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.
In recent years for the fabrication of millimetre wave circuits, the removal of the substrate has been proposed as a
solution for the reduction of losses, especially for silicon substrates. However, the micromachining of GaAs is an
exciting less explored alternative for manufacturing high performance communication systems. GaAs micromachining is
very interesting for the millimeter and submillimeter wave applications, due to the potential for easy monolithic
integration of passive circuit elements with active devices manufactured on the same chip.
This paper presents the monolithic integration of a two-director membrane supported Yagi-Uda antenna with a Schottky
diode, both having as support a 2 μm thick GaAs membrane. The design was based on the full-wave electromagnetic simulation software Zeland-IE3D. The following Molecular Beam Epitaxy (MBE) structure was grown on a
semiinsulating GaAs wafer: 0.2 μm thin AlxGa<sub>1-x</sub> As layer with x > 0.55 (the etch-stop layer) followed by a 2 μm Low
Temperature (LT) GaAs layer ("the membrane layer") and then by a 0.3 μm thin GaAs, (1x10<sup>18</sup> cm<sup>-3</sup>-"ohmic layer").
Finally a 0.3 μm thin GaAs (1x10<sup>17</sup> cm<sup>-3</sup>-"Schottky layer") was grown. An eight-mask process was developed for the
receiver manufacturing. The process includes some difficult steps regarding the integration of a very small Schottky
diode (with a diameter of about 3 μm) with the antenna with dimensions of a few millimeters, the polyimide-bridge
manufacturing, and the membrane formation using Reactive Ion Etching (RIE). The receiver characterization, including
the isotropic voltage sensitivity, was performed using "on wafer" measurements and has shown a good agreement with
the simulated results. High performance receiver circuits for operating frequency of 45 GHz have been demonstrated.
The technology developed can be used for applications up to THz.
We present an original RF-MEMS switch topology associated with an efficient design methodology. The proposed switch has been optimized thank to a scalable electrical model, fabricated and measured and exhibits isolations better than -23 dB and losses less than 0.25 dB at 24 GHz for a pull down voltage of 22V. The proposed topology and design methodology can then be efficiently used to optimize more complex RF-MEMS with enhanced microwave performances.
AlGaN/GaN HEMTs are promising devices not only for high frequency power amplification but also for non-linear applications such as VCO. Therefore an assessment of their low frequency noise (LFN) is needed since it can be up-converted around the RF carrier. We have therefore compared different devices either made on sapphire or silicon in order to know which ones feature the lowest LFN. This study involves static and low frequency noise measurements (two different LFN set-up will be used and compared). GaN HEMT devices featuring several gate dimensions have been measured for different biasing conditions both in ohmic and saturation regime. We have compared sapphire based devices with silicon based ones with respect to their LFN levels.
In a second part of this work, we report on some reliability results of HEMT on sapphire substrates: identification of defects has been achieved with the help of static measurements, and we make use of low frequency noise as well as physical simulation in order to understand the operating mode of the device. For the first time, we correlate the γ of the 1/f<sup>γ</sup> LFN spectrum with transport mechanisms of the carriers: we found that γ strongly depends on the carriers conduction path. This hypothesis has been checked for HEMT on silicon substrate.
In this paper, we report low frequency noise (LFN) data obtained on passivated AlGaN/GaN HEMT’s grown by MBE on a silicon substrate. In order to localize the LFN sources, we have measured all the extrinsic gate and drain current noise generators and their coherence versus bias in the linear regime. We have found that the gate noise sources result from leakage phenomena at gate-source and gate-drain regions. Drain noise sources are mostly located in the active channel below the gate and they feature an equivalent Hooge coefficient of about 10<sup>-3</sup>. Secondly, in order to build a LFN model that fits the requirements of a CAD simulator, we have measured the LFN sources for numerous bias points in the saturation region and therefore we have studied the bias dependence of the different noise sources under normal operating conditions. Results show that the gate terminal noise current impacts heavily the overall LFN of the transistor contrary to others III-V HEMTs, and that specific bias conditions are needed in order to reduce the LFN.