Dielectric Phenomena in Solids

Kwan Chi Kao

• Publisher: Academic Press
• Year: 2004
• Print ISBN:
  9780123965615
• eBook ISBN:
  9780080470160
• Topic: Technology & Engineering
• Subtopic: Electromagnetism
• Index: Technology & Engineering

In general, a dielectric is considered as a non-conducting or insulating material (such as a ceramic or polymer used to manufacture a microelectronic device). This book describes the laws governing all dielectric phenomena.·A unified approach is used in describing each of the dielectric phenomena, with the aim of answering "what?", "how?" and "why" for the occurrence of each phenomenon;·Coverage unavailable in other books on ferroelectrics, piezoelectrics, pyroelectrics, electro-optic processes, and electrets;·Theoretical analyses are general and broadly applicable;·Mathematics is simplified and emphasis is placed on the physical insight of the mechanisms responsible for the phenomena;·Truly comprehensive coverage not available in the current literature.

1

Introduction

Learning without thought is labor forgone; thought without learning is perilous.

Confucius (600 BC)

The basic distinction between a semiconductor and a dielectric (or insulator) lies in the difference in the energy band gap. At the normal ranges of temperatures and pressures, the dominant charge carriers in a semiconductor are generated mainly by thermal excitation in the bulk because the semiconductor has a small energy band gap; hence, a small amount of energy is sufficient to excite electrons from full valence band to an upper empty conduction band. In a dielectric, charge carriers are mainly injected from the electrical contacts or other external sources simply because a dielectric’s energy band gap is relatively large, so a higher amount of energy is required for such band-to-band transitions. A material consists mainly of atoms or molecules, which comprise electrons and nuclei. The electrons in the outermost shell of atoms, bound to the atoms or molecules coupled with the free charges, interact with external forces, such as electric fields, magnetic fields, electromagnetic waves, mechanical stress, or temperature, resulting in the occurrence of all dielectric phenomena. For nonmagnetic dielectric materials, the dielectric phenomena include mainly electric polarization; resonance; relaxation; energy storage; energy dissipation; thermal, mechanical, and optical effects and their interrelations; and electrical aging and destructive breakdown. The discussion of these phenomena is the scope of this book.

Dielectric phenomena, like other natural phenomena, were noticed long before the time of Christ. As early as 600 BC, the Greek philosopher Thales discovered that amber, when rubbed with cloth, attracted light objects such as bits of chaff. In Greek, “amber” was referred to as electricity. However, it is now well known that many substances possess this property to some extent. A glass or metal rod, after being rubbed with a polyester sheet, will attract a light piece of paper. This attraction phenomenon may be considered due to the charge on the rod tip polarizing the paper nearby. The electric polarization produces an opposite charge on the paper surface close to the charged rod tip, resulting in this attraction. Any electromagnetic wave will induce polarization in dielectric materials and magnetization in magnetic materials. Both the polarization and the magnetization also produce their own fields, which interact with the external fields, resulting in a vast scope of dielectric and magnetic phenomena.

However, dielectric phenomena did not receive much attention until the middle of the 18th century, although the Leyden jar condenser, which could store charges, was discovered in 1745 by the Dutch physicist van Musschenbrack, of the University of Leyden.¹ About 90 years later (in 1837) Faraday, in England, was the first to report² that the capacitance of a condenser was dependent on the material inside the condenser. At that time, he called the ratio of the capacitance of the condenser filled with a dielectric material to that of the same condenser, empty inside (free space), the specific inductive capacity, which is now called the permittivity. In 1873, following the discovery of Coulomb’s law on forces between charges, Ohm’s law on electrical conductivity, Faraday’s law, and Ampère’s law on magnetic and electric induction, Maxwell³ welded these discoveries together to formulate a unified approach. He developed four equations, known as Maxwell’s equations, to govern all the macroscopic electromagnetic phenomena. Obviously, dielectric phenomena are part of the electromagnetic phenomena, which result from the interaction of the material with electromagnetic fields. Therefore, it is very important to understand the meaning of these four equations.

1.1 Maxwell’s Equations

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Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• Preface
• Chapter 1: Introduction
• Chapter 2: Electric Polarization and Relaxation
• Chapter 3: Optical and Electro-Optic Processes
• Chapter 4: Ferroelectrics, Piezoelectrics, and Pyroelectrics
• Chapter 5: Electrets
• Chapter 6: Charge Carrier Injection from Electrical Contacts
• Chapter 7: Electrical Conduction and Photoconduction
• Chapter 8: Electrical Aging, Discharge, and Breakdown Phenomena
• Index