Power Electronics has nowadays become an enabling discipline and has originated thousands of diverse applications. The core of a Power Electronic converter is the Power Electronic device. Power Electronic devices can be classified as uncontrolled, semi -controllable and fully -controllable. According to this classification, and because of the nonideal behavior, e.g. in limited blocking voltage, nonzero on state voltage drop and noninfinite switching speed, many different kinds of power devices have populated the Power Electronics arena in the past five decades.

Thyristor is a four-layered p-n-p-n structure in which the current flow between anode and cathode is triggered by a current pulse into the gate electrode. The gate trigger current flows from a current or voltage source connected between the gate and cathode, altogether forming the gate (control) circuit. If the impedance of the main circuit connected between the anode and cathode allows the flow of anode current higher than the so-called latching current, the thyristor stays in the forward conduction state (ON-state) even after removing the gate current. In other words, thyristor can be triggered to the ON-state by a current pulse containing a sufficient integral charge and remain ON as long as the anode current is higher than the socalled holding current.

Chapter 5 covers silicon-based IGBT devices with a focus on device structure, operation, performance requirements and development trends. First, a brief historical background is presented covering the conception and evolution of the IGBT structure from the basic principles of the unipolar power MOSFET and bipolar power transistor. This is followed in Section 5.2 with a detailed explanation of the basic IGBT structure and principle of operation from both the device physics and equivalent circuit model viewpoints. Sections 5.3 and 5.4 cover the basic static and dynamic characteristics of the IGBT. The static characteristics discuss the forward and reverse bias modes of operation while also including the transfer characteristics for the IGBT MOS cell structure. The dynamic performance is explained for both the turn-on and turn-off periods with the help of the internal IGBT capacitive effects and excess carrier charge dynamics during the switching transients. Section 5.5 is focused on the main requirements of the IGBT with respect to mainstream applications and how such demands have influenced the device structural evolution over the years. A number of critical design and performance tradeoff relationships are presented with respect to the structural changes made at both MOS cell (planar, trench) and bulk design (PT, NPT) and their impact on the total device losses, switching control and robustness. Sections 5.6 and 5.7 present the IGBT requirements and design considerations for increasing the device SOA under both short circuit fault mode and switching transients. The different failure modes occurring under such conditions and their causes are discussed and analysed while highlighting the device design impact for providing wider margins and more robust behaviour. Section 5.8 provides the reader with an overview of the IGBT current and future development trends. The main target is to provide continuous increments in power handling capability through a number of independent and often combined technology paths. This includes the traditional trend with a focus on reduced losses and increased margins and new trends with respect to device integration, such as for reverse conducting IGBTs and allowing operation at increased junction temperatures.

In Section 7.2, the authors present the most common SiC SBD device structures and discuss their properties important to applications. Section 7.3 is concerned with diode edge termination structures and their reliability and Section 7.4 covers electrical and thermal device properties. In Section 7.5, we present some example applications and demonstrate the advantages of SiC SBDs over their bipolar silicon counterparts. Finally, we conclude with some remarks about possible future developments in Section 7.6 (integration into switches).

The recent progress and primary challenges in GaN power devices are reviewed and discussed in this chapter. The interface/border trapping at/near the dielectric/ GaN interface in MIS-gate GaN transistor, as well as the hole deficiency in p-GaN HEMT with a Schottky gate, could result in the gate instability issue. The negatively charged states in the gate region would cause a positive V_TH shift, whereas the reduced gate overdrive voltage (V_{G _ ON}-V_TH ) at a preset VG_oN value could lead to the dynamic RoN increase. The gate instability -induced dynamic R_ON degradation can be alleviated with a sufficient gate overdrive. For normally-off MIS-gate GaN transistors, the gate instability-induced dynamic RoN can be further reduced by increasing the channel mobility in the recessed gate region and reducing the channel resistance. A monolithically integrated gate driver is desirable from the perspective of gate reliability for p-GaN HEMT with limited gate drive headroom. Meanwhile, bulk trapping in the III-nitride buffer stack could also cause dynamic R_ON degradation in GaN-on-Si devices. The buffer-related dynamic RoN degradation can be suppressed by compensating the negative buffer traps with hole injection, or through buffer stack optimization with carefully introduced positive charges. On the other hand, the emerging vertical GaN-on-GaN power devices are capable of delivering superior dynamic performance, owing to the low susceptibility of the vertical current path to surface trapping and the minimized bulk trapping in the high-quality homo-epitaxial GaN drift layer with precisely controlled background/compensation impurities.

Reliability is a core requirement for semiconductor devices in power energy switching applications. In this chapter, reliability-oriented design, simulation, packaging material and process have been covered, especially for high voltage, high current and high power density semiconductor devices.

This chapter has presented an overview of state-of-the-art advanced gate driver techniques for enhancing the reliability of IGBT modules. Broadly speaking, methods can be classified in detection methods, optimization methods, and protection methods. Additionally, optimization and protection methods can be roughly classified in simple (and cheap) and advanced (even more expensive). Simple methods, like the open -loop and passivity -based ones, perform well in normal applications, but advanced methods, like closed -loop control strategies, even if more expensive, are necessary for special applications, like high -power IGBT modules. In the near future, benefiting from the increase of data processing speed and reducing the cost of digital controllers, the advanced techniques discussed in this chapter could become more and more affordable and popular, even in low-cost applications, for both considerably reducing short-term and long-term reliability issues. In fact, basing on a large number of different failure mechanisms, more and more complex strategies will be needed including most of the mature detection and protection methods toward the so-called reliability -oriented gate driver design.