Schizophrenia, psychosis, and the basal ganglia

Schizophrenia is one of the most common and perhaps the most disabling of mental disorders, for which effective forms of treatment have not yet been established definitively. The findings reviewed in this article strongly suggest that basal ganglia abnormalities are involved in the pathophysiology of psychotic syndromes in general, and schizophrenia in particular.     

Reverse bias instabilities in bipolar power transistors withcellular layout

The different instabilities exhibited by power BJTs during inductive turn-off are classified, and then studied theoretically, by means of two-dimensional (2-D) simulator in which the device is simulated within a realistic external circuit, and experimentally, by means of a nondestructive method. It is shown that many instabilities originate by an interaction between electric field and charge within a single cell, which causes transit time oscillation phenomena. The role of the stray capacitance of the circuit in favoring these instabilities is described. Other kinds of instability cannot be understood by studying a single cell but rather require accounting for the interactions between cells. Finally, an “instability map” is used as a synthetic picture of the device behavior which ensures an easy way to link device behavior with its physical features     

Physical modeling of bipolar mode JFET for CAE/CAD simulation

A circuit model of a power bipolar JFET, based on a specific formulation of its charge control model,is presented. The circuit obtained accurately describes both unipolar and bipolar modes of operation of the device, and is presented in a form suitable to be incorporated in circuit CAD (computer-aided design) simulators. The model was developed on a physical basis, and its parameters can in principle be directly computed from geometrical and physical characteristics of the device. The author also presents the implementation of the model into the version 4.02 of PSPICE obtained by modifying a device subroutine     

Investigation of MOSFET failure in soft-switching conditions

Thanks to an ad-hoc experimental test equipment, the reliability of MOSFET devices in soft-switching operations has been investigated aimed to discovering the role of the freewheeling phase in the device reliability reduction. Extensive tests at several temperatures, on-state currents, reverse current peaks, dc-voltages and gate timings have been done, showing that specific devices for soft-switching are needed to improve the overall converter reliability. Standard commercial MOSFETs are more prone to failures descending from huge power dissipation at the gate turn-off, related to preceding body diode usage.     

Experimental evidence of “latent gate oxide damages” in medium voltage power MOSFET as a result of heavy ions exposure

The results presented in this paper are related to an experimental study that has the aim to evidence the formation of “latent gate oxide damages” in medium voltage power MOSFETs during the impact with energetic particles. The understanding of these “latent defectiveness” can be an helpful aid in the comprehension of the mechanisms of breach of the oxide layer of MOS structures induced by single energetic particles impact (single event gate rupture). To properly detect the presence of “latent damages” we have developed a high resolution experimental set-up and identified an appropriate region in which the device have to be biased in order to trigger this kind of damage.     

Effects of metallization lay-out on turn-off failure of modern power bipolar transistors

A new simulation tool is presented which is able to describe the behaviour of the modern cellular power BJTs. It is based on SPICE circuit simulation of a rather complex circuit where each cell is described by a single transistor and all of the cells are interconnected by a resistive network. The tool is able to predict current and electric field distribution over the chip during device turn-off. The effects of metallization lay-out on failure of cellular BJTs are studied. It is demonstrated both experimentally and numerically, for the first time, that current crowding over the chip of these devices is related to different storage times of each cell and not to the emitter depolarization as it is usually assumed for devices of traditional design.