Physical Properties New

7/31/2019 Physical Properties New

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Physical properties


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Physical properties

ISSUES TO ADDRESS...

How are electrical conductance and resistance

characterized?

1

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?

ELECTRICAL PROPERTIES


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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.

0.5mm45m

Al

Si(doped)

Fig. (a), (b), (c) from Fig. 18.0,

Callister 6e.

Fig. (d) from Fig. 18.25, Callister 6e. (Fig. 18.25 is courtesy

Nick Gonzales, National Semiconductor Corp., West Jordan,

UT.)

(a)

(b)

(c)

(d)

VIEW OF AN INTEGRATED CIRCUIT


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Ohm's Law:DV = I R

voltage drop (volts) resistance (Ohms)

current (amps)

Resistivity, r and Conductivity, s:

--geometry-independent forms of Ohm's Law

DV

L

I

Ar

E: electric

fieldintensity

resistivity

(Ohm-m)J: current density

s I

r

conductivity

Resistance: R rL

A

L

As

ELECTRICAL CONDUCTION


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Room T values (Ohm-m) -1

Selected values from Tables 18.1, 18.2, and 18.3, Callister 6e.

CONDUCTIVITY: COMPARISON


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Question 18.2, p. 649, Callister 6e:

What is the minimum diameter (D) of the wire so that

DV < 1.5V?

R L

As

DV

I

< 1.5V

2.5A

6.07 x 10 (Ohm-m)7 -1D

2

4

100m

Solve to get D > 1.88 mm

EX: CONDUCTIVITY PROBLEM


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Metals:

-- Thermal energy puts

many electrons into

a higher energy state.

Energy States:

-- the cases below

for metals showthat nearby

energy states

are accessible

by thermal

fluctuations.

CONDUCTION & ELECTRON TRANSPORT


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Insulators:--Higher energy states not

accessible due to gap.

Semiconductors:--Higher energy states

separated by a smaller gap.

ENERGY STATES: INSULATORS AND

SEMICONDUCTORS


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Imperfections increase resistivity

--grain boundaries

--dislocations

--impurity atoms

--vacancies

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These act to scatter

electrons so that they

take a less direct path.

Resistivity

increases with:--temperature

--wt% impurity

--%CW

r rthermal

rthermal

rdefAdapted from Fig. 18.8, Callister 6e. (Fig. 18.8 adapted from J.O. Linde,

Ann. Physik5, p. 219 (1932); and C.A. Wert and R.M. Thomson, Physics of

Solids, 2nd ed., McGraw-Hill Book Company, New York, 1970.)

METALS: RESISTIVITY VS T, IMPURITIES


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Question:

--Estimate the electrical conductivity of a Cu-Ni alloythat has a yield strength of 125MPa.

r 30x108 Ohm m

s

1

r 3.3x106 (Ohm m)1

Adapted from Fig.

18.9, Callister 6e.

Adapted from Fig.

7.14(b), Callister 6e.

EX: ESTIMATING CONDUCTIVITY


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Data for Pure Silicon:

--s increases with T--opposite to metals

sundoped eEgap / kT

electrons

can cross

gap at

higher T

material

Si

Ge

GaP

CdS

band gap (eV)

1.11

0.67

2.25

2.40

Adapted from Fig. 19.15, Callister 5e. (Fig. 19.15 adapted

from G.L. Pearson and J. Bardeen, Phys. Rev. 75, p. 865,

1949.)

Selected values from Table

18.2, Callister 6e.

PURE SEMICONDUCTORS: CONDUCTIVITY VS T


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Electrical Conductivity given by:

s ne e p e h

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# electrons/m 3 electron mobility

# holes/m 3

hole mobility

Concept of electrons and holes:

Adapted from Fig. 18.10,

Callister 6e.

CONDUCTION IN TERMS OF

ELECTRON AND HOLE MIGRATION


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Intrinsic:

# electrons = # holes (n = p)

--case for pure Si

Extrinsic:

--n p

--occurs when impurities are added with a different

# valence electrons than the host (e.g., Si atoms) N-type Extrinsic: (n >> p) P-type Extrinsic: (p >> n)

s n e e s p e h

no appliedelectric field

5+4+ 4+ 4+ 4+

4+

4+4+4+4+

4+ 4+

Phosphorus atom

no appliedelectric field

Boron atom

valenceelectron

Si atom

conductionelectron

hole

3+4+ 4+ 4+ 4+

4+

4+4+4+4+

4+ 4+

INTRINSIC VS EXTRINSIC CONDUCTION


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Data for Doped Silicon:

--s increases doping--reason: imperfection siteslower the activation energy to

produce mobile electrons.

Adapted from Fig. 19.15, Callister 5e. (Fig. 19.15 adapted

from G.L. Pearson and J. Bardeen, Phys. Rev. 75, p. 865,

1949.)

Comparison: intrinsic vs

extrinsic conduction...--extrinsic doping level:

1021/m3 of a n-type donor

impurity (such as P).

--for T < 100K: "freeze-out"

thermal energy insufficient to

excite electrons.--for 150K < T < 450K: "extrinsic"

--for T >> 450K: "intrinsic"

Adapted from Fig. 18.16,

Callister 6e. (Fig. 18.16

from S.M. Sze,

Semiconductor Devices,

Physics, and Technology,

Bell Telephone

Laboratories, Inc., 1985.)

DOPED SEMICON: CONDUCTIVITY VS T


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Allows flow of electrons in one direction only (e.g., usefulto convert alternating current to direct current.

Processing: diffuse P into one side of a B-doped crystal.

Results:

--No applied potential:

no net current flow.

--Forward bias: carrier

flow through p-type and

n-type regions; holes and

electrons recombine at

p-n junction; current flows.

--Reverse bias: carrier

flow away from p-n junction;

carrier conc. greatly reduced

at junction; little current flow.

P-N RECTIFYING JUNCTION


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ISSUES TO ADDRESS...

How do we measure magnetic properties?

1

What are the atomic reasons for magnetism?

Materials design for magnetic storage.

How are magnetic material classified?

MAGNETIC PROPERTIES


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Created by current through a coil:

Relation for the applied magnetic field, H:

H NI

L

applied magnetic fieldunits = (ampere-turns/m)

current

APPLIED MAGNETIC FIELD


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Magnetic induction results in the material

current I

B = Magnetic Induction (tesla)

inside the material

Magnetic susceptibility, c (dimensionless)

c measures thematerial responserelative to a vacuum.

RESPONSE TO A MAGNETIC FIELD


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Measures the response of electrons to a magneticfield.

Electrons produce magnetic moments:

magnetic moments

electron

nucleus

electron

spin

Net magnetic moment:

--sum of moments from all electrons. Three types of response...

Adapted from Fig. 20.4,Callister 6e.

MAGNETIC SUSCEPTIBILITY


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B (1 c)oH

permeability of a vacuum:(1.26 x 10-6 Henries/m)

Plot adapted from Fig. 20.6, Callister 6e. Values andmaterials from Table 20.2 and discussion in Section

20.4, Callister 6e.

3 TYPES OF MAGNETISM


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Adapted from Fig.20.5(a), Callister 6e.

Adapted from Fig.20.5(b), Callister 6e.


MAGNETIC MOMENTS FOR 3 TYPES


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As the applied field (H) increases...

--the magnetic moment aligns with H.

Adapted from Fig. 20.13,Callister 6e. (Fig. 20.13adapted from O.H.Wyatt and D. Dew-Hughes, Metals,

Ceramics, andPolymers, CambridgeUniversity Press, 1974.)

FERRO- & FERRI-MAGNETIC MATERIALS


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large coercivity--good for perm magnets--add particles/voids to

make domain wallshard to move (e.g.,tungsten steel:Hc = 5900 amp-turn/m)

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Process:

Hard vs Soft Magnets

Applied Magnetic

Field (H)

B

Hard

Soft

Hard

small coercivity--good for elec. motors(e.g., commercial iron 99.95 Fe)


Adapted from Fig. 20.16,Callister 6e. (Fig. 20.16 fromK.M. Ralls, T.H. Courtney, andJ. Wulff, Introduction toMaterials Science andEngineering, John Wiley andSons, Inc., 1976.)

PERMANENT MAGNETS


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Information is stored by magnetizing material.

recording head

recording medium

Simulation of hard drivecourtesy Martin Chen.Reprinted with permissionfrom International BusinessMachines Corporation.

Head can...

--apply magnetic field H &align domains (i.e.,magnetize the medium).

--detect a change in themagnetization of the

medium.

Two media types:

--Particulate: needle-shaped

g-Fe2O3. +/- mag. moment

along axis. (tape, floppy)

~2.5 m

--Thin film: CoPtCr or CoCrTaalloy. Domains are ~ 10-30nm!

(hard drive)

Adapted from Fig. 20.18, Callister 6e.(Fig. 20.18 from J.U. Lemke, MRSBulletin, Vol. XV, No. 3, p. 31, 1990.)

Adapted from Fig.20.19, Callister 6e.(Fig. 20.19courtesy P. Raynerand N.L. Head, IBMCorporation.)

Adapted from Fig. 20.20(a),Callister 6e. (Fig. 20.20(a)from M.R. Kim, S.Guruswamy, and K.E.Johnson, J. Appl. Phys.,Vol. 74 (7), p. 4646, 1993. )

MAGNETIC STORAGE

Physical Properties New

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