Performance of low loss RF MEMS Fixed - Fixed capacitive switch characterization

Linearity characteristics of capacitive tuners under large radio frequency (RF) power have become an important issue for today’s cellphone industry. The use of these devices as antenna tuners has become critically important due to the RF spectrum opening in the low-frequency range. Capacitive tuners connected directly to the antenna to change the RF voltage/current pattern and tune lower frequencies are subjected to suffer large voltage swings, especially in the isolation state or minimum capacitance. In this article, we analyze the effects of the large RF power or equivalent rms voltage to capacitive micro-electromechanical systems (MEMS) switches. The theoretical analysis combined with Coventor MEMS+ simulations will allow us to study the capacitance change and MEMS mechanical frequency response. This article evaluates two types of measurement setups to investigate the RF power effects on nominal capacitance and mechanical frequency response. Measurements up to 6 W were completed with two capacitive MEMS tuner products, confirming the modeling predictions and demonstrating the robustness of this technology under large RF power or voltage swings.

We report a novel pull-up type radio frequency (RF) microelectromechanical system (MEMS) switch with no elastic deformation of the cantilever involved in the actuation. At a voltage of 4.5V, reliable actuations are achieved such that the movable lower contact pad is pulled up by the electrostatic force to make contact with the upper pad. At a frequency of 50GHz, an insertion loss of 0.5dB, a return loss of 12.4dB, and an isolation of 55dB are obtained from the switch. The measured transient times for switch-on and switch-off are 120 and 130ns, respectively. Compared to the MEMS switches reported thus far, the pull-up type switch shows the best switching speed and isolation characteristic at 50GHz.

The objective of this paper is to investigate novel configurations of planar multiport radio-frequency (RF) microelectromechanical systems (MEMS) C-type and R-type switches and redundancy switch matrices for satellite communications. An in-house monolithic fabrication process dedicated to electrostatic multiport RF MEMS switches and switch matrices is developed and fine tuned. The proposed C-type switch is a four-port device with two operational states. This switch exhibits an insertion loss of less than 0.3 dB and isolation of about 25 dB at satellite C-band frequency range. The novel R-type switch is also a four-port device with an additional operational state. The measured results show an insertion loss of better than 0.4 dB and an isolation of better than 25 dB at C-band. This is the first time that an R-type RF MEMS switch is ever reported. Several of these switches are integrated in the form of redundancy switch matrices, and two novel monolithic five to seven redundancy switch matrices are developed, fabricated, and tested. It is shown that the additional operating state of the R-type switch not only decreases the number of elements by 50% but also reduces the size drastically

Theoretical and graphical analysis of pull-in-voltage and figure of merit for a fixed-fixed capacitive Micro Electromechanical Systems (MEMS) switch is presented in this paper. MEMS switch consists of a thin electrode called bridge suspended over a central line and both ends of the bridge are fixed at the ground planes of a coplanar waveguide (CPW) structure. A thin layer of dielectric material is deposited between the bridge and centre conductor to avoid stiction and provide low impedance path between the electrodes. When an actuation voltage is applied between the electrodes, the metal bridge acquires pull in effect as it crosses one third of distance between them. In this study, we describe behavior of pull-in voltage and figure of merit (or capacitance ratio) of capacitive MEMS switch for five different dielectric materials. The effects of dielectric thicknesses are also considered to calculate the values of pull-in-voltage and capacitance ratio. This work shows that a reduced pull-in-voltage with increase in capacitance ratio can be achieved by using dielectric material of high dielectric constant above the central line of CPW.

Influence of metal stress on RF MEMS capacitive switches

Surface roughness effects on electromechanical performance of RF-MEMS capacitive switches

In this paper, fully integrated radio frequency (RF) microelectromechanical system (MEMS) switches with piezoelectric actuation have been proposed, designed, fabricated, and characterized. At a very low operation voltage of 2.5V, reliable and reproducible operation of the fabricated switch was obtained. The proposed RF MEMS switch is comprised of a piezoelectric cantilever actuator with a floated contact electrode and isolated CPW transmission line suspended above the silicon substrate. The measured insertion loss and isolation of the fabricated piezoelectric switch are -0.22 dB and -42dB at a frequency of 2GHz, respectively.

Chapter Five - RF MEMS Devices for Communication Systems

Microelectromechanical systems (MEMS) radio frequency (RF) switches hold great promise in a myriad of commercial, aerospace, and military applications. In particular, capacitive type switches with metal-to-dielectric contacts (typically Au- on-silicon nitride) are suitable for high frequency (≥10 GHz) applications. However, there is little fundamental understanding of the factors determining the performance and reliability of these devices. To address this void in understanding, we conducted fundamental studies of Au-on-Si3N4 contacts at various bias voltages using a micro/nanoadhesion apparatus as a switch simulator. The experiments were conducted in air at 45% relative humidity. The switch simulator allows us to measure fundamental parameters such as contact force and adhesion, which cannot be directly measured with actual MEMS switches. Adhesion was found to be the primary failure mechanism. Both a mechanical and electrical effect contributed to high adhesion. The mechanical effect is adhesion growth with cycling due to surface smoothening, which allows increased van der Waals interaction. The electrical effect on adhesion is due to electrostatic force associated with excess charge trapped in the dielectric, and was only observed at 40 V bias and above. The two effects are additive, but the electrical effect was not present until surfaces were worn smooth by cycling. Surface smoothening increases the electric field in the dielectric, which leads to trapped charge and higher adhesion. Excessive adhesion can explain decreased lifetime at high bias voltage previously reported with actual capacitive MEMS switches. Aging of open contacts in air was found to reduce adhesion. Surface analysis data show the presence and growth (in air) of an adventitious film containing carbon and oxygen. The adventitious film is responsible for aging related adhesion reduction by increasing surface separation and/or reducing surface energy. No junction growth and force relaxation with time were observed in capacitive switch contacts, as was previously observed with Au–Au contacts at low current in direct current MEMS switches.

Creep is a critical physical mechanism responsible for the failure of radio-frequency (RF) capacitive micro-electro-mechanical systems (MEMS) switches, especially those operating at high RF power. Accurate modeling of creep in RF MEMS metallic membranes is necessary to estimate device lifetime and to improve their reliability. Moreover, the devices are frequently very thin, with aspect ratios as high as 1:500, and conventional three-dimensional structural modeling is onerous and unnecessary. In this article we extend a cell-centered finite-volume approach, previously developed to model thin membranes using Mindlin-Reissner plate theory, to study creep in RF MEMS devices. Results show that the present methodology can accurately predict the long-term creep behavior in thin RF MEMS devices in a computationally efficient manner.

The development of a thick-film hermetic BGA package for a radio-frequency (RF) microelectromechanical systems (MEMS) 2-bit phase shifter is presented. The measured packaged MEMS phase shifter average in-band insertion loss was 1.14 dB with an average return loss of 15.9 dB. The package transition insertion loss was less than 0.1 dB per transition with excellent agreement between simulated and measured results. It was also demonstrated that the RF MEMS phase shift performance could be improved to obtain a phase error of less than 3.3 degrees. The first reported measurements of the average rise and fall times associated with a MEMS circuit (in this case a 2-bit phase shifter) were 26 and 70 /spl mu/s, respectively. The advent of packaged RF MEMS phase shifters will reduce the cost (both design and building) of future phase arrays.

We report a novel multicontact radio frequency (RF) microelectromechanical system (MEMS) switch with mechanical independent switch elements and microspring contacts. The consistent contact arrangement and the robust contact design can effectively increase the contact area, reduce the current density, and therefore improve the power-/current-handling capability. The working mechanism of the switch with microspring contact is investigated by CoventorWare® simulation tools. The switch, fabricated by the Cu-Ni dual-metallic-sacrificial-layer surface micromachining, is actuated at 55 V for characterization. The closing time is 11 μs, and the opening time is 13.5 μs. The isolation is -30.9 dB at 2 GHz and -11.5 dB at 20 GHz; the insertion loss is -0.12 dB at 2 GHz and -0.22 dB at 20 GHz. The contact metal is Pt-Au, and the measured switch resistance drops from 48 to 1.2 Ω when the actuation voltage increases from 40 to 65 V. The switch element handles a current of 300 mA at 0.1 Hz. The switch is an excellent candidate for microwave applications requiring high-power handling.

Micro Electro Mechanical Systems (MEMS) Switches have become very popular in the Electronics industry and we need to carefully select beam material and structural parameters for reliability and better performance. A variety of materials can be used as beam material in RF MEMS switches. The cantilever beam is used to change the state of RF switch and for actuation is made mostly using aluminum, copper, gold, molybdenum, nickel and platinum. This paper investigates which is the best material to be used for beam for achieving lower pull-in voltage and also represents the effect of structural parameters such as air gap and beam thickness on the performance of MEMS series switches. Characterization of cantilever MEMS switches is carried out with 3D simulation using COMSOL Multiphysics based on Finite Element Method [FEM]. Reduction of Pull-in voltage can be done by carefully selecting beam material and it can further be reduced by decreasing air gap and beam thickness.

In this paper, a fully integrated CMOS and high voltage compatible RF MEMS (radio frequency microelectromechanical systems) technology is proposed and demonstrated for the first time. The high performance RF MEMS switch, high voltage MOSFET, and CMOS devices are all obtained using a simple process. The fabricated high voltage device has a breakdown voltage of over 35V. The MEMS capacitive switch fabricated on a high resistivity SOI substrate and with high-k dielectric (HfO/sub 2/) exhibits a low insertion loss (0.14dB at 5GHz) and a good isolation (9.5dB at 5GHz). This technology demonstrates the feasibility of building fully integrated RF systems for wireless communication applications.

Micro electro mechanical systems (MEMS) have experienced an explosive growth over the past few years driven mainly by its physical properties and its promising technological applications in many different fields, particularly in space and Radio Frequency (RF) systems. MEMS technology exhibits greater advantages over the existing semiconductor switches. In this paper, electro-thermal performances of a two hot arms actuator MEMS switch have been investigated. The switch is designed using CST Microwave Studio. Some mathematical equations have been developed to see the temperature distribution of the hot arms as voltage applied on it. Based on this thermal distribution, the linear thermal expansion of the hot arms and the air gap used in this switch is expressed mathematically. The developed equations have been solved and analyzed using the MATLAB software. This analysis shows that this MEMS switch has a wider range of linear operation and has extremely higher breakdown voltage.