J.T.M. van Beek

Dynamics and squeeze film gas damping of a capacitive RF MEMS switch

We report on measurements of the time-dependent capacitance of an RF MEMS shunt switch. A high time-resolution detection set-up is used to determine switching time and motion of the device. From the equation of motion the damping force is extracted. The measured damping force is found to be approximately proportional to the speed over the gap to the third power (FD v/z3), in good agreement with squeeze film damping theory. Significant influence of slip–flow effects on the motion is observed. Measurements at low pressure show underdamped harmonic oscillations in the opening motion and contact bounce effects in the closing motion. Effects of dielectric charging on the C–V curves are discussed. Experimental results are compared with electromechanical and damping simulations.

RF MEMS tunable capacitors with large tuning ratio

MEMS tunable capacitors have been fabricated in a thin-film technology for passive integration. Using a dual-gap relay-type design, continuous and reversible capacitance tuning with a tuning ratio up to 17 has been demonstrated, while requiring an actuation voltage of only 20 V. A quality factor of 150 to 500 has been measured in the frequency range of 1 to 6 GHz, making these devices very suitable as building blocks in many RF applications. These are the highest tuning ratio and quality factor reported to date for parallel-plate tunable capacitors.

Microelectromechanical tunable capacitors for reconfigurable RF architectures

This paper reports on metal-based MEMS tunable capacitors, fabricated in a thin-film process on high-ohmic silicon. Continuous and reversible tuning has been demonstrated with an average tuning ratio of 4.5. A quality factor between 100 and 300 has been obtained in a frequency range of 0.5 to 4 GHz. The combination of a high quality factor and large tuning range makes these tunable capacitors very suitable as building blocks in many radio-frequency (RF) applications. The tuning speed, temperature stability and RF power handling have been studied in terms of self-actuation. Finally, the need for a hermetic package as well as a packaging concept which can potentially provide this has been demonstrated. After packaging, the devices can be handled as standard silicon dies, making them fit very well with a system-in-package approach.

The influence of mechanical shock on the operation of electrostatically driven RF-MEMS switches

A closed-form relationship between the insertion loss, the externally applied mechanical shock and the RF signal voltage of a capacitive RF-MEMS shunt switch is derived. It is shown that, based on this relationship, the minimum required mechanical stiffness of the suspended structure can be calculated. This allows determination of the minimum electrostatic switching voltage in a given process flow. The results are illustrated for specifications regarding shock resistance of electronic equipment as set out in MIL-STD-883. Even under the least severe test conditions, the shocks can affect the insertion loss of RF-MEMS switches, and can provoke self-biasing. This paper gives guidelines to avoid such false operation modes. The method can also be extended to yield the sensitivity of RF-MEMS devices to harmonic vibrations.

Elimination of accumulation charge effects for high-resistive silicon substrates

A dedicated silicon process, called PASSI/spl trade/, was developed for passive functions in the GHz regime. The process, using high-resistive silicon with a SiO/sub 2/ top layer as a carrier, is fully compatible with common silicon infrastructures. While the passives perform far better than passives integrated in CMOS or BICMOS chips, their performance is limited by accumulation of charge underneath the SiO/sub 2/ layer. A very effective way to diminish the influence of. this charge is an implantation that creates traps at the Si/SiO/sub 2/ interface, thus reducing the charge mobility. The capacitors and inductors on wafers that were subject to such an implantation step can no longer be distinguished from their counterparts on insulating substrates.

Design and characterization of integrated passive elements on high ohmic silicon

This work presents ultra low-loss coplanar waveguides and Marchand type baluns implemented in an optimized high ohmic silicon substrate technology for RF/microwave applications. The CPW configured baluns operate from 15 to 25 GHz with a minimum insertion loss of 0.8 dB at center frequency.

MEMS tunable capacitors and switches for RF applications

RF MEMS capacitive switches and tunable capacitors have been realized in an industrialized thin-film process developed for manufacturing high-quality inductors and capacitors. Combining integrated passives with high-performance tuning and switching elements on the same die offers a potential for building a new generation of RF front-ends for hand-held mobile communication. Capacitive switches with an insertion loss of 0.4 dB and an isolation of 17 dB at 1 GHz have been demonstrated. Dual-gap relay type tunable capacitors have been fabricated that show a continuous and reversible tuning ratio of 12 together with a quality factor larger than 150 at frequencies higher than 0.5 GHz. These are the highest tuning ratio and quality factor reported to date. A 0-level packaging concept that is compatible with the fabrication technology has been adopted.

Passive integration and RF MEMS: a toolkit for adaptive LC circuits

RF MEMS variable capacitors have been realized in an industrialized thin-film process for manufacturing high-quality inductors and capacitors on high-ohmic silicon. The fixed as well as the moveable electrode consists of aluminium, the native aluminium oxide is used as a dielectric. A tuning ratio of 1.35 and a switching ratio up to 29 have been measured. At RF frequencies they show low ohmic losses, which make them very suitable for use in high-quality adaptive LC networks. The feasibility of the application of switched capacitors for load switching in GSM power amplifiers has been demonstrated through simulations based on experimentally derived components and systems parameters.

Passive integration on Si for RF circuits in wireless applications

A technology is described for the integration of high quality factor inductors and capacitors on high ohmic silicon. The performance is optimised for resonator and matching circuits in RF wireless applications. This is demonstrated by the design and measurement of an integrated output match for a GSM power amplifier which has comparable performance to a conventional hybrid module.

MEMS-based MCM VCO for space applications

This paper presents the implementation and test of prototype RF MEMS based voltage controlled oscillators (VCO) for space applications. RF MEMS tunable capacitors based on a dual gap architecture have been manufactured with a thin film technology on silicon and have demonstrated high tuning ratio (Cmax/Cmin ~ 4) and high Q factors (up to 100) with a good reproducibility. These tunable capacitors have been integrated as frequency tuning element in the LC tank of multi chip modules (MCM) VCO operating around 1.6 GHz with a tuning range greater than 16% and a phase noise as low as -125 dBc/Hz at 1 MHz offset from the carrier