The graphene is an interesting material for high-frequency applications. Its high mobility values, exceeding 10000 cm2/Vs, and the mean free path for ballistic transport of over 400 nm at room temperature are the basic ingredients for graphene-based devices with cutoff frequencies that exceed 50-100 GHz. The paper will focus on some basic devices based on graphene for high-frequency applications, such as: (i) graphene transistors, and (ii) metallic coplanar waveguides (CPW) on graphene
The aim of this work was to develop a new MEMS switch structure for millimeter wave applications, which can be
integrated with other more complex devices for developing of reconfigurable filters or antennae for microwave or
millimeter wave frequency range. Electrostatic force was chosen for the switching operation, which seams to be the only way
to obtain high reliable and wafer scale manufacturing techniques at these frequencies. Different geometries of the switching
element were designed and manufactured in order to study the mechanical stability of these structures; the measured actuation
voltage, of about 24,5V, shows an acceptable value for the further applications. Measured and simulated results of these
structures (insertion losses of about 0.75dB@60GHz and isolation >50dB@60GHz) were in good agreement and are
promising for further applications in this frequency range.
GaN exhibits unique physical properties, which make this material very attractive for wide range of applications and
among them ultraviolet detection.
For the first time a MSM type UV photodetector structure was manufactured on a 2.2 μm. thick GaN membrane obtained
using micromachining techniques. The low unintentionally doped GaN layer structure was grown by MOCVD on high
resistivity (ρ<10kΩcm) <111< oriented silicon wafers, 500μm thick. The epitaxially grown layers include a thin AlN
layer in order to reduce the stress in the GaN layer and avoid cracking. Conventional contact lithography, e-gun Ni/Au
(10nm /200nm) evaporation and lift-off techniques were used to define the interdigitated Schottky metalization on the
top of the wafer. Ten digits with a width of 1μm and a length of 100μm were defined for each electrode. The distance
between the digits was also 1μm. After the backside lapping of the wafer to a thickness of approximately 150μm, a
400nm thick Al layer was patterned and deposited on the backside, to be used as mask for the selective reactive ion
etching of silicon. The backside mask, for the membrane formation, was patterned using double side alignment
techniques and silicon was etched down to the 2.2μm thin GaN layer using SF6 plasma. A very low dark current (30ρA
at 3V) was obtained. Optical responsivity measurements were performed at 1.5V. A maximum responsivity of 18mA/W
was obtained at a wavelength of 370nm. This value is very good and can be further improved using transparent contacts
for the interdigitated structure.
The principle of optical actuation of arrays of micromechanical cantilevers has widespread applications in optical signal
processing. The paper demonstrates that, depending on the configuration and operating mode of the micromechanical
cantilever array, optical actuation can be used to design broadband detectors, optical computing units for addition,
integration or differentiation of optical signals, to implement devices that can measure simultaneously the wavelength
and the optical power of a laser source with constant efficiency from UV to FIR, or to determine the amplitude and phase
profile of an incident light beam. Moreover, an array of optically actuated biased cantilevers can work as an optical data
storage device that encodes arrays of optical pixels (images) with a predetermined number of gray levels.
The aim of this paper is to determine an optimum nonselective etching solution in order to manufacture an as thin as possible, uniform and high quality GaAs membrane. Three different etching systems in various proportions of the components were analyzed. A high quality 10 micrometer thin GaAs membrane was obtained using the [1(H3PO4)]: [1(CH3OH)]: [3(H2O2)] etching solution. The micromachined GaAs membranes are manufactured to be used as support for microwave circuits as well as in high temperature sensor applications.
We report about measurements of optical bistability in hybrid AlAs/GaAs Bragg reflectors. We have estimated an optical switching energy of 0.1 fJmicrometers -2, a switching intensity of about 1 Wcm-2, and an electro-optical modulation of 40% using a voltage swing of 60 V.
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