Paola Farinelli

A Novel MEMS-Tunable Hairpin Line Filter on Silicon Substrate

In this paper a novel MEMS-tunable hairpin line filter is presented. The circuit has been realized on a 525 mum high resistivity silicon substrate using a well established micromachining process at ITC-IRST in Trento, Italy. The tunability of the device is obtained by line sections added to the U-line branches of the resonators of the hairpin filter through 10 identical MEMS ohmic contact cantilever switches. Measurements of the MEMS switch show an isolation and an insertion loss better than 20 dB and 0.3 dB, respectively, in the filter frequency range. Measured S-parameters of the MEMS-filter exhibit an insertion loss and a return loss better than 4.5 dB and 17 dB respectively, with a 15% passband at 6.2 GHz and 10% tuning range

Broadband RF-MEMS Based SPDT

A broadband single pole double throw (SPDT) switch has been developed for use in the range of 0 to 30 GHz. The switch consists of a cascade of a MEMS ohmic series and a capaci-tive shunt switch with floating electrode in each branch. It is manufactured on high-resistive silicon using surface micro-machining technology. The SPDT switch provides an insertion loss better than -0.6 dB, return loss smaller than -20dB, and isolation better than -40 dB in nearly the whole band. A switching voltage around 50 V is needed. The switch is used as a building block for more complex switching networks. The fabrication process is described and the measured RF-performances are reported and discussed. A failure analysis exhibits a lifetime up to 109 actuations

A MEMS-Reconfigurable Power Divider on High Resistivity Silicon Substrate

This paper presents a MEMS-reconfigurable power divider on high resistivity silicon substrate with variable power ratio. The circuit is based on two cascaded hybrid couplers connected through a tunable phase shifter that produces the required power ratio. A 5 state prototype has been fabricated on a 525 m high resistivity silicon substrate employing two 3 dB branch line couplers and a reflection-line MEMS phase shifter. The latter is reconfigured through two MEMS-switched open ended lines, whose lengths can be varied through the actuation of eight ohmic contact MEMS switches. Measurements of the MEMS switch show an isolation and an insertion loss better than 15 dB and 0.2 dB, respectively, with a contact resistance lower than 1 Ohm in the entire power divider bandwidth. RF measurements of the power divider exhibit a return loss better than 16 dB and an isolation better than 17 dB in the bandwidth [11.8-12.2] GHz with nominal power ratios of 1:0, 6:1,1:1,1:6, and 0:1.

RF-MEMS SPDT switch on silicon substrate for space applications

The paper illustrates the activity carried out under an ESA contract for the development of a miniaturized RF-MEMS SPDT switch and switch matrix using micromachining technology on a silicon substrate for power applications. A manufacturing procedure, based on an eight masks process, has been set up. At present, a broadband single-pole-double-throw (SPDT) switch operating in the 0-30 GHz frequency range has been fabricated and measured. Isolation of about -40 dB and insertion loss better than -0.7 dB have been obtained.

High-

To reduce the complexity and cost of future telecommunication systems, electrically tunable or reconfigurable filters based on radio frequency microelectromechanical systems (RF MEMS) and waveguide technology constitute a very promising solution, since they allow for very high Q and good tunability. Three concepts for tunable waveguide filters using ohmic RF MEMS switches are described in this paper, and compared in terms of performance and manufacturing complexity. Quality factors of the order of 1000 and frequency tunability of the order of 5% are shown both by High-Frequency Structure Simulator simulations and experimental results in K-band.

Q

In this paper, a circuit model to predict the microwave response of a shunt-connected capacitive microelectromechanical coplanar switch is proposed. The numerical values of the lumped elements composing the equivalent circuit are computed by means of a fully analytic approach. In particular, the contribution of resistive and inductive parasitic elements has been evaluated by using closed-form expressions. Configurations characterized by different technological solutions have been obtained and modeled. Simulations performed with the proposed approach correlate very well with actual measurements.

Tunable Waveguide Filters Using Ohmic RF MEMS Switches

This paper presents a novel wide tuning range MEMS varactor based on a toggle push - pull mechanism for high RF power applications and improved reliability. The device anchoring utilizes a torsion spring mechanism which virtually allows for a full capacitance tuning range. Improved mechanical stability is also provided by the actively controlled pull-out implementation that is realized without increasing the MEMS manufacturing complexity. As a proof of concept, a toggle MEMS varactor has been modeled, designed and manufactured in shunt configuration on a 50 Omega coplanar transmission line. Analytical and full wave electromechanical models are provided as well as electromagnetic characterization. The device has been manufactured on HR Silicon substrate by using the standard FBK-irst RF MEMS process. Optical profile, DC and RF measurements are presented in the 0-40 GHz frequency band. Excellent RF performance as well as a capacitance tuning ratio of 2.5 has been obtained.

An equivalent-circuit model for shunt-connected coplanar microelectromechanical system switches for high frequency applications

The evolution of the main electrical parameters of dielectric-less ohmic RF-MEMS cantilever-based switches during continuous actuation stress was investigated in this work. Thanks to different designs, the main electrical parameters changes were attributed to a charging phenomena of the oxide over the substrate near the polysilicon actuator, leading to both narrowing and shifting of traditional hysteresis-like curves. Recovery procedures were also analyzed. Furthermore, the breakdown occurrence was also investigated, supported by both emission microscope and optical images.

A Wide Tuning Range MEMS Varactor Based on a Toggle Push-Pull Mechanism

This work presents the design, manufacturing and testing of three 5-bit K-band MEMS phase shifters based on similar architectures (combination of switched line and loaded line) but employing different MEMS switch typologies (cantilevers & air-bridges) and RF junctions (SP2T & SP4T). All devices have been monolithically manufactured on 200 μm thick high resistivity silicon substrate (4”) by using the FBK MEMS process. The performance of the different devices have been compared in order to identify the best configuration to be implemented in electronically steerable phased arrays antennas for Satellite COTM (Communication On The Move) Terminals. Excellent performances were measured for the dielectric-free pad MEMS switches as well as the single bits constituting the phase shifter. The three 5-bit devices show return loss better than 15 dB for all states, with average insertion loss of 3.5dB for the clamped-clamped, SP2T-based design, 2.2 dB for the cantilever, SP2T-based device and 2.1 dB for the cantilever, SP4T-based design. The measurements of the packaged devices are on-going.

Evolution of electrical parameters of dielectric-less ohmic RF-MEMS switches during continuous actuation stress

A broadband reconfigurable coupler has been realized at Ku band making use of RF-MEMS switches. The coupler is directly printed on the same Silicon substrate on which the MEMS are built. The device works at 16-20 GHz, and it is designed to provide two different coupling levels of -10 dB and -17 dB, maintaining good matching and isolation in both states. Performance significantly matches the simulations, verifying how close the MEMS switches perform to the predicted behavior. This also demonstrates that the MEMS fabrication process is repeatable and predictable.