Fabrication of stabilized piezoelectric thick film for silicon-based MEMS device

Electrical properties of piezoelectric thick films with controlled microstructure were investigated. In order to enhance the electromechanical properties (e.g. d₃₁, d₃₃) of a thick film by control of its microstructure, a mixed powder, referred to as BNP, consisting of both nano-sized and micro-sized piezoelectric particles, was employed as a starting precursor in the film fabrication process. According to a scanning electron microscopy study, it is shown that a BNP thick film exhibits the densest homogeneous microstructures. According to surface area measurements, the BNP thick film was sufficiently densified without an additional infiltration process of Pb(Zr_1-xTi_x)O₃ sol for densification. The screen-printed BNP thick film possesses a dielectric constant and a remanent polarization much higher than those of a thick film composed of only micro-sized piezoelectric particles by a factor of more than two. This suggests the potential application of the BNP thick film, in conjunction with a silicon substrate, to a micromachined monolithic PZT thick film device on the silicon substrate. PACS 85.40.Xx; 85.85.+j; 85.50.-n; 77.65.-j; 68.37.-d     

Acousto-mechanical and thermal properties of clotted blood

The efficacy of ultrasound-assisted thrombolysis as an adjunct treatment of ischemic stroke is being widely investigated. To determine the role of ultrasound hyperthermia in the process of blood clot disruption, the acousto-mechanical and thermal properties of clotted blood were measured in vitro, namely, density, speed of sound, frequency-dependent attenuation, specific heat, and thermal conductivity. The amplitude coefficient of attenuation of the clots was determined for 120 kHz, 1.0 MHz, and 3.5 MHz ultrasound at room temperature (20 +/- 2 degrees C). The attenuation coefficient ranged from 0.10 to 0.30 Np/cm in porcine clots and from 0.09 to 0.23 Np/cm in human clots. The experimentally determined values of specific heat and thermal conductivity for porcine clotted blood are (3.2 +/- 0.5) x 10(3) J/kg x K and 0.55 +/- 0.13 W/m x K, respectively, and for human clotted blood are (3.5 +/- 0.8) x 10(3) J/kg x K and 0.59 +/- 0.11 W/m x K, respectively. Measurements of the acousto-mechanical and thermal properties of clotted blood can be helpful in theoretical modeling of ultrasound hyperthermia in ultrasound-assisted thrombolysis and other high-intensity focused ultrasound applications.     

Measuring inter-DNA potentials in solution

Interactions between short strands of DNA can be tuned from repulsive to attractive by varying solution conditions and have been quantified using small angle x-ray scattering techniques. The effective DNA interaction charge was extracted by fitting the scattering profiles with the generalized one-component method and inter-DNA Yukawa pair potentials. A significant charge is measured at low to moderate monovalent counterion concentrations, resulting in strong inter-DNA repulsion. The charge and repulsion diminish rapidly upon the addition of divalent counterions. An intriguing short range attraction is observed at surprisingly low divalent cation concentrations, approximately 16 mM Mg2+. Quantitative measurements of inter-DNA potentials are essential for improving models of fundamental interactions in biological systems.     

The effect of surface crystalline layers on asymmetric off-diagonal magnetoimpedance in field-annealed CoFeSiB amorphous ribbons

The off-diagonal magnetoimpedance in field-annealed CoFeSiB amorphous ribbons was measured using a pick-up coil wound around the sample. One side of a ribbon was etched in hydrofluoric acid solution during various times in order to change the thickness of the surface crystalline layer appearing after annealing. The asymmetric two-peak field dependence of the off-diagonal impedance was observed for all samples. The evolution of the off-diagonal magnetoimpedance with the change in the ribbon thickness is analyzed.     

Insertion loss of sound waves through composite acoustic window materials

This study evaluated the insertion loss of sound waves through composite acoustic window materials for sonar dome applications, and examined the influence of dome shape on the sonar performance. The insertion loss of sound waves through acoustic window materials was experimentally measured as a function of frequency at normal incidence. The insertion loss was also theoretically estimated with three- and four-medium layer models. The theoretical estimation of insertion loss showed good agreement with the experimental measurements. The insertion loss was also measured as a function of angle of incidence. The characteristics of longitudinal and converted shear waves were observed at various angles of incidence. This study will be useful to select acoustic window materials with the appropriate acoustic characteristics for practical sonar dome applications.     

Future Direction for a Diffusion Barrier in Future High-Density Volatile and Nonvolatile Memory Devices

This article reviews the current status of high-density capacitor for volatile memory devices. The dielectric properties for both the Ta₂O₅ film and the (Ba, Sr)TiO₃ (BST) dielectric materials using either the metal organic chemical vapor deposition (MOCVD) or the atomic layer deposition (ALD) are reviewed briefly. New challenges of dielectric material for the next generation, and serious problems emerged during integration to date using Ta₂O₅ and BST. The material characteristics of many electrode materials for the high dielectric materials are introduced. We present the basic properties and integration issued for MOCVD-ruthenium (Ru). The second part of this review summarized the failure mechanisms from barrier properties of previously reported diffusion barriers and emphasizes new design concepts of diffusion barrier for high-density memory devices. Finally, the future direction for a diffusion barrier to advance high-density memory capacitors is suggested.     

A Paper‐Based Platform for Long‐Term Deposition of Nanoparticles with Exceptional Redispersibility,Stability, and Functionality

Although nanoparticles (NPs) can be carefully engineered to have maximal stability and functionality desirable for use in diverse applications, they are generally not suitable for long‐term storage in solution. It is also difficult to store NPs in a dry state because dried NPs generally become aggregated and cannot easily be redispersed. Thus, a new strategy allowing long‐term storage of NPs with high stability, redispersibility, and functionality is highly demanded. By passivating the 13 nm gold nanoparticle (AuNP) surface with stabilizing agents and treating a paper substrate with both bovine serum albumin and sucrose after coating with a hydrophobic polyvinyl butyral layer, it is possible to fully redisperse (≈100%) dried AuNPs with colloidal stability comparable to that of as‐prepared AuNPs. Furthermore, AuNPs physically stabilized with polyvinylpyrrolidone can react with thiol‐containing compounds, such as 1,4‐dithiothreitol (DTT). Taking advantage of the oxidation reaction of hypochlorous acid with DTT, it is possible to demonstrate a paper‐based colorimetric sensor for detection of residual chlorine in water. Since this strategy is applicable to large‐sized AuNPs (30–90 nm), silver NPs, oleic acid‐capped magnetic NPs, and cetrimonium bromide‐passivated gold nanorods, it can be used for diverse NPs requiring long‐term storage for many applications.