Brandon W. Pillans

Lifetime characterization of capacitive RF MEMS switches

The first experimental characterization of dielectric charging within capacitive RF MEMS switches has been demonstrated. Standard devices have been inserted into a time domain setup and their lifetimes have been characterized as a function of actuation voltage. Switch lifetimes were measured using a dual-pulse waveform with 30 to 65 V of actuation voltage. Resulting lifetimes were between 10/sup 4/ and 10/sup 8/ switch actuations, demonstrating an exponential relationship between lifetime and actuation voltage.

X-band RF MEMS phase shifters for phased array applications

In this work, development of a low-loss radio frequency (RF) microelectromechanical (MEMS) 4-bit X-band monolithic phase shifter is presented. These microstrip circuits are fabricated on 0.021-in-thick high-resistivity silicon and are based on a reflection topology using 3-dB Lange couplers. The average insertion loss of the circuit is 1.4 dB with the return loss >11 dB at 8 GHz. To the best of our knowledge, this is a lowest reported loss for X-band phase shifter and promises to greatly reduce the cost of designing and building phase arrays.

Ka-band RF MEMS phase shifters

As the need for low-loss phase shifters increases, so does the interest in radio frequency (RF) MEMS as a solution to provide them. In this paper, progress in building low loss Ka-band phase shifters using RF MEMS capacitive switches is demonstrated. Using a switched transmission line 4-bit resonant phase shifter, an average insertion loss of 2.25 dB was obtained with better than 15-dB return loss, a similar 3-bit phase shifter produced an average insertion loss of 1.7 dB with better than 13-dB return loss. Both devices had a phase error of less than 13/spl deg/ in the fundamental states. To our knowledge, these devices represent the lowest loss Ka-band phase shifters reported to date.

An intelligently controlled RF power amplifier with a reconfigurable MEMS-varactor tuner

This paper presents an intelligently controlled RF power amplifier with a reconfigurable output tuner using microelectromechanical system (MEMS) switches and a varactor. By switching on/off the MEMS switches and varying the bias voltage of the varactor, the performance of the amplifier is optimized for input signals with known or unknown frequencies in a range of 8-12 GHz. Fabrication-related unit-to-unit variations of the amplifier are overcome by the reconfigurable tuner. Directed algorithms based on a characterization table and on black-box genetic algorithms are developed for optimization and search.

RF power handling of capacitive RF MEMS devices

RF MEMS switches provide a low-cost, high-performance solution to many RF/microwave applications. In this paper, progress in characterizing capacitive MEMS devices under high RF power is presented. The switches tested demonstrated power handling capabilities of 510 mW for continuous RF power and 4 W for pulsed RF power. In addition, the reliability of these switches was tested at various power levels indicating that under continuous RF power, the lifetime is not affected until the 510 mW power level is reached. Once a power failure is observed, it is completely recoverable by lowering the RF power level below the threshold point. A description of the power failures and their associated operating conditions is presented.

Impact of Humidity on Dielectric Charging in RF MEMS Capacitive Switches

A novel technique is used to distinguish the charging of the surface from that of the bulk of the dielectrics of different types of RF MEMS capacitive switches under different electric fields and humidity levels. In general, bulk charging dominates in dry air, while surface charging increases linearly with increasing humidity. Under comparable electric fields and humidity levels, switches made of silicon dioxide are less susceptible to surface charging than switches made of silicon nitride. These quantitative results not only underscore the importance of packaging the switches in a dry ambient atmosphere, but also validate the novel technique for evaluating the effectiveness of dielectric preparation and packaging.

Thin-Film Aluminum RF MEMS Switched Capacitors With Stress Tolerance and Temperature Stability

This paper presents an RF microelectromechanical system switched capacitor which is based on a thin-film alu minum circular beam geometry that exhibits reduced sensitivity to both initial residual stress and stress changes versus ambient temperature. This novel design results in a pull-in voltage slope of -55 mV/°C from -5°C to 125°C, a capacitance ratio of 20 (C_u =50 fF, C_d = 1 pF), a down-state quality factor of 85 at 3127 MHz (Z_d = -j50 Ω), and a switching time of <; 10 μs from 25°C to 95°C. The device symmetry also facilitates low-series-inductance compact device arrays for high-value capac itances. Both 2×2 and 3×2 device arrays are demonstrated with down-state capacitances of 3.95 and 5.89 pF, which result in switched impedances of 135-4 Ω and 91-3 Ω at 0.3-10 GHz, respectively. The array impedances vary as 1/ω over a 33:1 frequency range, with down-state quality factors of 50-60 at 541-806 MHz (Z_d = -j50 Ω). The application areas are in high-linearity RF/microwave switches, phase shifters, and tunable matching networks and filters.

A Stress-Tolerant Temperature-Stable RF MEMS Switched Capacitor

We present the design, fabrication, and measurement of an RF MEMS (Radio Frequency Micro-Electromechanical System) switched capacitor that exhibits reduced sensitivity to residual stress and temperature. The device is based on a circularly symmetric geometry with arc-type springs placed between the anchors and suspended beam. This design compensates for the effects of the residual biaxial stress in the beam, resulting in a pull-in voltage slope versus temperature of only -50 mV/ °C from -5 °C to 95 °C. Reducing the device sensitivity to residual stress improves the performance uniformity on a wafer-scale, and from wafer-to-wafer lots.

Effect of packaging on dielectric charging in RF MEMS capacitive switches

A novel technique was used to evaluate the effectiveness of packaging in maintaining a dry ambient atmosphere for electrostatically actuated RF MEMS capacitive switches and in preventing the charging of the dielectric surface after prolonged operation. It was found that as-packaged switches exhibited different degrees of surface charging, probably due to different amounts of moisture inadvertently sealed in the essentially hermetic packages. However, after the switches were delidded and baked dry, all switches showed minimum surface charging. The results imply that the switches can have consistently long lifetimes by improving the yield of the packaging process.

Micromachined on-chip high-aspect ratio air core solenoid inductor for multi-GHz applications

We present high aspect air-core solenoid inductors with 100 /spl mu/m and 200 /spl mu/m tall via structures on Pyrex wafer. The effect of various parameters such as different number of turns, via heights, pitch distance between turns on inductors radio frequency (RF) characteristics have been studied. The highest Q factor we obtained from various solenoid inductors is 72.8 at 9.7 GHz, which was produced by a 3-turn inductor. The highest inductance we obtained was from a 20-turn inductor and it was from /spl sim/28 nH at peak Q frequency of 2 GHz 200 /spl mu/m tall via structures. This inductor occupies 0.75 mm/sup 2/ in area and hold a Q factor of 43 and a self-resonant frequency (SRF) of 5.1 GHz.