Sara S. Attar

Low-Temperature Superconducting DC-Contact RF MEMS Switch for Cryogenic Reconfigurable RF Front-Ends

A niobium-based superconducting dc-contact RF microelectromechanical systems switch is introduced and is thoroughly analyzed. The switch is amenable to integration with superconducting microelectronics technology. A comparison of the switchs RF performance at room and cryogenic temperatures indicates a significant improvement in the insertion loss of the switch when niobium is superconducting. The mechanical characteristic of the switch at extremely low temperature (4 K) is also investigated. The switch exhibits an increase of 18% on the actuation voltage as the temperature changes from 293 K (room temperature) to 4 K. A niobium superconducting tunable resonator is designed and tested, employing the proposed switch as the tuning element in the form of a switched capacitor bank monolithically integrated with the resonator. The measured results at 4 K clearly indicate the discrete resonance frequency states of the resonator. A three-pole tunable bandstop filter is designed with a center frequency of 1.2 GHz and dimensions of only 5 mm × 1.2 mm. The results demonstrate a tuning range of 12% while maintaining an excellent RF response of the filter.

Low temperature superconductive tunable bandstop resonators and filters

A superconducting MEMS varactor is reported. The device is fabricated using a standard Niobium superconductor foundry process. Utilizing this varactor a superconducting tunable notch resonator is implemented. The tunable resonator has a measured tunability of more than 20% from 3.22 GHz to 2.54 GHz with a biasing voltage from 0 V to 78 V. A 3-pole bandstop filter is also fabricated and tested. Simulation results of the tunable bandstop filter demonstrates a 20% shift in center frequency.

Low temperature superconducting DC-contact RF MEMS switch for superconducting tunable resonators

A novel niobium-based superconducting DC-contact RF MEMS switch is presented for the first time. The switch is amenable to integration with the superconducting micro-electronics (SME) technology. A comparison of the switch RF performance at room and cryogenic temperatures indicates a great improvement in the insertion loss of the switch when niobium is superconducting. The mechanical characteristic of the switch at extremely low temperature (4K) is investigated. The switch exhibits only 18% increase in the actuation voltage as temperature changes from room temperature (300K) to 4K. A niobium superconducting tunable resonator is designed and fabricated employing the proposed switch as the tuning element. The concept can be extended to realize a high-Q switched capacitor bank for reconfigurable RF front-end components in SME receivers.

Low Temperature Superconducting RF MEMS Devices

A dc contact and a capacitive contact niobium-based superconducting radio frequency (RF) microelectro-mechanical systems switches are presented for the first time. The switches are amenable to integration with superconducting-micro-electronics technology. A comparison of the RF performance of the switches at room and cryogenic temperatures indicate a significant improvement in the insertion loss of the switch when niobium is superconducting. A niobium-based dc contact single-port-double-throw switch is designed, fabricated, and tested. Two types of switched capacitor banks are also designed each implementing one of the two types of the introduced switches. The measured results of the capacitor bank with capacitive contact switches show variation of the capacitance value from 0.4 to 0.94 pF. The measured results of the capacitor bank with dc contact switches show variation of the capacitance value from 0.2 to 1 pF at 4 K.

Tunable RF MEMS-based Frequency Dependent Power Limiter

A novel approach for Frequency Dependent Power Limiters (FDPL) is proposed. RF MEMS switches are integrated with bandpass filters to form a power limiter where the output RF power is limited to specific levels based on the frequency band. An RF MEMS-based power limiter is analyzed both theoretically and experimentally for one frequency band. The limiter attenuates the high power signal only within the bandwidth of the integrated filter. The design of the proposed power limiter is expanded to achieve power limiting for various frequency bands. The flatness of the threshold level can be set to the desired value by controlling the return loss of the filters used in the FDPL circuit. Measured results for a FDPL circuit are presented demonstrating that the limiting power level can be controlled by adjusting the dc bias of the MEMS switches.

Integration of Niobium Low-Temperature-Superconducting RF Circuits With Gold-Based RF MEMS Switches

A novel eight-mask fabrication process for the integration of low-temperature-superconducting niobium (Nb) RF circuits with gold-based RF microelectromechanical system (MEMS) switches is proposed. DC-contact and capacitive-contact RF MEMS switches integrated with Nb-based transmission lines are presented for the first time. A comparison of the RF performance of the switches at room and cryogenic temperatures indicate that the proposed gold-based MEMS fabrication process did have a major impact on the superconducting characteristics of Nb. A switched capacitor bank is also designed, implementing a dc-contact RF MEMS switch. The measured results of the capacitor bank show the variation of the capacitance value from 0.22 to 5.25 pF at 4 K. A thermal analysis of the devices under test (DUTs) is also performed, and an investigation is carried out to minimize the thermal loss between the chuck and the DUT.

Low Temperature Superconducting Tunable Bandstop Resonator and Filter Using Superconducting RF MEMS Varactors

A novel niobium-based superconducting RF microelectromechanical system (MEMS) varactor is presented, and its mechanical performance is characterized at both room and cryogenic temperatures. The device is amenable to integration with superconducting microelectronics (SME) technology. The RF performance of the varactor at cryogenic (4 K) temperatures indicates capacitance variations from 40 fF to 0.46 pF. Hence, the varactor is used to design a monolithically integrated tunable resonator, whose measured results at cryogenic temperature show a sweep of frequency from 2.62 to 2.54 GHz and a discrete shift from 2.54 to 1.95 GHz, when the biasing voltage varies from 0 to 58 V. Using the same fabrication process, a fixed niobium-based three-pole bandstop filter is designed with a center frequency of 2 GHz and a size of 5 mm × 0.85 mm. Tunable versions of the three-pole filter using semiconductor varactors and monolithically integrated MEMS varactors are also designed and characterized at 4 K. The results of the tunable bandstop filters are analyzed both theoretically and experimentally.

A novel concept for post-fabrication tuning of microwave filters

A novel method for global post-fabrication tuning of microwave filters is presented. The method is based on designing and adding a compensating passive circuit in parallel with the detuned filter. This concept, which is demonstrated by experimental results, has several advantages over traditional techniques for filter tuning that use screws. It can be employed to filter structures that are not easily amenable to the use of tuning screws such as planar filters. Another important advantage of the proposed concept is that it can be employed without knowing details of the filter configuration. The compensating circuit that is added in parallel to the detuned filter, does not affect the individual elements of the filter. The experimental results obtained demonstrate the validity of this concept.