Because of its special properties and commercial significance, Poly(phenylene sulfide) (PPS) has been the subject of many research efforts since its commercial introduction in 1967. Intensive work has been done on its crystalline structure and morphology and its thermal behaviour. But fewer investigations have been carried out to understand long term behaviour in high temperature environments. Always anticipating industrial needs linked to power integration, we have launched an extensive study on thermal aging in air of PPS at 250°C. This study has shown that PPS thermal degradation in air happens by intermolecular branching reaction, similar to crosslinking. This phenomenon was already known for temperature above 300°C. This crosslinking is evidenced by rheometry where the relative position of G’ and G’’ above melting temperature changes with aging. IR spectroscopy confirms that para substituted benzene in PPS molecule is transformed in 1,2,4 trisubstituted benzene. DSC measurements evidence both an elevation of melting temperature and a change in melting endotherm showing significant changes in crystalline morphology along aging, which tends to indicate that crosslinking occurs in crystalline phase. Then degradation implies drastic loss of mechanical properties leading to destruction of the sample.

Dielectric properties of CaCu3Ti4O12 (CCTO)-based ceramics and thick films (e similar to 50 mu m) prepared from powders synthesized by a soft chemistry method (co-precipitation) are presented and discussed, The characteristics of pellets and thick films are compared.The pellets exhibit high values of the dielectric permittivity (epsilon(r) similar to 1.4 x 10(5)) and relatively small dielectric losses (tan delta similar to 0.16) at 1 kHz and room temperature. These properties are independent of the nature of the metallization of the electrodes. In addition, the dielectric permittivity decreases when the diameter of the electrodes of the pellets increases, while the losses remain constant. This result, which is strongly related to the nature of the dielectric material in between the electrodes, constitutes a strong indication that the high dielectric permittivity values observed in this material are not related to an interfacial (electrode material) related mechanism but is an internal barrier layer capacitor (IBLC) type.Very high values of the dielectric permittivity of CCTO thick films are measured (epsilon(r) similar to 5 x 10(4)). The differences in dielectric permittivity between thick films and dense pellets may be attributed to the difference in grain size due to different CuO contents, and to the different reactivity of the materials. (C) 2008 Elsevier Ltd. All rights reserved.

Power electronics packaging, like integrated power modules, constitute an advanced technology leading to power density increase, weight and volume decrease and enhancing the reliability level. However, the continuous increase of the voltage lead to questions regarding power device environment. We discuss in the following different solutions able to achieve the electric stress gradation.

One of the most attractive ways to increase power handling capability in power modules is to increase the operating temperature. Aluminium nitride based ceramics are claimed to be the ideal candidates to be used as substrates. However, depending on the elaboration process a decrease of the AlN dielectric strength may be observed. These results are discussed in the following paper.

Power electronics packaging, like integrated power modules, constitute an advanced technology leading to power density increase, weight and volume decrease and enhancing the reliability level. However, the continuous increase of the voltage lead to questions regarding power device environment. We discuss in the following different solutions able to achieve the electric stress gradation.

A new criterion allowing for the choice of the most appropriate substrate for high voltage high temperature power electronics applications is introduced. Different insulating materials (A1N, Alumina and BN) are tested up to 450degC regarding their dielectric strength. These results are presented and discussed.

Partial discharges measurements have been performed on 3.3 kV IGBT power modules. Results using both the normalized and a new proposed test are compared. The new test, allowing the detection of partial discharges in all the insulating materials, is detailed. Elementary defect patterns are used to distinguish the main cause (dies or insulating materials) of the observed partial discharges in IGBT modules.

IGBT hybrid power modules used in high voltage applications (ex. railway traction systems) are built using several dielectric materials. This stack may be a source of partial discharges. Up to now these modules are tested as regards partial discharges using a normalized test (EIC 270), which despite its quality is not representative of the real applied stresses endured during normal operating conditions, as it does not stress all the materials present in the stack. A new method for determining partial discharges activity in such power modules has been developed. Application of this test to IGBT modules leads to a PD ignition threshold lower than the one found using the normalized test. In this paper the different results obtained up to now in this field are summarized and discussed. Additionally, the test is modified in order to apply it to different structures in order to identify the possible cause of PD developments in such power modules.

Wide band gap semiconductors are discussed as materials for photonic or electron-beam controlled switches. Chemical vapour deposited (CVD) diamond has recently become the subject of intense research activity mainly due to its unique combination of thermal, mechanical and optoelectronical properties. The very high thermal conductivity, added to a high working temperature and a high dielectric strength, make CVD diamond as a promising candidate material, for high voltage electronics applications. Its semi conducting properties, such as wide band gap and high electron and hole mobilities are also noteworthy. The nature of CVD diamond is the most prominent obstacle against fabrication of any kind of electronic devices. This paper presents different grades of CVD diamond substrates and the comparison between them, especially between the natural Ha and other kind of CVD diamond. Dielectric strength investigation and surface conductivity with or without chemical treatment are presented, then the influence of the metal to diamond interface on the electronic properties have been investigated. Interdigitated planar contacts and plane back contacts have been photolithographically deposited on each sample, using different layered metals. The I(V) measurement allows to determine the optimal metallization for electronic applications. Finally, the authors investigate the response of metal-diamond-silicon components under UV illumination