Electronic Materials [제 18장 전자재료]
Homepage: http://home.pusan.ac.kr/~yescho 강의 보조자료
Chapter 18. Electronic materials
1. 플라스틱을 이용해서 flexible 전자회로를 만들 수 있는가?
2. MRI용 강력한 전자석을 만들기 위해 어떤 재료가 사용되나?
3. 도체와 초전도체의 차이는 무엇인가?
4. 극초단파는 어떻게 음식을 가열시키는가?
5. 가스그릴의 점화장치는 어떻게 작동하는가?
6. 세라믹은 반도체나 초전도체가 될 수 있는가?
Have You Ever Wondered?
Electronic materials의 기술적 분류
전자재료의 4가지 종류?
Dielectrics vs. Insulator?
[Fig. 18-1]
Ohm’s Law
Electrical Power
Current Density
A l A R l
IR V
ρ =σ
=
=
18.1 Ohm’s Law & Electrical Conductivity
• Resistance and conductance depend on the dimensions, microstructure and compositions.
• Resistivity and conductivity are not depend on the dimensions.
• Resistivity is microstructure sensitive property
ex) Bulk and thin film BaTiO
3:
microstructure, chemical homogeneity, presence of pores, magnitude of applied electric field, and so on.
R I VI
P = = 2 A l A
R l
IR V
ρ = σ
=
=
2
1 µ
µ σ
µ σ
σ σ
σ
⋅
⋅ +
⋅
⋅
=
⋅
⋅
=
=
⋅
⋅
=
=
=
q n q
n q n
E nq v
v q n J
E J
l V A
I
Application of Superconductors
(a) Charge carriers, such as electrons, are deflected by atoms or defects and take an irregular path through a conductor. The
average rate at which the carrier move is the drift velocity v.
(b) Valence electrons in the metallic bond
move easily.
(c) Covalent bonds must be broken in
semiconductors and insulator for an electron to be able to move.
(d) Entire ions must diffuse to carry charge in many ionically bonded materials.
σ = n e µ (18-15a) [Fig. 18-2]
18.1 Ohm’s Law & Electrical Conductivity
Conductivity σ의 범위??
18.1 Ohm’s Law & Electrical Conductivity
18.1 Ohm’s Law & Electrical Conductivity
1. 1 eV의 의미?
2. 1J의 에너지란? [energy=work]
: 1 N∙m
: 1 Kg∙m2/s2 (MKS 단위) [Force F= ma, 1N = 1Kg m/s2 ] : (1000g)∙(100cm)2/s2 = 105 dyn∙100cm (cgs 단위) = 107 erg 3. 1 Kg의 물체가 1m/s의 속도로 움직일 때의 에너지?
= ½ mV2 = ½ Kg(m2/s2) = ½ N∙m = ½ J 4. J과 A와 V의 상관관계
:1 J 이란? =1V의 전압을 걸어서 1A의 전류를 1초 동안 흘렸을 경우의 에너지
5. 1 A란?
: 1C의 전기량이 1초 동안 흐르는 양
: 전자 1개가 가지고 있는 전기량은? (1.6x10-19C)
∴ 1A = 6.2 x 1018개의 전자가 1초 동안에 흐르는 전기량.
6. 1V의 전압에서 1A의 전류를 1초 동안에 흘렸을 경우, 전자 1개에 대한 에너지는?
: 1J / (6.2x1018)= 1.6x10-19J = 1 eV
7. 지금까지 알고 있는 상식으로 지구의 지름을 구해보세요 : ( ? ) Km
숙제 : Example 18-1, 2, 3 다음주 이 시간 수업 시작 이전까지 제출요망
18.1 Ohm’s Law & Electrical Conductivity
18.2 Band Structure of Solids
Quantum mechanics for atomic orbitals : shape and energy of atomic orbitals determined by the 4 quantum number.
1. n – principal quantum number (Size) : n↑, energy ↑, distance from nucleus ↑
2. l – orbital quantum number : determines shapes of orbitals
3. m
e– magnetic quantum number 4. s – spin quantum number
Pauli exclusive principle : no two electrons can have the same
quantum number.
The energy levels broaden into bands as the number of electrons grouped together increases [in solid].
[Fig. 18-3]
18.2 Band Structure of Solids
The simplified band structure for sodium(Na=11).
[Electronic structure: 1s
22s
21p
63s
1The energy levels broadens into
bands.
The 3s band, which is only half filled with electrons, is
responsible for conductor in sodium.
그림 18-4에서 Valence band와 conduction band를 정의하시오!!
[Fig. 18-4]
18.2 Band Structure of Solids
(a) At absolute zero, all of the electrons in the outer energy level have the lowest possible energy.
(b) When the temperature is increased, some electrons are excited into unfilled levels. Note that the Fermi energy is unchanged.
hole fully filled e-
Fermi Energy Ef를 정의하시오!!
[Fig. 18-5]
18.2 Band Structure of Solids
Band Structure of Magnesium and Other Metals [bivalent metal]
Magnesium and other metals in of the periodic table have two elections in their outermost s band.
Highly conductive due to the overlapping of p band and s band at equilibrium inter atomic spacing.
Overlapping 3s and 3p bands in aluminum and other metals in column 3B provide a similar effect.
Transition metals : Overlapping of unfilled 3d band and 4s band
Complex interactions between the bands prevent the conductivity from being as high as in some of the better conductors.
– However, for the inner 3d band is completely filled;
– ex) Copper, silver, gold ; little interaction between 3d and 4s good conductivity!!
18.2 Band Structure of Solids
Band structure of semiconductors and insulators [Group 4]
Covalently bonded electrons in the outer S and P are rigidly bound to the atoms Hybridization produce two bands with
energy gap between valence and conduction bands.
(The valence band is completely filled and the conduction band is empty)
Temperature dependant of conductivity Metals : n is constant with temperature
Semiconductors :
Insulators :
↓
↓
↑ µ thenσ T , ,
↑
↑↑
↓
↑ µ n thenσ
T , , ,
↑
↑
↑ µ thenσ T , ,
The band structure of carbon in the diamond form.
The 2s and 2p levels combine to form two hybrid bands separated by an energy gap, Eg.
[Fig. 18-6]
18.2 Band Structure of Solids
각각의 band는 4N electrons 만 가질 수 있음.
In chemistry, the mixing of atomic orbitals to form new orbitals suitable for bonding (Orbital hybridisation) ; 혼성 오비탈
Schematic of band structure for (a) metals, (b) semiconductors, (c) dielectrics or insulators.( Temperature is 0 K.)
Metal, Semiconductor, Insulator를 구분해서 설명하시오!! What about Si, Ag ??
[Fig. 18-7]
18.2 Band Structure of Solids
The conductivity of a pure, defect-free metals is determined by the electronic structure of the atoms.
But, the conductivity is influenced by the mobility of the carriers.
Mean free path : average distance between collisions.
Temperature effect : ρ = ρRT (1+ αR∆T)
18.3 Conductivity of Metals and Alloys
ν τ λ
e =Movement of an electron through (a) a perfect
crystal, (b) a crystal heated to a high temperature, and (c) a crystal containing atomic level defects.
Scattering of the electrons reduces the mobility and
conductivity.
[Fig. 18-8]
Conductivity 지배인자 중 mobility에 미치는 요소는 ??
The effect of temperature on the electrical resistivity of a metal with a perfect crystal structure. The slope of the curve is the temperature resistivity
coefficient (αR).
[Fig. 18-9]
18.3 Conductivity of Metals and Alloys
Lattice vibration 효과!!!
18.3 Conductivity of Metals and Alloys
The electrical resistivity of a metal is composed of a constant defect contribution ρd and a variable temperature contribution ρT.
[Fig. 18-10]
18.3 Conductivity of Metals and Alloys
Effect of processing and strengthening
– Solid-solution strengthening ; mean free paths are very short due to the random distribution of the interstitial or substitutional atoms.
– Age hardening and dispersion strengthening ; reduce the condu ctivity to an extent that is less than solid-solution strengthening.
– Strain hardening and grain-size control; less effect on conductivity.
– ex) cold working is an effective way to increase the strength of a metallic conductor without seriously impairing the electrical properties.
Conductivity of alloys
– Ordering of atoms in alloys by heat treatment can decrease their resistivity
– Less temperature effect compare to that of the pure metals; heating element.
18.3 Conductivity of Metals and Alloys
(a) The effect of solid-solution strengthening and cold working on the electrical conductivity of copper.
(b) the effect of addition of selected elements on the electrical conductivity of copper.
[Fig. 18-11]
18.3 Conductivity of Metals and Alloys
Conductivity 지배인자 중 mobility에 미치는 요소는 ??
σ = n e µ (18-15a)
18.3 Conductivity of Metals and Alloys
금속과 alloy에서 Conductivity 핵심 지배인자는? Mobility !!!
18.4 Superconductivity
Superconductor is a material that exhibits zero electrical resistance under certain conditions and expels a magnetic field completely.
Superconductivity in materials disappears above a certain temperature known as the critical temperature (Tc).
Superconductivity also disappears when a certain level of magnetic field is present.
Critical current density (Jc); superconductor cannot carry an infinite amount of current even at zero magnetic field – grain boundaries and grain orientation or texture are very important. Defects such as pores or second phase also can block the supercurrent.
Many applications of superconductors :
power transmission line, electronic circuits, MRI(강력한 전자석), etc.
Superconductor를 정의하고 주요 응용사례 2가지에 대해서 논하시오.
The electrical resistivity of a superconductor becomes zero below some critical temperature Tc .
[Fig. 18-12]
18.4 Superconductivity
연구의 방향: High Tc
현재의 경우: Tc는 대략 액체질소 온도
[Fig. 18-13]
18.4 Superconductivity
Superconductivity를 파괴시키는 방법: 높은 온도 혹은 높은 자기장
18.4 Superconductivity
TEM of carbon nanotube (CNT) Two carbon nanotubes that are bent considerably
The ends of these nanotubes were “welded”
using a nanomanipulator in the TEM Those materials are promising for
microelectronics and other applications
[Fig. 18-14]
18.4 Superconductivity
Application of Superconductors
Superconductor의 application에 대해서 설명!!
- Electrical applications:
대표적인 superconductor의 Tc는 얼마인가?
Conduction in ionic materials often occurs by movement of entire ions:
Examples of Ionically Conductive Oxide
ITO : Transparent oxide electrode
YSZ : Solid electrolyte
Lithium cobalt oxide : Solid electrolyte
18.5 Conduction in Ionic Materialsµ σ
µ
nZq T K
ZqD
B
=
= ⋅
온도 T의 상승은 ionic materials에서 conductivity에 어떤 영향을 줄까 ? Example 18-6 참조: ionic Conduction in MgO
Diffusion!!!
Polymers have a band structure with a large energy gap due to the covalent bonding characteristics.
Polymer-matrix composites can reduce resistivity.
Conducting polymers (2000 Novel Prize) ; Doping, cross-link, etc.
Effect of carbon fibers on the electrical resistivity of nylon.
[Fig. 18-15]
18.5 Conduction in Ionic Materials
숙제 : Example 18-4, 5, 6 다음주 이 시간 수업 시작 이전까지 제출요망
* Carbon fiber의 기능: conductive filler
18.6 Semiconductors
Intrinsic semiconductor is one whose properties are not controlled by impurities or dopants. [순수한 재료]
Extrinsic semiconductor is preferred for devices since its properties are temperature stable and can be controlled using ion implantation or diffuse of dopants. [도핑하는 이유 conductivity 증가]
– Elemental Semiconductor: Si, Ge – Compound Semiconductor
• Ⅱ-Ⅳ: CdS, CdSe, CdTe, HgCdTe, etc.
• Ⅲ-Ⅴ: GaW, GaAs, AlAs, AlP, InP, etc.
– Oxide Semiconductor: ZnO+Zn – Organic Semiconductor
Application : switches, amplifiers, information storage devices.
