This work describes a practical and high-yield method of fabricating optical microelectromechanical-system (MEMS) switches. The method features the use of thick-plated gold multilevel interconnections for the mirror-drive electrodes and polyimide coating to protect the fragile and easily-movable micromachined mirror. The multilevel electrode developed was over 80-µm high providing enough space for the tilting mirror placed above it. Open-short circuit yield was 100% on 6-inch wafers. All the processes for fabricating the electrodes were carried out at under 310°C, meaning the electrodes could be successively formed after mirror-control large-scale integrated circuits (LSIs) were fabricated on a wafer. The fragile mirrors are sealed in polyimide during the fabrication processes. As this method protects the mirrors against the shock and damage caused by factors such as the dicing process, it enables 3-dimensional MEMS structures that have moving portions to be handled through conventional fabrication processes without the need for any special care. The static and dynamic characteristics of the optical MEMS switches fabricated are shown.
This paper describes a novel structure and fabrication process for the integration of several types of RF microelectromechanical-system (MEMS) device, such as switches and varactors having different structures. It also describes an encapsulation technique suitable for the integrated devices to protect movable parts during packaging. An adaptable multilayer structure and its fabrication process, which includes planarization with photosensitive polyimide, are proposed for integration. A capsule structure fabricated using spin-coating film transfer and hot-pressing technology is also proposed for protection. Several types of RF MEMS device were simultaneously fabricated on the same substrate using these techniques. The results confirm that these techniques will pave the way for the development of single-chip RF transceivers with integrated RF MEMS devices.
We show the existence of a new class of astrophysical objects where the self-gravity of the dust is balanced by the force arising from shielded electric fields on the charged dust. The problem of equilibrium dust clouds is formulated in terms of an equation of hydrostatic force balance together with an equation of state. Because of the dust charge reduction at high dust density, the adiabatic index reduces from two to zero. This gives rise to a mass limit M AS for the maximum dust mass that can be supported against gravitational collapse by these fields. If the total mass M D of the dust in the interstellar cloud exceeds M AS , the dust collapses, while in the case M D < M AS , equilibrium may be achieved. The physics of the mass limit is similar to the Chandrasekhar's mass limit for compact objects, such as white dwarfs and neutron stars.
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