418 research outputs found
Investigation of degradation mechanisms in low-voltage p-channel power MOSFETs under High Temperature Gate Bias stress
No full textIn this work we investigate the degradation mechanisms occurring in a p-channel trench-gate power MOSFET under High Temperature Gate Bias (HTGB) stress. The impact of negative bias temperature stress is analysed by evaluating relevant figures of merit for the considered device: threshold voltage, transconductance and on-resistance. Temperatures and gate voltages as large as 175 °C and −24 V, respectively, are adopted to accelerate the degradation in the device. Moreover, in order to investigate the origin of degradation mechanisms we analyse the interface states generation and the charge trapping processes, the impact of a switching gate voltage during the stress phase and the recovery phase after HTGB stress
A Methodology to Estimate On-Voltage Degradation of Power Devices According to a Power Cycling Mission Profile
No full textAnalysis of thermal cycling effects in power devices under non-constant cumulative stress
No full textThis work experimentally investigates the reliability of TO-247 packaged power devices, with the goal of analyzing the impact of non-constant cumulative power cycling tests. Power devices are first stressed with a constant junction temperature cycling. Cumulative distribution function is experimentally evalu-ated and fitted with a Weibull statistics. According to the Miner's rule, the lifetime of components is calculated under a given non-constant cumulative stress at different levels of probabilities of failure. Experimental power cycling tests are then carried out to verify the accuracy of the predicted lifetime values
Influence of Power Cycling Test Methodology on the Applicability of the Linear Damage Accumulation Rule for the Lifetime Estimation in Power Devices
No full textThe lifetime of power semiconductor devices, operating under a given mission profile and subjected to power cycling stress, is conventionally estimated under the assumption of linear damage accumulation rule, that is the application of the Miner's rule. To this purpose, lifetime models must be properly defined allowing to take into account for the relevant parameters of power cycling stress. This work shows how to estimate a cumulative distribution function in the case of an arbitrary temperature swing profile, starting from the statistical distribution at constant power cycling conditions. It is found that the accuracy of the linear damage accumulation rule is related to the experimental methodology adopted for power cycling tests. A detailed experimental activity is carried out on packaged IGBT devices, providing useful guidelines for the definition of lifetime models to be adopted in the Miner's rule
Floodlighting the Deluge: Traditions in Comparison
No full textThe deluge myth, while enjoying a wide diffusion all over the Eurasian continent, has found its most important literary developments in the Near-eastern, Classical and Indian worlds. Apropos of these traditions, the question has often been raised of their mutual relationship. As regards the Indian tradition in particular, several renowned scholars of the past have postulated its dependance on the sumero-semitic tradition, but nowadays the prevailing opinion speaks in favour of its autonomous development. Nevertheless, the structure of the Indian myth, whose careful recognition should indeed constitute the requisite basis for any further insight into the problem of its relationships, has not been adequately investigated. In my paper I purpose first of all a survey of the extant material by presenting, besides the well-known versions of the Śatapatha Brāhmaṇa, Mahābhārata, Matsya and Bhāgavata Purāṇa, to which the analysis has usually been confined so far, some other less known versions, like those of the Viṣṇudharmottara and Kālikā Purāṇa, which add highly significant traits to the picture. Secondly, on the basis of that material, I intend to show as the Indian myth as a whole exhibits its own peculiar structure, quite different from the structure of the myths of the other great traditions, except for a couple of very generic features, which are, I should think, almost unavoidable in any deluge myth by reason of its very internal structure, and are as such quite worthless in either establishing or denying any historical relationship whatsoever. It had already been remarked, in this connection, that the Indian myth lacks all kind of ethical motivation, as the deluge itself is part of the ongoing cosmogonic process, hence naturally grounded; or that the closing sacrifice has an utterly different meaning in the Indian and semitic myth. However, scholars had hitherto failed to notice, as I believe, the specifically Indian import of the symbolism of the ship — tipically preexistent, and not fashioned by the protégé —, the peculiarity of the symbolic plexus of the ship and fish, later enriched by the rope as third element, and its solidarity with other mythical representations, with which a deep-rooted homology unexpectedly comes to light in spite of the seeming eterogeneity. In conclusion, the Indian deluge myth shows unmistakable original traits in its indissoluble connection with such typically Indian themes as (to mention but a few) the multilevel cyclical cosmic structure, the notion of residue, the avatāra, the divine monoceros, the earth foundering under the burden of the living
Sivadharmottara Purana: a Survey
No full textIn the frame of my current work towards a critical edition of the hitherto unpublished Śivadharmottarapurāṇa, this paper purposes to present a brief analysis of the contents of the upapurāṇa in 12 chapters, (i. e., according to the colophons of some MS: goṣaḍaṅgavidhi, vidyādānaphala, pañcamahāyajñaguṇādhyāya, satpātraguṇa, śivasaṃgati, pāpabheda, narakaviśeṣa, saṁsāraprasavākhyāna, svarganarakacihna, jñānayoga, prāyaścittakathana and [lokanirūpaṇa]), highlighting in particular some noteworthy aspects of the doctrines of śivajñāna, bhukti and mukti, as well as a rather unusual version of ṣaḍaṅga yoga
La risposta di un gimnosofista al quesito di Alessandro sull’origine del tempo: dottrina indiana?
No full text[Does the gymnosophist’s reply to Alexander’s question on the origin of time indeed reflect an Indian doctrine?] The episode of Alexander’s interview with the gymnosophists has come down to us in several versions, among which the one in Plutarch’s Vita Alexandri is the most renowned. In this connection, the question arises whether the solutions given by the naked philosophers to the puzzles propounded by Alexander can be shown to reflect genuine Indian doctrines. Challenging Dumézil’s reply in the affirmative, the author contends that they cannot. While most questions and answers are scarcely relevant to the investigation, as being of little (if any) philosophical import, the analysis concentrates on the more significant ones, and especially on the solution offered to the question as to which of the two — day or night — came first. According to Dumézil, the gymnosophist’s answer reported by Plutarch, i. e. that the day came first, by one day, reflects the vedic doctrine of the primeval cosmogonic role of Dawn and Light. Against this may be argued in the first place that such doctrine does not enjoy any prominent status in the Vedas themselves — quite to the contrary, it stands up disadvantegeously to many all-important texts, such as the Nāsadīyasūkta, which assign the primeval status to Darkness — and cannot therefore be regarded as being specifically Indian any more than its opposite. Secondly, it is shown that the Greek tradition is at great variance on this very point, to the extent that all logically conceivable solutions (i. e., precedence of day by one day / day by one night / night by one day / night by one night) are represented in some version or other. This inconsistency appears to stem from the fact that no particular doctrine (Indian or whatever) was envisaged; according to the present author, we have reason to believe that the gymnosophist’s reply was rather meant to set off by means of a paradox the sheer impossibility of a solution (all four alternatives being equivalent to that effect). This interpretation is reinforced by the gymnosophist’s own remark confessing the aporetical nature of his reply, and finally by a further recourse to paradox — this time a variant of the well-known “paradox of the liar” — which the author lays bare in the otherwise inexplicable dénouement of the anecdote
Limiting power cycling stress in power MOSFETs by active thermal control
No full textIn this work we propose a system which is able to actively control the temperature of a power MOSFET, in order to limit the temperature swing and hence to reduce the power/thermal cycling effect. To this purpose a dedicated driving circuit, allowing to control the gate voltage of the switching device under investigation, is used in a synchronous buck converter. Therefore, power losses can be modulated in order to reach the desired temperature through self-heating effects. The implemented control system is able to compensate the non-linear relationship between the gate voltage and the on-resistance. Moreover, to improve the response of the system, a predictor has been implemented, having the capability of on-line tuning the thermal resistance of the device. Experimental results are reported to demonstrate the suitability of this solution to control the temperature in the semiconductor device. The reduction of temperature swing under power and thermal cycling is also demonstrated
Impact of Field-Plate Insulating Layer on Junction Breakdown Instability in OFT-Pw.MOSFET Devices
No full textIn this article, we investigate the junction breakdown instability in oxide-filled trench power MOSFETs, as a function of field-plate oxide characteristics. We compare the junction breakdown instability in devices adopting field-plate insulating layers thermally grown and low-pressure chemical vapor deposition process (LPCVD) deposited. We experimentally observe a different junction breakdown walk-out, depending on the field-plate insulating material. We found out that, by applying an electrical stress, besides the junction breakdown instability, a damage of the channel region is observed in the case of thermally grown field-plate oxide layer
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