Chapter 18 - Part II: Functional Properties of Materials...

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Part II: Functional Properties of Materials Chapters 18,19.
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2 Electrical Properties of Solids (Chapter 18)
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3 What you should understand by the end of this chapter: The physical basis for electrical conductivity in metals, semiconductors and ceramics. This involves band theory. The effect of temperature on conductivity for each class of material. The importance of pure Si to semiconductor technology. The role of dopants in semiconductors.
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4 Examples Devices requiring specific properties: Magnetic latches Electronic devices Optical fibers Precision positioning devices Computer chips Thermal tiles
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5 www.memx.com mems.colorado.edu/c1.gen.intro/mems.shtml MEMS Devices M icro E lectro M echanical S ystems A new technology for producing superminiature mechanical devices (motors and sensors). Silicon devices mass produced like integrated circuits MEMS device used as a sensor: Becomes integral part of an integrated circuit Programmed to make decisions based on conditions sensed
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6 Bell Labs MEMS Mirror Array An array of 256 microscopic mirrors. Each mirror is the size of the head of a pin. The mirrors tilt to steer lightwave signals from one optical fibre to another.
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7 Example: Power Mac G5 Electronic Devices
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Venturing deeper…
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Semiconductors The Brains of the Operation
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10 Making it Possible
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11
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12 The race for faster chips Graph: Intel website: presentation “towards the 65nm node” , Yokohama Japan
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13 Fundamentals Ohm’s Law: V = I R or J = σ ε Resistance ( R ) depends on the configuration of the system. The related material property is resistivity ( ρ ). Conductivity is related to resistivity: A l R = ρ ρ σ 1 =
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14 Conduction Mechanisms Electronic Flow of electrons (or holes) This dominates in most electronic device applications. Ionic Diffusion of charged ions This is important for high temperature and specialized devices. e.g. fuel cells
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15 Band Structure Electronic conduction Depends strongly on how electrons fill orbitals in an atom band structure Pauli exclusion principle Each electron occupies an independent state isolated atoms orbital states solid (many atoms) energy bands
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16 Band Structure Simple picture of band structure Think of a solid with N atoms: s shell N states (2 electrons / state) p shell 3 N states d shell 5 N states
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17 Conductor or Insulator? Whether or not a material is a conductor or an insulator depends on the outermost shell of its atoms. There are four main possibilities: Fermi energy E F energy of the last filled state at 0 K If a band is partially full or bands overlap conductor . If the valence band is full and the conduction band is empty insulator or semiconductor.
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This note was uploaded on 03/03/2011 for the course MATLS 101 taught by Professor Dr.kish during the Spring '11 term at McMaster University.

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Chapter 18 - Part II: Functional Properties of Materials...

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