MEMS switches are devices that use mechanical movement to achieve a short circuit or an open circuit in the RF transmission line. RF MEMS switches are the specific micromechanical switches that are designed to operate at RF-to-millimeter-wave frequencies (0.1 to 100 GHz). The forces required for the mechanical movement can be obtained using electrostatic, magnetostatic, piezoelectric, or thermal designs. To date, only electrostatic-type switches have been demonstrated at 0.1-100 GHz with high reliability (100 million to 10 billion cycles) and wafer-scale manufacturing techniques. It is for this reason that this article will concentrate on electrostatic switches.

RF MEMS switches and switch circuits

Thin film piezoelectric materials offer a number of advantages in microelectromechanical systems (MEMS), due to the large motions that can be generated, often with low hysteresis, the high available energy densities, as well as high sensitivity sensors with wide dynamic ranges, and low power requirements This paper reviews the literature in this field, with an emphasis on the factors that impact the magnitude of the available piezoelectric response For non-ferroelectric piezoelectrics such as ZnO and AlN, the importance of film orientation is discussed The high available electrical resistivity in AlN, its compatibility with CMOS processing, and its high frequency constant make it especially attractive in resonator applications The higher piezoelectric response available in ferroelectric films enables lower voltage operation of actuators, as well as high sensitivity sensors Among ferroelectric films, the majority of the MEMS sensors and actuators developed have utilized lead zirconate titanate (PZT) films as the transducer Randomly oriented PZT films show piezoelectric e(31, f) coefficients of about - 7 C/m(2) at the morphotropic phase boundary In PZT films, orientation, composition, grain size, defect chemistry, and mechanical boundary conditions all impact the observed piezoelectric coefficients The highest achievable piezoelectric responses can be observed in {001} oriented rhombohedrally-distorted perovskites For a variety of such films, e(31,f) coefficients of - 12 to - 27 C/m(2) have been reported

Thin Film Piezoelectrics for MEMS

Sensors and actuators based on carbon nanotubes and their composites: A review

A fully integrated solution providing scan-beam capability with a single antenna is presented in this paper for the first time. The proposed system includes a reconfigurable rectangular spiral antenna with a set of micro electro mechanical system (MEMS) switches, which are monolithically integrated and packaged onto the same substrate. The system is based on a single-arm rectangular spiral antenna, capable of changing its radiation pattern using radio frequency-MEMS (RF-MEMS) switches. The rectangular spiral and RF-MEMS switches are monolithically integrated on a conventional microwave substrate printed circuit board (/spl epsiv//sub r/=3.27 and tan/spl delta/=0.004) and quartz substrate (/spl epsiv//sub r/=3.78 and tan/spl delta/=0.0002). The spiral is made out of multiple lines, which are interconnected by RF-MEMS switches strategically located along the spiral. On activating these switches, the spiral overall arm length is changed and consequently its radiation beam direction is changed. The two proposed antennas radiate right hand circular polarization (RHCP) and left hand circular polarization (LHCP) for printed circuit board and quartz substrate respectively. The gain of the two antennas varies between 3/spl sim/6 dBi. They both satisfy the 3-dB axial ratio criterion at their operating frequency band, i.e., at 10 GHz and 6 GHz for the printed circuit board and the quartz substrate respectively. To the best of our knowledge, this is the first truly reconfigurable printed antenna design using MEMS devices as active elements integrated in the same low loss substrate. The excellent performance of the proposed system emphasizes the importance of being able to integrate MEMS switches into the same low loss substrate for antenna applications. This technology pioneers the design of arbitrarily shaped reconfigurable antennas including the design of reconfigurable antenna arrays.

Reconfigurable scan-beam single-arm spiral antenna integrated with RF-MEMS switches

In this paper the design of a compact, efficient and electronically tunable antenna is presented. A single-fed resonant slot loaded with a series of PIN diode switches constitute the fundamental structure of the antenna. The antenna tuning is realized by changing its effective electrical length, which is controlled by the bias voltages of the solid state shunt switches along the slot antenna. Although the design is based on a resonant configuration, an effective bandwidth of 1.7:1 is obtained through this tuning without requiring a reconfigurable matching network. Four resonant frequencies from 540-890 MHz are selected in this bandwidth and very good matching is achieved for all resonant frequencies. Theoretical and experimental behavior of the antenna parameters is presented and it is demonstrated that the radiation pattern, efficiency and polarization state of the antenna remain essentially unaffected by the frequency tuning

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Design of reconfigurable slot antennas

This paper reports on the design, fabrication, and testing of a low-actuation voltage Microelectromechanical systems (MEMS) switch for high-frequency applications. The mechanical design of low spring-constant folded-suspension beams is presented first, and switches using these beams are demonstrated with measured actuation voltages of as low as 6 V. Furthermore, common nonidealities such as residual in-plane and gradient stress, as well as down-state stiction problems are addressed, and possible solutions are discussed. Finally, both experimental and theoretical data for the dynamic behavior of these devices are presented. The results of this paper clearly underline the need of an integrated design approach for the development of ultra low-voltage RF MEMS switches.

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Electromechanical considerations in developing low-voltage RF MEMS switches

This paper presents a novel design scheme for tunable coplanar waveguide components with applications to compact lumped-element MEMS reconfigurable filters. Shunt MEMS switches are employed for tuning the values of lumped components frequently encountered in microwave integrated circuits. In particular, shunt capacitors, series inductors and shunt inductive stubs are the main tunable circuit elements utilized in this work. Furthermore, accurate equivalent circuits that include the most important parasitics introduced by the tuning mechanism are provided. Finally, the proposed method is applied to the design and implementation of very compact low-pass and bandpass tunable filters. The very high tunability range, the compactness of the resulting networks and their very wideband response constitute the main advantages of this technique.

Tunable lumped components with applications to reconfigurable MEMS filters

This paper reports on the experimental and theoretical characterization of RF microelectromechanical systems (MEMS) switches for high-power applications. First, we investigate the problem of self-actuation due to high RF power and we demonstrate switches that do not self-actuate or catastrophically fail with a measured RF power of up to 5.5 W. Second, the problem of switch stiction to the down state as a function of the applied RF power is also theoretically and experimentally studied. Finally, a novel switch design with a top electrode is introduced and its advantages related to RF power-handling capabilities are presented. By applying this technology, we demonstrate hot-switching measurements with a maximum power of 0.8 W. Our results, backed by theory and measurements, illustrate that careful design can significantly improve the power-handling capabilities of RF MEMS switches.

RF MEMS switches with enhanced power-handling capabilities

This paper presents resonant capacitive microelectromechanical switches and their possible applications in tunable filtering. Single switches with a down capacitance of 2.9 pF and inductive sections of 3 to 50 pH are demonstrated, resulting in resonant frequencies from 13 to 54 GHz. Designs of resonant switches connected in parallel are also implemented with major advantages in isolation and bandwidth. Finally, tunable filters using these switches are discussed.

MEMS devices for high isolation switching and tunable filtering

Single-pole double-throw (SPDT) X and K-band circuit designs incorporating low-loss microelectromechanical shunt capacitive switches are reported. The switches incorporate highly inductive connecting beams which aid in further increasing the isolation at the desired operational RF frequency. Measurements show an isolation of better than 40 dB at both 7 and 20 GHz. Insertion loss was measured at -0.95 dB at 7 GHz and -0.69 dB at 20 GHz for the two respective designs.

S.P. Pacheco

Papers

Electromechanical considerations in developing low-voltage RF MEMS switches

Tunable lumped components with applications to reconfigurable MEMS filters

RF MEMS switches with enhanced power-handling capabilities

MEMS devices for high isolation switching and tunable filtering

MEMS single-pole double-throw (SPDT) X and K-band switching circuits