Italian Universities Nano Electronics Team

Bologna, Italy

Italian Universities Nano Electronics Team

Bologna, Italy
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Tazzoli A.,University of Padua | Tazzoli A.,University of Pennsylvania | Meneghesso G.,University of Padua | Meneghesso G.,Italian Universities Nano Electronics Team
Journal of Microelectromechanical Systems | Year: 2011

This letter aims to propose a new setup for systematically inducing microwelding formation on ohmic RF microelectromechanical systems (MEMS) switches using electrostatic discharge events in a controllable manner. The established procedure was verified with success on different typologies of clamped-free and clampedclamped electrostatically actuated switches, but it can be easily extended to other families of MEMS devices. This setup makes possible the evaluation of the intrinsic robustness of different designs to the stiction caused by microwelding events, and it can be adopted to evaluate the efficiency of an active restoring mechanism implemented within the RF-MEMS switch. © 2011 IEEE.


Persano A.,CNR Institute for Microelectronics and Microsystems | Tazzoli A.,University of Padua | Tazzoli A.,University of Pennsylvania | Cola A.,CNR Institute for Microelectronics and Microsystems | And 4 more authors.
Journal of Microelectromechanical Systems | Year: 2012

In this paper, the reliability of shunt capacitive radio frequency microelectromechanical systems switches developed on GaAs substrate using a III-V technology fabrication process, which is fully compatible with standard monolithic microwave integrated circuit fabrication, is investigated. A comprehensive cycling test is carried out under the application of different unipolar and bipolar polarization waveforms in order to infer how the reliability of the realized capacitive switches, which is still limited with respect to the silicon-based devices due to the less consolidation of the III-V technology, can be improved. Under the application of unipolar waveforms, the switches show a short lifetime and a no correct deactuation for positive pulses longer than ∼10 ms probably due to the charging phenomena occurring in the dielectric layer underneath the moveable membrane. These charging effects are found to vanish under the application of a waveform including consecutive positive and negative voltage pulses, provided that proper durations of the positive and negative voltage pulses are used. Specifically, a correct switch deactuation and a lifetime longer than 1 million cycles, being this value limited by the duration of the used testing excitation, are achieved by applying a 1-kHz waveform with 20-μ s-long positive and negative consecutive pulses. © 2012 IEEE.


Meneghesso G.,University of Padua | Meneghesso G.,Italian Universities Nano Electronics Team | Zanandrea A.,University of Padua | Stocco A.,University of Padua | And 10 more authors.
IEEE International Reliability Physics Symposium Proceedings | Year: 2013

We report on an extensive study of single- (SH) and double-heterostructure (DH) HEMTs based on gallium nitride, for power switching applications. The analysis is based on dc, pulsed and breakdown measurements, which were carried out on five different epitaxial structures. © 2013 IEEE.


Zanandrea A.,University of Padua | Bahat-Treidel E.,Ferdinand - Braun - Institute | Rampazzo F.,University of Padua | Stocco A.,University of Padua | And 8 more authors.
Microelectronics Reliability | Year: 2012

This paper reports on a detailed characterization of single- (SH) and double-heterostructure (DH) GaN-based HEMTs developed for the employment on power switching applications. DC, pulsed and breakdown characterizations have been performed in five different epitaxial structures. SH devices present higher I D current, however, DH devices present much lower leakage current and higher breakdown voltage, thanks to the better confinement provided by the back barrier layer. Kink effect have also been observed in these devices and the effect is enhanced in double heterostructure devices. Off-state step-stress, carried out on a sub-set of the available devices, revealed good reliability performances of DH devices. The limited reliability of the SH devices could be related to the punch-through leakage current. Correlation between current degradation and electroluminescence hot-spot in electroluminescence (EL) measurements has also been found. © 2012 Elsevier Ltd. All rights reserved.


Persano A.,CNR Institute of Neuroscience | Tazzoli A.,University of Padua | Tazzoli A.,Carnegie Mellon University | Farinelli P.,University of Perugia | And 4 more authors.
Microelectronics Reliability | Year: 2012

Shunt capacitive RF MEMS switches were developed on GaAs substrate, using a III-V technology process that is fully compatible with standard MMIC fabrication. The switches show an insertion loss lower than 0.8 dB and isolation better than 30 dB with resonance frequencies in K-band, according to the switch geometric parameters. Reliability limits due to dielectric charging were overcome by applying suitable fast bipolar actuation waveforms, making the developed switches good candidates for both redundancy (always on/off) and cycled applications. © 2012 Elsevier Ltd. All rights reserved.


Meneghesso G.,University of Padua | Meneghesso G.,Italian Universities Nano Electronics Team | Meneghini M.,University of Padua | Stocco A.,University of Padua | And 7 more authors.
Microelectronic Engineering | Year: 2013

This paper describes a deep investigation of the degradation mechanisms induced by off-state and on-state stress in AlGaN/GaN HEMTs. Concerning reverse-bias degradation, results underline that the exposure to reverse-bias stress can induce (i) a recoverable change in the gate current due to the accumulation of negative charges under the gate, (ii) and a permanent degradation of gate characteristics due to the generation of vertical parasitic leakage paths through the AlGaN layer. Further analysis of the kinetics of this degradation mechanism, correlated with time-resolved Electroluminescence (EL) measurements, allowed to define a model that explains the time-dependence of the phenomenon and the role of gate voltage as accelerating factor, providing an interpretation for both recoverable and permanent modifications of the main device characteristics induced by reverse-bias stress. On the other hand, on devices that have shown an improved robustness against the reverse-bias gate degradation, we investigated the origin of the degradation under on-state stress. In this case, results obtained with a combined electrical and optical analysis, showed that on-state stress may induce a significant decrease in drain saturation current and Electroluminescence (EL) signal, with a degradation rate that strongly depends on the EL intensity measured before stress, which is representative of the presence of hot-electrons in the channel. On-state degradation can be ascribed to a decrease in the electric-field, due to the trapping of electrons within the barrier or at the surface induced by hot-electrons. Therefore, by using the EL signal as measure of the stress accelerating factor, it was possible to derive an acceleration law for hot-electron degradation on GaN HEMTs. © 2013 Elsevier Ltd. All rights reserved.


Meneghesso G.,University of Padua | Meneghesso G.,Italian Universities Nano Electronics Team | Meneghini M.,University of Padua | Bisi D.,University of Padua | And 5 more authors.
Semiconductor Science and Technology | Year: 2013

Slow trapping phenomenon in AlGaN/GaN HEMTs has been extensively analyzed and described in this paper. Thanks to a detailed investigation, based on a combined pulsed and transient investigation of the current/voltage characteristics (carried out over on an 8-decade time scale), we report a detailed description of the properties of trap levels located in the gate-drain surface, and in the region under the gate of AlGaN/GaN HEMTs. More specifically, the following, relevant results have been identified: (i) the presence of surface trap states may determine a significant current collapse, and reduction of the peak transconductance. During a current transient measurement, the emission of electrons trapped at surface states proceeds through hopping, as demonstrated by means of temperature-dependent measurements. The activation energy of the de-trapping process is equal to 99 meV. (ii) The presence of a high density of defects under the gate may induce a significant shift in the threshold voltage, when devices are submitted to pulsed transconductance measurements. The traps responsible for this process have an activation energy of 0.63 eV, and are detected only on samples with high gate leakage, since gate current allows for a more effective charging/de-charging of the defects. © 2013 IOP Publishing Ltd.


Barbato M.,University of Padua | Meneghini M.,University of Padua | Cester A.,Italian Universities Nano Electronics Team | Cester A.,University of Cagliari | And 4 more authors.
IEEE Transactions on Device and Materials Reliability | Year: 2014

This paper presents an extensive study of how a solar cell with low shunt resistance can affect the performance and reliability of a solar panel. The analysis is based on both simulations and experimental tests and provides the following results: 1) the cell with low shunt resistance significantly reduces the efficiency of a panel; 2) this is particularly pronounced if the shunted cell is partially shaded: in this case, the shunt resistance of the cell acts as a load for the entire panel; 3) in these conditions, the shunted cell can significantly degrade: in fact, the small-size shunt paths are crossed by a high current density, generated by the other cells in the panel, thus reaching high temperature levels. Stress tests have been also carried out to fully characterize the degradation process and its dynamics and to understand the physical origin of the failure of shunted cells. © 2014 IEEE.


Barbato M.,University of Padua | Giliberto V.,University of Padua | Cester A.,University of Padua | Meneghesso G.,University of Padua | Meneghesso G.,Italian Universities Nano Electronics Team
IEEE Transactions on Device and Materials Reliability | Year: 2014

This paper shows the potentialities of two characterization procedures on the electrical and mechanical characterizations of ohmic RF microelectromechanical systems (MEMS) switches. The first is a 'fast electrical' procedure that uses an electrical stimulus and monitors the RF signals at the input and output ports of the switch; the second is a 'fast hybrid' procedure, i.e., electrical and mechanical, with an electrical input adopted to actuate the device and a mechanical measurement conducted with an optical profilometer, which monitors the displacement and the velocity of the moving membrane when the input electrical signal is applied. Both systems are validated on cantilever and clamped-clamped resistive RF-MEMS switches. We developed these measurement procedures to speed up the measurement process and, consequently, to limit charge trapping during the characterization process. In future analyses, the procedure will be systematically applied to investigate reliability issues when the switch is subjected to multiple impacts and long-term actuation. The use of such procedures will permit separating electrical and mechanical failure mechanisms. © 2013 IEEE.


Persano A.,CNR Institute of Neuroscience | Tazzoli A.,University of Padua | Tazzoli A.,Carnegie Mellon University | Quaranta F.,CNR Institute of Neuroscience | And 4 more authors.
2013 Symposium on Design, Test, Integration and Packaging of MEMS/MOEMS, DTIP 2013 | Year: 2013

In this work, the bridge imaging and the reliability of surface-micromachined capacitive RF MEMS switches in III-V technology are presented. A low cost scanning technique allowed us to image the shape of the moveable bridge with a micrometer spatial resolution, thus quantitatively valuating its lowering as a function of the applied voltage. The reliability of the switches was tested under the application of different unipolar and bipolar voltage waveforms, showing that a significant improvement of the switch operation and lifetime can be achieved by applying high frequency bipolar square pulses with suitable durations. © 2013 CMP.

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