Sergio P. Pacheco

Electromechanical considerations in developing low-voltage RF MEMS switches

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.

Tunable lumped components with applications to reconfigurable MEMS filters

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.

Micromechanical electrostatic K-band switches

Two novel designs of micromechanical capacitive switches using serpentine and cantilever springs for low actuation voltage applications are reported. Both designs also incorporate an electrode situated above the switching structure in order to provide system stability. DC measurements indicate pull-in voltages of 14 and 16 V, with RF isolation of better than -30 dB up to 40 GHz.

RF MEMS switches with enhanced power-handling capabilities

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.

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

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.

Micromachined filters on synthesized substrates

Effective frequency spectrum usage requires high performance filters with a sharp cut-off frequency and high stopband attenuation. Stepped impedance lowpass designs achieve this with large ratios of high and low impedance values. In high index materials, however, such as Si (11.7) and GaAs (12.9), these ratios are around 5 which significantly limit filter performance. This paper presents the use of Si micromachining to produce synthesized substrates with stepped-impedance low filter designs. Of the two designs, one offers a reduction of the low impedance value while the other offers an increase of the high impedance value to produce Z/sub H//Z/sub L/ ratios that are 1.5 to 2 times larger than conventional designs.

Alleviating the Adverse Effects of Residual Stress in RF MEMS Switches

This paper presents two methods for counteracting the unwanted deflection due to warping or buckling effects, which are serious potential problems in many fabrication processes of microelectromechanical (MEMS) structures due to thin film phenomena. This study is primarily suited for electrostatically actuated RF MEMS switches whose RF and DC performance can be significantly deteriorated by out of plane warping. It can also be applied to MEMS accelerometers, resonators and other similar systems. The first technique focuses on modifying the support structure and the spring constant of the switch, while the second involves a more complicated fabrication process, which selectively increases the switch thickness. Both these techniques yield switches with two to ten times less warping under the same fabrication conditions. The second method, however, presents the additional advantage of maintaining the actuation voltage almost unaffected.

Microelectromechanical K-Band Switching Circuits

Two single-pole single-throw (SPST) K-band circuit designs incorporating low-loss microelectromechanical systems (MEMS) microwave shunt switches are reported. DC measurements indicate actuation voltages in the order of 20 V with an on-to-off capacitance ratio of 30. RF measurements show an isolation between the input port ad the output arm with the switch in the order of better than 15 dB across most of the frequency band. Insertion loss was measured at ¿0.4 dB at 18 GHz and ¿0.7 dB at 34 GHz for the two respective designs.