Space charge behaviour in epoxy laminates under high constant electric field

The development of space charge in insulating materials is one of the main causes of their electrical ageing. The pulsed electro-acoustic method is often used to determine space charge distribution, but the signal analysis in the case of laminate structures is much more complex to analyse. In this paper the authors describe and use a simulated signal in order to study laminates made of epoxy resin and fibre mat. The relatively large conductivity of the fibres compared with that of the resin seems to produce a rapid charge dissociation and recombination in the fibres. Under voltage the presence of fibres close to an electrode seems to promote charge injection

Open crack depth sizing by multi-speed continuous laser stimulated lock-in thermography

International audienceA crack located in the thermal diffusion zone of a heat source behaves like a thermal barrier modifying the heat diffusion. For a moving continuous source, the sample surface is heated on a little area near the crack for a duration which depends on the speed of the thermal source. A lock-in process synchronized by the displacement of the continuous heat source along the crack is studied. The thermal signature of the crack is extracted via a space operator applied to the amplitude and the phase of surface temperature images for various speeds of the thermal source. With the technical solution presented in this article, the thermal signature images are analysed according to a length representative of the thermal diffusion length to give a local evaluation of the crack depth (around 3 mm at the maximum) for crack lengths of about few centimetres long. The multi-speed lock-in thermography approach is initially studied with finite element method simulations. Experimental tests using an infra-red camera validate the method in a second part. The results do not depend on the heating source if its power is sufficient to produce a temperature rise detectable by an infra-red camera. The depth estimations are obtained independently of the crack width and heat source trajectory. The multi-speed lock-in thermography is a method without contact, without sample preparation, non-polluting, non-destructive and with simple optical adjustments

An Insight into Space Charge Measurements

International audienceThis paper aims at giving an insight into the field of non-destructive methods for localizing and quantifying electric charges and field distribution in dielectrics. The fundamentals of the influence (or "stimuli") methods used for measuring space charge and polarization distributions in solid insulating structures are first presented. The possibilities offered today by these methods and their fallouts in the domains of dielectric materials, electrical engineering and electronics structures are then put into evidence using various supporting examples. Experimental set-ups and results obtained in recent years are reviewed, and perspectives of evolution of these methods are discussed. Challenges and expected achievements in the near future are brought into focus

Nano and microscale thermal transport experimental measurements

Modern Silicon microelectronic components are nowadays in the nanometer scale regime. The thermal transport can be modified by the close proximity of interfaces and the extremely small volume of heat dissipation. The thermal management being more and more difficult to achieve, strong efforts have been done both on theoretical and experimental points of view. In this paper we will discuss the advances in measurement methods such as: Raman and photoluminescence spectroscopies, modulated thermoreflectance set-ups and scanning thermal microscopy which enable new capabilities for nanometer and micrometer scale thermal metrology. The optical methods will be presented and discussed in details, specially their lateral resolution, and their sensitivity for thermal mapping and thermal properties determination. The paper will be illustrated with examples taken in the microelectronics and material science fields

Hot spot detection in integrated circuits working at up to 1 GHz

Constraints on integration densities and on operating frequencies of integrated circuits have become so important that thermal phenomena can not be neglected any longer. A high resolution thermal mapping of such circuits under operation is then needed. As we show in this paper, the thermoreflectance technique, based on the reflection coefficient variation with temperature give access to the elevation of temperature produced by the circuit after the execution of benchmarks. In this paper, the frequency of the benchmark can be as high as 1 GHz and we show that using a low repetition rate of these benchmarks makes it possible to retrieve the thermal response of the circuit working at high frequency. These measurements can be very useful to adjust thermal dissipation models and to analyse failures

High resolution thermoreflectance imaging on transistor arrays with defect-induced leakage

Crystal defects are very harmful in present silicon devices when responsible for a source-to-drain junction piping and hence for a transistor leakage current. These effects are difficult to characterise with existing methods. Two transistor arrays including patterns critical for defect formation have been constructed and then characterised using a multiplexed CCD-based thermoreflectance microscope. Since this technique measures heating associated to defects, it does not discriminate dielectric breakdown and actual source-to-drain leakage. Both types of defects, buried under 6 $\mu$m of intermetal and encapsulation dielectric, are clearly detected with a spatial resolution of 350 nm

Rb2Ti2O5 : Superionic conductor with colossal dielectric constant

International audienc