Laurent Bary

Experimental determination of microwave attenuation and electrical permittivity of double-walled carbon nanotubes

The attenuation and the electrical permittivity of the double-walled carbon nanotubes (DWCNTs) were determined in the frequency range of 1–65GHz. A micromachined coplanar waveguide transmission line supported on a Si membrane with a thickness of 1.4μm was filled with a mixture of DWCNTs. The propagation constants were then determined from the S parameter measurements. The DWCNTs mixture behaves like a dielectric in the range of 1–65GHz with moderate losses and an abrupt change of the effective permittivity that is very useful for gas sensor detection.

Millimeter wave carbon nanotube gas sensor

This Letter reports experimental observations regarding the significant changes in the transmission modulus and phase of the propagating microwave signals up to 110 GHz in a micromachined coplanar waveguide supported on a dielectric membrane with a thickness of 1.4u2009μm filled with a mixture of carbon nanotubes when exposed to nitrogen gas. These large shifts of amplitude and phase of microwave signals due to gas absorption represent the experimental basis on which a miniature wireless gas sensor could be implemented.

Reliability overview of RF MEMS devices and circuits

This paper outlines the reliability properties of RF MEMS devices and circuits. The tools used to evaluate the reliability properties are presented. Results are shown on both moveable and non moveable devices. Key parametrers that drive the reliability are pointed out : stress, roughness, temperature dependance, dielectric properties. Finally, it is presented some solutions to improve the reliability performance of these devices in term of technology and design.

Microwave FBAR Structures Fabricated using Micromachined GaN Membranes

This paper reports on microwave characteristics of micromachined GaN-based thin-film bulk acoustic resonator devices. The 2.2 micron active piezoelectric layer was epitaxially grown on (111)-oriented high-resistivity silicon substrate. Bulk micromachining techniques were used for the release of the resonating GaN membrane structure. S-parameter measurements have shown a fundamental mode resonance around 1.3 GHz. Extracted material parameters such as an acoustic velocity of 5700 m/s and an effective coupling coefficient of about 2% are in good agreement with those reported in the literature using other fabrication methods.

High performance thin film bulk acoustic resonator covered with carbon nanotubes

This letter presents experimental results concerning a thin film bulk acoustic wave resonator realized on a thin GaN membrane and covered with a thin film of double walled carbon nanotube mixture. The quality factor was measured before and after the coating of the resonator with the nanotube thin film. The quality factor has increased more than ten times when the resonator was coated with nanotubes, due to their high elasticity modulus and low density, which confers a much higher acoustic impedance of the resonator electrodes and thus confines much better the longitudinal acoustic standing waves inside the resonator.

Dry followed by wet backside etching processes for micromachined endfire antennae

This paper presents a novel technological process based on dry followed by wet backside silicon etching for the manufacturing of quasi-three edge membranes-supported millimeter wave circuits. The process is based on a backside deep reactive ion etching used to remove the first 350 µm of silicon, followed by wet etching in KOH solution, to eliminate the remaining 50 µm of silicon and create quasi-free edge membranes, according to the undercut mechanism. In order to validate the technology, a Yagi–Uda antenna for 45 GHz was designed using the Zeland IE3D software package, and fabricated. The demonstrator was characterized in terms of return loss and isotropic gain using on wafer measurements. The agreement between the modeling and the measurements is very good, and validates the new technological approach, which assures free-space propagation conditions for endfire membrane-supported antennae structures.

Membrane-supported Yagi-Uda MM-Wave antennas

This paper presents the design, fabrication and on wafer characterization of membrane-supported Yagi-Uda CPW fed antenna structures. The antennas were designed for the 60 GHz and 77 GHz frequency operating ranges. The 60 GHz antennas were fabricated on a semi-insulating GaAs membrane using GaAs micromachining. The 77 GHz antennas were manufactured on 1.4 mum thin SiO2/Si3N4 membranes obtained by micromachining of high resistivity silicon, using backside wet etching process. The design was based on electromagnetic simulations, using Zeland IE3D software package. The antenna structures were measured on wafer and have shown good experimental results in good agreement with the simulated ones.

Generation-Recombination Defects In AlGaN/GaN HEMT On SiC Substrate, Evidenced By Low Frequency Noise Measurements And SIMS Characterization

Wide bandgap devices such as AlGaN/GaN High Electron Mobility Transistors (HEMT) grown on silicon carbide (SiC) substrate are investigated. Low frequency noise (LFN) measurements have been carried out to evaluate the structural perfection of dual gated HEMT devices featuring 0.25×2×75μm2 gate area: generation‐recombination (GR) processes are evidenced. Two sets of GR‐bulges related respectively to AlGaN/GaN interface and quantum well are identified. Each GR‐bulge is composed of two GR centers. The devices are then characterized in a temperature controlled oven, and these GR centers are extracted from LFN spectra versus temperature. Activation energies of the defects located at the AlGaN/GaN interface are measured at 0.38±0.05eV and 0.21±0.05eV using Arrhenius plots under saturated biasing conditions. Equivalent activation energies are extracted under ohmic biasing conditions. These results are compared with SIMS measurements, using the deuterium in diffusion condition as a probe to integrally explore the ...

Carbon nanotubes-based microwave and millimeter wave sensors

The aim of this paper is to experimentally demonstrate the applications of carbon nanotubes as microwave and millimeter wave sensors. In this respect, two different sensors are presented. The first sensor is a microwave mass sensor termed as RF nanobalance able to detect 1 ng (10-9 g) of matter. The nanolabalance consists in a GaN membrane bulk acoustic wave resonator covered with a thin film of carbon nanotubes. The second sensor is a gas sensor which is a micromachined coplanar waveguide filled with carbon nanotubes. When exposed to gas, significantly changes in the modulus and phase of the transmission as observed for a wide range of frequencies up to 110 GHz.

New topologies of tunable bandstop MEMS filters for millimeter wave applications

This paper addresses the design and the realization of tunable bandstop filters using MEMS (micro-electro-mechanical-Systems) technology for millimeter wave applications. In order to design bandstop tunable MEMS filters, three new topologies are presented. The presented measurement and simulation results validate the proposed topologies. The tunable behavior is achieved using MEMS switches. These switches, based on original topology of two cantilever shunt switch (TCSS), have a typical shunt switch behavior and intrinsic low actuation voltage. The overall structures, including TCSS, have been manufactured using dielectric membrane, in order to minimize the insertion losses.