Robert Plana

Terahertz antenna based on graphene

We have investigated several configurations of antennas based on graphene. We show that patterned metallic dipole antennas or arrays of dipole antennas deposited on graphene highly benefit from the reversible high-resistivity-to-low-resistivity transition in graphene, tuned by a gate voltage. The radiation pattern and the efficiency of such antennas are changed via the gate voltage applied on graphene.

Reliability modeling of capacitive RF MEMS

The kinetic of dielectric charging in capacitive RF microelectromechanical systems (RF MEMS) is investigated using an original method of stress and monitoring. This effect is investigated through a new parameter: the shift rate of the actuation voltages. We demonstrate that this lifetime parameter has to be considered as a function of the applied voltage normalized by the contact quality between the bridge and the dielectric. We also demonstrate that this phenomenon is related to Frenkel-Poole conduction, which takes place into the dielectric. We finally propose a model that describes the dielectric charging kinetic in capacitive RF MEMS. This model is used to extract a figure-of-merit of capacitive switches lifetime.

Evaluation of noise parameter extraction methods

The influence of the algorithm used for noise parameter fitting on the accuracy of the microwave noise parameter measurements is investigated. Five different commonly used algorithms are compared by a statistical analysis including instrument accuracy specifications. Some of these algorithms are found to be more efficient in terms of available accuracy and computer time. The best predicted available accuracies reported betwen 4 and 20 GHz for each noise parameter compare well with observed accuracies on noise parameter measurements performed with a dedicated test set on a noise standard made of a passive two-port. The accuracy on minimum noise figure is found to be 0.1 dB maximum. >

Noise modeling of microwave heterojunction bipolar transistors

Analytical expressions of microwave heterojunction bipolar transistors minimum noise figure and noise parameter are reported in this paper. These expressions are derived from a noise model including nonideal junctions, emitter and base resistances and have been compared with measured data obtained on a Si-SiGe HBT. An agreement between theoretical and experimental data was as observed up to 20 GHz for several bias conditions. The limits of the model or the range of validity of the proposed equations have been also examined with the help of an appropriate CAD software. The analysis of the influence of parasitic elements on noise parameters has shown a strong influence of the extrinsic base collector capacitance at microwave frequencies. >

Micromachined Loop Antennas on Low Resistivity Silicon Substrates

The integration of K-band (20-40 GHz) full wavelength square wire- and slot-loop antennas on low resistivity (11-70 Omegacm) silicon substrates is addressed. By the use of polymer or silicon oxide/nitride membranes to support the slot or wire loop over micromachined trenches the efficiency of the antennas is enhanced while the majority of the bulk silicon within the aperture of the antenna is preserved to enable the integration of active devices. A 3.6times3.6 mm2 large slot loop antenna chip with 200 mum micromachined trench width yields 1.5 dBi gain at 29.5 GHz, while 1.0 dBi gain is obtained at 24 GHz for a wire loop antenna on a 4.5times4.5 mm2 large chip with 360 mum wide trenches

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.

Microwave propagation in graphene

We report on measurements and modeling of microwave propagation in graphene. In deep contrast with carbon nanotubes, which display very high impedances in the microwave range, planar waveguides patterned directly on graphene display a 50 Ω impedance, which is tuned slightly by an applied dc. The high values of kinetic impedance in carbon nanotubes were not observed in graphene.

Graphene for Microwaves

Graphene nanoelectronics is an emerging area of research. The 2010 Nobel Prize for physics was awarded to A. Geim and K. Novoselov for the discovery of graphene and its unexpected physical properties, paving the way for many new applications in the area of nanoelectronics, nanooptics, and solid state physics. The most-studied microwave device is the graphene transistor, which, in only three years, has reached a cutoff frequency of 100 GHz. As consequence of this impressive development, the prediction that a 0.5-1 THz graphene FET transistor will soon be demonstrated is quite realistic. Moreover, graphene multipliers and other microwave graphene devices are expected to follow the graphene FET development dynamics and reach 100 GHz in few years.

Small-signal and noise model extraction technique for heterojunction bipolar transistor at microwave frequencies

The increasing use of Heterojunction Bipolar Transistors (HBTs) in microwave analog circuits requires a valid description of these devices by means of an equivalent circuit including noise sources in an extended bias and frequency range. This paper describes a technique to extract the elements of the equivalent circuit from simultaneous noise and S-parameter measurements. Additionally, the conventional high frequency bipolar junction transistor (BJT) noise model is shown to work well with HBTs. Recent results obtained from GaInP/GaAs HBTs are reported. >

Writing simple RF electronic devices on paper with carbon nanotube ink

This paper shows that we can print on paper simple high-frequency electronic devices such as resistances, capacitances or inductances, with values that can be changed in a controllable manner by an applied dc voltage. This tunability is achieved with the help of an ink containing functionalized carbon nanotubes and water. After the water is evaporated from the paper, the nanotubes remain steadily imprinted on paper, showing a semiconducting behavior and tunable electrical properties.