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International audience; This work deals with the study of thermoset-thermoplastic blend forming an epoxy-amine/poly-etherimide phase separated to assess the dielectric and thermal performances. These materials would be good candidates to replace the passivation layer in semiconductors, particularly ones used as switches in power electronic applications. Polyimide and Parylene are usually quoted and studied. Mixtures based on polymers would be a novel candidate that can manage to be an insulator for the system. The modified and non-modified systems where characterized by transmission electron microscopy, scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, dielectric analysis and analytical simulation was carried out on dielectric measurements. These complementary techniques were used first to investigate the presence of the phase separation phenomenon and second to quantify the separated nodules size. The effect of this phase separation was examined and showed enhancement in the dielectric values compared to the pure epoxy system. It was finally simulated to show a close assumption of what is found experimentally.

This field trial transmits 1.5Tb/s superchannel with 5b/s/Hz spectral efficiency over 875km of EDFA-amplified SMF, using six 250Gb/s real time elastic transponders featuring 1dB minimum Q margin over 48 hours. Channels are 50GHz spaced.

In power electronics, electrical insulation encapsulation at high temperatures and/or high voltages is a challenge for the systems such as IGBT. Different materials are used and tested in industry and literature. Silicone elastomers for example associated with a primary passivation layer of polyimide are considered to be good candidates but are limited to 180 – 200 °C. Epoxy thermosets are known to be good insulator to protect electrical devices from moisture, dust and short circuits electrical breakdown. Thermoset/thermoplastic blends can be another good candidate for electrical insulation properties. The thermoplastic, its percentages as well as the curing conditions control the final morphology (phase separation with disperse thermoplastic phase, bicontinuous phases or inverted structure …) and thus the electrical properties of the sample. In our study, polyetherimide (PEI) and Polystyrene (PS) thermoplastics were introduced with different percentages into the epoxy system. Electronic microscopy images showed similar phase separation phenomenon with different size of nodules of the thermoplastics. The effect of the morphology on mechanical, electrical and thermal properties has been investigated. The addition of 6 wt% of PS and 10%wt of PEI gives nodules of thermoplastic with a micrometer size inside the epoxy amine network where it did not affect either the storage modulus or the thermal resistance under air or nitrogen atmosphere. Whereas, the dielectric spectroscopy points out that, the addition of polystyrene into the epoxy system increased the relative permittivity of the blend. Contrariwise, the addition of polyetherimide into the epoxy system has decreases the relative permittivity by 15 % in all the temperature and frequency ranges compared with the pure epoxy amine network.

Numerous techniques have been used to improve the breakdown voltage (VBR) capability of high voltage devices with the aim of getting closer to the breakdown voltage of a plane parallel junction. In this work, a peripheral protection for a 3 kV SiC bipolar diode is presented. This protection concept is based on a large and deep trench filled by an insulating material. This trench is called Deep Trench Termination (DT2) already validated in Si technology. Our results show that, on the basis of simulations with TCAD Sentaurus, it is possible to protect effectively with this type of trench. The simulation allows to optimize the characteristics of peripheral protection. To take into account the close environment of the semiconductor, the positive and negative fixed charges at the semiconductor - insulating interface have been considered. The work was focused on a 3 kV SiC bipolar diode, but the proposed solutions could be easily scale to any range of voltage.

Among materials used for electrical insulation in power electronics systems like IGBT, silicone elastomers used are considered as good candidates but are limited to 180–200°C. In this work, new thermoset/thermoplastic composites are investigated. The addition of some thermoplastics to epoxy amine systems can lead to system exhibiting phase separation. The thermal degradation under some conditions reaches 300°C, which is interesting for power electronics applications. The mixture of thermoplastic inside epoxy prepolymer governs the final microstructure. For example, the addition of 10 % wt of PEI gives inclusions of thermoplastic with a micrometer size. Even if the T alpha of epoxy matrix was changed upon the addition of PEI, the dielectric spectroscopy points out that the addition of some thermoplastic decreases the permittivity compared with the pure epoxy amine network.

The existing interpretation and models of electroluminescence (EL) in poly(ethylene-2, 6-naphthalate) (PEN) suggest a mechanism triggered by the impact excitation and/or ionization of the luminescent centres by hot electrons. Excitation by bipolar charge recombination has not been considered extensively because of the lack of knowledge of the behaviour of electrons and holes in insulating films subjected to a dc stress. An investigation of the internal space charge distribution versus field is believed to constitute a relevant approach to discussing the EL excitation process. Transient and steady-state EL of PEN films are analysed with the support of space charge profiles obtained by the laser induced pressure pulse (LIPP) method for dc fields in the range of 25-225 kV mm-1. For field values up to 75 kV mm-1, the internal charge is dominated by dipolar polarization without any excitation of EL. Space charge polarization is evidenced from 75 kV mm-1 upwards, the LIPP response being a superposition of space charge and dipolar polarization effects. Space charge polarization dominates in the field range where EL is continuously emitted (E>150 kV mm-1). The EL excitation mechanism is discussed on the basis of the recorded charge profiles.

It has been proposed recently that the lowest level of dc field, above which electrical degradation may occur, is associated with the formation of space charges in insulation. Therefore, inference of field levels above which space charge accumulates in a given material may provide fundamental information for material characterization and system design. Threshold field values were estimated through evidence of space charge accumulation derived from conduction current, space charge amplitude and electroluminescence (EL) counts vs, electrical field characteristics. Press-molded plates of polyethylene-based materials were used for this investigation. In order to be able to detect even by EL experiments the presence of the space charge accumulated at low fields, measurements were carried out during both polarization and short-circuit of specimens. It is shown that the threshold corresponding to the onset of EL upon grounding the specimen is close to the space charge accumulation threshold derived from space charge and conduction current measurements. This earlier value is considerably lower than the one previously detected from constant dc-voltage EL measurements, thus confirming that even at low fields and in the presence of voltage reversals or transients, space charges can trigger luminescence phenomena. The methodology developed in this paper enlarges the applicability of the EL technique to accommodate a wider electrical field range in view of insulation characterization.

Wavelength-resolved electroluminescence and current measurements have been performed on polyethylene naphthalate thin films submitted to high direct current fields (3.4 MV cm-1) for several days. The change in the shape of the emission spectrum over time resembles that observed in short-term experiments when the field is increased. This behaviour provides the basis for a model in which the time evolution of the spectrum shape is attributed to the progressive charging of the material, through homopolar injection. The net result is an increase of the internal field in the charge-free region where luminescence occurs.

This paper presents an experimental study of Partial Discharges and light emission with ceramic substrates embedded in silicone oil, under ac and square high voltage. Two types of ceramic materials used in power electronics modules are considered: Aluminum Nitrite (AlN) and Alumina (Al2O3). With AlN, a large light emission due to the electroluminescence of the ceramics occurs during the negative dV/dt. This phenomenon is not observed with Al2O3. With Al2O3 and silicon oil, the light emitted is only due to PDs, and recording under square voltage wave shows that PDs are more numerous and/or more intense compared to ac. Square voltage is more relevant to actual working conditions within power electronics modules than ac.

The introduction of bit rate variable transceivers is expected to improve network reconfiguration and optimization. The different network margins are discussed along with the related strategies to reduce them.

In Insulated gate Bipolar Transistor (IGBT) modules, ceramic substrates are used as insulation between semiconductor chips and the ground potential. The substrate, semiconductor chips and connections are covered with silicone gel to prevent partial discharges (PDs) from occurring. In this work, partial discharges are investigated on laboratory samples made of metalized substrates embedded in silicone gel and various liquids. Substrates are made of aluminum nitride (AlN), alumina (Al2O3), or glass/epoxy composite. The objective is to determine the actual origin of PDs, by changing the nature of encapsulating material and substrate. The various liquids used are first characterized using a point-plane geometry. Experiments show that a rather large discrepancy on the PD behavior can be due to the ceramic substrate itself. "Good" and "bad" substrates can be identified on the basis of PD measurements. The influence of the sample preparation (degassing procedure) is also evidenced. The main conclusion obtained in this paper shows that partial discharges do not occur within the encapsulating material, contrary to most previous hypotheses, but within pores existing in sintered ceramic materials. Changing the substrate nature has a large influence on PD behavior, whereas a modification of the encapsulating material has almost no effect.

Injection and transport of space charges have been observed in a semi-crystalline PET under 6.25 kV/mm dc at 60°C. Measurements were made 30 s after volt-off along a 74 h poling using the Laser-Induced Pressure Pulse (LIPP) method. They revealed only negative charges that spread throughout the inter-electrode gap and accumulated near the anode. The space charge distribution stabilized after about 30 hours. Once stabilized, the distribution of charges led to an increase of the field at the anode of 30% and a decrease of the field at the cathode of 20%. The measured density of charges held at the anode was in good agreement with the computed densities of charges induced by the space charges. The measured transient current is similar to the current derived from the charges induced at the anode. This suggests that in these conditions the transient current is a kind of displacement current entirely due to the transport of the space charges. A criterion taking into account the fields at the anode and at the cathode is proposed to explain the end of the transient regime.

Aluminium nitrite (AlN) or alumina (Al 2 O 3 ) substrates are widely used in power electronics modules, due to their ability to provide both electrical insulation, and heat conduction properties. A silicon gel usually covers the substrate, semiconductor chips, and bondings to prevent partial discharges (PD) from occurring within the module. However, at high voltage PDs can be observed in high electric field regions, mainly at the sharp edges of copper tracks on the substrate. In this study, we try to determine the origin of these PDs. Phase resolved PD recordings (PRPD) and optical visualization at very high sensitivity are carried out on substrates embedded in gel or insulating liquids. PD features are very different from those obtained in needle-plane geometry in gel or liquid, and do not depend on the nature of the liquid or gel. The main conclusion is that PDs recorded with substrates originate from the ceramic material itself, due to the presence of numerous μm-sized pores in sintered materials.

The laser induced pressure pulse method -LIPP- is commonly used for measurement of distribution of space charge in insulating materials. The aim of this paper is to study the mechanisms giving rise to the generation of the pressure pulse and to optimize the generating process to obtain the better sensitivity of the technique. For transparent liquids at the laser wavelength, the two mechanisms which may generate the pressure pulse, i.e. thermal expansion and thermal vaporization at the liquid/target interface, are clearly identified depending on the laser energy. The surface roughness of the target also played an important role in this generation. For opaque liquids, thermal dilatation and evaporation at the liquid/air interface are involved. With the use of Indian ink, the energetic conversion revealed better for the smaller investigated liquid thickness, i.e. 20 µm. A concentration of 20% of Indian ink in water provides the best sensitivity at 20°C, respectively 25% at 60°C.

Aluminium nitrite (AlN) or alumina (Al 2 O 3 ) substrates are widely used in power electronics modules, due to their ability to provide both electrical insulation, and heat conduction properties. A gel layer usually covers the substrate, semiconductor chips, and bondings to prevent partial discharges (PD) from occurring within the module. However, at high voltage PDs can be observed in high electric field regions, mainly at the sharp edges of copper tracks on the substrate. In this study, we try to determine the origin of these PDs. Phase resolved PD recordings (PRPD) and optical visualisation at very high sensitivity are carried out on substrates embedded in gel or insulating liquids. PD features are very different from those obtained in needle-plane geometry in gel or liquid. The main conclusion is that PDs of low amplitudes probably originate from the ceramic itself, due to the presence of numerous µm-sized pores in sintered materials.

This paper presents an experimental study of streamer inception in a silicone gel. Many parameters are able to influence the inception of discharges in a gel: voltage wave shape, electrode geometry, temperature, etc. In this work, streamer inception is studied in various conditions of electrode shapes (from sharp points up to quasi-uniform field), voltage (ac, dc, impulse voltage) and temperature. Streamer inception is detected by the measurement of breakdown voltages in selected conditions. The results obtained show that streamer inception field varies when the electrode shape is changed, in a similar way as in liquids: the inception field decreases when the electrode surface increases. On the other hand, temperature and voltage wave shape have almost no influence on the inception field. Results are discussed in comparison with data already obtained in liquids in similar conditions.

We compare the performance of 40G and 100G coherent PDM-QPSK solutions for the upgrade of existing 10G-based optical networks. This comparison is performed on the Alcatel-Lucent 1626LM commercial system.

In this paper, we have investigated the behavior of dielectric properties (partial discharges) of liquids of different natures (silicon oil, aromatic liquid). Partial discharges measurements have been done over the voltage range (0-25 kVpp). Two types of devices have been analyzed. The first one consists of a ceramic covered by liquid, the second one of a needle-plane system embedded in liquid. The origin of partial discharges for the both devices is discussed. A mixture of corona effect and discharge in micro voids appear for the ceramic based system whereas only the corona effect was identified for the second one. Results are then discussed in correlation with potential applications in power electronic components where rubber and gel are used for IGBT module.

Silicone gels are widely used to encapsulate power electronics modules. The objective of this paper is to study the partial discharge (PD) mechanism in a silicone gel, using electrical measurements and fast visualization. Experiments are carried out in a pointplane geometry, using either impulse voltage or ac. Under impulse voltage, the visualization shows that the first discharges recorded in a new sample are due to the initiation and propagation of "streamers", with features close to those previously reported in viscous liquids. Under ac, a stable PD regime rapidly establishes: a streamer creates a cavity with a long lifetime, and PDs occur in this cavity during the subsequent ac waves. Since slow streamers develop during long times (some ms), classical PD measurements do not provide an adequate evaluation of the actual discharge magnitude: very small PDs (1 pC) are recorded, whereas large cavities with a total charge in excess of 10 pC are actually present in the gel. When PDs are repeated permanent degradations of the gel rapidly occur, showing the limited self-healing capabilities of silicone gels.

Thanks to the dielectric relaxation spectroscopy method we present results of measurements of dielectric losses versus frequency in alumina substrates before and after thermal treatment. This one consists in applying thermal step of negative and positive values. This type of stress corresponds to those encountered in railway applications. The role of thermal cycling is evaluated, and is rather important. Losses are essentially due to polarization, while the effect of conduction phenomena is less important. For the low frequency range, interfacial phenomena are attributed to the polarization. Results are discussed using the Maxwell-Wagners-Sillars law and Havriliak-Negami's model. On the other hand, the electrical field dependence of losses shows not non-linear phenomenon in the range of voltage [0-3.5kV].

Charging and discharging currents have been measured in an alumina substrate before and after thermal treatment consisting in applying thermal step of negative and positive values (?20°C-50°C). Both transient and steady-state current have been analysed. The average applied voltage ranged from 0 to 5kV. Transient currents suggested a phenomenon generating space charges in the bulk of the material at high fields. Below the high field regime, ohmic and sub-ohmic regime are been identified. Anyway, it was obvious that the thermal treatment increased hugely the conduction current with a factor of almost two decades. No usually Schottky-type injection or tunnel-type was found from our measurements.

Using the LIPP method, negative homocharges have been observed in PET sheets after a few hours poling under 6kV/mm DC at 60 °C. This observation was made with various electrode metals: gold (Au), aluminium (Al) and silver (Ag). With gold electrodes, the injection is much slower than with the other two metals. Furthermore, the gold metallization is the only one leading to the injection of positive space charges in the same conditions. Similarly, at 55 °C under 7kV/mm, positive homocharges have been observed in epoxy sheets only with gold-deposited electrodes and not with aluminium electrodes.

In order to increase the knowledge of the processes involved during the degradation of insulating silicone gels under ac stress, recordings of the activity of partial discharges (PD) are performed. Silicone gels are commonly used for the insulation and packaging of high voltage semiconductors such as IGBT modules. We worked on a commercially available dielectric silicone gel. Electrical and optical apparatus allows the measurement of PD's and their location, either on actual power module substrates, or in a point-plane gap. The temperature dependence of PD inception voltage is moderate, while the number of PD's and their charge steeply increases versus temperature. We show that the formation of cavities constitutes the main factor responsible for the degradation under ac conditions. The actual self-healing capabilities of silicone gels are also studied and discussed.

Silicone gels are used for the packaging and insulation of power electronic components such as high voltage IGBT modules, mainly due to their good mechanical and thermal properties. Nevertheless, the knowledge of their dielectric properties is still uncompleted. The aim of this paper is to present the results of measurements of dielectric losses versus frequency, as well as breakdown field under a large temperature range (up to 160 degC). Losses are essentially due to conduction phenomena, while the effect of polarization is less important. The influence of temperature is rather large, and a marked effect of time (ageing) is also recorded, especially when the temperature is raised. Results are discussed with the perspective of use in high temperature power semiconductors.

The results obtained here indicate that this Agere device shows very good performance as a short pulse source for OTDM based systems. It has been demonstrated that, thanks to lower operating losses, theoretical noise figures and experimental Q values are significantly better than the values for. standard pulse source comprised of an electroabsorption modulator (EAM) and a LiNbO/sub 3/ modulator. Moreover, its high extinction ratio makes it attractive for OTDM applications. Finally, its stability and compactness make this device a potentially cost effective solution for the future high line rate transmitters.

The intent of this paper is to cross-correlate the information obtained by space charge profile analysis and electroluminescence (EL) detection in crass-linked polyethylene samples submitted to de fields, with the objective to make a link between space charge phenomena and energy release as revealed by detection of visible photons. Space charge measurements carried out at different electrical fields by the pulsed electro-acoustic method show the presence of a low-field threshold, close to 15 to 20 kV/mm, above which space charge begins to accumulate considerably in the insulation. Charges are seen to cross the insulation thickness through a packet-like behavior at higher fields, starting at about 60 to 70 kV/mm. EL measurements show the existence of two distinct thresholds, one related to the permanent excitation of EL under voltage, the other being transient EL detected upon specimen short-circuit. The former occurs at values of field corresponding to space charge packet formation, and the latter to the on-set of space charge accumulation. The two techniques give therefore consistent information on space charge phenomena and associated energy release in the optical EM spectrum.

Power module reliability can be increased if problems due to high electric fields can be better understood. This paper proposes a global analysis using finite element simulations. Results are confirmed thanks to optical detection of partial discharge localization. Solutions to reduce field reinforcement are proposed and discussed. A discussion of maximum electric field handled by insulation gel is also provided.

International audience; This paper presents an investigation on the current and breakdown voltage measurements in thermoset-thermoplastic blends based on an epoxy-amine/poly-etherimide phase separated material. Thermosetthermoplastic separated blends could be a novel material for insulation applications and can be compared to epoxy/inorganic composites systems. Pure epoxy network as well as the blends with 10 wt% of PEI were studied in terms of conduction and transient currents. An ohmic behavior below the threshold field (E th) and space-chargelimited conduction (SCLC) above E th are pointed out. Contact emission phenomenon was investigated by means of Schottky model and seems to be valid for both materials. The addition of 5 and 10 wt% of PEI into the epoxy system showed an increase in the values of breakdown voltage with the increase of the PEI amount.

Under DC stress, electroluminescence in polyethylene naphthalate films is stable, current-proportional, above a threshold field of 150 kV/mm. At this field level, the luminescence is thought to be triggered by impact excitation and/or ionization of the luminescent centers by hot electrons, or, alternatively, by electron and hole injection, migration and recombination. Investigation of the internal space charge distribution versus field is believed to constitute a relevant approach to discuss the excitation process.

Today, high voltage power semiconductors such as IGBTs, are being developed. As the voltage is increased, local electric fields applied to dielectric materials also increase. Local deterioration of dielectric materials due to partial discharges (PD) may appear and affect the reliability of the whole component. The usual way to detect PD's under ac voltage via electrical measurements is no longer applicable with the pulsed voltage wave shape encountered in power semiconductor applications. This paper presents investigations carried out with optical measurements of PD's in silicone gels, in a typical IGBT module structure. In addition, a very faint light emission is detected below the PD inception voltage. This light can presumably be attributed to an electroluminescence phenomena, such as previously reported in solids or aromatic liquids, and can constitute a non destructive technique that allows to detect the existence of local high fields in the gel.