M. Riccio

Experimental Detection and Numerical Validation of Different Failure Mechanisms in IGBTs During Unclamped Inductive Switching

The physics of the different failure modes that limit the maximum avalanche capability during unclamped inductive switching (UIS) in punchthrough (PT) and not PT (NPT) insulated-gate bipolar transistor (IGBT) structures is analyzed in this paper. Both 3-D electrothermal numerical simulations and experimental evaluations support the theoretical analysis. Experimental results for UIS test show that, at low time duration (or inductance value) of the test, the UIS limit moves from energy limitation to current limitation. While the energy limitation is well known, the current-limited failures are less studied. In this paper, the current limit for UIS test is analyzed in detail, and the cause is attributed to a filamentary current conduction due to the presence of a negative differential resistance (NDR) region in the IC- VCE curve in breakdown. The filamentary current conduction locally increases the current density causing early device latch-up and possible device failure at a current much lower than the one dictated by energy limitations. The physical parameters that affect both the onset of NDR region and the failure current are discussed for both an NPT trench IGBT structure with a local lifetime control and a PT trench IGBT structure with a field-stop layer.

Electro-thermal instability in multi-cellular Trench-IGBTs in avalanche condition: Experiments and simulations

This paper reports on the results of a study on electro-thermal instability induced in multi-cellular Trench-IGBTs in avalanche condition. Experimental measurements, made on T-IGBTs, show possible inhomogeneous current distribution under Unclamped Inductive Switching (UIS) confirmed by transient infrared thermography measurements. Together with this, an analytical modeling of avalanche behavior has been included in a compact electro-thermal simulator to study the interaction between a large numbers of elementary cells of T-IGBTs forced in avalanche condition. Electro-thermal simulations qualitatively replicate the possible inhomogeneous operation observed experimentally. Finally a possible theoretical interpretation of the instability in avalanche condition for T-IGBT is given.

SiC power MOSFETs performance, robustness and technology maturity

Relatively recently, SiC power MOSFETs have transitioned from being a research exercise to becoming an industrial reality. The potential benefits that can be drawn from this technology in the electrical energy conversion domain have been amply discussed and partly demonstrated. Before their widespread use in the field, the transistors need to be thoroughly investigated and later validated for robustness and longer term stability and reliability. This paper proposes a review of commercial SiC power MOSFETs state-of-the-art characteristics and discusses trends and needs for further technology improvements, as well as device design and engineering advancements to meet the increasing demands of power electronics.

Detection of localized UIS failure on IGBTs with the aid of lock-in thermography

Abstract IGBTs with embedded current monitors, i.e. realized by separating a small part of the main device emitter and using it as the current sense terminal, are currently used to integrate intelligent power modules (IPMs). In a previous paper [Breglio G, Irace A, Napoli E, Spirito P, Hamada K, Nishijima T, et al. Study of a failure mechanism during UIS switching of planar PT-IGBT with current sense cell. Microelectron Reliab 2007;47(9–11):1756–60] we have demonstrated how, during UIS switching in particular circuit configurations, the interplay between the sense-emitter cell and the rest of the device can lead to latch-up of the lateral p–n–p bipolar transistor and current focalization in the sense-emitter cell which finally causes device failure. In this paper, we show how the location of this very localized failure spot can be very accurately determined with the aid of a very sensitive lock-in thermography setup. The main advantage of this approach is the direct applicability to the failed device without the need of time consuming sample preparation as in other failure analysis (FA) techniques.

Short-circuit robustness of SiC Power MOSFETs: Experimental analysis

This paper proposes a thorough experimental characterization of the performance of commercially available SiC Power MOSFETs under short-circuit conditions. The purpose is to assess and understand the degradation process and the failure mechanisms that limit device reliability to identify optimal routes for subsequent technology development. This paper complements electro-thermal functional tests with structural characterization offering deeper insight into device technology related aspects.

Analysis of the UIS behavior of power devices by means of SPICE-based electrothermal simulations

Abstract This paper presents an accurate, yet computationally effective, 3-D simulation strategy devised for the UIS analysis of multicellular power transistors, which accounts for electrothermal effects and is based on a circuit representation of the whole device under test. The approach is exploited to examine the correlation between the shape of the avalanche curve of IGBTs and the physical mechanisms occurring during UIS discharging. In particular, an in-depth investigation is performed on a current hopping phenomenon that – although not usually destructive – entails a reduction in both ruggedness and reliability of the device.

SPICE modeling and dynamic electrothermal simulation of SiC power MOSFETs

This paper presents a computationally efficient 3-D simulation approach for the dynamic electrothermal analysis of SiC power MOSFETs. The strategy relies on a circuit representation of the whole device, where the electrothermal feedback is enabled through an equivalent electrical network, and the elementary device cell is described by a novel behavioral model accounting for the non-intuitive temperature dependences of key physical parameters.

Short-circuit failure mechanism of SiC power MOSFETs

Failure mechanisms during short-circuit conditions of Silicon Carbide Power MOSFETs are analysed in this work, and a possible theoretical explanation is provided. Insight into the physics involved in such processes was inferred through experimental and numerical analyses. The TCAD structure used for electro-thermal simulations was calibrated to fit the ID-VGS characteristics of a commercial device. Adequate physical effects were considered, such as the presence of charges and traps at the oxide-SiC interface and their effect on threshold voltage and carrier mobility. Experimental evidences were explained by analyzing the numerical results. The high temperature reached during these operating conditions was addressed as the main cause of the device failure. The effect on the leakage current and the activation of a parasitic bipolar transistor are also shown.

Current distribution effects in organic sexithiophene field effect transistors investigated by lock-in thermography: Mobility evaluation issues

In this Letter, a lock-in thermography technique has been used to investigate the actual current distribution profile in the active channel region of organic field effect transistors. The high accuracy of the setup shows an evidence of nonuniformity in the current flow over the device area. The physical origin of this experimental occurrence is tentatively ascribed to a not uniform contact resistance distribution along the channel width or to inhomogeneities in the interface traps distribution. The subsequent implications on the carrier mobility evaluation are discussed too.

Compact electro-thermal modeling and simulation of large area multicellular Trench-IGBT

In this contribution we report on electro-thermal modeling and simulation strategy of large area multicellular Trench-IGBT (TIGBT). The proposed solution is based on two coupled systems: a 3D thermal simulator and a 1D electrical (with temperature dependent parameters) physical model of single TIGBT cell. The single cell electrical model has been calibrated to fit the experimental characteristics of a 1200Volt-1000Ampere commercial TIGBT and the influence on the breakdown behaviour of the second order effects has also been included. The unit cell model has been inserted in the 3D thermal simulator and the time dependent thermal maps have been obtained. As a final results we will present electro-thermal simulations in short-circuit condition; the latch-up onset of the parasitic thyristor will be analyzed.