Dung-Shing Hung

Intrinsic low dielectric behaviour of a highly thermally stable Sr-based metal–organic framework for interlayer dielectric materials

A Sr-based metal–organic framework {[Sr2(1,3-bdc)2(H2O)2]·H2O}n (1) was synthesized under hydrothermal conditions by the reaction of Sr(NO3)2 and 1,3-bis(4,5-dihydro-2-oxazolyl)benzene. A single-crystal X-ray diffraction analysis revealed that compound 1 adopts a 2D layer structure with a monoclinic (C2/c) space group. The distance between the layers of the structure adjusts upon the removal of the water molecules from 95 °C to 330 °C. In addition, the dehydrated compound 1′ retains its crystalline morphology and shows a high thermal stability at temperatures of up to 420 °C. Significantly, the dehydrated compound 1′ has a very low dielectric constant (2.4), suggesting that it might be useful as an interlayer dielectric in integrated circuits. As indicated by impedance spectroscopy, such low dielectric constant behavior is due to the intrinsic nature of the bulk material. The preparation of a low dielectric constant Sr-based metal–organic framework with a high thermal stability opens new directions for research into its applications.

Investigation on electromagnetic and microwave absorbing properties of La0.7Sr0.3MnO3−δ/carbon nanotube composites

In this study, the influence of the addition of carbon nanotube (CNT) (0, 0.5, 1.0, and 2.0 wt %) on complex permittivity, complex permeability, and reflection loss for La0.7Sr0.3MnO3−δ (LSMO)/polymer composites was investigated. Microwave absorbing composites were prepared by molding and curing a mixture of LSMO powders, CNTs, and epoxy resin. The complex permittivity and complex permeability for LSMO/CNT composites were examined by a cavity perturbation technique. The experimental results showed that the complex permittivity increased with increasing CNT addition and the imaginary part of the permeability decreased with rising frequency. In the present study, a microwave absorbing composite filled with 80 wt % LSOM powders and 2 wt % CNTs exhibited the optimum performance, that is, the microwave absorbing peak was −22.85 dB at 9.5 GHz and the −10 dB absorbing bandwidth reached 3.3 GHz for the sample with a matching thickness of 3 mm.

Complex permittivity and permeability of iron-based composite absorbers measured by cavity perturbation method in X-band frequency range

A cavity perturbation resonance technique is used to determine the complex permittivity and permeability of iron-based composite absorbers prepared by mixing various weight percentages of carbonyl iron powder with epoxy as the matrix. The complex permittivity (e′-je″) and permeability (μ′-jμ″) are measured around X-band (7–12.5 GHz for permittivity and 7.5–14 GHz for permeability) by the cavity perturbation resonance technique and the results are compared with those obtained by the transmission/reflection method. Experimental results show that the average differences of real parts of permittivity (e′) and real and imaginary parts of permeability (μ′ and μ″) measured by these two techniques are less than 10%. The differences in e″, however, is apparently higher than the others. As a general trend, the difference increases with increasing weight percentage of carbonyl iron.

Engineering Water-Dispersible FePt Nanoparticles for Biomedical Applications

We reported the synthesis and characterization of water-based FePt nanoparticles for biomedical applications. The superparamagnetic and hydrophilic FePt nanoparticles were synthesized by phase transfer method and the particles size were just only 2-4 nm. The functional FePt nanoparticles through ligand exchanging were achieved to bind the specific biomolecules. The streptavidin-biotin binding pair was used to demonstrate that water-based FePt nanoparticles could be further functionalized to provide a biotin moiety for specific interaction with streptavidin protein.

Relaxation behaviors of the bismuth-substituted yttrium iron garnet in the microwave range

The spin damping behavior of the bismuth-substituted yttrium iron garnets (BixY3−xFe5O12) prepared by the coprecipitation process was investigated using the ferromagnetic resonant (FMR) in this study. By analyzing the FMR responses, the spin damping coefficient of the x=0.25–1.25 in polycrystalline Bi:YIG (yttrium aluminum garnet) samples was obtained from the 3 dB linewidth of their FMR spectra. The data demonstrated that the damping coefficient started from 3.21×10−3 for x=0.25 and went to its minimum value of 0.31×10−3 for x=0.75. However, the damping coefficient enhanced to 8.55×10−3 with increasing of the bismuth concentration to x=1.25. The results revealed that the spin damping behavior of the Bi:YIG garnets was strongly dependent on a YFeO3 (111) phase.

Dielectric constant at x-band microwave frequencies for multiferroic BiFeO3 thin films

The magnetic-induced dielectric responses of BiFeO3 (BFO) thin films were measured at the X-band microwave frequency ranged from 7 to 12.5 GHz. The measurement was given initially by a high-precision cavity microwave resonator without magnetic field. Both the real and imaginary parts of the permittivity showed its dielectric property as a function of the measuring frequency. The X-band dielectric responses of the BFO thin film were then measured by a controlled magnetic field at room temperature. The data demonstrated up to 2.2% dielectric tunability by using only 3.46 kOe magnetic field at TE107 mode (9.97705 GHz).

Permittivity study of multiferroic AlN∕NiFe∕AlN multilayer films

NiFe inserted layer with different thicknesses on the dielectric properties of multiferroic AlN∕NiFe∕AlN multilayer films fabricated on the B270 glass substrates by the reactive sputtering technique was studied. The variation of dielectric constant for multilayer films is dependent on the thickness of the NiFe inserted layer observed from 40Hzto30MHz. In this work, single AlN layer exhibits dielectric constant value of around 6.5. However, we find that the dielectric constant of the AlN∕NiFe∕AlN multilayer films is raised up to 60 for even with a 1nm thick NiFe inserted layer. Additionally, this work also indicates that the dielectric tunability of AlN∕NiFe∕AlN films is dependent on the external magnetic field. These results conclude some magnetoelectric properties of AlN films those in relation to the NiFe ferromagnetic inserted layer. Possible mechanisms for the enhanced dielectric constant in the AlN∕NiFe∕AlN films have been discussed in the paper.

Permittivity Enhancement of

Co inserted layer with different thickness on the permittivity of Ta₂O₅(60 nm)/Co(x nm)/Ta₂O₅(60 nm) trilayer films fabricated on the B270 glass substrates by the reactive sputtering technique was studied. The variation of dielectric constant of the samples is dependent on the thickness of the Co inserted layer observed from 1 kHz and 30 MHz. The dielectric constant of the Ta₂O₅(60 nm)/Co(x nm)/Ta₂O₅(60 nm) thin films was varied roughly from 7.9 up to 90.6 with the thickness (x) of the Co interlayer varied from 0 nm to 20 nm. The value of the dielectric constant is roughly near 7.9 for samples with x between 0 and 2 nm. However, it increases abruptly for samples with x larger than 2 nm, this large enhancement behavior of the dielectric constant could be explained due to the growth mechanism of the Cobalt inter-layer from island clusters to continuous Co layer for samples with x between 2 and 3 nm. For the magnetic induced ferroelectric variation, the variation of the dielectric constant increased with thickness of Co for samples with x larger than 3 nm. However this increase behavior is roughly saturated for applied magnetic field roughly above 20 Oe. This magnetic tunability of the dielectric constant is clearly attributed to the Co layer in the films. From the electric consideration, the adding of a Co inter-layer in Ta₂O₅/Co/Ta₂O₅ structures redistributes the interface charges between Co and Ta₂O₅ layers, and that enhances both the intrinsic polarization and its dielectric constant. The magnetoelectric properties in Ta₂O₅/Co/Ta₂O₅ films are manifested and it has potential for a ferroic sensor application.

\hbox{Ta}_{2}\hbox{O}_{5}/\hbox{Co/Ta}_{2}\hbox{O}_{5}

Single-layer Fe films 800 A thick, with and without a 10-A-thick Ag buffer layer, were prepared at various growtht emperature,Tg, on GaAs(001) substrates by molecular-beam epitaxy. For Tg around 200 °C, high-quality single crystal films were obtained without the Ag buffer layer. For Tg ⩽100 °C, a defect structure was observed in the iron layer. However, the addition of an ultrathin Ag buffer layer between GaAs and Fe has the desirable effects of eliminating the defect structure and significantly enhancing the FMR absorption.

Trilayer Films

The effect of Co inserted layer with thickness below 20 nm on the dielectric permittivity of SiO2 (60 nm)/Co(x nm)/SiO2 (60 nm) thin films fabricated on glass B270 substrates by the reactive sputtering technique was studied. The dielectric constant is around 7.4 for B270 glass substrate and SiO2 /B270 film. However, it is rapidly raised up to roughly 55 for all the SiO2/Co/SiO2 samples with the thickness of Co inserted layer larger than 2 nm. From the cross section TEM pictures of the SiO2 /Co/SiO2 films with 1 and 2 nm Co thickness, we have experimentally demonstrated that this enhancement behavior of the dielectric constant is due to the growth mechanism of the Cobalt inter-layer from island clusters to continuous Co layer for samples with x larger than 2 nm. The adding of a Co inter-layer redistributes the interface charges between Co and SiO 2 layers, and that enhances both the intrinsic polarization and its dielectric constant. For the magnetic induced dielectric variation, the variation of the dielectric constant also increased with thickness of Co for samples with x larger than 2 nm. A direct observation of a 0.04-0.20% dielectric variation is induced by external magnetic field. However this increase behavior is roughly saturated for applied magnetic field roughly above 60 Oe. The magnetodielectric properties in SiO2/Co/SiO2 films are manifested and it has potential for a ferroic sensor application.