RF MEMS

... the development of a broadband, low insertion loss, ohmic-contact MEMs switch for microwave ... The switch has an actuation voltage of 30 V, a response time of ... scattering model developed iteratively with the electromechanical modeling predicts RF performance demonstrated to ...

Abstract- MEMS have been popular these days due to its
multifarious utilities and diverse application. Radio
frequency technology is one of such potential areas where
MEMS has proved its worth. Though RF MEMS being a
little newer than other MEMS technologies has progressed
tremendously and holds rein of communication
engineering which is the most important sector for chip
industries. In this article various applications of RF
MEMS and related switching devices has been focused.
Above all, the best possible effort has been given to realize
a state of art of RF MEMS related issues from multiple
angles of design, application, manufacturing, marketing
and industry.

This paper presents the design optimization and
simulation of low-voltage series and capacitive radio frequency
(RF) Micro-electromechanical (MEMS) switches using ANSYS
Multiphysics. First, a series switch is simulated using shape
memory alloy (SMA) which shows that the use of SMA beam to
actuate switching, allows the excitation voltage to be relatively
much lower (5 V) compared to that needed for electrostatic
actuation (30 V). Secondly, in the capacitive switch structure both
contact plates of the switch are designed as displaceable
membranes with similar dimensions and conditions, differing on
only membrane materials. The obtained results (5 V) indicate about
30% reductions in actuation voltage from the conventional single
beam (15 V). The stress on the beam due to the actuation voltage is
also reduced increasing the switching life time.

Today the need of the our is to make everything
small. Recent advancements in silicon and
fabrication techniques (like VLSI,ULSI) made our
dreams come true and layed paths for new
technologies like Micro Electro Mechanical
Systems(MEMS). This has enabled very
compact, autonomous and mobile nodes, each
containing one or more sensors, computation
and communication capabilities, and a power
supply embedded into a cubic millimetre
package known as “ELECTRONIC DUST “ or
“SMART DUST”. Can we imagine tiny electronic
dust particles which are size of a grain of
sand connect to each other via wireless
transmission , creating an invisible network of
whispering dwarfs .They will share data
,reporting high temperatures or extreme
vibrations. These dust motes are developed
using MEMS technology. We review the key
elements of the emergent technology of “Smart
Dust” and outline the wide range of
applications of this technology using MEMS . Let
us see why these dust motes are smart.

MEMS (Micro Electro-Mechanical Systems) sensors enable a vast range of applications: among others, the use of MEMS accelerometers for seismology related applications has been emerging considerably in the last decade. In this paper, we provide a comprehensive review of the capacitive MEMS accelerometers: from the physical functioning principles, to the details of the technical precautions, and to the manufacturing procedures. We introduce the applications within seismology and earth sciences related disciplines, namely: earthquake observation and seismological studies, seismic surveying and imaging, structural health monitoring of buildings. Moreover, we describe how the use of the miniaturized technologies is revolutionizing these fields and we present some cutting edge applications that, in the very last years, are taking advantage from the use of MEMS sensors, such as rotational seismology and gravity measurements. In a ten-year outlook, the capability of MEMS sensors will certainly improve through the optimization of existing technologies, the development of new materials, and the implementation of innovative production processes. In particular, the next generation of MEMS seismometers could be capable of reaching a noise floor under the lower seismic noise (few tenths of ng/ √ Hz) and expanding the bandwidth towards lower frequencies (∼0.01 Hz).

This paper presents a novel design of single-pole four-throw (SP4T) RF-MEMS switch employing both capacitive and ohmic switches. It is designed on high-resistivity silicon substrate and has a compact area of 1.06mm2. The series or ohmic switches have been designed to provide low insertion loss with good ohmic contact. The pull-in voltage for ohmic switches is calculated to be 7.19 V. Shunt or capacitive switches have been used in each port to improve the isolation for higher frequencies. The proposed SP4T switch provides excellent RF performances with isolation better than 70.64 dB and insertion loss less than 0.72 dB for X-band between the input port and each output port.

This paper presents a frequency tunable 5-bit true-time-delay digital phase shifter using the radio frequency micro-electromechanical system (RFMEMS) technology. The phase shifter is based on distributed MEMS transmission line (DMTL) concept utilizing MEMS varactor. Bridge actuation mechanism followed by capacitance variation is the main source of frequency tuning in this work. Two stages of actuation mechanisms (push and pull) are used to achieve 2:1 tuning ratio. Accurate control of actuation voltage between pull to push stage contributes differential phase shift over the band of interest. Functional behavior of the push-pull actuation over the phase shifter application is theoretically established, experimentally investigated and validated with simulation. The phase shifter is fabricated monolithically using gold based surface micro-machining process on an alumina substrate. The individual primary phase-bits (11.250/22.50/450/900/1800) that are fundamental building blocks of complete 5-bit phase shifter are designed, fabricated and experimentally characterized from 10-25 GHz for specific applications. Finally, complete 5-bit phase shifter demonstrates an average phase error of 4.320, 2.80, 10 and 1.580, average insertion loss of 3.76, 4.1, 4.2 and 4.84 dB and average return loss of 11.7, 12, 14 and 11.8 dB at 10, 12, 17.2 and 25 GHz, respectively. To the best of the authors’ knowledge, this is the first reported band tunable stand alone 5-bit phase shifter in the literature which can work over the large spectrum for different applications. Total area of the 5-bit phase shifter is 15.6 mm2. Furthermore, cold-switched reliability on the unit cell and complete 5-bit MEMS phase shifter are extensively investigated and presented.

The oscillator architecture is proposed to reduce the close-in phase noise as well as power consumption. The proposed Colpitts oscillator removes the current source which is the main source of the 1/f noise conversion. The removal of the current source is compensated by using the transformer and cross-coupled capacitors. The 2-GHz film bulk acoustic resonator (FBAR) is used for the high Q frequency selective elements in the oscillator design. According to measurement results, this FBAR-based oscillator shows ≥ 10 dB reduction in close-in phase noise. Specifically, 12-dB lower phase noise is achieved at 100 Hz offset frequency. Measured power consumption is 350 uW, which is almost half of the conventional Colpitts oscillator using same FBAR device.

This presentation presents a review of novel technology which provides a promising solution for designing self-powered microsystems. Micro-Electro Mechanical  System (MEMS) energy harvesting is an emerging alternative for scavenging energy from natural sources. It has extensive potential in wireless sensor applications to provide a natural energy source that is essentially inexhaustible. It is an increasingly attractive alternative to costly batteries. This essentially free energy source is available maintenance-free throughout the lifetime of the application. Many systems, such as wireless sensor networks, portable electronics and cell phones, can use this technology as a power source. Although some types of MEMS, such as electro-magnetic MEMS, electrostatic MEMS, and piezoelectric MEMS, are used to provide energy in various applications, they have several technical barriers that limit their applications, including low efficiency, issues of scaling, and high cost.Novel MEMS solar energy harvesting technology is scalable and also easily integrated in microsystems. The RF MEMS design not only has to provide functional efficiency, but also must work within the limits of maximum charge and discharge conversion efficiency. The energy harvesting technologies currently available which utilizes RF MEMS to convert solar energy into charge, can achieve better benefits than photovoltaic cells. In this presentation the design,fabrication, testing and evaluation of RF MEMS and its working limits in charging and discharging  is illustrated .

This paper presents the design, fabrication, and characterization of a lateral contact series-shunt ohmic RF microelectromechanical systems (MEMS) switch actuated by an electrothermal actuator. Since the proposed RF MEMS switch is actuated electrothermally, it can be operated at an extremely low operation voltage of 0.16 V. In this switch, two series switches are cascaded by a quarter wavelength section of transmission line suspended over the trench of the substrate to form a series-shunt configuration according to the principle of impedance transforming. By using a single bidirectional thermal MEMS actuator to control the signal, the switch provides higher reliability when through high power microwave signal. The measured results show that an insertion loss of 1.2 dB or better is achieved from DC-40 GHz. The isolation is −50 dB at 5 GHz, −45 dB at 20 GHz and −60 dB at 35 GHz. What is more, this switch also exhibits high linearity, and high power handing for DC-40-GHz applications. In the switch OFF state, self-actuation does not happen up to the input power of 40 dBm at 1 GHz. In the switch ON state, no significant insertion loss variations or problems in the contacts, due to the RF power, can be observed below 31 dBm input power.

A new micromachined wideband frequency reconfigurable microstrip patch antenna is demonstrated in this paper. The tunable antenna system is fabricated by a combination of surface and bulk micromachining processes. Thermal actuation is employed to precisely adjust the operating frequency with voltage ranges compatible with today's CMOS circuitries. A bulk micromachined silicon membrane containing thermal actuators serves as a platform for antenna patch. The patch is excited by a 50Ω feed line through proximity coupling. The out-of-plane motion of the thermal actuators normal to the antenna surface deflects the patch downward respect to the fixed ground plane. This deflection reduces the air gap height between the antenna patch and feed line and consequently, resonant frequency of the antenna. The effect of initial air gap height on achievable tuning range and bandwidth of the antenna is also investigated and the optimum range is presented. The up-state operating frequency of the antenna is 22.61GHz which continuously can be lowered to 22.17GHz. A tuning range of 440MHz was achieved by a CMOS compatible actuation voltage of 1.5V. The bandwidth of the antenna for up and down-state positions are 1.34 and 1.27GHz respectively. The RF performance of the antenna and its mechanical behavior is investigated by FEM analysis and satisfactory results are obtained within the tuning range.