Fabio Coccetti

Voltage and temperature effect on dielectric charging for RF-MEMS capacitive switches reliability investigation

In this paper, we study the effect of stress voltage and temperature on the dielectric charging and discharging processes of silicon nitride thin films used in RF-MEMS capacitive switches. The investigation has been performed on PECVD-SiNx dielectric materials deposited under different deposition conditions. The leakage current was found to obey the Poole–Frenkel law. The charging current decay was found to be affected by the presence of defects which are generated by electron injection at high electric fields. At high temperatures power law decay was monitored. Finally, the temperature dependence of leakage current revealed the presence of thermally activated mechanisms with similar activation energies in all materials.

Design and Implementation of Two-Layer Compact Wideband Butler Matrices in SIW Technology for Ku-Band Applications

The design and realization of a novel wideband two-layer 4 × 4 Butler matrix in substrate integrated waveguide (SIW) technology are addressed. The two-layer SIW design is exploited through a two-fold enhancement approach. The two-layer topology is first explored in a simple matrix layout with minimum number of components. A space saving design is then proposed making optimum use of the two-layer topology and the SIW technology leading to a significant size reduction. A two-level, low-loss, wideband SIW transition is designed and optimized using its equivalent circuit model. The two corresponding Butler matrix prototypes are optimized, fabricated and measured. Measured and simulated results are in good agreement. Isolation characteristics better than -15 dB with input reflection levels lower than - 12 dB are experimentally validated over 24% frequency bandwidth centered at 12.5 GHz. Measured transmission magnitudes and phases exhibit good dispersive characteristics of 1 dB, around an average value of -6.8 dB, and 10° with respect to the theoretical phase values, respectively, over the entire frequency band. The impact of the measured transmission phases and magnitudes on the radiation pattern of a 4-element antenna array is also investigated.

Electrostatic discharge failure analysis of capacitive RF MEMS switches

This paper reports on the investigation of failure mechanisms of aluminum nitride (AlN)-based capacitive RF MEMS switches. Electrostatic discharge (ESD) experiments have been carried out by means of a transmission line pulsing (TLP) technique and a first experiment under human body model (HBM) stresses has been done. It has been observed that TLP stresses gives rise to electric arcs and the degradations have been analyzed and are reported in this paper. Microwave measurements have shown that TLP stresses impact the quality of the capacitive contact. HBM robustness in upstate configuration and its different failure modes have been also reported.

A comprehensive study for dielectric charging process in silicon nitride films for RF MEMS switches using Kelvin Probe Microscopy

In this work we present for the first time a systematic investigation for the dielectric charging in silicon nitride films for RF MEMS capacitive switches based on Kelvin Probe Microscopy methodology. The effect of the underneath physical layer over which the dielectric will be deposited has been first investigated through depositing SiN films over thermally grown oxide, evaporated gold and electroplated gold layers. Then, the dielectric films have been deposited with different thicknesses in order to study the impact of dielectric thickness. Finally, the effect of the deposition conditions has been investigated through depositing SiN films using low and high frequency PECVD method.

A novel reconfigurable DGS cell for multi-stopband filter on CPW technology

A novel defected ground structure cell was presented. The cell was built on coplanar waveguide technology. Two diodes in each side of the ground planes allow us to switch the filter between different passbands. Simulated and measured responses were presented showing very good agreement. An electromagnetic explanation of the structure based on slot transmission line was also presented. The cell shows very promising features for the implementation of small and efficiently reconfigurable building block for filters. The very narrow stopbands in the responses may be enhanced by putting more cells in cascade. This work is a first step toward implementation of a silicon integrated reconfigurable filter using MEMS switches in place of diodes.

Electromagnetic simulations via parallel computing: an application using scale changing technique for modeling of passive planar reflectarrays in grid environment

Electromagnetic simulation continues to be the primary method by which engineers and researchers analyze and design circuits and systems. Nowadays, the complexification related to the rise of microwaves circuits results in the coexistence of several scales in the same circuit and in the appearance of important dimensions ratios. As the dimensions of modern Electromagnetic circuits continue to shrink, the fabrication and parametric testing of such structures have become more challenging. Increasing market pressures are driving engineers and researchers to minimize the time-to-the-market. So more efficient simulation strategies to accelerate the simulation process are required. Parallel and distributed simulation approaches seem to be a promising approach in this direction. With the growing incidence of computer modeling and simulation, the scope of this paper is to show that parallel simulation of multi-scale models can achieve several orders of magnitude speedup. When mapped onto distributed memory multicomputer systems like Computational Grid, additional speedup is obtained.

Novel two-layer broadband 4 × 4 Butler matrix in SIW technology for Ku-band applications

In this paper, the design of a broadband 4x4 Butler matrix is presented for the first time on a two-layer Substrate Integrated Waveguide (SIW) structure. The presence of path crossings in the matrix structure often imposes the use of extra OdB couplers - usually obtained using back to back pairs of 3dB couplers - for planar realizations. Specific designs that overcome the use of OdB couplers can be found, but these realizations may not be easily generalized to larger matrices. On the other hand, realizations with suspended lines suffer from being narrow band and rather adapted to microstrip technology [4]. A two-layer implementation in SIW technology appears then as a good compromise as it remains compact in height and compatible with both waveguide-like and microstrip technologies.

A novel compact reconfigurable defected ground structure resonator on coplanar waveguide technology for filter applications

Recently, there has been a great interest in the implementation of reconfigurable Defected Ground Structures (DGS) where the number and location of the transmission zeros may be controllable [1]-[4]. This paper presents a novel reconfigurable DGS resonator on coplanar waveguide technology. This structure may be considered as a development of that presented by the authors in [3], where layout compactness is achieved. The paper is organized as follows; Section 2 gives the structure description with complete dimensions, Section 3 gives the simulated and measured responses, in addition to the equivalent circuit model, Section 4 gives the design rules, while Section 5 is devoted to the conclusion.

A modified CRLH cell optimized for easy reconfigurability

A novel CRLH cell is hereby presented providing easy integration and reconfigurability. First, the straight access line to the interdigital-capacitor was replaced by a bent access to improve the propagation without using cumbersome tapered access. Second, a stub-capacitor was added to facilitate the reconfigurability providing added degree of freedom for the values of the circuit model. These modifications allow the control of the characteristic frequencies of LH and RH branches of CRLH structures. Proposed future work consists of experimental validation of this cell and reconfigurability by MEMS technology of both the stub-inductor and the stub-capacitor.

Experimental study of a modified silicon-based CRLH cell for enhanced reconfigurability

Up to now there has been an intense research on metamaterials based on Composite Right/Left Handed (CRLH) approach [1–3] and several applications based on this approach have been developed. Most of the published CRLH cells are composed of an interdigital-capacitor and a stub-inductor implemented on microstrip technology [4]. In previous work, the design and simulation results of a modified CRLH unit cell endowed of a new stub-capacitor in order to facilitate the reconfigurability have been presented [5]. In this paper, the fabricated structures based on silicon technology will be experimentally investigated. The equivalent circuit of the basic and the modified CRLH structures are extracted in order to give the dispersion diagrams. The experimental study demonstrates that the stub added to the design could help to avoid the shunt capacitance parasitic by controlling its value. This allows to tune the characteristic frequencies of the Left Handed (LH) and the Right Handed (RH) bands.