ISBN-10:
0471695971
ISBN-13:
9780471695974
Pub. Date:
03/11/2005
Publisher:
Wiley
Electronic Materials Science / Edition 1

Electronic Materials Science / Edition 1

by Eugene A. Irene, Irene
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Product Details

ISBN-13: 9780471695974
Publisher: Wiley
Publication date: 03/11/2005
Pages: 320
Product dimensions: 6.34(w) x 9.17(h) x 1.03(d)

About the Author

EUGENE A. IRENE is Professor of Physical Chemistry at the University of North Carolina, Chapel Hill. He received his PhD in solid-state and physical chemistry from Rensselaer Polytechnic Institute in 1972 and worked for IBM for ten years in the Thomas J. Watson Research Center.

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Electronic Materials Science


By Eugene A. Irene

John Wiley & Sons

Copyright © 2005 John Wiley & Sons, Inc.
All right reserved.

ISBN: 0-471-69597-1


Chapter One

INTRODUCTION TO ELECTRONIC MATERIALS SCIENCE

1.1 INTRODUCTION

Materials science can be thought of as a combination of the sciences of chemistry and physics within a backdrop of engineering. Chemistry helps to define the synthetic pathways, and provides the chemical makeup of a material, as well as its molecular structure. Physics provides an understanding of the ordering (or lack thereof) of atoms and/ molecules and electronic structure, and physics also provides the basic principles that enable a description of materials properties. The combined information provided by physics and chemistry about a material leads to the determination and correlation of materials properties with the process used to prepare the material, and with the materials structure and morphology. The properties once determined and understood are exploited through judicious engineering. In a sense engineering brings focus to the properties that materials possess, and to the material itself if suitable applications are found. Evidence for the leadership of engineering is witnessed by the many national goals that pervade the national research funding agencies such as nanotechnology, biotechnology, and microelectronics. In each of these fields the advantages of certainmaterials properties are extolled. The goals in every case include the preparation of new materials with enhanced properties for particular engineering objectives.

Materials science as we know it today finds its origins in traditional metallurgy and metallurgical engineering departments. Consequently many university materials science curricula and textbooks in use in these curricula are heavily weighted toward traditional topics related to metallurgy. More modern areas are relegated toward special topics courses and textbooks covering selected areas. This text is aimed toward electronic materials science where the engineering objective is better materials for microelectronics and photonics.

While there has been growing interest and understanding in electronic materials for centuries, there was a major revolution in electronics that began in the late 1940s with the invention of the transistor by Bardeen, Brattain, and Shockley. This invention irreversibly changed the entire electronics arena. Essentially before this time all active electronic circuits components were made of closely spaced similar metal elements (electron-emitting filaments, grids, electrodes) contained within a glass vacuum envelope, so-called vacuum tubes. These devices could switch currents, provide amplification and rectification, and along with passive components enable the construction of radios, televisions, and even analog and digital computers. About the early electronic devices based on vacuum tubes, it is amusing to recall that these early electronic marvels were all larger than today's versions. None were larger than the early (1960s) analog and digital computers that used vacuum tubes, and that filled large rooms and even entire buildings, but had less computing power that the laptop with which this text is written. Then, after the invention of the transistor, is was more than 10 years before the ideas about the solid state devices could be truly felt with the implementation of reliable discrete transistors replacing vacuum tubes on the electronics market, and in all kinds of consumer devices. During this period of incubation from invention to widespread applications, there were somewhat dormant areas of science and engineering that became very active and made major advances that were spurred on by the potential markets for the new solid state devices. First it was realized that single crystals of semiconductor electronic materials had to be made in large quantities rather than in laboratory sizes and with crystalline perfection and chemical purity never before imagined in manufacturing. Then the notion of electronic band structure that derived from the earliest days of quantum mechanics had to be modernized and understood for the new solid state electronic materials. From the new results of electronic energy band structure, doping could be understood, and the role of crystallographic defects became central to electronics materials. Lattice diffusion of dopants into crystals developed greatly in this era. It was also realized that the new class of electronic devices would require the joining of different solid state materials such as metals with semiconductors with insulators in every permutation. Thus there was renewed interest in phase equilibria, not only to understand the important metallurigical transformations that govern steel and other alloys but, with emphasis on alloys between electronically dissimilar materials and with homogeneity ranges, so as to understand atomic vacancies and correlate crystal lattice vacancies with resulting electronic properties. Along with all these advances in understanding and practice of the solid state since the invention of the transistor, another invention came to the fore that also revolutionized the way we live. This invention is the integrated circuit (IC). The integrated circuit enables the configuring of solid state electronic materials in order to fabricate devices such as transistors and rectifiers on the surface of semiconductors, and to link them all together to make a complete electronic system or subsystem to be further linked. The IC has paved the way for all the modern electronic devices especially the digital devices that perform logic and memory. In addition to enabling the efficient manufacture of multiple solid state devices, the IC paved the way for another major revolution, namely nanotechnology or nanoscience. The very heart of the IC, as it is implemented with planar technology, enables the downward size scaling to present device dimensions in the nanoscale range. The areas of electronic materials science and microelectronics are clearly the forerunners of nanotechnology, and many of the techniques developed for ICs are fully integrated into modern nanotechnology. Thus the areas of electronics materials/ microelectronics and nanotechnology are intimately related in that it is clear that microelectronics is the predecessor of nanotechnology, and that advances in nanotechnology will undoubtedly impact microelectronics. As microelectronics took hold of all the devices we use, the area of optical devices or photonics also developed using the solid state ideas about materials as well as the ability to integrate optical and electronic devices on a chip.

The study of electronic materials science must then include the factors that enable a material to be prepared and understood, and its properties determined and optimized for defined applications, in particular, electronics and/or photonics applications. These typical factors selected for study comprise the names of Chapters 2 through 11: Structure, Diffraction, Defects, Phase Equilibria, Diffusion, Mechanical Properties (two chapters), Electronic Structure, Electronic Properties, and Devices. Many of these topics and chapters have the same names one finds in traditional materials science texts, and that is no accident. It is clear that a foundation in traditional materials science is implicit in electronics materials science. The difference is in emphasis, since as a practical matter one text or one course cannot do it all. In the following paragraphs the reasons are discussed why these headings are chosen for a study of electronics materials science, and the emphasis is explained.

1.2 STRUCTURE AND DIFFRACTION

Materials science is often described as being comprised of structure-property relationships. In this context structure refers not only to the arrangement of the basic building blocks, or long-range ordering but also to the chemical structure or short-range ordering. This more complete notion of ordering is discussed early in Chapter 2 of this text with the appropriate nomenclature, and this theme is revisited many times throughout the book. Different structures can represent both different chemical bonding and different arrangements of atoms and/or molecules, and possibly even different states of aggregation (roughness, large grained, etc.). All these structural aspects can lead to different properties, including electronic and optical properties. It is important to use a consistent nomenclature to identify the unique structural features so that materials scientists communicate in a standard language. These topics are discussed in Chapter 2 on the structure of solids.

In Chapter 3 on diffraction we study the determination of crystal structure. The basic idea that underlies this important family of techniques, diffraction techniques, is the principle of superposition. It will be seen in the text that much of the fundamentals of materials science can be understood by referring to a few the basic tenets of chemistry and physics. Among the tenets that are continually revisited is the superposition principle that is used for diffraction, mechanical properties, and electronic structure (with the first review of this tenet in Chapter 3 and again more thoroughly in Chapter 9). For example, the nature of a wave function that is used to describe an electron can be understood by considering the wave function to be made up of many waves in a complex blend, namely the notion of modulation.

Later in Chapter 3 the concept of reciprocal space is introduced. The idea follows from the notion that it is important in science to operate in the coordinate space most appropriate to the system. It is found that for crystal structure obtained by diffraction, reciprocal distances correlate the structure with diffraction experiments.

From a study of structure and diffraction one may glean the erroneous idea that only, or at least mostly, crystalline materials are important in materials science and electronic materials science. This is far from the truth, but it is a natural tendency that follows from paying close and early attention to only perfect crystals. In fact a large fraction of useful materials in all fields are not crystalline at all (e.g., the dielectrics used in microelectronic ICs), and another large fraction is partially crystalline (alloys used for contacts in microelectronics) or at least defective in their crystalline nature. However, the nonperfectly crystalline materials are more difficult to describe universally and simply. That is to say, each material must be described using a number of structural aspects where crystallinity may be one of the important aspects. However, as is usual in science, the ideal state is the easiest to describe thoroughly, and this is the reason why virtually all studies of materials science commence with a discussion of ideal or perfect crystals.

Also electronic structure that is discussed in Chapter 9 on electronic structure is important for determining many properties particularly electrical properties. It will be seen in Chapter 9 that the structure of the material will greatly influence the electronic structure and in turn the electronic and optical properties.

1.3 DEFECTS

To dispel the misleading attention to perfect crystals, in Chapter 4 on defects in solids we look at different kinds of defects. The definitions for several of the more common material defects are discussed. It has been found over and over that simple structural defects such as substitutional and interstitial defects can alter electrical properties and mass transport via diffusion by orders of magnitude, while at the same time hardly affect the melting point or the thermal conductivity for a material. Furthermore line defects are implicated as the main factor in the plastic deformation of crystalline materials. The notion of grain boundaries as the boundaries in between single crystal grains is also implicated in the mechanical properties of materials and in electronic properties of polycrystalline semiconductors. Thus both the structure and its level of perfection provide a backdrop from which the behavior and properties of a material are understood, particularly, electronic materials.

Also in Chapter 4 another fundamental tenet of materials science is introduced and used liberally in following chapters. This tenet is the Boltzmann distribution from which both equilibrium thermodynamics and activation energies, or energy barriers, for processes can be understood. This concept is introduced by considering a simple two allowed state problem, and assessing how two energetically distinct states separated by a difference in energy, [DELTA]E, can be populated. The result is a familiar exponential term [e.sup.-[DELTA]E/kT] often referred to as the Boltzmann factor. However, in the field of chemical kinetics an Arrhenius factor with the same form as the Boltzmann factor is often discussed in relation to the velocity of chemical reactions, but the Arrhenius factor is often introduced without adequate discussion about its origin, or at best as an empirical result. The importance of this idea is such that it is introduced and discussed early in the text. Furthermore the laws of thermodynamics derive from the average or statistical nature of atoms or compounds that comprise a material. This statistical notion is crucial toward the understanding the average properties of a macroscopic piece of a material that contains a large number of atoms and/or molecules. Such thermodynamics properties include the phase of the material, the vapor pressure, and decomposition temperature. On the other hand, quantum mechanics may be required to understand the properties that depend on the specific interactions of atoms and/or molecules within a material such as the absorption or emission of light and the electronic and thermal conductivity.

1.4 DIFFUSION

In virtually all solid state reactions and transformation, matter moves; that is, atoms and/or molecules are transported to and from the reaction site. Often in the solid state that motion is by a random process, and such random processes are termed diffusive processes. Early in Chapter 5 on diffusion in solids the form for a variety of diffusion equations are compared, and it is observed that seemingly unrelated phenomena are governed by equations with the same form, namely there is a flux in response to a force. That flux (with units of amount/area * time) can be matter, heat, charge, energy, and so on. Even the famous Schroedinger equation of quantum mechanics (see Chapter 9) has the form of a diffusion equation. Although only mass diffusion is covered in Chapter 5, heat transport, for example, involves the solution of similar equations.

In the field of mass diffusion many treatments deal purely with the underlying physics that enable random matter transport, while other approaches deal exclusively with the mathematics of solving the differential diffusion equations. In Chapter 5 both areas are addressed. In addition another fundamental tenet in materials science is introduced, namely the random walk problem. While applied strictly to diffusion in this chapter, the random walk problem yields insight into how random processes can yield simple understandable results precisely because of the assumed randomness of the system. This is a powerful idea that helps hone the intuition of a materials scientist who must often deal with seemingly unsolvable problems involving randomness and complexity. In the field of electronic materials diffusion plays a central role that includes the transport of dopants, other point defects (vacancies and impurities, and electronic carrier diffusion in electronic and optical devices.

(Continues...)



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Table of Contents

Preface.

1 Introduction to Electronic Materials Science.

1.1 Introduction.

1.2 Structure and Diffraction.

1.3 Defects.

1.4 Diffusion.

1.5 Phase Equilibria.

1.6 Mechanical Properties.

1.7 Electronic Structure.

1.8 Electronic Properties and Devices.

1.9 Electronic Materials Science.

2 Structure of Solids.

2.1 Introduction.

2.2 Order.

2.3 The Lattice.

2.4 Crystal Structure.

2.5 Notation.

2.6 Lattice Geometry.

2.7 The Wigner-Seitz Cell.

2.8 Crystal Structures.

Related Reading.

Exercises.

3 Diffraction.

3.1 Introduction.

3.2 Phase Difference and Bragg’s Law.

3.3 The Scattering Problem.

3.4 Reciprocal Space, RESP.

3.5 Diffraction Techniques.

3.6 Wave Vector Representation.

Related Reading.

Exercises.

4 Defects in Solids.

4.1 Introduction.

4.2 Why Do Defects Form?

4.3 Point Defects.

4.4 The Statistics of Point Defects.

4.5 Line Defects—Dislocations.

4.6 Planar Defects.

4.7 Three-Dimensional Defects.

Related Reading.

Exercises.

5 Diffusion in Solids.

5.1 Introduction to Diffusion Equations.

5.2 Atomistic Theory of Diffusion: Fick’s Laws and a Theory for the Diffusion Construct D.

5.3 Random Walk Problem.

5.4 Other Mass Transport Mechanisms.

5.5 Mathematics of Diffusion.

Related Reading.

Exercises.

6 Phase Equilibria.

6.1 Introduction.

6.2 The Gibbs Phase Rule.

6.3 Nucleation and Growth of Phases.

Related Reading.

Exercises.

7 Mechanical Properties of Solids—Elasticity.

7.1 Introduction.

7.2 Elasticity Relationships.

7.3 An Analysis of Stress by the Equation of Motion.

7.4 Hooke’s Law for Pure Dilatation and Pure Shear.

7.5 Poisson’s Ratio.

7.6 Relationships Among E, e, and v.

7.7 Relationships Among E, G, and n.

7.8 Resolving the Normal Forces.

Related Reading.

Exercises.

8 Mechanical Properties of Solids—Plasticity.

8.1 Introduction.

8.2 Plasticity Observations.

8.3 Role of Dislocations.

8.4 Deformation of Noncrystalline Materials.

Related Reading.

Exercises.

9 Electronic Structure of Solids.

9.1 Introduction.

9.2 Waves, Electrons, and the Wave Function.

9.3 Quantum Mechanics.

9.4 Electron Energy Band Representations.

9.5 Real Energy Band Structures.

9.6 Other Aspects of Electron Energy Band Structure.

Related Reading.

Exercises.

10 Electronic Properties of Materials.

10.1 Introduction.

10.2 Occupation of Electronic States.

10.3 Position of the Fermi Energy.

10.4 Electronic Properties of Metals: Conduction and Superconductivity.

10.5 Semiconductors.

10.6 Electrical Behavior of Organic Materials.

Related Reading.

Exercises.

11 Junctions and Devices and the Nanoscale.

11.1 Introduction.

11.2 Junctions.

11.3 Selected Devices.

11.4 Nanostructures and Nanodevices.

Index.

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"...very worthwhile text to learn advanced material science theories that are focused on electronic materials." (IEEE Electrical Insulation Magazine, May/June 2006)

"…the book is written well with good quality figures…" (Journal of Metals Online, July 29, 2005)

“…a good treatment of…materials science…brings together key aspects of applied physics, chemistry and mechanical engineering…” (Journal of Materials Technology, Vol 20 (3) 2005)

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