Chirag D. Patel

High-

This paper presents a miniature high-Q tunable evanescent-mode cavity filter using planar capacitive RF microelectromechanical system (MEMS) switch networks and with a frequency coverage of 4.07-5.58 GHz. The two-pole filter, with an internal volume of 1.5 cm3, results in an insertion loss of 4.91-3.18- and a 1-dB bandwidth of 17.8-41.1 MHz, respectively, and an ultimate rejection of > 80 dB. RF-MEMS switches with digital/analog tuning capabilities were used in the tunable networks so as to align the two poles together and result in a near-ideal frequency response. The measured Qu of the filter is 300-500 over the tuning range, which is the best reported Q using RF-MEMS technology. The filter can withstand an acceleration of 55-110 g without affecting its frequency response. The topology can be extended to a multiple-pole design with the use of several RF-MEMS tuning networks inside the evanescent-mode cavity. To our knowledge, these results represent the state-of-the-art in RF-MEMS tunable filters.

Q

The RF community has long been searching for the ideal switch since the birth of electronics, and it is defined as a device having virtually no insertion loss (Ron = 0 Ω) over a wide frequency range, very high isolation [off-state capacitance (Coff)] = 0 fF), extremely high linearity (IIP2 and IIP3 → infinite), medium- to high-power handling (100 mW to 1 kW), and no dc power consumption. Our entire RF infrastructure ecosystem, from communication system networks, to satellite systems, to wideband spectral analysis, to instrumentation and radar systems, uses a variety of switches for signal routing and control (attenuation, phase shifting, etc.). The ideal switch was achieved long time ago using electromechanical relays, and even after nearly 100 years, it is still the best RF switch ever made from an electrical perspective [1]. It has very low insertion loss (Ron <;1 Ω), very high isolation (Coff of few fF), very high linearity and high power handling (100 mW to 50 W). However, it is bulky, expensive, and has an average lifetime of few million cycles.

RF-MEMS 4–6-GHz Tunable Evanescent-Mode Cavity Filter

This paper presents an mN-level contact and restoring force RF microelectromechanical systems metal-contact switch exhibiting high reliability, high linearity, and high power handing for dc-40-GHz applications. The device, which is insensitive to stress and temperature effects, achieves 1.2-1.5 mN of contact force (per contact) from 80 to 90 V and 1.0 mN of restoring force (per contact). The up-state capacitance is 8 fF, resulting in an isolation of 46, 31, and 14 dB at 1, 6, and 40 GHz, respectively. Measured results show switch resistances of 1-2 Ω and a reliability of >; 100 million cycles at 2-5 W under cold switching at 100 mW under hot-switching conditions, in an unpackaged and standard laboratory environment. Furthermore, the device was tested under prolonged hold-down conditions and demonstrated excellent RF power handling (>;10 W) and dc current handling (>;1 A) capability.

The Search for a Reliable MEMS Switch

This paper presents an electrostatic RF microelectromechanical systems (MEMS) metal contact switch based on a tethered cantilever topology. The use of tethers results in a design that has low sensitivity to stress gradients, biaxial stresses, and temperature. A switch with a footprint of 160 × 190 μm2 and based on a 8-μm-thick gold cantilever with an Au/Ru contact is implemented on a high-resistivity silicon substrate and results in a total contact force of 0.8-1.2 mN at 80-90 V, a restoring force of 0.5 mN, a pull-in voltage of 61 V, an up-state capacitance of 24 fF, and an actuation time of 6.4 μ s. The device achieves a switch resistance of 2.4±1.4 Ω to 1.8±0.6 Ω at 90-100 V in open laboratory environments (nonpackaged). This design has the potential to replace conventional electromagnetic relays in application areas such as automated testing equipment and high-performance switching networks.

A High-Reliability High-Linearity High-Power RF MEMS Metal-Contact Switch for DC–40-GHz Applications

This paper presents a new RF MEMS switch design which is capable of generating large forces under electrostatic actuation. The switch is 155×130 µm², and results in 0.8–1.8 mN of contact force at 80–100 V, with a release force of 0.50 mN. The design is also highly insensitive to biaxial stress and to stress gradients. A prototype switch, fabricated on a high resistivity silicon substrates using an 8 µm-thick gold cantilever, results in pull-in voltage of 62 V, a switching time of 6 µs, and an upstate capacitance of 24 fF. The contact metal is Au-Ru and the measured switch resistance dropped from 250 Ω to 1.2 Ω for V<inf>act</inf> = 60 − 100 V, showing the large contact-force operation of the switch. Measurements versus temperature show excellent stability from 25 – 105° C.

RF MEMS Metal-Contact Switches With mN-Contact and Restoring Forces and Low Process Sensitivity

This paper presents a temperature stable metal-contact RF MEMS switch capable of handling >5 W of RF power. The device achieves 0.7 – 1.5 mN of contact force for actuation voltages of 80 – 90 V, with a restoring force of 0.63 mN. Furthermore, the device is insensitive to stress effects and temperature. Temperature measurements showed excellent thermal stability - no deflection in the beam, and a change in pull-in voltage of only 4 V from 25 – 125 °C. The switch was tested under prolonged (>24 hrs) high-power RF conditions with excellent reliability.

An RF-MEMS switch with mN contact forces

A high-Q digitally tunable capacitor is demonstrated with 3 and 4 b resolutions for 0.8-3 GHz applications. The device shows a tuning range of 1.0-3.75 pF in the 3 b configuration and 1.25-3.80 pF in the 4 b configuration ( ~ 1-4 pF simulated). In addition to digital tuning, 30-530 fF of analog tuning is achieved and allows for precision tuning. The measured Q of the digitally tunable capacitor is >;100 at 1 GHz and >;60 at 2 GHz for all tuning states. A novel circular geometry maintains a high- Q as the capacitance is increased. The device is 2×1.8 mm which is ideal for tunable filters, matching networks and antennas.

A high power (>5 W) temperature stable RF MEMS metal-contact switch with orthogonal anchors and force-enhancing stoppers

This paper presents a stress- and temperature-stable RF-MEMS metal-contact switch exhibiting high power handling (>10 W) and high reliability (>100 million cycles at 2 W of RF power) for DC- to 40-GHz applications. The device, which employs a hybrid Au/Ru contact, is fabricated with an all-metal surface micro-machining process and achieves a contact force of 1.5 mN per contact pair at 90 V actuation, as well as a restoring force of 1.0 mN. Measured results based on unpackaged devices in open-air conditions show that the on-resistance is 1–2 Ω (&#60;1 Ω with cleaning), the off-capacitance is 8 fF, the pull-in voltage is 68 V, and the switching and release time is &#60;10 µs.