A Barium Strontium Titanate (BST) Rectangular Dielectric Resonator Antenna (RDRA) was constructed on a FR4 Printed Circuit Board (PCB). The RDRA was innovatively glued to the PCB using dried sol-gel BST composite as opposed to epoxy, which has not been done before. Adhesion pull tests indicated that an average load of 161 grams can be applied before separation of RDRA and PCB occurs. The RDRA antenna gain was 3.6 dB for the RDRA in TE1δ1 mode at 10.1 GHz.

Ba0.7Sr0.3TiO3 (BST) capacitors for high frequency circuits have been fabricated at 175 degrees C on epoxy-based copper-clad printed circuit boards, having a glass transition temperature of approximate to 200(degrees)C by hydrothermal processing of dried BST acetate-based sol-gel powder slurries. The film thickness was 2-10m. BST powders were prepared respectively as ceramic derived powders processed from oxide mixtures fired to 1100 degrees C, sol-gel derived powders fired to 750 and 1100 degrees C, and a low temperature solution process dried at 500 degrees C. The performance of the capacitor was determined by both the dielectric properties of the powder and the interaction between the crystallizing gel and the powder surface. High relative permittivity is obtained for sol-gel derived powders fired to 750 degrees C, while high voltage tunability is a characteristic of the ceramic derived powders. Low temperature powders are ineffective. The difference is attributed to the nature of the crystalline interface formed between the surface of the powder particles and the hydrothermally crystallized BST formed from the dried gel within the composite. The optimum molar concentration of the hydrothermal solution was 0.1M with a Ba content larger than that of the powder. Capacitor composites having a relative permittivity of up to 300 at 20MHz were demonstrated.

Procedures are described to fabricate barium strontium titanate (BST) gap capacitors within a microstrip resonator fabricated directly on a printed circuit board (PCB). This is the first time that an all-BST ceramic has been processed on epoxy-based PCBs at 175 °C. In order to accommodate the temperature limitations of the underlying PCB (<;200 °C), and to achieve the required dimensions, ~75-μm (3 mil) gap capacitors have been fabricated by hydrothermal processing of BST sol-gel composites. The performance of voltage-tunable microstrip resonators operating from 5 to 10 GHz showed a permittivity of 52 at 7.05 GHz and a voltage tunability consistent with that expected for thin-film BST devices. Measurements of these resonators are presented.

ABSTRACT Barium strontium titanate (BST) and BST doped with 5 at% Mn films have been fabricated on gold-patterned alumina substrates by hydrothermal sol-gel composite recrystallization at < 200°C. A spun-on sol-gel BST composite film is hydrothermally treated in an alkaline aqueous solution at elevated pressure. The dielectric constant and loss tangent between 5 and 40 GHz has been determined using the response of a series of coplanar waveguide spur-line band stop filters. The film shows a maximum dielectric constant between 15–40 GHz of 94 ± 5 for a film 2.6 μ m in thickness. The loss tangent at 15 GHz is 0.07.

A new micromolding technique for fabricating high-frequency (>20 MHz) ultrasound transducers has been developed. The technique combines sol gel processing with an epoxy-based, photo-resist Su-8 micromold to form miniature PZT structures. An advantage of this technique as compared to more traditional lithographic galvanforming and abforming (LIGA) processing is that the intermediate step of producing a nickel-plated mold is avoided. Instead, the PZT is formed directly using a photo-resist. The resulting structures can be fabricated with aspect ratios up to 3:1 and thicknesses up to 50 micro. We have successfully fabricated 50-micro-thick linear array elements with 23-micro-wide elements separated by 15 kerfs. A 50-micro thick, 2.5-mm diameter, five-element annular array structure with 20-micro kerfs also has been fabricated. The micromolded PZT composite has a density of 5.7-5.8 micro 0.4 g/cm3 and a thickness coupling coefficient as high as 0.32.

Silicon stabilized tricalcium phosphate [Si-TCP] is formed within the calcium hydroxyapatite (HA)-tricalcium phosphate (TCP) system when a stoichiometric precipitate of hydroxyapatite is fired at 1,000 degrees in the presence of SiO(2). This paper proposes a composition range and crystallographic structure for Si-TCP. Reitveld XRD powder diffraction, transmission electron microscopy, infrared and proton nuclear magnetic resonance measurements show that crystalline Si-TCP is associated with the displacement of OH from an initial hydroxyapatite structure. The resulting calcium phosphate is modified by the incorporation of silicon into its structure with excess silica contributing to an amorphous component. Si-TCP has a monoclinic structure with a space group P2(1)/a akin to alpha-TCP with estimated lattice constants of a=12.863+/-0.004 A, b=9.119 +/-0.003 A, c=15.232+/-0.004 A, beta=126.3+/-0.1 degrees. It is proposed that Si(4+) substitutes for P(5+)in the TCP lattice with the average chemical composition of Si-TCP set primarily by the mechanisms available for charge compensation. While the formation of OH vacancies in HA initiates the transformation to Si-TCP, two mechanisms of charge compensation in the Si-TCP structure are plausible. If O(2-) vacancies provide charge compensation, the composition of Si-TCP is Ca(3)(P(0.9)Si(0.1)O(3.95))(2) derived for the addition of 0.33 mol SiO(2):mol HA. If excess Ca(2+) compensates, the composition is Ca(3.08)(P(0.92)Si(0.08)O(4))(2) derived for the addition of 0.25 mol SiO(2):mol HA. The reaction occurs most effectively when SiO(2) is added as a colloidal suspension rather than by the in-situ thermal decomposition of a silicon metallorganic compound. The material is a bioceramic of major biological interest because of its osteoconductivity and unique influence on skeletal tissue repair and remodeling.

A sol gel composite process has been used to produce lead zirconate titanate coatings in the thickness range of 3 to 100 /spl mu/m on aluminum substrates. The complex permittivity (/spl epsi//sub 33//sup S/), elastic stiffness (c/sub 33//sup D/), and the piezoelectric constant (h/sub 33/) of the coating and the complex elastic stiffness (c/sub 33//sup D/) of the substrate have been determined using impedance measurements and a commercially available software program [Piezoelectric Resonance Analysis Program PRAP 2.0, TASI Technical Software, Kingston, Ontario, Canada]. The complex components of the material parameters account for the losses within the film and the substrate. Sol gel composite films on aluminum have a dielectric constant of 220 with an imaginary component of 1% and an electromechanical coupling coefficient of up to 0.24 with an imaginary component of 3%. These films are applied to the fabrication of a high frequency transducers suitable for ultrasound biomicroscopy (UBM). By combining the sol gel composite material with existing transducer fabrication techniques, single-element focusing transducers have been produced that operate in the frequency range of 70 to 160 MHz. Devices have -6-dB bandwidths up to 52% and minimum insertion losses ranging from -47 to -58 dB. Real-time images of phantom materials and ex vivo biological samples are shown.

A robust scratch tester for industrial application has been developed to evaluate PVD TiN coatings on M2 tool steel by plots of the effective coefficient of friction for indenter movement, mu(eff) = F-H/F-V, as a function of the vertical force applied to a Rockwell C diamond indenter. A clear transition between different slopes in such a graph is correlated with the critical load for coating failure as identified by microscopic observations. The variation in mu(eff) as a function of vertical load is explained initially by the work hardening of the surface region due to contact with the indenter. As the applied load is further increased, the ploughing force within the coating and the shearing force due to adhesion between the coating and the substrate begin to dominate the behaviour of mu(eff). Results for coatings on different substrates are presented to demonstrate the versatility of the unit for industrial testing. (C) 1999 Elsevier Science S.A. All rights reserved.

Piezoelectric arrays suitable for high frequency ultrasound have been fabricated using PZT sol gel composite coatings in the thickness range of 5-100 mu m on aluminum and platinized alumina substrates. The coatings have been quantitatively characterized using impedance measurements to 100 MHz. The analysis provides a direct measure of the piezoelectric coupling coefficient of k(t) < 0.34. 16 element linear array structures suitable for ultrasound biomicroscopy at 30-40 MHz with elements having dimensions similar to 40 mu m thick, 20-25 mu m wide and 15 mu m spacing have been patterned using excimer based laser micromachining. The dielectric and pulse echo responses have been measured.

Piezoelectric devices generally require film thicknesses in the range 2-200µm and have a response which is perturbed by the substrate. Sol gel and sol gel composite technology provide a manufacturable process for many purposes with a piezoelectric coupling coefficient for 40ptm thick PZT approaching k t = 0.34. Techniques such as laser machining or micromolding are required for patterning thick devices. Measurement and applications of piezoelectric coatings in medical imaging, high temperature ultrasonics and flexure devices are discussed.

PZT coatings have been produced in the thickness range of 5-200 microns using a composite sol gel process [1]. The application of this process in the fabrication of high frequency transducers suitable for ultrasound biomicroscopy (UBM) has been investigated. Curved single element transducers have been produced in a range of 70-165MHz with -6dB bandwidths as high as 52% and minimum insertion losses ranging from -47 to -58dB. Laser micromachining techniques for patterning linear array structures to operate at similar frequencies have been developed. Trenches <10 mu m wide with a 50% taper through 20 mu m of ceramic have been achieved with a pulsed frequency doubled Nd:YAG laser. Trenches 5 mu m wide with straight walls have been achieved using a pulsed KrF excimer laser.

Chemical solution deposition (CSD) allows the integration of ferroelectric and piezoelectric coatings with both silicon technology and in large scale macroscopic devices: Applications of coatings as actuators, in high frequency ultrasonic transducers and for piezoelectric transformers are discussed.

Lead zirconate titanate (PZT) ceramic films of thickness 5-200 mu m have been produced on various substrates using a modified sol gel process. A subset of these films (5-27 mu m) open the possibility of fabricating ceramic ultrasound transducers in the frequency range of 80-200 MHz. The technique involves mixing PZT powder conventional PZT sol gel to form a paint which is then coated onto a flat substrate. Initial characterization has included the dielectric and impedance response of the PZT film supported by a metal substrate. The films resonate within the desired frequency range, but the substrate is not conductive for ultrasonic transducers. A technique has been developed to mount the PZT onto conductive silver epoxy using 80 mu m aluminum foil as a sacrificial layer. The pulse echo response of this structure demonstrates the broadband response required for ultrasound imaging transducers.

The chemical reactions underlying the formation of a water based alkoxide sol gel process for lead zirconate titanate thin films using solutions of Ti and Zr alkoxides are outlined. Titanium isopropoxide and zirconium propoxide are chemically modified by acetic acid in order to use water as a solvent. The nature of the hydrolysis reactions in the presence of acetic acid is reviewed. It is shown that the formation of ions and charged polymeric species reduces their rates of condensation and aggregation.

Barium strontium titanate (BST) films have been fabricated using a modified sol gel method. The crystallization temperature was 100 degrees C higher than that for lead zirconate titanate. The electrical properties improved when multiple rapid thermal processing was used. The dielectric constant of BST films was of the order of 250 which was characteristic of a small grain size and the presence of a low dielectric constant barrier. Doping by La, Nb, Mg, Y, Ru, Mn and Gd had an adverse effect on the dielectric constant even for small concentrations of about 1 at. %. Doping with cerium up to 3 at. % increased the dielectric constant of BST films up to 300 while dielectric losses remained low approximate to 0.025. The leakage current densities improved for donor type doping and were < 10 nA/cm(2) at E=60 kV/cm. BST films 1900 Angstrom thick doped with 3 at. % of Ce had a charge storage density and capacitance density of 50 fC/mu m(2) and 15 fF/mu m(2) respectively.

Air-coupled capacitance transducers have been manufactured using anisotropically etched silicon backplates and commercially available dielectric films (Kapton and Mylar). The small backplate pits which result from etching, provide well ordered and highly uniform air layers between the backplate surface and thin dielectric film. Such uniformity allows the transducers to be manufactured with reproducible characteristics (a property difficult to achieve through conventional manufacturing). Impulse response studies in generation and detection, have indicated well-damped, wideband behavior, with bandwidths extending from <100 kHz to 2.3 MHz (at the -6 dB points). These bandwidths are investigated as a function of excitation pulse width, applied bias potential, and dielectric film thickness. An estimate of detection sensitivity is also provided by comparison with a calibrated laser interferometer.< >

The applicability of critical current theory to macroscopic magnetic phenomena related to the magnetic shielding ability of high temperature superconductors is discussed and some misuse of the Bean model is demonstrated. Critical current theory is used to analyze the relationships among magnetic shielding factors, breakthrough fields, the waveforms of penetrated fields, as well as their dependence on AC and DC bias fields and sample thickness. Good agreement between the waveforms of penetrated fields observed with an oscilloscope and those predicted theoretically was obtained. The axial gradient of the magnetic field in an axial direction inside a superconductor under a normal magnetic field has been analyzed both qualitatively and quantitatively. Finally, a novel experimental method to measure the distribution of the axial component of a magnetic field inside a high temperature superconductor is presented.

Thin films of RuO2 can be prepared by low-temperature chemical vapor deposition from pure RuO4, and the best films are obtained by CVD at atmospheric pressure with the substrate at 150-degrees-C. Overlayers of lead zirconate titanate (PZT) can then be prepared, and hysteresis in the Si/RuO2/PZT/Au structure can be demonstrated, thus suggesting potential applications in ferroelectric memory materials.

A thermally stimulated current (TSC) technique has been used to characterize natural and electric-field-induced defect distributions in PZT (lead zirconate titanate) films. The principal defects give rise to TSC peaks near 400 K and 500 K, with defect concentrations of about 10 21 cm-3 and an activation energy of about 0.8 eV. Changes in the defect structures as a function of the number of switching cycles and processing conditions are described, and their relationship to fatigue are discussed. It is suggested that the defects distributions measured by TSC arise from extended defects rather than from point defects. Domain splitting and pinning as a result of such defects generated during polarization reversals may account for fatigue in PZT films

Techniques are described for the sol-gel fabrication of ferroelectric PZT (lead zirconate titanate) films on different substrates up to 1.5 μm in thickness by a single coating and up to 8 μm by multiple coating. A microscopic and macroscopic review of the sources of stress in films during drying and firing suggests procedures for fabricating thick PZT films. These include the use of additives such as glycerol to reduce internal stress during firing, and appropriate firing schedules to accommodate the film thickness. A mechanical model for guiding the development of such films is presented