Gate stability of GaN-Based HEMTs with P-Type Gate

status: publishe

Neuroinflammation, Mast Cells, and Glia: Dangerous Liaisons

The perspective of neuroinflammation as an epiphenomenon following neuron damage is being replaced by the awareness of glia and their importance in neural functions and disorders. Systemic inflammation generates signals that communicate with the brain and leads to changes in metabolism and behavior, with microglia assuming a pro-inflammatory phenotype. Identification of potential peripheral-to-central cellular links is thus a critical step in designing effective therapeutics. Mast cells may fulfill such a role. These resident immune cells are found close to and within peripheral nerves and in brain parenchyma/meninges, where they exercise a key role in orchestrating the inflammatory process from initiation through chronic activation. Mast cells and glia engage in crosstalk that contributes to accelerate disease progression; such interactions become exaggerated with aging and increased cell sensitivity to stress. Emerging evidence for oligodendrocytes, independent of myelin and support of axonal integrity, points to their having strong immune functions, innate immune receptor expression, and production/response to chemokines and cytokines that modulate immune responses in the central nervous system while engaging in crosstalk with microglia and astrocytes. In this review, we summarize the findings related to our understanding of the biology and cellular signaling mechanisms of neuroinflammation, with emphasis on mast cell-glia interactions

Correlation between hot-electron-stress-induced degradation and cathodoluminescence in InP based HEMTs

Low temperature spectrally resolved cathodoluminescence has been used to study the effects of electrical degradation induced by hot-electron-stress on the optical transitions in lattice matched InAlAs/InGaAs/InP HEMTs. A clear reduction of the cathodoluminescence emission collected from the gate\u2013drain region of stressed devices has been found, indicating a modification of the trap density inside the device. Depth resolved analyses from the gate\u2013drain region before and after stress evidenced that the electric field due to the traps induced by the hot-electron-stress mainly influenced a device region between the highly doped InAlAs and InGaAs cap layers and the n+ doped donor and undoped spacer? InAlAs layers. The effect of the hot electron stress has been evidenced mainly on the cathodoluminescence transitions from the InAlAs layers. No evidence of a possible influence on the intrinsic InGaAs channel has been found

Drain current DLTS analysis of recoverable and permanent degradation effects in AlGaAs/GaAs and AlGaAs/InGaAs HEMT's

We present a detailed study of drain current DLTS spectra performed on asreceived and failed A1GaAs/GaAs and A1GaAs/InGaAs HEMT's of four different suppliers submitted to hot-electron tests. We demonstrate that a remarkable correlation exists between DLTS features and permanent and recoverable degradation effects. In particular, different behaviours have been found: (i) recoverable effects seems to be correlated with modulation of charge trapped on DX and ME6 centers. (ii) permanent degradation consisting in a decrease in Id and V T is due to negative charge trapping and is associated with a large increase of a peak having Ea=l.22 eV in the DLTS spectra of failed devices; (iii) development of traps in the gate-to-drain access region induces a permanent increase in drain parasitic resistance Rd and decrease in Id, and is correlated with the growth of a "hole-like" peak in DLTS spectra measured after hot-electron tests

A Discussion of the Susceptibility of a Brokaw Bandgap to EMI

In this paper, the susceptibility of a Brokaw bandgap voltage reference towards Electromagnetic Interferences (EMI) superimposed to the power supply is investigated. The attention is focused on the bandgap cell itself, verifying that it is the main responsible for the device malfunction when radio frequency noises are injected in the chip through the supply rail. In particular, the rectification phenomena of bipolar transistors, used in the bandgap cell, are proved to cause the voltage reference performance degradation. Some possible hints to overcome this problem are also explored, suggesting design modifications, filtering solutions and layout changes

On the Key Role of the Brokaw Cell on Bandgap Immunity to EMI

In this paper the immunity of a Brokaw bandgap towards electromagnetic interferences superimposed to the supply voltage is investigated. The attention has been focused on the bandgap cell itself, verifying that it is the main responsible of device performance degradation in the presence of radio frequency noises. The bandgap model is firstly validated comparing experimental measurements with computer simulations, using both S-pararneters and susceptibility analyses. The most important stray components responsible for a correct susceptibility prediction are highlighted. Finally some suggestions to possibly reduce the bandgap susceptibility are presented at both design and layout/technology level

Study of Neutron Damage in GaAs MESFETs

Implanted channel GaAs MESFETs subjected to neutron irradiation show large inodifications of the pinch-off voltage, open-channel saturation current, and transconductance in agreement with previous results. In this work we demonstrate how an experimental technique, based on the frequency dispersion of the transconductance, gm(f), and output conductance, gD(f), can identify the deep levels induced by neutron irradiation through measurements performed directly on packaged devices. After irradiation, a frequency dispersion of the transconductance has been observed, while it was flat in the unirradiated device. The gm(f) curve shape depends on tlie device bias conditions, and it has permitted for tlie first time to evaluate the activation energy of different deep levels induced by neutron irradiation in MIESFETs

HBM and CDM ESD stress test results in 0.6 \u3bcm CMOS structures

In this work, we present new results concerning electrostatic discharge (ESD) robustness in 0.6 \u3bcm device structure. Devices have been submitted to both HBM and socketed CDM (sCDM) ESD tests. A systematic failure analysis of the stressed structures has been carried out obtaining important information on the dependence of the behaviour of these on layout parameters. Typical LDD MOSFET devices show damages which mainly consist in drain/substrate junction spiking in correspondence of the contacts: breakdown of the less deeper P implant junction (n+-substrate) can be responsible for the observed degradation. Devices having P deeper implant source and drain are more resistant than the previous ones and their failure mechanisms consist in lateral spiking. For some large structures adopting lateral bipolar transistor with or without gate polysilicon over Field oxide technology, SEM analysis and emission microscopy clearly demonstrate that early ESD failures can be attributed to a non uniform current distribution within the structure

Optimization of ESD protection structures suitable for BCD6 smart power technology

In this work we present results concerning the optimization of BCD6 ESD protection structures based on the lateral DMOS transistor to be used in ESD protection structures adopting the \u201cBig-Clamp\u201d approach. The influence of common lines parasitic resistance on ESD robustness has been characterized, both by means of TLP measurements and HBM testing. Threshold voltage shift in NMOS input buffer transistor, following HBM test, has been detected, suggesting a new failure criteria that should be taken into account for these protection structures. Simple gate-coupled LDMOS devices with different N-well doping has also been investigated with the aim to identify the effect of the well doping on the ESD robustness