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Abstract

This paper addresses the design and modeling of millimeter wave tunable filters using CoPlanar Waveguide (CPW) quarter wavelength stubs and MEMS (Micro-Electro- Mechanical-Systems) switches. In order to design bandstop and bandpass tunable MEMS filters an accurate design methodology based on the transmission line theory is presented. The tunable behavior is achieved using original MEMS switches: Two Cantilever Shunt Switch (TCSS). The overall structures, including TCSS, have been manufactured using dielectric membrane, in order to minimize the insertion losses. The obtained simulation and experimental results confirm the accuracy of the proposed design methodology and indicates very good performances in millimeter wave band.

Abstract

A VLSI readout front end architecture, dedicated for X-ray imaging, using specific capacitive silicon detectors, with capacitance ranging from 2 to 10 pF, is described. Critical design issues such as the noise optimization and the shaper implementation technique are addressed and the first performance test results of a fabricated prototype in a 0.35 ¼ m 3.3 V CMOS process, are presented. Important feature of the design is the novel CR-RC 2 pulse shaper configuration since in this section, transconductor circuits are used in order to provide a broad range of continuous variable peaking time, programmable gain and adjustable undershoot while still maintaining the noise performance and the required linearity of the specific radiation detection application. Regarding the readout ASIC performance characteristics, the power consumption is 1 mW per channel, the equivalent noise charge at 1.81 ¼ s peaking time is 382 e - plus 21 e - per pF of detector capacitance. The topology achieves a conversion gain equal to 3.31 mV/fC and a linearity of 0.69%.

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Abstract

GaN related devices have demonstrated excellent performances for high power, high temperature up to X-band applications. However, even if the reliability studies on AlGaN/GaN high electron mobility transistors (HEMT) have led to higher mean time to failure (MTTF), physical mechanisms induced by stresses are still not well known. This paper proposes an original solution to improve the robustness of the devices by passivating the traps that are supposed to be related to the degradation process. Based on the experience of previous works, we use Deuterium H+ to block the traps located at the AlGaN/GaN interface above the gated zone of the device, and the traps in the bulk of the conducting channel (2 dimensions electron gas : 2DEG). 2 batches of devices are processed with and without deuterium, and submitted to temperature stresses at 500°C. Low frequency noise (LFN) measurements are performed to track the evolution of the spectral current density of the drain current, which is known to be related to the structural evolution of the traps and of the crystal structure perfection. Devices with deuterium feature stable LFN spectra, while LFN spectra of the devices without deuterium evolve during the different stress steps. Thus, deuterium can offer an interesting alternative to enhance the robustness of AlGaN/GaN devices operating under stringent temperature conditions.

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A nonlinear noise model of a SiGe bipolar transistor is presented. This model includes a nonlinear noise source and is able to predict the noise conversion phenomena in circuits using this transistor such as oscillator phase noise. It is based on two main low frequency noise sources, which are extracted thanks to noise measurements under large RF signal superposition. An original low phase noise X band amplifier is also presented. This amplifier features a phase noise performance of 160 dBrad2· Hz1 at 10 kHz offset frequency together with a low DC power consumption of 50 mW.

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An electrical stress test has been conducted on 98 Zener conventional reference diodes structures and it has been observed that 45 % of these devices failed after 3000 hours. However this high failure ratio can be reduced to below 25 %, or less, providing that an appropriate low frequency noise (LFN) characterization is initially performed and that all the devices exhibiting the larger LFN are subtracted from the lot subjected to electrical stress test. Further results obtained after a 4500 hours electrical stress test conducted on a reduced number of diodes fully validate this finding.

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Abstract

This paper reports on the investigation of failure mechanisms of AlN-based capacitive RF MEMS switches. Electrostatic Discharge (ESD) experiments have been carried out by means of a Transmission Line Pulsing (TLP) technique. It has been observed that ESD stresses create some electric arcs and the degradations have been observed and analyzed. Microwave measurements have shown that ESD stress impacts the quality of the capacitive contact.