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Jesús A. Del Alamo - One of the best experts on this subject based on the ideXlab platform.

  • evolution of structural defects associated with electrical degradation in algan gan high electron mobility transistors
    Applied Physics Letters, 2010
    Co-Authors: Prashanth Makaram, Jesús A. Del Alamo, Tomas Palacios, C V Thompson
    Abstract:

    We have investigated the surface morphology of electrically stressed AlGaN/GaN high electron mobility transistors using atomic force microscopy and scanning electron microscopy after removing the gate metallization by chemical etching. Changes in surface morphology were correlated with degradation in electrical characteristics. Linear grooves formed along the gate edges in the GaN cap layer for all electrically stressed devices. Beyond a Critical Voltage that corresponds to a sharp increase in the gate leakage current, pits formed on the surface at the gate edges. The density and size of the pits increase with stress Voltage and time and correlate with degradation in the drain current and current collapse. We believe that high mechanical stress in the AlGaN layer due to high-Voltage stressing is relieved by the formation of these defects which act as paths for gate leakage current and result in electron trapping and degradation in the transport properties of the channel underneath.

  • a model for the Critical Voltage for electrical degradation of gan high electron mobility transistors
    Microelectronics Reliability, 2010
    Co-Authors: Tomas Palacios, Jesús A. Del Alamo
    Abstract:

    Abstract It has recently been postulated that GaN high electron mobility transistors under high Voltage stress degrade as a result of defect formation induced by excessive mechanical stress that is introduced through the inverse piezoelectric effect. This mechanism is characterized by a Critical Voltage beyond which irreversible degradation takes place. In order to improve the electrical reliability of GaN HEMTs, it is important to understand and model this degradation process. In this paper, we formulate a first-order model for mechanical stress and elastic energy induced by the inverse piezoelectric effect in GaN HEMTs which allows the computation of the Critical Voltage for degradation in these devices.

  • a model for the Critical Voltage for electrical degradation of gan high electron mobility transistors
    2009 Reliability of Compound Semiconductors Digest (ROCS), 2009
    Co-Authors: Tomas Palacios, Jesús A. Del Alamo
    Abstract:

    It has recently been postulated that GaN high electron mobility transistors under high Voltage stress degrade as a result of defect formation induced by excessive mechanical stress that is introduced through the inverse piezoelectric effect. This mechanism is characterized by a Critical Voltage beyond which irreversible degradation takes place. We have built a firstorder model for the Critical Voltage for degradation of GaN HEMTs. In our model, electrical degradation occurs when the elastic energy stored in the AlGaN barrier exceeds a Critical value. When using estimations of this Critical elastic energy that come from epitaxial studies of strain relaxation in Al-GaN/GaN heterostructures, our proposed model yields predictions for the Critical Voltage that match experimental observations.

  • impact of electrical degradation on trapping characteristics of gan high electron mobility transistors
    International Electron Devices Meeting, 2008
    Co-Authors: Jesús A. Del Alamo
    Abstract:

    One of the most deleterious effects of electrical degradation of GaN HEMTs is an increase in carrier trapping and subsequent current collapse. In this work, we have investigated the trapping and detrapping characteristics of GaN HEMTs before and after device degradation through a new current transient analysis methodology. We have found that electrical stress beyond a Critical Voltage significantly enhances trapping behavior inside the AlGaN barrier layer or at the surface. However, trapping in the buffer was found to be intact after device degradation.

  • Critical Voltage for electrical degradation of gan high electron mobility transistors
    IEEE Electron Device Letters, 2008
    Co-Authors: Jesús A. Del Alamo
    Abstract:

    We have found that there is a Critical drain-to-gate Voltage beyond which GaN high-electron mobility transistors start to degrade in electrical-stress experiments. The Critical Voltage depends on the detailed Voltage biasing of the device during electrical stress. It is higher in the OFF state and high-power state than at VDS = 0. In addition, as |VGS| increases, the Critical Voltage decreases. We have also found that the stress current does not affect the Critical Voltage although soft degradation at low Voltages takes place at high stress currents. All of our findings are consistent with a degradation mechanism based on crystallographic-defect formation due to the inverse piezoelectric effect. Hot-electron-based mechanisms seem to be in contradiction with our experimental results.

Anbarasu Manivannan - One of the best experts on this subject based on the ideXlab platform.

  • redefining the speed limit of phase change memory revealed by time resolved steep threshold switching dynamics of aginsbte devices
    Scientific Reports, 2016
    Co-Authors: Krishna Dayal Shukla, Nishant Saxena, Suresh Durai, Anbarasu Manivannan
    Abstract:

    Although phase-change memory (PCM) offers promising features for a ‘universal memory’ owing to high-speed and non-volatility, achieving fast electrical switching remains a key challenge. In this work, a correlation between the rate of applied Voltage and the dynamics of threshold-switching is investigated at picosecond-timescale. A distinct characteristic feature of enabling a rapid threshold-switching at a Critical Voltage known as the threshold Voltage as validated by an instantaneous response of steep current rise from an amorphous off to on state is achieved within 250 picoseconds and this is followed by a slower current rise leading to crystallization. Also, we demonstrate that the extraordinary nature of threshold-switching dynamics in AgInSbTe cells is independent to the rate of applied Voltage unlike other chalcogenide-based phase change materials exhibiting the Voltage dependent transient switching characteristics. Furthermore, numerical solutions of time-dependent conduction process validate the experimental results, which reveal the electronic nature of threshold-switching. These findings of steep threshold-switching of ‘sub-50 ps delay time’, opens up a new way for achieving high-speed non-volatile memory for mainstream computing.

  • sub nanosecond threshold switching dynamics and set process of in3sbte2 phase change memory devices
    Applied Physics Letters, 2016
    Co-Authors: Shivendra Kumar Pandey, Anbarasu Manivannan
    Abstract:

    Phase-change materials show promising features for high-speed, non-volatile, random access memory, however achieving a fast electrical switching is a key challenge. We report here, the dependence of electrical switching dynamics including transient parameters such as delay time, switching time, etc., on the applied Voltage and the set process of In3SbTe2 phase-change memory devices at the picosecond (ps) timescale. These devices are found to exhibit threshold-switching at a Critical Voltage called threshold-Voltage, VT of 1.9 ± 0.1 V, having a delay time of 25 ns. Further, the delay time decreases exponentially to a remarkably smaller value, as short as 300 ± 50 ps upon increasing the applied Voltage up to 1.1VT. Furthermore, we demonstrate a rapid phase-change behavior from amorphous (∼10 MΩ) to poly-crystalline (∼10 kΩ) phase using time-resolved measurements revealing an ultrafast set process, which is primarily initiated by the threshold-switching process within 550 ps for an applied Voltage pulse with a pulse-width of 1.5 ns and an amplitude of 2.3 V.

Mauricio Morel - One of the best experts on this subject based on the ideXlab platform.

  • colorimetry characterization of molecular reorientation transition in thin nematic cells
    Chaos, 2020
    Co-Authors: Mauricio Morel, U Bortolozzo, Marcel G Clerc, Aurelie Jullien, S Residori
    Abstract:

    The characterization of equilibria and their transition is fundamental in dynamic systems. Experimentally, the characterization of transitions is complex due to time scales separation, the effect of thermal fluctuations, and inherent experimental imperfections. Liquid crystal devices are derived from the manipulation of the molecular reorientation and transition between them by employing external electrical and magnetic fields. Here, we investigate and determine the Freedericksz transition using hue measurements of the transmitted light in thin nematic liquid crystal cells. Based on birefringent retardation experienced by transmitted light due to molecular reorientation, the color adjustment of the nematic liquid crystal cells under white light illumination is characterized. By monitoring the hue of the transmitted light, the bifurcation diagram is determined. As a function of the Voltage frequency, the Critical transition Voltage is characterized. The Critical Voltage increases with the applied frequency.

Pietro Gambardella - One of the best experts on this subject based on the ideXlab platform.

  • field free switching of magnetic tunnel junctions driven by spin orbit torques at sub ns timescales
    Applied Physics Letters, 2020
    Co-Authors: Viola Krizakova, Kevin Garello, Eva Grimaldi, Gouri Sankar Kar, Pietro Gambardella
    Abstract:

    We report time-resolved measurements of magnetization switching by spin–orbit torques in the absence of an external magnetic field in perpendicularly magnetized magnetic tunnel junctions (MTJs). Field-free switching is enabled by the dipolar field of an in-plane magnetized layer integrated above the MTJ stack, the orientation of which determines the switching polarity. Real-time single-shot measurements provide direct evidence of magnetization reversal and switching distributions. Close to the Critical switching Voltage, we observe stochastic reversal events due to a finite incubation delay preceding the magnetization reversal. Upon increasing the pulse amplitude to twice the Critical Voltage, the reversal becomes quasi-deterministic, leading to reliable bipolar switching at sub-ns timescales in zero external field. We further investigate the switching probability as a function of dc bias of the MTJ and external magnetic field, providing insight into the parameters that determine the Critical switching Voltage.

S Residori - One of the best experts on this subject based on the ideXlab platform.

  • colorimetry characterization of molecular reorientation transition in thin nematic cells
    Chaos, 2020
    Co-Authors: Mauricio Morel, U Bortolozzo, Marcel G Clerc, Aurelie Jullien, S Residori
    Abstract:

    The characterization of equilibria and their transition is fundamental in dynamic systems. Experimentally, the characterization of transitions is complex due to time scales separation, the effect of thermal fluctuations, and inherent experimental imperfections. Liquid crystal devices are derived from the manipulation of the molecular reorientation and transition between them by employing external electrical and magnetic fields. Here, we investigate and determine the Freedericksz transition using hue measurements of the transmitted light in thin nematic liquid crystal cells. Based on birefringent retardation experienced by transmitted light due to molecular reorientation, the color adjustment of the nematic liquid crystal cells under white light illumination is characterized. By monitoring the hue of the transmitted light, the bifurcation diagram is determined. As a function of the Voltage frequency, the Critical transition Voltage is characterized. The Critical Voltage increases with the applied frequency.