Porous thin films containing very small closed pores (∼ 20 Å) with a low dielectric constant (∼ 2.0) and excellent mechanical properties have been prepared using the mixture of cyclic silsesquioxane (CSSQ) and a new porogen, heptakis(2,3,6‐tri‐O‐methyl)‐β‐cyclodextrin (tCD). The pore sizes vary from 16.3 Å to 22.2 Å when the content of tCD in the coating mixture increases to 45 wt.‐% according to positronium annihilation lifetime spectroscopy (PALS) analysis. It has also been found that the pore percolation threshold (the onset of pore interconnectivity) occurs as the ∼ 50 % tCD porogen load. The dielectric constants (k = 2.4 ∼ 1.9) and refractive indices of these porous thin films decreased systematically as the amount of porogen loading increased in the coating mixture. The electrical properties and mechanical properties of such porous thin films were fairly good as interlayer dielectrics.
An optimum design has been performed to maximize the specific energy density (SED) of a composite flywheel rotor for an energy storage system. The flywheel rotor consists of multiple rings, and the interferences and ply angles vary in the radial direction. For the structural analysis the rotor is assumed to be an axisymmetric thick laminated shell with a plane strain state. Considering the ring-by-ring variation of fiber orientations, a symmetric local stiffness matrix was derived for each ring. Using the stiffness matrix, the continuity conditions of radial stresses and displacements between the rings with a consideration of the interferences can be easily incorporated. A symmetric global stiffness matrix is then obtained assembling the local stiffness matrices. Displacements are obtained by solving the global stiffness matrix, and the stresses in each ring are then calculated. Three-dimensional intra-laminar quadratic Tsai-Wu criterion for the strength analysis is used yielding the strength ratio for each ring. The optimization has been also performed maximizing the kinetic energy stored in the rotor. For that purpose the sensitivities of the strength ratios and displacements with respect to the design variables have been derived. As a result, the optimal design has attained 2.4 times of total energy compared to the case of 0 degree ply angle and no interference. The effects of interferences are found to be much more considerable than those of fiber orientations.
Porous cyclic silsesquioxane (CSSQ) thin films containing nanopores (∼ 2 nm) with low dielectric constant (k < 2.2), have been prepared by using various kinds of cyclodextrin (CD) derivatives as porogenic materials. The pore structure, including average pore size and interconnectivity, can be controlled by changing the functional groups of the cyclodextrin derivatives. The pore structure is found to be strongly related to the affinity of the functional groups between CD molecules. The electrical and mechanical properties of the porous thin films were monitored in order to determine the relationship between the pore structure and film properties. The mechanical properties of porous low‐k thin films (total porosity ∼ 30 %) prepared with CD derivatives are found to be correlated with the pore interconnection length. The longer the deduced interconnection length in the thin film, the worse the mechanical properties (such as hardness and modulus) of the thin film, even though the porogen‐induced pore diameters are very small (∼ 2 nm).
A micro XY-stage with a 5 5 mm 2 -area shuttle is fabricated for application in a nanometer-scale data storage device. A central shuttle of the device is designed as a large square on which a high-density recording medium is deposited. Perpendicularly combined comb-drive actuators allow the large shuttle free access in the x-y plane. No etching holes on the central shuttle are preferred in order to maximize the effective recording area. Therefore, a novel release process, Micro-Channel Assisted Release Process ( CARP) is proposed to release a large plate structure without any etching holes and to resist downward sticking. The static and dynamic strokes of the device were measured. Mechanical interferences between x-and y-directional drives were estimated by finite-element method (FEM) analysis and compared with the experimental results.[876]Index Terms-High-density storage, large area shuttle, micro XY-stage, scanning probe microscopy (SPM), micro-channel assisted release process ( CARP).
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