films via a tuned coupled/split dielectric resonator system and at 100 kHz using metal–insulator–metal capacitors. The structure, microstructure, surface morphology and film/substrate compositional quality were analyzed and correlated to the films dielectric and insulating properties. The Mg doped BST films exhibited improved dielectric loss and insulating characteristics compared to the undoped BST thin films. The improved dielectric properties, low leakage current, and good tunability of the low level Mg doped BST thin films merits strong potential for utilization in microwave tunable devices.
    No preview · Article · Oct 2004 · Mechanics of Materials
  • [Show abstract] [Hide abstract]
    ABSTRACT: The crystal structure of Ba11FeTi27O66.5 was determined using single-crystal and powder X-ray diffraction methods. This phase crystallizes in the monoclinic space group C2/m (No. 12) (a = 23.324(1) Å, b = 11.388(1) Å, c = 9.8499(3) Å, β = 90.104(3)°; Z = 2; ρcalcd. = 4.98 g/cm3), and exhibits a 10-layer structure built from close-packed [O,(Ba,O)] layers with a stacking sequence (cchhc)2. Octahedral sites are occupied by a mixture of Fe3+ and Ti4+, with some preferential ordering suggested by analysis of bond valence sums. The structure features vertex-, edge-, and face-sharing of the [Ti(Fe)O6] octahedra. Indexed X-ray powder diffraction data for a polycrystalline specimen are given. Ba11FeTi27O66.5 and the 8-layer phase Ba4Fe2Ti10O27 are built from the same types of polyhedral layers, some of which feature vacant sites between two Ba ions, which substitute for three oxygens in a row. The single-crystal results suggest that the basic structural formula of the phase is A11B28O66+x, with the value of x (and hence the Fe/Ti ratio) determined by partial occupancy of one of these vacant sites. Variation of this occupancy factor with synthesis temperature may account for apparent slight differences in the stoichiometry of this phase in polycrystalline and single-crystal form. However, solid solution formation was not observed for polycrystalline specimens. A comparison of the crystal structure obtained for Ba11FeTi27O66.5 with that previously proposed for “Zr4+-stabilized Ba2Ti5O12” indicates that the phase “Ba2Ti5O12” is actually a ternary compound which forms upon addition (either deliberately or inadvertently) of a trivalent ion such as Fe3+ or Al3+. The specimens Ba11Al2Ti26O66, Ba11Al2Ti24Sn2O66, and Ba11Al2Ti24Zr2O66 were also prepared and were found to form the A11B28O66+x-type phase. Ba11FeTi27O66.5 exhibits paramagnetic behavior that deviates somewhat from the Curie−Weiss Law below 75 K. Application of this formalism to the 1/χ vs. T data above 75 K yields an effective moment consistent with the presence of high-spin Fe3+ (S = 5/2), and a negative Weiss constant (about −25 K) indicating weak cooperative magnetic interactions that are overall antiferromagnetic. The relative permittivity and dielectric loss tangent of a sintered polycrystalline disk were measured at 5.33 GHz, yielding values (corrected for theoretical density) of 55 and 7.7(±0.3) × 10−4, respectively. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
    No preview · Article · Aug 2004 · ChemInform
  • Source
    M.W. Cole · R.G. Geyer
    [Show abstract] [Hide abstract]
    ABSTRACT: The materials properties of undoped and low concentration Mg doped Ba0:6Sr0:4TiO3 (BST) thin films are reported. The films were fabricated on single crystal (100) MgO and Pt coated Si substrates via the metalorganic solution deposition (MOSD) technique using carboxylatealkoxide precursors and post-deposition annealed at 800±C (film/MgO substrates) and 750±C (film/Pt-Si substrates). The dielectric properties were measured at 10 GHz using unpatterned/non-metallized films via a tuned coupled/split dielectric resonator system and at 100 kHz using metal-insulator-metal capacitors. The structure, microstructure, surface morphology and film/substrate compositional quality were analyzed and correlated to the films dielectric and insulating properties. The Mg doped BST films exhibited improved dielectric loss and insulating characteristics compared to the undoped BST thin films. The improved dielectric properties, low leakage current, and good tunability of the low level Mg doped BST thin films merits strong potential for utilization in microwave tunable devices.
    Full-text · Article · Jun 2004 · Revista Mexicana de Fisica
  • Source

    Preview · Article · Jan 2003
  • RG Geyer · MW Cole
    [Show abstract] [Hide abstract]
    ABSTRACT: The influence of Mg-doping on the structure, microstructure, surface morphology, and dielectric properties of Ba 1-xSr xTiO 3 (BST) thin films is measured and analyzed. The films were fabricated on MgO substrates with the metalorganic solution deposition technique using carboxylate-alkoxide precursors and annealed at 800°C in an oxygen atmosphere. The structure, microstructure, surface morphology, and film/substrate compositional quality were evaluated with 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 and tuned split dielectric resonator system. The Mg-doped BST films exhibited improved dielectric and insulating properties compared to undoped Ba 0.6Sr 0.4TiO 3 thin films and are candidates for integration into tunable microwave devices.
    No preview · Article · Jan 2003
  • M. W. Cole · C. Hubbard · E. Ngo · M. Ervin · M. Wood · R. G. Geyer
    [Show abstract] [Hide abstract]
    ABSTRACT: The influence of low concentration (1 mol %) Mg doping on the structural, microstructural, surface morphological, and dielectric properties of Ba1−xSrxTiO3 (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 Ba0.6Sr0.4TiO3 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. © 2002 American Institute of Physics.
    No preview · Article · Jun 2002 · Journal of Applied Physics
  • R.G. Geyer · P. Kabos · J. Baker-Jarvis
    [Show abstract] [Hide abstract]
    ABSTRACT: Closed-form analytical solutions are derived for accurate microwave dielectric characterization of rod test specimens inserted into dielectric sleeve resonators placed centrally in a metal cavity. Low-loss sleeve resonators can be used advantageously for multiple frequency measurements of the same specimen and may be employed for accurate dielectric characterization of high-permittivity specimens having dielectric loss factors greater than 0.001. Uncertainty relations for permittivity and dielectric loss are also shown, which demonstrate that when sample electric energy filling factors are greater than 0.4, relative uncertainties in measured permittivity and dielectric loss tangent are less than 1% and 4%, even for relative permittivities greater than 600. Example measurements are given that illustrate how this dielectric resonator system can be employed for dielectric characterization of ferroelectric materials at temperatures both near or far from their Curie temperatures
    No preview · Article · May 2002 · IEEE Transactions on Instrumentation and Measurement
  • Richard G. Geyer · Pavel Kabos · James Baker-Jarvis
    [Show abstract] [Hide abstract]
    ABSTRACT: Closed-form analytical solutions are derived for accurate microwave dielectric characterization of rod test specimens inserted into dielectric sleeve resonators placed centrally in a metal cavity. Low-loss sleeve resonators can be used advantageously for multiple frequency measurements of the same specimen and may be employed for accurate dielectric characterization of high-permittivity specimens having dielectric loss factors greater than 0.001. Uncertainty relations for permittivity and dielectric loss are also shown, which demonstrate that when sample electric energy filling factors are greater than 0.4, relative uncertainties in measured permittivity and dielectric loss tangent are less than 1% and 4%, even for relative permittivities greater than 600. Example measurements are given that illustrate how this dielectric resonator system can be employed for dielectric characterization of ferroelectric materials at temperatures both near or far from their Curie temperatures
    No preview · Article · Apr 2002 · IEEE Transactions on Instrumentation and Measurement
  • [Show abstract] [Hide abstract]
    ABSTRACT: The dielectric resonator technique is frequently used for surface resistance measurements of superconducting films. Generally, an effective surface resistance has been measured which neglects the finite thickness of superconducting films. The thickness dependence of the surface impedance of superconducting films, whose thickness is comparable to the London penetration depth, is presented.
    No preview · Conference Paper · Feb 2002
  • R.G. Geyer · P. Kabos · J. Baker-Jarvis
    [Show abstract] [Hide abstract]
    ABSTRACT: Low-loss sleeve resonators can be used for accurate microwave dielectric characterization of rod-shaped test specimens. The test specimen is inserted into the dielectric sleeve resonator and placed centrally in a metal cavity. With the use of additional sleeve resonators having differing external diameters or permittivities, a single specimen can be characterized at multiple frequencies. Sleeve resonators can also be employed for accurate dielectric characterization of high-permittivity specimens having dielectric loss factors greater than 0.001. Closed-form solutions for TE<sub>0np</sub> resonant mode structure are given. Uncertainty relations for permittivity and dielectric loss are also shown, which demonstrate that when sample electric energy filling factors are greater than 0.4, relative uncertainties in measured permittivity and dielectric loss tangent are less than 1% and 4%, even for relative permittivities greater than 600. Example measurements are given that illustrate how this dielectric resonator system can be employed for dielectric characterization of ferroelectric materials at temperatures both near or far from their Curie temperatures
    No preview · Conference Paper · Feb 2002
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The influence of low concentration (1 mol%) Mg doping on the structural, microstructural, surface morphological and dielectric properties of Ba1-xSrxTiO3 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 post deposition 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 and correlated to the films dielectric and insulating properties. Dielectric properties of unpatterned films were measured at 10 GHz with a coupled/split dielectric resonator system and at 100 kHz using metal-insulator-metal capacitors. The Mg-doped BST films exhibited improved dielectric loss and insulating characteristics compared to the undoped Ba0.6Sr0.4TiO3 thin films. The improved dielectric properties, low leakage current, and good tunability of the low level Mgdoped BST thin films merit strong potential for utilization in microwave tunable devices.
    Full-text · Article · Dec 2001
  • [Show abstract] [Hide abstract]
    ABSTRACT: Aspects of the development of low-cost (Sr,Ca)<sub>3</sub>Al<sub>2 </sub>O<sub>6</sub> dielectrics for Bi<sub>2</sub>Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>8+δ</sub> superconductor applications were investigated, A tie-line phase equilibrium relationship between Bi<sub>2</sub>Sr<sub>2</sub>CaCu<sub>2 </sub>O<sub>8+δ</sub> and Sr<sub>2</sub>CaAl<sub>2</sub>O<sub>6 </sub> compositions was observed at 860°C, When the Bi-2212 and (Sr,Ca)<sub>3</sub>Al<sub>2</sub>O<sub>6</sub> solid-solution compositions were changed slightly, the tie-line relationship was not preserved, and a new phase was observed to form with composition ~BiSr <sub>1.5</sub>Ca<sub>0.5</sub>Al<sub>2</sub>O<sub>x</sub>. Composites of (0 to 24) volume fraction % Sr<sub>2</sub>CaAl<sub>2</sub>O<sub>6</sub>-Bi<sub>2</sub>Sr<sub>2 </sub>CaCu<sub>2</sub>O<sub>8+δ</sub> equilibrated at 860°C slightly reduced the T<sub>c</sub> (by 2 K to 4 K) and superconducting volume percentage of the 2212 phase. The dielectric properties of (Sr=1.0 to 2.5) members of solid-solution (Sr,Ca)<sub>3</sub>Al<sub>2 </sub>O<sub>6</sub> were measured at 77 K and 297 K in the range of (10 to 11) GHz for cylindrical samples using resonant system methods. The dielectric constant ε<sub>r</sub> varied from 9.7 to 13.2, and the loss tangent tan δ was from 3×10<sup>-4</sup> to 8×10 <sup>-4</sup>
    No preview · Article · Apr 2001 · IEEE Transactions on Applied Superconductivity

Publication Stats

2k Citations
51.94 Total Impact Points

Institutions

  • 1990-2011
    • National Institute of Standards and Technology
      • • Electromagnetics Division
      • • Materials Science and Engineering Division
      Maryland, United States
  • 2001
    • University of Colorado at Boulder
      Boulder, Colorado, United States
  • 1999
    • University of Western Australia
      • School of Physics
      Perth City, Western Australia, Australia
    • U.S. Department of Commerce
      Washington, Washington, D.C., United States
    • Colorado State University
      Fort Collins, Colorado, United States
    • Warsaw University of Technology
      • Institute of Microelectronics and Optoelectronics
      Warsaw, Masovian Voivodeship, Poland