TUTORIALS

Four tutorial lectures will be kept on Monday, October 1 on hot topics on reliability of power devices.

Non destructive diagnosis techniques for power devices under extreme stresses

Prof. Giovanni Busatto
University of Cassino, Italy

Power semiconductor devices (Diodes, BJTs, MOSFETs, JFETs, IGBTs, GTOs) are frequently employed in hard-switching applications, where these devices are used as switches and are required to turn on and off high currents and voltage. Due to the overlapping of high current and voltage levels, and to the ensuing temperature increase, the transition from the on to the off state, and vice versa, are stressful events, which can lead to a catastrophic failure of the device. This is even more true, in particular, when overload or abnormal conditions are considered (short circuit, over current, over voltage and high temperature). The ability of the device to sustain for short time operating conditions over its Safe Operating Area (SOA) may be considered to be an indication of the device robustness. The tests to determine the SOA of the device are commonly performed on a pass/fail procedure which results in an expensive job due to the number of samples to be destroyed to perform the characterization. Several authors in literature have faced the problem of performing SOA tests in a non-destructive way. For this purpose the device under test (DUT) is operated in presence of a protection circuit which is able to quickly zero the energy dissipated by the DUT at the occurrence of a potentially destructive unstable condition. The tutorial reviews the different circuit topologies which have been used so far for performing the protection action on the DUT. A large attention is placed on the choice of the protection switches, the related drivers, and on the methodologies and circuits to be used to detect the occurrence of the instabilities. The effects of the parasitic elements of the external circuit on the performance of these Non Destructive Testers (NDT) are also discussed. The basic instabilities occurring during the switching operations of the power devices are presented and a particular attention is devoted to the precursors which precedes these instabilities and help in performing the protection action. Some theoretical discussions about the physics of the recognized instable mechanisms are also reported.

Physical trends of HK oxides

Prof. Olof Engstrom
Microtechnology and Nanoscience Chalmers University of Technology, Sweden

The properties of rare-earth and transition metal oxides of interest for the development of future silicon nanoelectronics will be reviewed. As an introduction, the motivation for using high-k insulators for MOSFET applications will be given together with a basic enlightenment on two crucial intrinsic properties of gate insulators: the dielectric constant, k, and the energy offset value, ∆E, in relation to silicon. It will be demonstrated how these quantities govern initial navigation along metals in the periodic system to find future oxide candidates with feasible leakage characteristics. An overview will be included on the restraining influence of lower-k interlayers, interface states and oxide traps together with a critical survey of existing characterization methods for crucial quantities. Chemical properties like reactivity, structural stability and hygroscopic qualities of interesting oxides will be treated together with reliability issues. Finally, the future challenge of keeping up gate insulator development with the perspectives of the ITRS roadmap will be discussed.

Reliability issues in automotive microelectronic components and systems

Dr. Werner Kanert
Infineon Technologies, Germany

Automotive has a notorious reputation of combining both harsh application conditions and high reliability requirements. Zero Defect is an often used slogan that reflects the expectations of customers and car manufacturers today. Product qualification according to pertinent standards have increasingly been questioned recently. Alternative methodologies have been proposed, such as “Robustness Validation”. However, reliability testing and assessment meet with limitations both of technical and economic nature that yield results that are often contrary to customer expectations. The tutorial will look at reliability issues for semiconductor components in automotive environments. Examples of requirements of automotive applications serve as a basis for a discussion of reliability testing. Challenges arising from new concepts like e-mobility will be looked at. Deficiencies in common qualification procedures will be illustrated. Also, the implementation of methodologies that are based on the principles of accelerated testing and dedicated test structures, well established in silicon reliability, for product and package issues is far from being straighforward. These issues may be concisely phrased as the question: “Have we reached the end of testability?” In addition, much of what hurts the industry is caused by problems that are not related to intrinsic reliability of the system. This issue will also be discussed. The tutorial will try to provide an overview and some answers to reliability issues in automotive applications that are relevant not only to this market segment but arise in a similar manner in other applications, e.g. in industrial environments.

Basics of reliability physics

Dr. Joe McPherson
Texas Instruments, USA

All devices are expected to degrade with time --- so device reliability is of great practical importance. Reliability investigations generally start with measuring the degradation rate for a material/device and then modeling the time-to-failure versus the applied stress. The term “stress” is very general: any external agent (electrical, mechanical, chemical, thermal, electro-chemical, etc.) that is capable of producing material/device degradation. Time-to-failure occurs when the amount of degradation reaches some critical threshold level. Time-to-failure (TF) models generally assume either a power law or exponential stress-dependence and with either an Arrhenius or Erying-like activation energy. From these TF models, the all important acceleration factors can be established and serve as the foundation for accelerated testing. During this tutorial, the basics of reliability physics and accelerated testing methods are discussed: degradation rate modeling, TF model generation, TF statistical distribution determination, and acceleration factor development. Several TF models, which are commonly used for common IC failure mechanisms, will be discussed. These failure mechanisms include: Electromigration (EM), Stress Migration (SM), Time-Dependent Dielectric Breakdown (TDDB), Hot-Carrier Injection (HCI), Negative-Biased Temperature Instability (NBTI), Thermal Cycling (TC), Surface Inversion/Mobile-Ions, Plasma-Induced Damage (PID), and Single-Event Upset (SEU). This tutorial will provide the attendee the basics of reliability physics ---- which should serve as a solid foundation for a better understanding of the papers presented at ESREF.