Parametric FEM simulation of composite barrier FTJs under external bias at room temperature

A study on a parametrized model of a composite barrier FTJ (three-interface system, with a non-polar dielectric layer) under an external bias voltage and at room temperature, using FEM-based simulations, was performed. The approach involves the Thomas-Fermi model assuming incomplete screening of polarization charges for building the energy barrier profile, and numerically simulates the electron transport through the barrier by bias-voltage-dependent tunneling, using Tsu-Esaki formulation. That naturally include the temperature dependent contributions to the total current density. The TER coefficient and current densities are computed considering variation of a large set of parameters that describe the composite barrier FTJ system in realistic physical range of values with respect to a reference (prototypical) system. In this study, the parametric simulations were performed starting from selected data reported on the SRO/STO/BTO/SRO heterostructure. The most important results of our work can be stated as follows: i) The FEM simulations prove to be reliable approach when we are interested in the prediction of FTJ characteristics at temperatures close to 300 K, and ii) We show that several configurations with large TER values may be predicted, but at the expense of very low current densities in the ON state. We suggest that the results may be useful for assessing the FTJ performances at ambient temperature, as well as to design preoptimized FTJs by using different combinations of materials to comply with a set of properties of a specific model

BRIDGE TYPE AND CANTILEVER TYPE MEMS SWITCH STRUCTURES

MEMS (Micro-Electro-Mechanical Structures) switches are devices used to achieve a short or open circuit by mechanical movement of a specific component of the device. The mechanical movement of the component could be accomplished in different ways: electrostatic, magnetostatic, piezoelectric or thermal designs were used to obtain the displacement, but, finally, only first solution (electrostatic) shows a reliability good enough to be take into account [1]. In the last two decades RF MEMS switches have been becoming increasingly attractive for different application areas, like radar systems for defence applications, automotive radars, satellite communication systems, wireless communication systems or instrumentation systems mainly due to their advantages (very low insertion loss, very high isolation, near-zero power consumption, intermodulation products and very low cost) over their counterparts (pin diodes or FET). A major advantage represents the possibility of monolithically batch fabrication when they are used as system components in an integrated RF system, which means that the overall system cost become cheaper than the system where is used as a switching component that requires hybrid assembly [1, 2]. This paper presents preliminary theoretical and experimental results obtained by our group in this field. The main goal of this work was to develop a reliable method for switch manufacturing which could be integrated with other RF MEMS devices (filters or antennas). Two different structure types were analysed: bridge and cantilever. For each of these structures were taken into account different length (from 600μm up to 900μm for bridge type and from 750μm to 1150μm for the cantilever type) and different actuation pads size in order to analyse the actuation voltage vs. pads size and to compare the theoretical with the experimental results

Design and experiments for tunable optical sensor fabrication using (1 1 1)-oriented silicon micromachining

The paper presents the design and the experiments performed for integration of a micromechanical voltage tunable Fabry-Perot interferometer structure with a silicon p-n photodiode in order to obtain a tunable optical sensor. The Fabry-Perot interferometer can be used as a voltage tunable filter for the input radiation or as a voltage controlled attenuator to regulate the light from a monochromatic source. In our approach, the top mirror of the Fabry-Perot cavity is an Au/SiO2 movable membrane, formed by anisotropic etching of (111)-oriented Si wafers. The Au layer provides a good reflectivity of the upper mirror. The air-silicon surface acts as the lower mirror, as the anisotropic etching of (111)-oriented Si wafers provides very smooth surfaces. The upper movable mirror can be electrostatically actuated. This Fabry-Perot interferometer was realized on the top of a p-n photodiode. © 2004 Elsevier B.V. All rights reserved

Tunable Fabry-Perot surface micromachined interferometer-experiments and modeling

We present an optical tunable Fabry-Perot micromachined interferometer. The device is monolithically integrated with a p+-n photodiode on a silicon substrate, providing an adequate positioning of the photonic and microoptical components. The Fabry-Perot micro-interferometer consists of two parallel mirrors and lets the light with a particular wavelength pass through. The wavelength depends on the gap between the mirrors. We can change the gap of the micro-mechanical Fabry-Perot interferometer by applying a voltage to the mirrors, an electrostatic force inducing an attraction between the substrate and the top mirror. A simulation of the mechanical behavior was performed based on finite elements, using CoventorWare software. The method included an electro-mechanical simulation for a square parallel plate actuation with four connecting beams. The finite elements method (FEM) simulations of the device (the Fabry-Perot tunable filter) are performed for optimizing the design parameters in order to model the overall system performance, both the steady-state behavior and dynamic response

MEMS switch for 60 GHz band

The aim of this work was to develop a new MEMS switch structure for millimeter wave applications, which can be integrated with other more complex devices for developing of reconfigurable filters or antennae for microwave or millimeter wave frequency range. Electrostatic force was chosen for the switching operation, which seams to be the only way to obtain high reliable and wafer scale manufacturing techniques at these frequencies. Different geometries of the switching element were designed and manufactured in order to study the mechanical stability of these structures; the measured actuation voltage, of about 24,5V, shows an acceptable value for the further applications. Measured and simulated results of these structures (insertion losses of about 0.75dB@60GHz and isolation >50dB@60GHz) were in good agreement and are promising for further applications in this frequency range