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For Polyimides (PI) used as insulating inter-layers or passivation layers in microelectronics and power electronics, reliability and failure mechanisms are intimately linked to phenomena such as non-linear conduction, distortion of field distribution and electrical ageing that have all some relation to space charge processes. Knowledge about these space charge distributions is therefore of importance to optimize structures and designs involving PIs. However, in the thickness scale of interest for such applications, of the order of 10 ?m, no results were reported for PI, and only scarce studies for other materials. Space charge measurements carried out on PI using the laser intensity modulation method (LIMM) are reported in this work. PI-containing metal-insulator-semiconductor structures were pre-stressed under DC fields up to 2 MV/cm. The impact of the doping type of the substrate (either n-type or, p-type silicon) has been evaluated to address the mechanisms of space charge formation. The nature of electrode substrate substantially impacts the measured charge amount and charge nature, pointing towards charge injection as the origin of space charge build-up. The interpretation is substantiated by results obtained using a SiO2 layer as a barrier against electronic injection from the substrate into the PI layer. [ABSTRACT FROM PUBLISHER]

The electrical conduction and dielectric breakdown of polyimide/boron nitride (PI/BN) are investigated in a large temperature range up to 350 °C. This work shows that BN nanofillers act as deep traps for mobile ions. Below 150 °C, the nanostructuration of PI slightly improves the DC conductivity and the breakdown field. On the contrary above 150 °C, while neat PI exhibits ionic space charge contribution on the charging currents, PI/BN nanocomposites show a return to normal polarization currents. In such combined high field and high temperature ranges, the nanostructuration of PI allows increasing the mean free path of ions by decreasing the ionic hopping distance. The consequence of the improvement of the total trap density is a huge decrease (5 orders of magnitude) in the steady state currents and an increase (factor 2) in the breakdown field of PI/BN. This study proves the possibility to extend both the electric field and temperature ranges of PI films thanks to an adequate nanostructuration. [ABSTRACT FROM PUBLISHER]

The dielectric properties of a novel high-glass transition polyamide-imide (hTg-PAI, Tg=333 °C) are investigated for its high temperature use as an insulating material in the range above 250 °C in order to extend the limit of conventional PAI (c-PAI, Tg=277 °C). Four dielectric processes are identified between 50 °C and 400 °C. Among them, the electrical conduction (?-conduction) is clearly reduced particularly in the range from 250 °C to 320 °C, i.e. Tg(c-PAI)?T? Tg(hTg-PAI). The main reason explaining such an enhancement is the shift of ionic conduction contribution towards higher temperatures in hTg-PAI compared to c-PAI. In hTg-PAI, the higher-Tg value allows better controlling the free volume expansion responsible of large ions motions in the bulk. In the range of potential applications (i.e. 250 to 320 °C), the σ-conduction of hTg- PAI has an activation energy of 2.3 eV (~221.9 kJ mol-1). [ABSTRACT FROM AUTHOR]

The electrical conduction of Parylene HT films, a high performance fluorinated parylene, is investigated at high temperature (200 to 350 °C), high electric field (5 and 360 MV/m) and for different thicknesses (1.2 to 5 μm). The steady-state currents are analyzed by assuming different conduction models. Whereas the Schottky and Poole- Frenkel models are the less probable, the thermally assisted hopping mechanism appears as the most probable conduction mechanism for fields up to the threshold (~150 MV/m). Based on the analysis of the hopping jump distance and its evolution versus temperature, an ionic hopping conduction has been proposed as the most probable charge carriers' origin to describe our results. Finally, the film thickness and the field polarity are studied. Results indicate that positive carriers (holes) are the main contributors to the injection current for high electrical fields. [ABSTRACT FROM PUBLISHER]

In this paper, a new technique to reduce the noise in a reconstructed hologram image is proposed. Unlike all the techniques in the literature, the proposed approach not only takes into account spatial information but also temporal statistics associated with the pixels. This innovative solution enables, at first, the automatic detection of the areas of the image containing the objects (foreground). This way, all the pixels not belonging to any objects are directly cleaned up and the contrast between objects and background is consistently increased. The remaining pixels are then processed with a spatio-temporal filtering which cancels out the effects of speckle noise, while preserving the structural details of the objects. The proposed approach has been compared with other common speckle denoising techniques and it is found to give better both visual and quantitative results. [ABSTRACT FROM PUBLISHER]

Changes in the dielectric breakdown field of polyimide (PI) films have been studied from 25 to 400 °C under dc ramps. Both the area (from 0.0707 to 19.635 mm²) and thickness (from 1.4 to 6.7 μm) dependences of the dielectric breakdown field have been carried out using the Weibull distribution function. The 63%-breakdown field value (i.e. the a-scale parameter) of PI shows a decrease with increasing area, thickness and temperature but always remains above 2 MV/cm. The β-scale parameter of the distribution shows a typical decrease with increasing area, however, it exhibits an increase with increasing thickness. This 'curious' behavior is discussed on the basis of the percolation theory. No temperature-dependence is clearly observed. Moreover, physical interpretations are carried out using the pre-breakdown current analysis. [ABSTRACT FROM AUTHOR]