Masaya Nakamori

Electrical properties of hydroxyapatite thin films grown by pulsed laser deposition

Abstract The formation of bioceramic hydroxyapatite (HAp) thin films has been accomplished on various substrates, such as Ti, α -Al 2 O 3 , SiO 2 //Si(100) and SrTiO 3 (100) using an ArF pulsed laser deposition. The surface morphology of the HAp films was also examined using an atomic force microscope. Au/HAp/Nb doped SrTiO 3 (100) structures have been fabricated to measure the electrical properties of the HAp films, and the dielectric constant and breakdown voltage at 25 °C are 5.7 (at 1 MHz) and 10 4 V cm −1 , respectively. From our results, it is suggested that the HAp films are useful not only as a biocompatible coating material for implantation but also for insulating and dielectric materials used in electric circuits and bio-electronic devices.

Pulsed Laser Deposition of Bioceramic Hydroxyapatite Thin Films on Polymer Materials

The ArF excimer laser deposition technique has been used to fabricate bioceramic hydroxyapatite (HAp) thin films on polymer materials such as polyimides (PI), polytetrafluoroethylene (PTFE), silicone rubber (SR), and polyethyleneterephthalate (PET). The crystallinity, structure, composition and surface morphology of HAp films are evaluated by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX) and atomic force microscopy (AFM). Crystallized HAp films are obtained on PI and PTFE, and mechanical properties of HAp films on the polymer materials are examined using an Instron testing machine. This result is very important to enable the application of organic/inorganic-ceramic composite materials in medical fields.

Preparation of all-oxide ferromagnetic/ferroelectric/ superconducting heterostructures for advanced microwave applications

As candidates for functional layers, 3d transition metal oxides with perovskite structures show some interesting properties, such as ferromagnetism, ferroelectricity and superconductivity. Accordingly, combinations of these properties can be used to create new tunable microwave devices. Ferromagnetic/ferroelectric/superconducting multistructures, such as La0.70Sr0.30MnO3 (LSMO)/Pb(Zr0.52Ti0.48)O3 (PZT)/YBa2Cu3O7-y (YBCO) and YBCO/PZT/LSMO, have been fabricated by ArF excimer laser deposition on LaSrGaO4 (LSGO) [001] and (La0.30Sr0.70)(Al0.65Ta0.35)O3 (LSAT) [001] substrates. The resulting trilayer films have a highly c-axis oriented structure. Epitaxial YBCO films formed on PZT/LSMO//LSAT have a zero-resistance temperature of 87 K. Moreover, D-E and M-H hysteresis loop are observed for the LSMO/PZT/YBCO//LSGO structure using a conventional Sawyer-Tower circuit and a superconducting quantum interference device (SQUID). The remanent polarization and coercive field of the PZT layer are found to be 19 µC cm-2 and 275 kV cm-1 at 70 K, respectively. The remanent magnetic moment and coercive magnetic field are about 2.6 µB/site and 50 Oe respectively at 78 K. Furthermore, the microwave surface resistance (RS) (22 GHz) of the YBCO film in the YBCO/PZT/LSMO structure was 1.32 m at 77 K. These results suggest that LSMO/PZT/YBCO structures are favourable for use in superconducting microwave applications such as tunable phaseshifters and filters.

Study of mechanically tunable superconducting microwave filter using lumped elements

We propose a mechanically tunable superconducting microwave filter based on lumped elements composed of planar meander-line inductors (L) and inter-digital capacitors (C). As the first step, we have designed and evaluated a 3-pole Chebyshev bandpass filters with lumped elements using a circuit simulator. It is found that the center frequency, bandwidth and skirt rejection of the filter can be controlled by changing only the capacitance. The L and C elements values are estimated using an electromagnetic simulator. Furthermore, we have fabricated the inter-digital capacitor designed with the above procedure. We have evaluated change of the C values using mechanical tuning as a step toward a tunable superconducting microwave filter.

Formation of Hydroxyapatite Thin Films on Surface-Modified Polytetrafluoroethylene Substrates

An ArF excimer laser deposition technique is used to fabricate hydroxyapatite [Ca10(PO4)6(OH)2]-(HAp) thin films on surface-modified polytetrafluoroethylene (PTFE) substrates. The surface of PTFE is modified by a sodium-naphthalene complex in a glycol ether solvent. X-ray diffraction (XRD) studies indicate that as-deposited films prepared at substrate temperatures below the glass transition temperature of PTFE (327°C) are in an amorphous state. The crystallization of as-deposited films needed annealing for 10 h at 310°C. The structure, surface morphology and bond strength of HAp films were evaluated using XRD, the atomic force microscopy (AFM) and the Instron testing machine. The tensile bond strength of HAp films on surface-modified PTFE was 6.0 MPa, which is one order of magnitude larger than that of films on non-surface-modified PTFE, demonstrating its potential for practical applications.

Mechanically Tunable High-Temperature Superconducting Microwave Filter with Large Shift of Resonant Frequency

We propose a mechanically tunable superconducting microwave filter using a floating dielectric or magnetic plate which can be displaced by an actuator above the resonator for frequency tuning. We also examine the transmission and tunable characteristics of the mechanically tunable filter numerically and experimentally. The electromagnetic field simulation based on the moment method shows that a large shift in the resonant frequency by about 1.8 GHz is obtained by displacement of the (La0.3Sr0.7)(Al0.65Ta0.35)O3 [LSAT] floating dielectric plate by 0.1 mm. In the experiment, we obtained a 1.36 GHz shift from the initial center frequency of 7.05 GHz with little increase in the insertion loss by application of an electric voltage to the electromagnetic actuator. These results suggest that the mechanical tuning of superconducting microwave components is useful for optimizing frequency response and for the functioning of RF filter at the front end of the base station receiver of a software-defined radio (SDR).

Characteristics of mechanically tunable superconductive resonators

In order to realize superconductive microwave devices with large tuning characteristics, we have studied a mechanically tunable superconductive resonator beneath a dielectric and/or magnetic floating plate (FP) as a first step. The resonator consists of a half-wavelength coplanar waveguide (CPW). The principle of the mechanically tunable method is that variations of the effective permittivity and/or the effective permeability for the microwave waveguide line can be obtained by changing the distance between the resonator and the FP. In computer simulations of electromagnetic fields for the mechanically tunable half-wavelength CPW resonator, we have obtained a large shift of the resonant frequency with a band of 1.75 GHz to 7 GHz (tunability is approximately 25%) using the (La0.3Sr0.7)(Al0.65Ta0.35)O3 (LSAT) single crystal (dielectric constant (er) = 22.8, loss tangent (tanδ) = 1.7 × 10−4) as the FP. Based on the results, we have performed an experiment using a half-wavelength CPW resonator made from YBa2Cu3O7−δ thin film and the LSAT FP. The result shows a drastic resonant frequency shift of approximately 1.36 GHz (tunability is approximately 20%) when the LSAT FP is moved, using an electromagnetic actuator. In this experiment, it is also noted that the insertion loss is quite low, less than 0.8 dB, compared to previous reports for various tunable filters. Moreover, we have also measured the tuning characteristics with a TiO2 single crystal (er = 85.4, tanδ = 2.5 × 10−4) as the FP. As a result, we have obtained quite large tuning characteristics of approximately 2 GHz (tunability is approximately 28%).

Preparation and design of a mechanically tunable superconducting lumped-element filter

We have proposed a novel type of tunable superconducting microwave filter consisting of planar lumped elements which can independently change their centre frequency, bandwidth and skirt characteristics. The independent control is realized by applying the technique of mechanical tuning to the interdigital capacitors C which constitute the filter. We design a three-pole Chebyshev band-pass filter (BPF) with a centre frequency of 6 GHz, 3 dB fractional bandwidth (FBW) of 1.67% and passband ripple of 0.1 dB. The values of C and the meander line inductor L element are calculated using an electromagnetic simulator. The designed filter is fabricated using Y Ba2Cu3O7−δ (YBCO) film deposited on a MgO(100) substrate (10 mm × 10 mm × 0.5 mm). The measured transmission characteristic shows the typical BPF-like frequency dependence. This result is the first report on the planar lumped-element BPF with a high frequency of 6 GHz. Furthermore, the large shift of the centre frequency of the order of a gigahertz is obtained by an experiment in the mechanical tuning method.

Superconducting magnetostatic wave devices using HTS/perovskite-type manganite PCMO heterostructure

Pr1−xCaxMnO3 (PCMO) (x = 0.15~0.30) has good dielectric and magnetic properties at the microwave band. High-Tc superconductor (HTS)/ferromagnetic PCMO heterostructure has a high potential for superconducting tunable microwave filters and superconducting magnetostatic wave (MSW) devices. In order to demonstrate the preparation possibility of superconducting MSW devices, we investigated the microwave behaviour of YBa2Cu3O7−δ(YBCO)/PCMO heterostructures fabricated by a pulsed laser deposition technique on (La0.3Sr0.7)(Al0.65Ta0.35)O3 (100) substrate. We also fabricated superconducting MSW-band elimination filter (BEF) with YBCO/PCMO structure. The MSW-BEF exhibited notch characteristic that is caused by the energy conversion due to the coupling between the MSW mode and the transverse electromagnetic mode. These results suggest that the HTS/PCMO heterostructure is effective for the superconducting MSW application.

Formation of c-Axis Oriented YBa_2Cu_3O_ Thin Film on Amorphous Substrates with Al(111) Buffer Layer

C-axis-oriented YBa2Cu3O7-y (YBCO) films have been formed on (111)-oriented Al films using the pulsed-laser deposition method. The (111)-oriented Al films, which are grown at room temperature, are effective for the formation of a crystallized YBCO film on an amorphous substrate. Before YBCO film formation, the Al surface was oxidized in (O2+8% O3) gas atmosphere to create an AlOx layer on the top surface of the Al film. This AlOx plays the role of a buffer and seed layer which has a periodic potential of atomic order corresponding to the Al(111) plane. The optimal substrate temperature for YBCO deposition was 590° C. The Tc(onset) and Tc(zero) of the YBCO film formed on Al/glass were 90 K and 75 K, respectively.