201%20Week%203%202008%20Posted

201%20Week%203%202008%20Posted - Chapter 18 - 1 ISSUES TO...

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Unformatted text preview: Chapter 18 - 1 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, T , and deformation? For semiconductors, how is conductivity affected by impurities (doping) and T ? Chapter 18: Electrical Properties Chapter 18 - 2 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. Fig. (a), (b), (c) from Fig. 18.0, Callister 7e . Fig. (d) from Fig. 18.27 (a), Callister 7e . (Fig. 18.27 is courtesy Nick Gonzales, National Semiconductor Corp., West Jordan, UT.) (b) (c) View of an Integrated Circuit 0.5 mm (a) (d) 45 m Al Si (doped) (d) Chapter 18 - 3 Electrical Conduction Resistivity, and Conductivity, : -- geometry-independent forms of Ohm's Law E : electric field intensity resistivity (Ohm-m) J : current density conductivity -- Resistivity is a material property & is independent of sample Resistance: Ohm's Law: V = I R voltage drop (volts = J/C) C = Coulomb resistance (Ohms) current (amps = C/s) I e- A (cross sect. area) V L Chapter 18 - 4 Electrical Properties Which will conduct more electricity? Analogous to flow of water in a pipe So resistance depends on sample geometry, etc. D 2 D Chapter 18 - 5 Definitions Further definitions J = <= another way to state Ohms law J current density electric field potential = V / or ( V / ) Current carriers electrons in most solids ions can also carry (particularly in liquid solutions, and in some solids with ionic bonds) Electron flux conductivity voltage gradient J = ( V / ) 6 Classical Model of Electronic Conduction in Metals n conduction electrons/volume Apply electric field E to give electron accel. of eE/m , where m = electron mass Assume = average time between collisions v d = eE m J = nev d = ne 2 m E Drift velocity Current density 7 Classical Model of Electronic Conduction in Metals = ne 2 m = ne e m = ne For most metals, the conductivity decreases about 0.4% per K. This property is used for temperature measurements. = mobility Chapter 18 - 8 Room T values (Ohm-m) -1 Selected values from Tables 18.1, 18.3, and 18.4, Callister 7e . Conductivity: Comparison Silver 6.8 x 10 7 Copper 6.0 x 10 7 Iron 1.0 x 10 7 METALS conductors Silicon 4 x 10-4 Germanium 2 x 10 GaAs 10-6 SEMICONDUCTORS semiconductors = ( - m)-1 Polystyrene <10-14 Polyethylene 10-15-10-17 Soda-lime glass 10 Concrete 10-9 Aluminum oxide <10-13 CERAMICS POLYMERS insulators -10 -10 -11 Chapter 18 - 9 What is the minimum diameter ( D ) of the wire so that V < 1.5 V?...
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This note was uploaded on 11/21/2011 for the course MAT SCI 201 taught by Professor Matsci during the Spring '10 term at Northwestern.

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201%20Week%203%202008%20Posted - Chapter 18 - 1 ISSUES TO...

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