Isak C. Reines

A Soft-Landing Waveform for Actuation of a Single-Pole Single-Throw Ohmic RF MEMS Switch

A soft-landing actuation waveform was designed to reduce the bounce of a single-pole single-throw (SPST) ohmic radio frequency (RF) microelectromechanical systems (MEMS) switch during actuation. The waveform consisted of an actuation voltage pulse, a coast time, and a hold voltage. The actuation voltage pulse had a short duration relative to the transition time of the switch and imparted the kinetic energy necessary to close the switch. After the actuation pulse was stopped, damping and restoring forces slowed the switch to near-zero velocity as it approached the closed position. This is referred to as the coast time. The hold voltage was applied upon reaching closure to keep the switch from opening. An ideal waveform would close the switch with near zero impact velocity. The switch dynamics resulting from an ideal waveform were modeled using finite element methods and measured using laser Doppler vibrometry. The ideal waveform closed the switch with an impact velocity of less than 3 cm/s without rebound. Variations in the soft-landing waveform closed the switch with impact velocities of 12.5 cm/s with rebound amplitudes ranging from 75 to 150 nm compared to impact velocities of 22.5 cm/s and rebound amplitudes of 150 to 200 nm for a step waveform. The ideal waveform closed the switch faster than a simple step voltage actuation because there was no rebound and it reduced the impact force imparted on the contacting surfaces upon closure

A DC to 10-GHz 6-b RF MEMS time delay circuit

A 6-b radio frequency (RF) microelectromechanical system (MEMS) time-delay circuit operating from dc to 10 GHz with 393.75-ps total time delay is presented. The circuit is fabricated on 250-/spl mu/m-thick alumina and uses metal contacting RF MEMS switches to realize series-shunt SP4T switching networks. The circuit demonstrates 1.8+/-0.6 dB of loss at 10 GHz and has linear phase response across the entire band with accuracy of better than a least significant bit for most states.

A low loss RF MEMS Ku-band integrated switched filter bank

A switched Ku-band filter bank has been developed using two single-pole triple-throw (SP3T) microelectromechanical systems (MEMS) switching networks, and three fixed three-pole end-coupled bandpass filters. A tuning range of 17.7% from 14.9 to 17.8 GHz was achieved with a fractional bandwidth of 7.7 /spl plusmn/2.9%, and mid-band insertion loss ranging from 1.7 to 2.0 dB.

An X-band to Ku-band RF MEMS switched coplanar strip filter

Radio frequency microelectromechanical systems (RF MEMS) are key enabling technologies for miniature reconfigurable circuits such as microwave filters. We present a two-pole monolithic RF MEMS switched filter, fabricated on GaAs, that employs surface-micromachined capacitors to present a variable capacitance to a coupled coplanar strip filter, thereby switching the filter center frequency 37% between 10.7 GHz and 15.5 GHz with voltages of 20 and 0 V, respectively. This 15% bandwidth filter occupies a chip area of 2.2 /spl times/1.5 mm and demonstrates less than 2-dB of loss, making it promising for numerous applications within these critical frequency bands.

Fabrication and characterization of ohmic contacting RF MEMS switches

We have fabricated and characterized radio frequency microelectromechanical systems (RF MEMS) ohmic switches for applications in discrete tunable filters and phase shifters over a frequency range of 0 to 20 GHz. Our previously reported cantilever switches have been redesigned for higher isolation and are now achieving 22 dB of isolation at 10 GHz. The measured insertion loss is 0.15 dB at 10 GHz. We have also fabricated and characterized new devices, designated “crab” switches, to increase isolation and contact forces relative to the cantilever design. The measured insertion loss and isolation are 0.1 dB per switch at 20 GHz and 22 dB at 10 GHz, respectively. A simple and accurate equivalent model has been developed, consisting of a transmission line segment and either a series capacitor to represent the blocking state or a series resistor to represent the passing state. Experimental analysis of the switch shows that high contact and substrate capacitive coupling degrades the isolation performance. Simulations indicate that the isolation improves to 30 dB at 10 GHz by reducing these capacitances. The crab switch design has a measured contact force of 120 μN, which represents a factor of four increase over the cantilever switch contact force and results in consistent, low-loss performance.

MEMS high-Q tunable capacitor for reconfigurable microwave circuits

Future microwave networks require miniature high-performance tunable elements such as switches, inductors, and capacitors. We report a micro-machined high-performance tunable capacitor suitable for reconfigurable monolithic microwave integrated circuits (MMICs). The capacitor is fabricated on a GaAs substrate using low-temperature processing, making it suitable for post-process integration with MMICs, radio frequency integrated circuits (RFICs) and other miniaturized circuits. Additionally, the insulating substrate and high-conductivity metal provide low-loss operation at frequencies over 20 GHz. The device demonstrates a capacitance of 150 fF at 0 V bias, pull-in at about 15 V to 18 V, and further linear tuning from 290 fF to 350 fF over a voltage range of 7 V to 30 V. Also, the device demonstrates self-resonance frequencies over 50 GHz, and Q’s over 100 at 10 GHz. To enable integration into circuits, a simple equivalent circuit model of the device has been developed, demonstrating a good match to the measured data through 25 GHz. Initial testing to 1 billion cycles indicates that metal fatigue is the primary limitation to reliability and reproducibility, and that dielectric charging does not have a significant impact on the device. This device is promising for high-performance tunable filters, phase shifters, and other reconfigurable networks at frequencies through K-band.

Compact MMIC-Compatible RF MEMS Switch

We have fabricated and tested a surface micromachined, metal-metal contacting radio frequency microelectromechanical systems (RF MEMS) switch. The switch was fabricated out of electroplated metals on semi-insulating GaAs at process temperatures below 300°C. It was anchored by folded springs to one end of a coplanar waveguide (CPW) gap, forming a cantilever. This configuration allowed us to simplify the fabrication process by eliminating mechanical dielectric films that are normally necessary to isolate the switch contact from the actuation metal. The measured insertion loss and isolation at S band were 0.21 dB and 28 dB isolation, respectively. An average switching speed of 83 μs at 55 volts was measured. This switch demonstrated >105 cold switching cycles without sticking, however rapid increase of the contact resistance was observed. A new switch was designed to increase isolation and reduce insertion loss by decreasing the coupling capacitance and increasing the contact force.