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International audience; In this work, the thermo-optical properties of nematic liquid crystals are investigated through localized reflectance spectra measurements performed on a tunable LC-filter. The final aim is to insert such LC in the cavity of a tunable VCSEL device, in which local self-heating due to optical or electrical pumping must be taken into account. We demonstrate that, whereas standard LC E7 is not suited for real device operation, the maximal operating temperature of QYDPLC-36 LC is 95°C, with a birefringence at 1.55 μm higher than 0.18 at 60°C.

International audience; In this work we investigate a tunable 850nm laser based on a hybrid combination of a liquid crystal micro-cell and a half GaAs VCSEL. The target application is optical coherence tomography. The inherent tolerances of the hybrid technology, the presence of metals in the cavity and the need for a pure extraordinary mode lasing make challenging the optical design of this laser. Hence, VELM, a full 3D and vectorial VCSEL optical solver, is utilized to understand loss mechanisms and provide an optimized design.

A low cost packaging solution has been successfully implemented on RF MEMS switches. The encapsulation is made at wafer level by thin film packaging, it allows keeping very small footprint for the device and is fully compatible with wire bonding and flip chip assembly. In addition to their highly shrinked size, packaged switches excellent microwave performances and promising behaviors in terms of reliability, especially for redundancy schemes required by space applications.

This paper presents several experimental and simulation results on 130 nm SOI integrated inductors. Measurements and 3D electromagnetic simulations highlight the efficiency of different layout techniques and technological choices to improve the integrated inductor Q factor. We compare a variable-width spiral inductor with a classical spiral inductor keeping the inductance value constant as an essential parameter for RF circuit designers. A 30% Q factor enhancement is achieved for a same size device and same inductance value. The paper will attempt to provide keys to compromise between Q factor optimization and inductor compactness. The influence of the ratio between internal and external width of the coil's turns and the wire space is also examined.

Massive integration of RF-MEMS switches is still jeopardized due to reliability issues. To overcome this challenge, this contribution presents a novel electrostatically-actuated MEMS switch. This novel switch integrates a new design: on the one hand a dielectric free actuator on order to reduce drastically the dielectric charging; and on the other hand a symmetrical stacking of the silicon nitride suspended bridge in order to have a switch behavior insensitive to thermal stresses. In addition to that, the process flow has been totally reviewed so as to better control the different gap heights and also reduce contact surface contamination. Among others, thermal oxidations and wet etchings processes are used to fabricate the lower parts of the switch, and amorphous silicon is used as sacrificial layer. Finally, these major evolutions have allowed to demonstrate remarkable results in terms of process capability, microwave performances and lifetime.

Dielectric charging and contact degradations are the two major challenges to improve the lifetime of series ohmic electrostatic MEMS switches. This paper details our approach and our main results to overcome the failures due to dielectric charging. We introduce a time predictive model for charge accumulation that we use as a design tool for reliability. The key parameters are listed and a new switch design is proposed to reduce the charging: the dielectric materials between the actuation electrodes are removed as much as possible. This dielectric-free design gives remarkable results in terms of dielectric charging sensitivity: the pull-in voltage decreases a little bit at initial times, and remains steady for longer time. The second major challenge, that remains to be considered, deals with the contact reliability. For that purpose, gold and ruthenium contacts have been investigated under several operating conditions. Gold contacts give good results in cold switching conditions whereas ruthenium suffers from surface contamination which increases quickly the contact resistance. In hot switching conditions, both materials are sensitive to material transfer mechanism, the failure rate being proportional to the open circuit voltage. Nevertheless, ruthenium seems more resistant to a material transfer than gold, and offers performances acceptable for some specific applications. A hermetic packaging at wafer level should allow to improve the contact reliability thanks to an efficient management of the surface contamination issue.

This paper presents a new modeling method for integrated coplanar wave guides (CPW) and CPW discontinuities implemented in silicon on insulator (SOI) CMOS technology. Empirical equations, which are fitted to 3D EM simulations, are used to describe the electrical behavior of CPW as a function of the line's geometrical parameters. The models are validated through measurements up to 110 GHz. Thanks to accurate full wave simulations, discontinuities such as underpasses, 90deg bends, and tee and cross junctions are improved, and electrical models are developed. All models are easily implemented in commercial CAD tools. Finally, a 60 GHz band-pass filter is designed applying the described models and the simulations are compared to measurements.

Two new techniques based on the RF hot-via concept have been developed for use in chip-scale packaged (CSP) MMICs. The first one utilizes backside bumps for die attach onto a substrate carrier; excellent RF performance has been achieved on both active-, and passive MMIC devices up to 110 GHz. The second technique is based on direct soldering of the MMIC backside interconnects onto low cost substrate carrier (RO4003), making it ideal for a wire-bond free full surface mount approach. To the author's knowledge this is the first demonstration of such die attach-, and packaging techniques for MMICs. As application examples, experimental performance results obtained with both techniques, are presented for transmission lines, and broadband 30-GHz GaAs PHEMT amplifier MMICs.