Thyristor Design and Realization

Invented in the late 1950s, the power thyristor is a semiconductor device which has shown a remarkable ability to accept the challenge of technological advancement. Since it conception as a switching device with the then high power ratings of a few hundred watts, modern thyristors have been developed capable of megawatts of switching power. Furthermore, novel design concepts and improvements in semiconductor silicon processing techniques have led to special thyristor designs such as the gate turn-OFF thyristors, light triggered thyristors and more recently the field controlled thyristors or static induction thyristor. The design of both the basic thyristor and these several special types of thyristor is the subject of this book, which covers design from the selection of the starting silicon through to the design of the device encapsulation. In the first chapter the power thyristor is introduced to the reader unfamiliar with the subject, while in the second chapter the various operating modes of the device are discussed in terms of the detailed device physics.
These two initial chapters provide the basis for an understanding of thyristor design starting from the assumption of a degree level knowledge of semiconductor physics. Chapter 3 concerns the detailed design of the basic thyristor, leading the reader through the design stages of semiconductor selection, minority carrier lifetime, vertical strucxture design, cathode emitter shorts and the detailed thyristor gate design. The following chapter expands on the design discussions of Chapter 3 by considering the special requirements of advanced thyristor types including the gate assisted turn-OFF, the asymmetric, the gate turn-OFF, the reverse conducting and the light activated thristors. Also included are sections on field controlled thyristors, triacs and the new MOS-thyristor hybrid structures. In any design procedure for a power thyristor it is not possible to separate the structural design from the fabrication process design. In Chapter 5 the techniques used in thyristor fabrication are reviewed, covering such topics as diffusion, lifetime control, metallization and junction passivation.
The concluding Chapter 6 briefly examines the thermal and mechanical design of the thyristor, dealing with such topics as the encapsulating design and cooling techniques.