Encyclopedia of Nanotechnology

Abstract

SynonymsElectrostatic RF MEMS switches; Micromechanical switches; RF MEMS switches DefinitionCapacitive micro-electro-mechanical systems (MEMS) switches are a special type of micromachined switches that control radio frequency (RF) signal paths in microwave and millimeter-wave circuits through mechanical motion and contact. OverviewCapacitive and direct current (dc)-contact MEMS switches are among the most important micromachined devices for high-frequency applications due to their near-ideal RF performance. Dc-contact switches function similarly to conventional relays: micromachined beams or plates move under the influence of an appropriately applied force (e.g., electrostatic force) to open or close a metal-to-metal contact. While micromachined beams or plates are also utilized in capacitive switches, these switches rely on metal-to-dielectric contacts to implement their on and off states. Capacitive switches are particularly attractive for demanding high-frequency communications, electronic warfare, and radar systems due to their ultralow loss (< 0.1-0.2 dB up to 40 GHz), high isolation (>20-50 dB for frequencies beyond 10 GHz), very high linearity (>66 dBm third-order intercept point), and near-zero power consumption ($tens of nJ per switching cycle and zero quiescent power for electrostatically actuated switches). When compared to solid-state switches, capacitive switches are relatively slow devices with speeds ranging in the tens to hundreds of microseconds range. This speed is primarily limited by switch inertia and squeeze film damping. Their relatively large lateral dimensions of tens or hundreds of mm allow capacitive switches to handle several hundred mW of RF power. Long-term operation, however, can only be achieved if they are hermetically sealed in order to avoid contaminationand humidity-induced failure. Hermetically sealed capacitive switches have successfully switched over B. Bhushan (ed.), Encyclopedia of Nanotechnology, DOI 10.1007/978-90-481-9751-4, # Springer Science+Business Media B.V. 2012 100 billion cycles at room temperature and under low RF power conditions (20 dBm). Despite the aforementioned RF advantages, capacitive switches are currently not available commercially and are not widely utilized in defense or communication systems. This is primarily due to the facts that (1) high-yield manufacturing processes are not widely available yet and (2) their main failure modes such as dielectric charging, dc/RF gas discharge and metal creep and the physics behind them have not been adequately understood and addressed today. Figure 1 shows a typical capacitive MEMS switch [1]. This is a shunt switch configuration, and is the dominant capacitive switch configuration in the literature today. The signal travels down the center conductor, and if the switch closes, will return along the outside conductors. It is, however, possible to design geometries for series configurations. Their characteristics, nevertheless, are very similar to the ones found in shunt switches. Consequently, this entry focuses...

Photonic multilayer structure of Begonia chloroplasts enhances photosynthetic efficiency

“…Blue iridescent leaf colouration has been reported in the genus Begonia and explored in a single species, B.pavonina 16 . Unusual plastids containing highly ordered internal structures termed iridoplasts were observed in the adaxial epidermis and proposed as the source of the blue colouration 5 .…”

Imaging DNA Structure by Atomic Force Microscopy

“…The sample, the tip and the cantilever are immersed in liquid. Reproduced from [ 1 ] In addition to the sample preparation, a critical element for high resolution AFM imaging is force sensitivity and control [ 2 -4 ]. Generally, the AFM probe needs to exert a force on the sample to be able to record the surface topography.…”

Passive optical switches based on endohedral fullerenes

“…1). In reality, when the leading edge of a fast optical pulse is comparable to the electron-electron scattering times (hundreds of fs to sub-ps) of the optical switch material, the pulse may partially pass through the optical switch before the material is non-linearly activated [5][6][7]. This yields a realistic switch/limiter response that is intermediate between an ideal limiter and an ideal switch, as shown in Fig.…”