Optimized vertical RF-MEMS switch design with a small actuation voltage

This paper presents the design, analysis, modeling and simulation of a novel RF MEMS series switches with low actuation voltage. A mechanical modeling is presented to describe the behavior of the series switch. The switch is designed with special mechanical structures. The novel mechanical and mathematical modeling of the switch leads to calculation of the accurate actuation voltage. The spring constant has been calculated in relation to the presence of the residual stress in the beam. The calculated spring constant for this beam is used to determine the accurate actuation voltage. The size of the switch is 60 ? 110 µm2. The designed RF MEMS series switch was simulated using Intellisuite MEMS tool. He calculated actuation voltage is 4.05 V and simulated one is 4.2 V for 0.6 µm beam thickness. The calculated result is also very close with simulated one. The proposed switch compared with other electrostatic switches has low actuation voltage and small size. The RF characteristics were simulated using HFSS software and the switch has good RF performance. The insertion loss of 0.067 dB, return loss of 26 dB and isolation of 16 dB were achieved at 40 GHz.

RF-MEMS switches may be divided into capacitive and metal-to-metal types in terms of type of connection. In capacitive switches in the OFF-state the beam does not attach to the transmission line due to the presence of a thin dielectric layer and it gets released easily. Capacitive switches are better compared with the metal-to-metal types due to their ability to transmit signals of higher frequency and power. In this paper, a novel RF MEMS shunt capacitive switch with a unique spring design is proposed. The proposed design benefits from high isolation, low loss, low actuation voltage, small size and weight compared to similar switches and is designed for application in the Ka-band. Step structure is used in the mechanical design of the switch to reduce the air gap between the bridge and the transmission line that has resulted in reduction of actuation voltage to 2.2 V. The proposed switch has been placed upon a coplanar waveguide (CPW) line with an impedance of 50 Ohms. $${\text{SiO}}_{2}$$ with a thickness of 1000 A has been used as dielectric to increase isolation and down-state capacitance. The unique design of the spring results in the reduction of stress to a minimum at all points of the switch especially the springs at the time of applying the actuation voltage. This advantage would reduce switch failures as time passes and results in increased life of the switch. Up-state capacitance is 93.3 fF and down-state capacitance is 2.64 pF. Therefore, a capacitive ratio of 28 is obtained. The dynamic behavior of the switch is studied by using the COMSOL Multiphysics software package and the RF characteristics have been obtained by using the HFSS software and show good RF performance. The results show that in the up-state, the designed switch including S11 is less than − 11.5 dB and S21 is more than − 0.85 dB at 1–40 GHz. In the down-state, the switch has excellent isolation in the Ka-band. Maximum isolation is − 71 dB that occurs at the resonance frequency of 30.5 GHz.

Micro-electro-mechanical-systems(MEMS) switches have low resistive loss, negligible power consumption, good isolation and high power handling capability compared with semiconductor switches. Lifetime of capacitive shunt switches strongly depends on the actuation voltage so low voltage switches is necessary to enhance its performance as well as to broaden its application area. This paper presents the design and simulation of low voltage capacitive shunt MEMS switches together with its RF performance for high frequency applications. The low voltage switches are realized by lowering the spring constant of the beam using serpentine spring designs together with large capacitive area so as to achieve the good RF performance as well. The pull-in voltage is analyzed with commercial CAD finite element analysis software CoventorWare. The electromagnetic performance in terms of scattering parameters, insertion loss, and isolation are analyzed with software Ansoft HFSS10. The switches achieved insertion loss $$<$$ < 0.47 dB in on state from 2 to 40 GHz; it provided better than 25 dB isolation in off state with a capacitance ratio of 94---96. The actuation voltage as low as 1.5 V with actuation area $$110\,\times \,100\,\upmu \mathrm{m^2}$$ 110 × 100 μ m 2 along with good RF performance is reported. The design parameter optimization including selection of appropriate number of meanders and its width found to be one of the most sensitive factors affecting the spring stiffness and actuation voltage.

This paper proposes a series of optimized scalable contact-capacitive radio frequency micro- electro-mechanical systems (RF MEMS) switches for millimeter wave applications. Due to the contact-capacitive topology, the ON-state and OFF-state of the switch can be designed separately to obtain smaller <inline-formula> <tex-math notation="LaTeX">$C_{ON}$ </tex-math></inline-formula> and larger <inline-formula> <tex-math notation="LaTeX">$C_{OFF}$ </tex-math></inline-formula>, which results in high capacitance ratio (<inline-formula> <tex-math notation="LaTeX">$C_{r}$ </tex-math></inline-formula>). The <inline-formula> <tex-math notation="LaTeX">$C_{ON}$ </tex-math></inline-formula> is defined by capacitance of the contacts, and it is optimized for low insertion loss (<inline-formula> <tex-math notation="LaTeX">$IL_{ON}$ </tex-math></inline-formula>). The <inline-formula> <tex-math notation="LaTeX">$C_{OFF}$ </tex-math></inline-formula> is defined by the metal-insulator-metal (MIM) capacitor, and it is designed for working band and scalable performance. The measurements of the fabricated devices show acceptable agreements with design and simulation. The optimized switches perform well with <inline-formula> <tex-math notation="LaTeX">$IL_{ON}$ </tex-math></inline-formula> better than 1.5dB and capacitive ratio about 124. The switches follow scaling rules from 20GHz to 110GHz. Linearity (IIP3) of the switches are tested to be higher than 60dBm, and calculated to be higher than 80dBm. Performances of the switch can be further improved and optimized in the future study.

Design, fabrication and characterization of miniature RF MEMS switched capacitor based phase shifter

Design and Simulation of RF MEMS Switch for X-band Applications

A DC contact series MEMS switch for reconfigurable antenna system application is designed, fabricated, and its RF characteristics are measured. Variable pivot seesaw concept is applied because this design minimize the driving voltage and prevent stiction of membrane. The proposed switch structure is fabricated on the Si wafer, a coplanar waveguide(CPW) signal lines and electrodes are fabricated on the glass wafer. Both wafer are bonded by anodic bonding method. The designed chip size is within 2 mmx2 mm and it is actuated by electrostatic force. Low actuation voltage has been achieved by means of small distance between signal line and membrane using the design scheme, switching is executed in the pull-in range. Minimum actuation voltage is about 10-12 V, isolation is around 50 dB and insertion loss is about 0.25 dB at 2 GHz.

In this paper, we propose the design of an ohmic contact RF microswitch with low voltage actuation, where the upper and lower microplates are displaceable. We develop a mathematical model for the RF microswitch made up of two electrostatically-actuated microplates; each microplate is attached to the end of a microcantilever. We assume that the microbeam is flexible, the microplates are rigid bodies and the electrostatic force is nonlinear function of the displacement and voltage applied between the microplates. We formulate the static and eigenvalue problems associated with the proposed microsystem. We show that the resulting static pull-in voltage and switching time are reduced by 30 and 45%, respectively, as compared to those associated with a RF microswitch formed of a single microbeam-microplate system. We also show that, unlike the second and higher frequencies, a selected range of applied DC voltages, affects significantly the first frequency.

In the last forty years the semiconductor industry focused on the downscaling process of the CMOS (Complementary Metal-Oxide-Semiconductor) technology, trying to follow as much as possible the empirical Moore's Law. In the last five years this trend has been facing technology limits that have led to the development of a new research field, named Beyond CMOS, which investigates new electron devices concept and materials that can replace or co-integrate the standard technology, to make large scale integrated (LSI), high performance, low power devices. Carbon nanotubes (CNTs) are considered one of the most promising materials for Beyond CMOS devices, both at front-end and back-end level. The development of the research on this new organic material is due to its nanometer scale dimensions and to its outstanding electrical (metallic and semiconducting behavior, ballistic conduction, current density > 109 A/cm2) and mechanical (Young's modulus ∼1 TPa) properties, nevertheless due to its low mass (mass density ρ = 1300 kg/m3). Among the several CNT applications already reported in literature (interconnections, sensors, transistors, memory, etc.), a particular interest is on their use to build Nano-Electro-Mechanical (NEM) devices, such as resonators and switches. NEM relays based on carbon nanotubes show large-current density drive and high speed operation compared to metal-based NEMS counterparts, low actuation voltage and low power, performances which are promising for radio-frequency (RF) applications, where RF MEM devices are considered as replacement solution for their off-chip and/or solid-state counterparts in front-end transceivers. Most of the previously reported CNT NEM switches concerns relay configuration based on one single movable nanotube and its DC characterization. Despite individual proof-of-concept merits, an electromechanical switch based on a single CNT usually presents an output signal level that is too low for practical applications and a poor reliable fabrication process, which opposes the precise control at wafer level achieved by standard technology. Alternatively, a very large-scale integration of NEM devices requires the exploitation of high-density aligned arrays of nanotubes, grown in precise locations and that could be patterned into well-defined and controlled configurations. The objective of this research work was to develop LSI NEM switches based on high dense carbon nanotube arrays in the back end of the line (BEOL), with conductive and capacitive contacts and tested from DC up to high frequency (RF), in order to evaluate their performances in a wide range of operations. The synthesis process of carbon nanotubes was performed by thermal CVD and temperature, gas concentration and catalyst pretreatment were optimized to achieve high dense aligned CNT arrays. A study on the catalyst geometries and on the substrate materials were performed in order to obtain horizontal aligned arrays grown directly on metallic substrate without density change. We developed a novel surface micromachining process to suspend CNT arrays. The DC characterization of CNT NEM switches was exploited to extract the equivalent electromechanical properties of the CNT membranes, since they behave as a new body material. We extracted an equivalent flexural modulus of 8.5 GPa and a resistivity of 0.0077 Ωcm. The devices, in both configurations, present a very low actuation voltage, below 10 V, lower than typical metal NEM switch for the same dimensions and a comparable switching time. The RF characterization was performed in the telecommunication frequency range (up to 6 GHz) showing reasonably high isolation and low insertion loss. The relay shows a lower reliability than the capacitive switch, due to the elevated drive current which induces the CNTs burning at the metal-to-metal interface. The RF measurements were used to extract the parameters of the proposed devices equivalent lumped model. Several implementations of CNT NEM switches, both for DC (reconfigurable interconnects, logic functions, memories) and RF (signal routing purposes in RF system Front-Ends, phase shifting networks or digitalized capacitor banks) applications, were reported.

To determine a micro electro mechanical systems (MEMS) inductor configuration that gives large inductance variations and high Q-factors, air-suspended MEMS inductor configurations are studied: (a) an inductor with two angularly meandered lines, (b) a solenoid inductor with a pair of movable shields, (c) a planar spiral inductor with a patterned shield of different areas, and (d) a planar spiral inductor with a metallic frame of different sizes. The configuration of (a) is shown to give a large inductance variation of 115%. However, its Q-factor is only about 10, and difficulties in fabrication are also expected. The configuration of (b) could be a reasonable engineering solution. The inductance variation is 67%, and the maximum Q-factor is over 22. The solenoidal inductor configuration is thus considered suitable for realizing an RF MEMS variable inductor with large inductance variations and high Q-factors.

Radio Frequency Micro Electro Mechanical Systems (RF MEMS) are devices showing exceptional potential to satisfy the demands of emerging RF electronic technologies, including those considered for high-power applications, such as for long distance communication systems. Operation in this regime requires an alternative way of thinking for these devices and, for example, a more accurate control of the pull-in voltage is of major importance due to the self-actuation effect. Therefore, the studies focusing on the features of the moving bridges are of great importance. This work presents the fabrication of a full family of RF MEMS switches suitable for high-power implementations having bridges deposited by Au electroplating and released using purely standard wet processes, as well as a carefully designed experimental study of their pull-in voltage. Depositing the bridge of the high-power RF MEMS by using only a single electroplating step makes the device fabrication easier, whilst the utilization of a purely wet release process is an asset. This method relies on low temperature processes, applicable simultaneously in bridges with various geometrical and perforation details without the need of any specialised infrastructure. The experimentally obtained results suggest that for this technology the bridge thickness is a critical factor for controlling the pull-in characteristics between devices fabricated in the same run. Moreover, it is revealed that for thicker bridges, geometry and hole perforation effects are more pronounced. This technology is therefore suitable for developing RF MEMS where the bridge thickness could be potentially utilized for enabling optimization engineering between devices that should be fabricated in the same run but need to satisfy diverse specifications during their operation.

Radio frequency micro electromechanical system (RF MEMS) based switches are widely used in microwave and millimeter wave communication systems for their low loss, excellent linearity, low power consumption and compact size compared to other contemporary solid state devices [1]. Surface micromachining technology is typically used to develop different types of single pole multi-throw (SPMT) switches like SPST, SPDT and SP4T. MEMS series and shunt switches are extensively used in SPMT RF switches for multiband selectors, filter banks, reconfigurable antennas and phase shifter applications in transmit/receive modules.

Hexagonal Shape radiating patch with reconfigurable characteristics for WiMAX/C/WLAN band is presented which is simulated on RT Duroid5880 substrate and is fed by CPW. Fractional bandwidth of antenna corresponds to 153.62% with high rejection dual band-notch reconfigurable characteristics excluding interfering bands WiMAX (3.30GHz–3.80GHz)/C-Band (3.80GHz–4.20GHz)/WLAN (IEEE802.11a/h/j/n5.15GHz–5.35GHz, 5.25GHz–5.35GHz, 5.47GHz–5.725GHz,5.725GHz–5.825GHz) using radio frequency micro electro mechanical systems (RF MEMS) shunt switch. The proposed antenna exhibits 3.4dBi–6.32dBi gain and 78–94% radiation efficiency. The group delay ≤1.0ns is also maintained in the entire operating band. Good dipole like radiation pattern in E-plane and omni-directional pattern in H-plane is also well maintained in the operating band with less co polarization with compact dimensions of 20 × 22 × 0.782 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> .

Epoxy based photo polymer - SU8 is evaluated as microwave packaging material for packaging of Radio Frequency Micro Electro Mechanical Systems (RFMEMS). Standard and Slotted Coplanar Waveguide transmission lines are chosen as test vehicles. Transmission lines of lengths up to 10mm are formed on ST-Cut Quartz substrates. The fabricated transmission lines are subjected to wafer level packaging. The measured S-parameter data shows a significant difference prior to and after packaging. Further, the effects due to the packaging are modeled using lumped components and the measured data are validated with simulations in Advanced Design System. The measured and simulated data agree favorably with each other, for both before and after packaging.

We propose a design, micro fabrication process, and nuclear magnetic resonance (NMR) based evaluation, of a magnetic field gradient chip. The uni-axial linear z-gradient coil design was computed by a stream-function method, with the optimisation goal to exhibit minimum power dissipation. The gradient coils were implemented on two bi-planes, which were built-up with Cu electroplating in combination with photo definable dry-film laminates. In the presented fabrication process, the initial seed layer served as a self-aligning back-side mask to define the electroplating mould, and also to implement resistive temperature detectors. The coil design and the electroplating process were tailored to enhance the electroplated height to construct low-resistive coils. Thermographic imaging in combination with the integrated temperature sensors allowed for investigating the heat-up, in order to analyse the current rating of the coil dual stack. The gradient coil was assembled with a radio frequency micro coil in a flip-chip configuration. To demonstrate the field linearity, a micro-engineered phantom was fabricated and subjected to a one-dimensional NMR experiment.