Low-loss lateral micromachined switches for high frequency applications

Abstract: To overcome the energy-efficiency limitations imposed by finite sub-threshold slope in CMOS transistors, this paper explores the design of integrated circuits based on nano-electro-mechanical (NEM) relays. A dynamical Verilog-A model of the NEM relay is described and correlated to device measurements. Using this model we explore NEM relay design strategies for digital logic and I/O that can significantly improve the energy efficiency of the whole VLSI system. By exploiting the low effective threshold voltage and zero leakage achievable with these relays, we show that NEM relay-based adders can achieve an order of magnitude or more improvement in energy efficiency over CMOS adders with ns-range delays and with no area penalty. By applying parallelism, this improvement in energy-efficiency can be achieved at higher throughputs as well, at the cost of increased area. Similar improvements in high-speed I/O energy are also predicted by making use of the relays to implement highly energy-efficient digital-to-analog and analog-to-digital converters.

Abstract: Microelectromechanical relays have recently been proposed for ultra-low-power digital logic because their nearly ideal switching behavior can potentially enable reductions in supply voltage (Vdd) and, hence, energy per operation beyond the limits of MOSFETs. Using a calibrated analytical model, a sensitivity-based energy-delay optimization approach is developed in order to establish simple relay design guidelines. It is found that, at the optimal design point, every 2 X energy increase can be traded off for a ~1.5x reduction in relay delay. A contact-gap-to-actuation-gap thickness ratio of 0.7-0.8 is shown to result in the most energy-efficient relay operation, implying that pull-in operation is preferred for an energy-efficient relay design. Based on the analytical model and design guidelines, a scaling theory for relays is presented. A scaled relay technology is projected to provide >; 10 X energy savings over an equivalent MOSFET technology, for circuits operating at clock frequencies up to ~100 MHz.

Abstract: In this paper, we have proposed, fabricated and characterized piezoelectrically actuated RF MEMS (radio-frequency micro-electro-mechanical system) switches. They have been designed to operate at a low operation voltage for advanced mobile/wireless handset applications. The proposed switches are largely composed of piezoelectric cantilever actuators with an Au contact electrode and CPW (coplanar wave) transmission lines suspended over the substrate. Two different types of RF MEMS switches have been suggested to find the better geometry. One has the structure of one single piezoelectric cantilever and a contact electrode attached to its edge with three hinges (type-A), and the other contains four piezoelectric cantilevers that are symmetrically combined through each hinge to support a centered contact electrode (type-B). The two different fabricated (type-A and type-B) RF MEMS switches have insertion losses of −0.22 and −0.23 dB at an operation voltage of 2.5 V and a frequency of 2 GHz, respectively. Although the difference in insertion loss is trivial, there exist different dependences of insertion loss on applied voltage between them. The insertion losses of type-A switches are changed with varying operation voltage because the touching area between the contact electrode and the signal transmission lines is variable. Meanwhile, the type-B switches show nearly constant insertion losses regardless of operation voltage. The type-A and type-B switches have isolation values of −40.8 and −42.5 dB at a frequency of 2 GHz, respectively.

Abstract: Characterization of nanomechanical graphene drum structures is presented in this paper. The structures were fabricated by mechanical exfoliation of graphite onto pre-etched circular trenches in silicon dioxide on a silicon substrate. Drum structures with diameters ranging from 3.8 to 5.7 µm and thicknesses down to 8 nm were achieved. Mechanical characterization of the devices was then carried out by using atomic force microscopy (AFM) to measure their electrostatic deflection. The structures were found to have linear spring constants ranging from 3.24 to 37.4 N m−1 and could be actuated to about 18–34% of their thickness before exhibiting nonlinear deflection. An analytical framework was formulated to model the deflection behaviour which was verified through finite element simulations (FEM). The experimental measurements agree well with analytical and finite element results using Young's modulus of 1 TPa. The resonance characteristics of the structures were derived by both plate theory and FEM simulations. It was found that our drum structures could potentially vibrate at frequencies in excess of 25 MHz. The small size and high operating frequencies of our nanomechanical graphene devices make them very promising for resonant mass sensing applications with 10−20 g Hz−1 sensitivity, a two order of magnitude improvement over other reported silicon structures.

Abstract: 'This letter details the construction and performance of metal membrane radio frequency MEMS switches at microwave and millimeter-wave frequencies. These shunt switches possess a movable metal membrane which pulls down onto a metal/dielectric sandwich to form a capacitive switch. These switches exhibit low loss (<0.25 dB at 35 GHz) with good isolation (35 dB at 35 GHz). These devices possess on-off capacitance ratios in the range of 80-110 with a cutoff frequency (figure of merit) in excess of 9000 GHz, significantly better than that achievable with electronic switching devices.

Abstract: Silicon has many advantages as a microwave substrate material including low cost and a mature technology. The aim of this paper is to evaluate the potential of using high-resistivity silicon as a low-cost low-loss microwave substrate through an experimental comparative study. Coplanar waveguides fabricated on Si, GaAs, and quartz substrates are tested and their characteristics are compared. Microwave spiral inductors and meander lines are also fabricated on various substrates, and their performance is also analyzed. The results demonstrate that the losses of a coplanar transmission line (CPW) realized on high-resistivity (3 k to 7 k /spl Omega/-cm) silicon substrates are comparable to the losses of a CPW realized on a GaAs substrate covered with insulators. Furthermore, measured unloaded Q's of microwave inductive structures on high-resistivity silicon substrates are comparable to the measured unloaded Q's of the same structures on GaAs and on quartz. This paper demonstrates that high-resistivity Si can be used as a microwave substrate. >

Abstract: In this paper, a push-pull type microwave switch is proposed, which utilizes torsion springs and leverage for low-voltage operation. The switching operation up to 4 GHz is demonstrated. The actuation voltage is /spl sim/5 V. The insertion loss of /spl sim/1 dB and the isolation as high as /spl sim/40 dB at 1 GHz are achieved by the push-pull operation.