Introduction to Materials Science and Engineering Chapter 10: Electrical Properties Textbook Chapter 19

Content Introduction Electrical Conduction Semiconductivity Electrical Conduction in Ionic Ceramics and in Polymers 5. Dielectric Behavior Other Electrical Characteristics of Materials Electronic Devices and Fabrication

Introduction ISSUES TO ADDRESS... • How are electrical conductance and resistance characterized? • What are the physical phenomena that distinguish conductors, semiconductors, and insulators? • For metals, how is conductivity affected by imperfections, temperature, and deformation? • For semiconductors, how is conductivity affected by impurities (doping) and temperature?

Content Introduction Electrical Conduction Semiconductivity Electrical Conduction in Ionic Ceramics and in Polymers 5. Dielectric Behavior Other Electrical Characteristics of Materials Electronic Devices and Fabrication

View of an Integrated Circuit • Scanning electron microscope images of an IC: • A dot map showing location of Si (a semiconductor): --Si shows up as light regions. • A dot map showing location of Al (a conductor): --Al shows up as light regions.

Electrical Conduction Ohm’s Law

Electrical Conductivity

Important Unit

Electronic vs. Ionic charge carrier electron (e=1.602x10-19 C) electron/hole cation anion

Energy Band:

Band Structure of Solids Valence band - The energy levels filled by electrons in their lowest energy states. Conduction band - The unfilled energy levels into which electrons can be excited to provide conductivity. Holes - Unfilled energy levels in the valence band. Because electrons move to fill these holes, the holes move and produce a current. Energy gap (Bandgap) - The energy between the top of the valence band and the bottom of the conduction band that a charge carrier must obtain before it can transfer a charge.

Energy Band

Formation of Energy Band

Energy Band of Na

Metal, Semiconductor, Insulator Metal Insulator Semiconductor Ex) Cu (3d104s1) Mg(3s2) > 2eV < 2eV

Energy band for Conductor

Conduction in terms of Band and Atomic Bonding Models metals insulators and semiconductors

Electron Mobility Drift Velocity

Electron Mobility conductivity For metals

Electrical Resistivity of Metals thermal scattering impurity scattering defect scattering

Electrical Resistivity of Metals temperature impurities

Content Introduction Electrical Conduction Semiconductivity Electrical Conduction in Ionic Ceramics and in Polymers 5. Dielectric Behavior Other Electrical Characteristics of Materials Electronic Devices and Fabrication

Semiconductor Intrinsic semiconductor - A semiconductor in which properties are controlled by the element or compound that makes the semiconductor and not by dopants or impurities. Extrinsic semiconductor - A semiconductor prepared by adding dopants, which determine the number and type of charge carriers. Doping - Deliberate addition of controlled amounts of other elements to increase the number of charge carriers in a semiconductor. Thermistor - A semiconductor device that is particularly sensitive to changes in temperature, permitting it to serve as an accurate measure of temperature. Radiative recombination - Recombination of holes and electrons that leads to emission of light; this occurs in direct bandgap materials.

Intrinsic Semiconductors

Intrinsic Semiconductors

Intrinsic Semiconductors

Intrinsic Semiconductors

Intrinsic Semiconductors

Extrinsic Semiconductors • Intrinsic: # electrons = # holes (n = p) • Extrinsic: --n ≠ p • N-type Extrinsic: (n >> p) • P-type Extrinsic: (p >> n)

N-type Semiconductors 60

N-type Semiconductors

N-type Semiconductors

P-type Semiconductors

P-type Semiconductors

P-type Semiconductors

Temperature Dependence of Mobility

Temperature Dependence of Mobility

Hall Effect B=1kG wc=2.8GHz

Hall Effect

Hall Effect

Semiconductor Devices p-n junction

Semiconductor Devices transistor

Semiconductor Devices Junction transistor MOSFET

Growth of Si crystal

IC Fabrication Process

Content Introduction Electrical Conduction Semiconductivity Electrical Conduction in Ionic Ceramics and in Polymers 5. Dielectric Behavior Other Electrical Characteristics of Materials Electronic Devices and Fabrication

Ionic Conduction nI: charge of ions

Conducting Polymer temperature dependence of the conductivity similar to that of semiconductor polymer- semicrystalline  require modification of band model polyacetylene-prototype of a conducting polymer (conjugated organic polymer-alternating single and double bonds between carbons)

Conducting Polymer conductivity p-electrons in the double bond act as a carrier

Content Introduction Electrical Conduction Semiconductivity Electrical Conduction in Ionic Ceramics and in Polymers 5. Dielectric Behavior Other Electrical Characteristics of Materials Electronic Devices and Fabrication

Dielectric Capacitance Capacitance ( ,F) e0:permittivity of a vacuum e:permittivity of the medium er:relative permittivity (dielectric constant) where, e=ere0

Polarization Electric dipole moment

dielectric displacement Polarization Surface charge density D, or quantity of charge per unit area is expressed as, (C/m2) dielectric displacement dipole

Polarization ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.

Types of Polarization Electronic Polarization (Pe) Ionic Polarization (Pi) Orientation Polarization (Po)

Frequency Response Dielectric Strength Dielectric Materials

Content Introduction Electrical Conduction Semiconductivity Electrical Conduction in Ionic Ceramics and in Polymers 5. Dielectric Behavior Other Electrical Characteristics of Materials Electronic Devices and Fabrication

Ferroelectricity BaTiO3 Rochelle salt(NaKC4H4O6·4H2O) KH2PO4 KNbO3 PZT

Piezoelectricity PbZrO3 NH4H2PO4 Quartz ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.

Summary • Electrical conductivity and resistivity are: -- material parameters. -- geometry independent. • Electrical resistance is: -- a geometry and material dependent parameter. • Conductors, semiconductors, and insulators... -- differ in accessibility of energy states for conductance electrons. • For metals, conductivity is increased by -- reducing deformation -- reducing imperfections -- decreasing temperature. • For pure semiconductors, conductivity is increased by -- increasing temperature -- doping (e.g., adding B to Si (p-type) or P to Si (n-type).