D.W. Greve
Department of Electrical and Computer Engineering
Carnegie Mellon University
Published by Prentice Hall, 1998. Currently out of print. Revised and updated material has been used in 18-412 and 18-610.
Chapter titles (1998 edition)
1. Preliminaries and Notation
2. Field Effect Devices-Overview and Classification
3. The MOS Capacitor
4. Charge-coupled Devices
5. The MOSFET
6. MOS Memory
7. Thin Film Transistors
8. Metal Semiconductor Field Effect Transistors (MESFETs)
PrefaceSemiconductor electronics has been at the heart of the information revolution. Transistor electronics made mainframe computers reliable enough to be useful for more than just a few highly specialized applications. Advances in semiconductor electronics, especially the development of the integrated circuit, made computers cheaper and useful for an ever-broader range of applications. And not so long ago, the microprocessor made it possible to apply computing to innumerable industrial and consumer products. Highly prominent among these products is the desktop computer, but microprocessors have also added value to products as diverse as washing machines and automobiles.
The ever-increasing ability to store and manipulate information continues to make new applications possible, and frequently unexpected ones. Only recently has it becomes possible to store and display images along with text information at a reasonable price; this has driven graphics-oriented computing, including the explosive development of the world wide web. High-definition television is now on the near horizon, with capabilities which would be impossible without the manipulation of massive quantities of digital information. Portable communications have also grown very rapidly; the portable telephone, once an expensive curiosity, is now ubiquitous. And laptop computers have functionality which was unattainable even with the most expensive mainframe computers not so many years ago.
The trend toward increasing device density and decreasing price which is expressed by Moore's law has remained remarkably consistent for more than two decades. But while the trends have been consistent, at various points entirely new classes of applications have become possible. For the near future, many of these new applications will be characterized by portability and the increasing use of images. These two aspects in a sense go together: a portable device, designed to be used without documentation and by the widest possible range of users, must interact with users in the most direct and simple way. So a graphical display is essential, which brings with it the need for more information storage and processing and more rapid and higher bandwidth communication.
This book treats many of the important semiconductor devices for this new class of applications in a unified way. At its heart, this is a device physics book, but it is a device physics book where the choice of topics is motivated by a particular class of systems applications. Because the topics discussed are motivated by systems applications, this book contains more than the usual amount of material describing these requirements and the ways in which devices are designed to meet these requirements. The reader will learn about simple digital circuits and their performance; the perception and reproduction of images; low temperature processing of semiconductor materials; and RF communications. This material is included so it can be understood not only how particular devices work but also why they are of interest.
This book is focused on field effect devices, because these are linked by common physical principles and also because they meet the future demands for low power consumption and high device density. (An equally unified book could be written about injection devices, covering junction diodes, bipolar transistors, and optoelectronic applications; perhaps such a book will be written, and used instead of, or in a sequence with, this book). This is not an encyclopaedic coverage of field effect devices, however. An enormous amount has been published about these devices, and it is increasingly clear that covering everything often has the effect of teaching nothing. In this book, I have tried to cover a limited set of topics carefully enough that the underlying physical principles can be learned well. This book represents my own personal view of which topics are most essential and interesting and which are not.
Now the details. This book is intended for a one-semester course, taught at the senior level, or possibly second semester junior level. The ideal student will have taken either an introduction to semiconductor physics; an introduction to electronic circuits and devices; or perhaps an introductory course in semiconductor devices. It is assumed that students know about electrons and holes and how they move, and how a pn junction works. Prior study of the bipolar or field effect transistor is not required. Some coursework at the introductory level in electronic circuits or materials science would be helpful for particular parts of the book but it is not essential.
Chapter 1 provides a brief summary of the essential semiconductor equations and Chapter 2 gives a short historical perspective and then presents the field effect device "family tree." Chapter 3 develops the physics of the MOS capacitor. If a thorough understanding of the pn junction is essential for the study of injection devices, the MOS capacitor plays the same role for field effect devices. This study is also motivated by the value of the MOS capacitor for process and material diagnostics.
In Chapter 4, MOS capacitor physics are applied to understand the charge-coupled device (CCD). One of the major applications of the CCD is in image sensors, and discussion of various types of image sensors forms a major part of this chapter. This chapter also introduces the gated diode (just an MOSFET without a drain) and develops confidence in the use of the basic MOS capacitor concepts.
Chapter 5 is the heart of the book, containing the discussion of the MOS field effect transistor. The device equations are developed, and there are descriptions of phenomena which are important in scaled devices such as short-channel effects, hot-carrier reliability, and subthreshold currents. Frequency and switching-speed limitations are addressed, as is the impact of scaling on speed and power consumption. Chapter 6 provides an introduction to the various types of MOS memories. While memories are very large and complex circuits, the elemental storage cell is small, sometimes consisting of only a single specialized transistor. Understanding the operation of the elemental storage cell requires many of the device physics concepts which are presented in earlier chapters.
The thin film field effect transistor (TFT), and its application in displays, is the topic of Chapter 7. After a long and rocky development path, the active matrix liquid crystal display has recently reached a relatively mature state, with active matrix displays now found in a majority of laptop computers. Additional applications are in avionics, medical imaging, and projection high-definition television displays. While the device concepts are similar to those applicable to single-crystal devices, the constraints of low-temperature processing lead to very different characteristics from single-crystal devices. Simple models presented in this chapter describe many of the characteristics of thin-film transistors and aid in understanding the strengths and weaknesses of different technologies.
Finally, Chapter 8 discusses the GaAs metal-semiconductor field effect transistor. This device is a major competitor for RF power amplifier and RF front end electronics in portable systems. This chapter also contains a development of the theory of the Schottky barrier diode. The structures of other high performance GaAs-based field effect transistors are also briefly discussed.
A one-semester course could easily cover the material in chapters 1-5 together with a selection of material from chapters 6-8, with the choice depending on instructor interest and the time available. The chapters contain examples, usually including several numerical examples using Mathcad. The use of Mathcad makes it possible to painlessly apply some of the more algebraically complex equations. A good selection of problems is provided with each chapter, some of which use Mathcad (or a similar tool) to facilitate calculations and comparisons of models.