Siamak Fouladi

Thermally Actuated Latching RF MEMS Switch and Its Characteristics

Here, a new thermally actuated latching wideband RF microelectromechanical systems (MEMS) switch is presented. The switch employs two thermal actuators connected to two thin metal arms which serve as signal lines of coplanar waveguide switch. The actuators pull the thin arms sequentially, and latch the switch. The switch can be actuated on and off by using either short voltage or current pulses. Using a dielectric bridge (nitride) as an interface between the actuators and the thin arms, the RF circuitry is separated from DC actuators, allowing wide-band operation. The switch demonstrates an excellent wideband RF performance with an insertion loss of better than 0.3 dB up to 20 GHz and better than 0.8 dB up to 40 GHz. The return loss and isolation of the switch is better than 20 dB for the entire frequency band. The switch also has a very satisfactory repeatability with better than 0.1-dB variation in insertion loss and less than 1-dB variation in return loss and isolation at 30-dB level up to 6000 times switching cycles. The switch has been also successfully tested for RF power handling capability up to 40 dBm. The proposed switch has very simple RF structure which makes it an ideal candidate to be integrated in the form of more complex circuitry. An application of the proposed switch for a band selection network which is used in multiband transceivers has been presented here.

Novel High-

Two microelectromechanical systems (MEMS) curled-plate variable capacitors, built in 0.35-mum CMOS technology, are presented. The plates of the presented capacitors are intentionally curled upward to control the tuning performance. A newly developed maskless post-processing technique that is appropriate for MEMS/CMOS circuits is also presented. This technique consists of dry-and wet-etching steps and is developed to implement the proposed MEMS variable capacitors in CMOS technology. The capacitors are simulated mechanically by using the finite-element method in ANSYS, and the results are compared with the measured results. Two novel structures are presented. The first capacitor is a tri-state structure that exhibits a measured tuning range of 460% at 1 GHz with a flat capacitance response that is superior to that of conventional digital capacitors. The proposed capacitor is simulated in Ansofts high frequency structure simulator (HFSS) and the capacitance extracted is compared with the measured capacitance over a frequency range of 1-5 GHz. The second capacitor is an analog continuous structure that demonstrates a measured continuous tuning range of 115% at 1 GHz with no pull-in. The measured quality factor is better than 300 at 1.5 GHz. The proposed curled-plate capacitors have a small area and can be realized to build a system-on-chip.

Q

The objective of this paper is to investigate the integration of capacitive type RF microelectromechanical systems (MEMS) switches in a standard CMOS technology. A maskless monolithic integration process dedicated to electrostatically actuated capacitive type RF MEMS switches is developed and optimized. The fabricated switches consist of composite metal-dielectric warped membranes. The warped-plate structure is used to increase the capacitance ratio of the switch. The switches are fabricated using the interconnect metal and dielectric layers available in a standard 0.35-μm CMOS process. Measurement results for the first switch show an insertion loss less than 0.98 dB, a return loss below 13 dB up to 20 GHz in the up-state, and a down-state isolation of 12.4-17.9 dB from 10 to 20 GHz. The capacitance ratio is enhanced up to 91:1 using the warped-plate structure. A second cascaded switch consisting of two shunt capacitive switches and a slow-wave high-impedance transmission line section is designed and fabricated for high-isolation applications. The measured insertion loss for this switch is less than 1.41 dB up to 20 GHz, the return loss is below 19 dB, and the isolation is 19-40 dB across the frequency band from 10 to 20 GHz. The proposed RF MEMS switches can be used in millimeter-wave CMOS RF front-ends where multiband functionality and reconfigurability is required.

MEMS Curled-Plate Variable Capacitors Fabricated in 0.35-

This paper presents the design and implementation of a new class of evanescent tunable combline bandpass filters based on electronic tuning with the use of RF microelectromechanical systems (RF-MEMS) capacitor banks and also mechanical tuning using piezomotors. The use of microelectromechanical systems tuning circuit results in compact implementation of the proposed filters with high-Q and near to zero dc power consumption. The proposed filter structures consist of combline resonators with tuning disks that are either mechanically moveable using piezomotors or are loaded with RF-MEMS capacitor banks. Two- and six-pole tunable bandpass filters are designed and measured based on the proposed tuning concept. The two-pole tunable filter operates at 2.5 GHz with a bandwidth of 22 MHz and demonstrates a tuning range of 110 MHz, while the quality factor is better than 374 (1300-374 over the tuning range). The six-pole tunable filter with RF-MEMS capacitor banks operates from 2.634 to 2.59 GHz (44-MHz tuning range). The proposed tunable filter structures can also be implemented using alternative technologies such as barium-strontium-titanate varactors.

\mu{\hbox {m}}

A design methodology for the distributed microelectromechanical system (MEMS) impedance matching networks based on the optimization of the uniformity of the Smith chart coverage has been developed. The proposed approach was validated through a comparison between a traditional coplanar waveguide (CPW) design and an improved design based on a slow-wave (SW) structure. The enhanced reconfigurable impedance matching network has been developed for low-frequency applications. The network is based on a distributed MEMS transmission line (DMTL) coupled with the SW structure to reduce the total physical length of the network by 25% in comparison with a traditional DMTL. An extensive analysis was performed to identify the impact of each design parameter in order to optimize the structure and reduce the required size for relatively low-frequency applications. Several parameters are extracted from the electromagnetic simulation results and are used to design the proposed impedance matching network. Measurement results confirm the efficiency of the proposed design methodology in improving the impedance coverage and also miniaturization of the DMTL impedance matching networks.

CMOS Technology

This paper presents an integrated tunable bandpass filter with RF MEMS varactors fabricated using the TSMC 0.35 μm CMOS process. A maskless post-processing technique is developed which enables the fabrication of RF MEMS parallel-plate capacitors with a high quality factor and a very compact size. A 2-pole coupled line tunable bandpass filter with a center frequency of 9.5 GHz and a 9% relative bandwidth is designed, fabricated and tested. A tuning range of 17% is achieved using integrated variable MEMS capacitors with a quality factor exceeding 20. The filter has an insertion loss of 5.66 dB and occupies a chip area of 1.2 × 2.1 mm2.

Capacitive RF MEMS Switches Fabricated in Standard 0.35-

High-Q tunable filters are in demand in both wireless and satellite applications. The need for tunability and configurability in wireless systems arises when deploying different systems that coexist geographically. Such deployments take place regularly when an operator has already installed a network and needs to add a new-generation network, for example, to add a long-term evolution (LTE) network to an existing third-generation (3G) network. The availability of tunable/reconfigurable hardware will also provide the network operator the means for efficiently managing hardware resources, while accommodating multistandards requirements and achieving network traffic/capacity optimization. Wireless systems can also benefit from tunable filter technologies in other areas; for example, installing wireless infrastructure equipment, such as a remote radio unit (RRU) on top of a 15-story high communication tower, is a very costly task. By using tunable filters, one installation can serve many years since if there is a need to change the frequency or bandwidth, it can be done through remote electronic tuning, rather than installing a new filter. Additionally, in urban areas, there is a very limited space for wireless service providers to install their base stations due to expensive real estate and/or maximum weight loading constrains on certain installation locations such as light poles or power lines. Therefore, once an installation site is acquired, it is natural for wireless service providers to use tunable filters to pack many functions, such as multistandards and multibands, into one site.

\mu{\hbox{m}}

By taking advantage of the MEMS contact type switches in tunable filters, a new method that allows both the adjustment of resonant frequency and the input/output and inter-resonator coupling is presented. A three-pole filter capable to switch to three different states is designed using this method. The measured center frequency for each state is 8, 9, and 10 GHz (25% tuning) with a constant bandwidth of around about 1 GHz. The measured insertion loss of the filter is better than 3.5 dB for all three states.

CMOS Technology

Waveguide antenna feeders with reconfigurable circular polarization sense are proposed in this paper. They can be switched between right and left hand circular polarization, without any mechanical rotation between the feeder and the antenna. Two types of feeders are presented. The polarizer works with a single switchable polarization for each state. The dual feeder can work with both polarizations at the same frequency band simultaneously, each one associated with a different rectangular waveguide port. The polarization sense is controlled by metallic posts that block or open the signal paths connecting the rectangular ports with a septum-orthomode polarizer. These posts are automated with piezo-motors integrated in the structure, leading to a very compact layout, reduced size, and practical for applications with diverse switching speed. The proof of concept and the automation are shown with experimental Ku-band prototypes.

High-

Here, a new thermally-actuated latching RF MEMS switch is presented. The switch uses two thermal actuators connected to two thin arms which serve as the signal lines of coplanar waveguide switch. The actuators pull the thin arms sequentially, and latch the switch. The switch can be actuated ON and OFF by using voltage or current pulse. Using a dielectric (nitride) as an interface between the actuators and the thin arms, the RF circuitry is separated from DC actuators, allowing wide band operation. The proposed switch has a simple RF circuitry that makes it suitable for integration in more complex configurations. The switch demonstrates excellent RF performance of better than 0.3dB insertion loss and a return loss of better than 20dB for the entire frequency band up to 20GHz.