D. Neculoiu

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.

Millimeter-Wave Identification—A New Short-Range Radio System for Low-Power High Data-Rate Applications

The radio-frequency identification (RFID) concept is expanded to millimeter-wave frequencies and millimeter-wave identification (MMID) in this paper. The MMID concept and a comparison with UHF RFID are presented, showing the limitations and benefits of MMID. Three feasible applications are suggested for MMID, which are: (1) wireless mass memory; (2) an automatic identification system with pointing functionality; and (3) transponder communication with automotive radar. To demonstrate the feasibility of the MMID system, experimental results for both downlink and backscattering-based uplink are presented at 60 GHz.

6.3-GHz Film Bulk Acoustic Resonator Structures Based on a Gallium Nitride/Silicon Thin Membrane

This letter describes the fabrication and the morphological and microwave characterization of film bulk acoustic resonator structures, supported on very thin GaN membranes. We have demonstrated, by employing both white-light profilometry as well as X-ray diffraction, the low deflection and low stress of the GaN membranes supporting the resonator metallization. Using as test structure two FBAR structures connected in series, by a floating backside metallization, we have obtained resonance frequencies of 6.3 GHz for a 0.5-mum-thick membrane. The quality factor, at 6.3 GHz, was higher than 1100.

Millimeter-wave generation via frequency multiplication in graphene

In this letter, we demonstrate that a graphene monolayer, over which three metallic electrodes forming a coplanar waveguide are patterned, acts as a frequency multiplier and generates frequencies at least up to 40 GHz. These results show that monolayer graphene is a natural frequency multiplier.

Coplanar waveguide on graphene in the range 40 MHz–110 GHz

We present the modeling and measurements of microwave propagation in a coplanar waveguide over graphene in the range of frequencies 40 MHz-110 GHz, which suggest that graphene could work well in a very large bandwidth. Graphene is acting as a natural matching device because its equivalent resistance at these frequencies is able to vary more than 75% when DC biases are applied in the range −4 V to 4 V on the graphene waveguide.

Effect of space charge polarization in radio frequency microelectromechanical system capacitive switch dielectric charging

The letter presents the investigation of the temperature dependence of the charging mechanism of dielectric layer in radio frequency microelectromechanical system switch. The accumulated charge kinetics are monitored through the transient response of device capacitance when a bias greater than pull-in is applied. The capacitance transient response is shown to follow a stretched exponential law. The “time scale” of the stretched exponential process is found to be thermally activated, with an activation energy that is determined from Arrhenius plot.

A tunable microwave slot antenna based on graphene

The paper presents the experimental and modeling results of a microwave slot antenna in a coplanar configuration based on graphene. The antennas are fabricated on a 4 in. high-resistivity Si wafer, with a ∼300 nm SiO2 layer grown through thermal oxidation. A CVD grown graphene layer is transferred on the SiO2. The paper shows that the reflection parameter of the antenna can be tuned by a DC voltage. 2D radiation patterns at various frequencies in the X band (8–12 GHz) are then presented using as antenna backside a microwave absorbent and a metalized surface. Although the radiation efficiency is lower than a metallic antenna, the graphene antenna is a wideband antenna while the metal antennas with the same geometry and working at the same frequencies are narrowband.

SAW Devices Manufactured on GaN/Si for Frequencies Beyond 5 GHz

This letter describes the manufacture and characterization of surface acoustic wave (SAW) devices on GaN/Si devoted to applications above the 5-GHz frequency range. The SAW structures consist of two face-to-face interdigitated transducers (IDTs), placed at different distances. Using a TiAu metallization, 80-nm-thick and advanced e-beam lithographical techniques with IDTs with fingers and spacings 200 nm wide have been obtained on the GaN layer. On wafer measurement of the S parameters have demonstrated the operation at approximately 5.6 GHz. The frequency response of the devices is explained in detail.

GaAs membrane supported millimeter-wave receiver structures

In this paper, we describe the design, manufacturing and characterization of a monolithically integrated micromachined millimeter-wave receiver module. The antenna array, the matching network, and the GaAs Schottky diode are supported on a thin GaAs membrane. The receiver structure benefits from the advantages of the membrane supported transmission lines as well as of the Schottky diode integration on the membrane. The 2.2 μm thin GaAs membranes were grown by molecular beam epitaxy and formed by reactive ion etching employing selective etch-stop techniques. The results from the measurements of the voltage sensitivity and the radiation pattern of the 38 GHz receiver demonstrated state-of-the-art performance of the micromachined structure fabricated with our process.