Semiconductor Device Electronics

Author: (USA) Werner / (USA) Gran / Lü Changzhi et al
Publisher:
Publish Date: 2005-02-01
Features: Semiconductor Device Electronics is a textbook designed for the core course of semiconductor devices. It is typically offered in the lower-level course schedules of Electrical Engineering and Computer Science departments. Before its publication, it was used as the textbook for a graded course in the 9th semester (1/4 year per semester) at the University of Minnesota, and was well-received. It was part of a 10-week course in electronics. In these 10 weeks, only the basic content of the book could be covered, so it can be easily extended into a semester (half-year) course. However, the rich material in the book is sufficient for a full academic year, making it better suited for upper-level elective courses or graduate programs.
Origin and Concepts: We have seen the urgent need for specialized textbooks on device electronics for beginners. A student once mentioned the need for a broad foundation in this subject. At least most electrical engineering students have been exposed to these essential topics. Our experience shows that, except for the most talented students, the rest still have only a superficial understanding of these subjects. For this reason, the book includes materials on fundamental topics, with review content that aligns deeply with pedagogical requirements. The narrative order of the book progresses from specific to general. First, simple and clear examples are presented as stepping stones, then more complex situations are addressed. Those with longer experience in a topic appreciate the elegant development from general to specific, while most beginners prefer the latter. They need specialized and manageable components to construct their own conceptual framework. We illustrate the application of principles, emphasizing field theory. We discuss a series of one-dimensional problems related to device theory, rather than starting with Maxwell's equations. We emphasize the importance of gaining intuitive understanding, understanding the essence of the Poisson equation in simple contexts, and then grasping more complex concepts like displacement current and dielectric relaxation time.
For the theory of devices, which is the theme of this book, we do not need to go beyond one-dimensional descriptions, nor are we limited to space. However, the book provides a solid foundation for the more general field theory needed for two-dimensional and three-dimensional problems and states that students will encounter later.
Using a similar approach, the Bohr atom is treated by attempting to explain its performance as an isolated atom in a single-crystal solid. On the other hand, crystallography is a topic that most electrical engineering students have not encountered before. However, it is a fundamental topic that device engineers use almost daily. Other fundamental topics discussed are foundational to all branches of engineering and science. These include the procedures and proficiency for solving general problems, the coordinated use of units.
The main goal of writing this book is clarity. We have freely used analogies and heuristic descriptions, avoiding unnecessary technical terms. In explanations, we have tried to choose a level that is understandable upon its first occurrence. In most derivations, intermediate equations are included, so students can easily follow the reasoning rather than just reading equations until "the end."
One of the authors has taught device electronics courses for more than 20 classes at the University of Minnesota for the Electrical Engineering department; during the same period, they taught 10 corporate part-time classes in different parts of the United States. The classes at the university were large, with student numbers exceeding 200, which created unique challenges. Small problems included speaking louder or writing larger characters on the blackboard. As every experienced person knows, a major issue for large classes is the responsibility of management, even requiring appropriate and authorized assistance. Our book provides a significant mitigation for this situation. The book provides 229 analytical problems and an accompanying solutions manual. After presenting these analytical problems and solutions, students can choose methods that adapt well to these intuitive states. A frequently used method is assigning problems, followed by providing solutions, of course, as an option. However, there is at least another valuable choice—we have successfully used for several years a method where, on the day of the lecture, we present problems and provide available solutions. Then, we inform students that test questions and exam questions will be closely related to these problems, so they must become familiar with them and solve them thoroughly. This method eliminates the burden of grading homework, as it is often copied by many students after a special course's homework solutions are provided. (There is no academic activity more time-consuming than grading homework.) This method can also further eliminate the need for instructors to assign computers, replacing them with design problems as homework. In our practice, we provide exercises and solutions to guide students to focus highly on understanding. The discussion of problems and related concepts dominates the narrative time and the time students spend visiting the office. To reinforce the instructor's focus in this regard, we often include problems directly taken from the book in early tests, even without changing the problem numbers. Of course, using such a system requires that closed-book methods be mandatory during tests and exams. To further emphasize the importance of understanding (rather than a filing clerk's technique), this system does not place unreasonable demands on students' memory. Students must know simple equations, generally involving three or four symbols. For example, students can truly understand that the diffusion current is proportional to the concentration gradient and can easily write the relevant equation. For more complex equations, such as the continuity equation, we state in the exercises the equations that must be mastered. Generally, we require students to understand the most complex equation, the transport equation.
Following the above direction, another example is appropriate. The equation for the depletion layer thickness in different types of abrupt junctions is important, but it can be quickly picked up by engineers in their work. We believe that memorizing these equations offers relatively little benefit in terms of energy investment. However, we require students to clearly understand why the depletion layer thickness in an abrupt junction varies with the square root of the potential difference between the two sides of the junction and why this relationship exists. Based on this foundation, it is easier to propose test questions that assess understanding rather than memory. We have selected review questions that emphasize fundamentals rather than current technological concepts. Only two main devices—the bipolar junction transistor (BJT) and the metal-oxide semiconductor field-effect transistor (MOSFET)—are discussed here, as a thorough understanding of these devices allows students to understand all other important IC devices. The current state of devices is constantly being revolutionized by their properties, and these changes are best learned on the job.
Content and Organization:
Chapter 1 presents the fundamentals of electricity in a fresh way, as well as unit conversions and problem-solving, the Bohr model, and crystallography.
Chapter 2 discusses the bulk properties of equilibrium and non-equilibrium semiconductors, with a focus on silicon, introducing band theory and explaining the differences between semiconductors, conductors, and insulators. It then introduces the concept of the Fermi level and its applications, which are frequently used in semiconductors along with basic approximations. The nature and conclusions of "doping" are further introduced into the fundamental equations, mass action law, neutrality equations, and the Boltzmann relation. This chapter also completes the discussion of carrier transport, recombination and generation, and the continuity equation as analytical tools for carrier properties.
Chapter 3 extensively covers PN junction problems, as well as their behavior under equilibrium and biased conditions. After introducing the basic concepts of the junction, a carefully selected series of examples using the depletion approximation are presented, followed by its extension to cases beyond abrupt junctions. Static theory is expanded through a set of carefully documented experimental data from specific silicon diodes. In addition to the typical textbook discussions, this chapter also covers breakdown phenomena. However, only our book provides a fresh and complete discussion of the dynamic properties of PN junction diodes, which is then used as the foundation for discussing BJT and MOSFET dynamic properties. This chapter also includes general discussions of abrupt junctions and semiconductor surface problems, which are only found in another book. It also discusses using high-low junctions as ohmic contacts—a description that can be found in many semiconductor devices but is often ignored in most electronics textbooks. This chapter introduces the principles of SPICE numerical analysis, with descriptions in some cases even exceeding those in the SPICE manual.
Chapter 4 provides the fundamentals of BJTs, basic device theory, biasing practices, and circuit structure selection, emphasizing the nature of each problem. It then discusses the real structure and characteristics of BJTs, with a detailed evaluation of the large-injection effects in BJTs. However, this effect is often omitted in most textbooks, as conventional BJTs are used under large-injection conditions, and this omission cannot be considered justified. In our Ebers-Moll static model section, clarity and the identification of the physical meaning of each step are emphasized, with rich examples of applications. The BJT small-signal dynamic model begins with the hybrid model, involving device physics, through the hybrid π model, charge-control model, to the figure of merit. It also introduces unique details of SPICE models, including large-signal, small-signal, and parasitic characteristics. This chapter also includes thermal resistance.
Chapter 5 discusses MOS capacitors and MOSFETs. After an initial theoretical introduction and the selection of inverters, it describes the most important phenomena that must be discussed in MOS capacitors. These phenomena are carefully simulated in this chapter using equivalent circuits and the general semiconductor surface analysis method introduced in Chapter 3. It includes a discussion of the physical and analytical interactions between MOS capacitors and junction diodes, comparing the nature of capacitance in these two devices. This is followed by advanced MOSFET simulation, including small-signal and large-signal SPICE treatment. This chapter also includes a detailed comparison of MOSFET-BJT performance, which is not found in any other textbook.
Study Aids: Following each chapter are two special features designed to provide a solid, qualitative understanding of the chapter's content. The first feature is a brief summary of the chapter's key elements. The second feature is a set of problems called "Review Sessions" (averaging 115 problems per chapter), allowing students to clearly determine whether they have mastered the key points or may have missed the entire topic. The basic problems presented in this section are also used for test and exam purposes. Another special feature of the book is the inclusion of exercises and solutions within the text. The average number of exercises presented in each chapter is 60. Here, we expect these problems to be reasonably accessible to an active reader's mind. (We desire feedback to achieve this success.) However, for more active or ambitious readers, they can ponder these problems before reading the solutions, attempting to support their own answers.
Our book has some aspects that differ from typical engineering textbooks. There are many spatial topics of great importance in this field, with the spatial lattice in Chapter 1 providing a good example. In such cases, perspective drawings are used instead of the usual original orthogonal cubic drawings. In recent years, theABET we appointed has effectively and increasingly emphasized design skills, as engineers do more synthesis than analysis in their work. For this reason, we have included design problems at the end of each chapter, in addition to the earlier-discussed analytical problems. Similarly, for the same reasons, computer problems are also accompanied by each chapter, with an average of more than two problems per chapter. Here, we have selected problems that require numerical processing. In the last three chapters, the focus of these problems is on SPICE models. Typically, we assign design and computer problems as homework. We have chosen to solve them using Pascal programs, but other programs are also clearly available to users of the book.
Finally, the accompanying solutions manual to this book has been prepared with extraordinary readability and precision. In particular, the careful treatment of units is emphasized, with a focus on reinforcing this topic in Chapter 1.
References: Like the material in the text, the subject index is provided with such care and thoroughness that it is unusually detailed. Important topics are generously cross-referenced. When we feel the effort involved, we sometimes assign non-technical staff to prepare the index. We believe that this additional investment will enhance the book's value as a research and reference resource.
Following a similar approach, our policy on references is to provide a substantial number, though far less than the list in an encyclopedia. (If there is any chauvinistic standard in this selection process, we hope our readers will understand.) We believe this book can be used as both a reference and a textbook.
In summary, we have tried to select and emphasize the most fundamental and enduring themes, then sought the clearest possible presentation. We hope this result will provide a balanced training in solid-state device electronics for many future students.
Acknowledgments: We are deeply grateful to the approximately 1,000 students who have used our manuscript as a textbook and provided their evaluations and numerous revisions. We are also sincerely appreciative of the long-term encouragement provided by Professor Alfons Tuszynski. We thank Professor Ronald D. Schrimpf for the insights included in Exercises 3-54 and Figure 5-48(b). We should specifically mention Mae Warner's relentless checks on every step of the publishing process and her computer entry of most of the manuscript. We are extremely grateful to our project editor, Mary Patton, for her professional and patient work during this period.
This book is a textbook for a course in semiconductor device electronics. It is divided into five chapters, starting with modern electronics fundamentals, and successively covers the fundamental and classic content of semiconductor device electronics, such as semiconductor bulk properties, PN junctions, bipolar junction transistors (BJTs), and metal-oxide semiconductor field-effect transistors (MOSFETs). The book also places special emphasis on SPICE analysis methods. It is a foundational textbook with classic content, suitable as a textbook for undergraduate or graduate students in electronic, electrical, and computer engineering or related fields, as well as a reference for engineering professionals.