Giorgio De Angelis

Composite Right / Left Handed (CRLH) Based Devices for Microwave Applications

Stefan Simion‡, Romolo Marcelli*, Giancarlo Bartolucci#, Florea Craciunoiu‡, Andrea Lucibello*, Giorgio De Angelis*, Andrei A. Muller‡, Alina Cristina Bunea‡, Gheorghe Ioan Sajin‡ ‡National Institute for Research and Development in Microtechnologies, Bucharest, Romania * CNR – Institute for Microelectronics and Microsystems, Rome Italy # University of Rome “Tor Vergata”, Department of Electronics Engineering, Rome Italy

Dynamics of RF Micro-Mechanical Capacitive Shunt Switches in Coplanar Waveguide Configuration

Micro-electromechanical switches for Radio Frequency applications (RF MEMS switches)[1][4] are movable micro-systems which pass from an ON to an OFF state by means of the collapse of a metalized beam. They can be actuated in several ways but, generally, the electrostatic actuation is preferred because no current is flowing in the device nor power absorption has to be involved in the process. The bias DC voltage signal is usually separated with respect to the RF signal for application purposes. Anyway, in the simplest mechanical model, a voltage difference V is imposed between the metal bridge, connected to the ground plane of a coplanar waveguide (CPW) structure, and the central conductor of the CPW, which also carries the high frequency signal. Under these circumstances, the switch will experience an electrostatic force which is balanced by its mechanical stiffness, measured in terms of a spring constant k. The balance is theoretically obtained until the bridge is going down approximately (1/3) of its initial height. After that, the bridge is fully actuated, and it needs a value of V less than the initial one to remain in the OFF (actuated) position, because contact forces and induced charging effects help in maintaining it in the down position. A general layout of the switch is diagrammed in Fig. 1a, with its simplified equivalent lumped electrical circuit. In Fig. 1b the cross-section of the device is shown, with the quantities to be used for the definition of the geometry and of the physical properties of the structure. The actuation as well as the de-actuation are affected also by the presence of a medium (typically air, or preferably nitrogen for eliminating humidity residual contributions in a packaged device) which introduces its own friction, causing a damping, and altering the speed of the switch [5]-[7]. Several models are currently available to account for a detailed treatment of the damping, including also the presence of holes in the metal beam [8]-[11]. Moreover, the damping modifies the natural frequency of oscillation for the bridge. In particular, the actuation and de-actuation mechanisms will be consequently affected, leading to simple oscillations (no fluid damping contribution) or damped oscillations (fluid contribution) up to over-damping for particular values of the bridge dimensions or material properties. Experimental problems related to the dynamic characterization of

Cycling reliability of RF-MEMS switches with gold-platinum multilayers as contact material

Low contact resistance and high cycling reliability are two important parameters for evaluating the quality of RF micro-electromechanical (RF-MEMS) switches. In this paper the use of a modified contact material is tested and compared to pure gold in cycling experiments performed on a RF MEMS switch in shunt capacitive configuration. The modified contact material is a gold-based multilayer with a thin layer of platinum sandwiched between two layers of gold. The experiment consists in comparing devices with the same layout but with different contact material. While the two types of switch start with similar RF performances, the device with the modified material shows a marked improvement in cycling stability and a lower series resistance up to 106 cycles when compared to gold contact devices.

Leaching Behavior of Salt Wastes Conditioned with Sodalite Blended with Two Different Glass Powders

Two different glass powders (a commercially available glass frit and a borosilicate glass) have been used as blending agents for sodalite, an aluminosilicate mineral able to condition chloride salt wastes from pyrometallurgical processes. The synthesis of the mineral phase has been made through a process recently proposed by Idaho National Laboratory in USA, starting from a homogeneous powder of nepheline, chloride salts and glass. The mix, put into an alumina crucible, was introduced in a furnace inside an argon-atmosphere glove-box. The furnace temperature was then raised to 925 C, where it was kept for 7 hours. Leach tests under static conditions, according to ASTM C1285-02, have then been carried out on the final waste forms at room temperature (23 C) and in an oven at 90 C. SEM investigations have also been made before and after leach tests, in order to check the status of the powders. In particular the effect of the leaching process on the surface of the sodalite grains at 90 C from 30 to 150 days has been evidenced. The results obtained in the present study have been usefully compared to those from a similar test on a sodalite added with a glass frit by Idaho National Laboratory. Financial support from the Nuclear Fission Safety Program of the European Union is gratefully acknowledged (project ACSEPT, contract FP7-CP-2007-211 267).

A New Matrix for Conditioning Chloride Salt Wastes from the Electrorefining of Spent Nuclear Fuel

A novel method proposed by Korea Atomic Energy Research Institute has been applied to the treatment of chloride salt wastes coming from electrorefining of spent nuclear fuel, which allows to separate uranium from fission products. It is based on a matrix, SAP (SiO2-Al2O3-P2O5), synthesized by a conventional sol-gel process, able to stabilize the volatile salt wastes due to the formation of metalaluminosilicates, metalaluminophosphates and metalphosphates. With this method a higher disposal efficiency and a lower waste volume can be obtained. Eutectic melt LiCl-KCl (59-41 mol%) has been used to simulate the waste salt. The composite SAP has been prepared by using tetraethyl ortosilicate (TEOS), aluminum chloride (AlCl3.6H2O) and phosphoric acid (H3PO4) as sources of Si, Al, and P, respectively. All reagents were dissolved in EtOH/H2O and the mixture, tightly sealed, was placed in an electric oven at 70 C. After a gelling/ageing for 3 days, the transparent hydrogels were dried at 110 C for 3 days and then thermally treated at 600 C for 2 hours. The final product (SAP) was reacted with metal chlorides at increasing temperatures for 20 hours inside an Argon-atmosphere glove-box, after mixing them at a SAP/metal chloride mixing ratio of 2. The obtained products have been characterized by means of density measurements, scanning electron microscopy, thermal analysis, as well as by XRD, FTIR and Raman spectra. Financial support from the Nuclear Fission Safety Program of the European Union (project SACSESS, contract FP7-CP-2012-323282) is gratefully acknowledged.

Characterization and Modeling of Charging Effects in Dielectrics for the Actuation of RF MEMS Ohmic Series and Capacitive Shunt Switches

Charge accumulation in dielectrics solicited by an applied voltage, and the associated temperature and time dependencies are well known in scientific literature since a number of years [1]. The potential utilization of materials being part of a device useful for space applications is a serious issue because of the harsh environmental conditions and the necessity of long term predictions about aging, out-gassing, charging and other characteristic responses [2], [3]. Micro-mechanical Systems (MEMS) for RF applications have been considered for sensor applications as well as for high frequency signal processing during more than one decade [4], [5], [6], [7], [8], [9]. In this framework, RF MEMS switches are micro-mechanical devices utilizing, preferably, a DC bias voltage for controlling the collapse of metalized beams [8]. Magnetic [10], thermal [11] and piezoelectric [12] actuations have been also evaluated, but the electrostatic one seems to be until now preferred for no current flowing, i.e. a virtual zero power consumption, less complicated manufacturing processes and more promising reliable devices [13]. During the last few years, several research activities started to release the feasibility of RF MEMS switches also for Space Applications [14], [15], [16]. The electrostatic actuation of clamped-clamped bridges or cantilevers determines the ON and OFF states depending on the chosen configuration. As well established, RF MEMS switches are widely investigated for providing low insertion loss [8], no or negligible distortion [17], [18] and somehow power handling capabilities [19], [20], [21], [22] for a huge number of structures already utilizing PIN diodes for high frequency signal processing. Actually, redundancy switches as well as single pole multiple throw (SPMT) configurations, [23], [24], matrices [25] true time delay lines (TTDL) [26], [27] and phase shifters [28], [29] for beam forming networks in antenna systems could benefit from their characteristics. On the

Development of capacitive RF MEMS switches with TaN and Ta2O5 thin films

We develop shunt capacitive RF MEMS switches in III-V technology making use of materials which can be alternative to the ones commonly used, in order to overcome some technological constraints concerning the RF MEMS reliability. Specifically, we evaluate the potential of tantalum nitride (TaN) and tantalum pentoxide (Ta2O5) to be used for the switches actuation pads and dielectric layers, respectively. To this scope, a compositional, structural and electrical characterization of TaN and Ta2O5 films as a function of the deposition parameters, such as the substrate temperature and the sputtering mixture composition, is performed. The realized switches show good actuation voltages, in the range 15- 20 V, an insertion loss better than -0.8 dB up to 30 GHz, and an isolation of ~ -40 dB at the resonant frequency. A comparison between the measured S-parameter values and the results of a circuit simulation is also presented and discussed, providing useful information on the operation of the fabricated switches.

The Image Phase Approach for the Design of RF MEMS Shunt Switches

In this paper a new method to solve the microwave matching problem of MEMS shunt nconnected switches is proposed, as an extension of a previously presented approach based on the image nparameter formulation. The image phase concept is used to impose the matching condition in the n“ON” state of the device, which is the most critical one. Two different configurations are investigated: na single basic cell and double basic cell topologies. For both of them an analytic modeling procedure is ndeveloped, and the equations for the synthesis of the structures are derived. In order to provide some nexamples, the method has been applied to a previously realized MEMS shunt variable capacitor.

Design and Optimization of Microwave Triangular Meta-Material Resonators in Coplanar Configuration

Complementary Sierpinski Triangular Resonators (C-STR) in coplanar waveguide (CPW) configuration have been studied for microwave applications. The peculiarity of the coupled triangular structures to exhibit multiple resonances is proposed for dual and three-band purposes, to obtain efficient metamaterial-inspired unit cells for high performance microwave tunable oscillators.