[半導體元件概論-2009]
3.
雙極性接面電晶體
(Bipolar Junction Transistor, BJT)
王水進 教授
成大電機系 微電子研究所
1
The first Transistor
[S. M. Sze, Semiconductor Device Physics and Technology, John Wiley, 1985]
Emitter
Collector
Base
2
1
雙極性電晶體發明人
The discovery of the point
contact transistor in 1947
This work resulted in their
receiving the Nobel Prize
for Physics in 1956.
[http://www.att.com/technology/history/chronolog/47transistor.html]
3
典型BJT封裝
[Earl D. Gates, Introduction to electronics, 4/e, Delmar, Thomson Learning Inc., 2001 ]
4
2
Perspective view of an oxide-isolated BJT
[http://ceiba.cc.ntu.edu.tw/542U0130/u0130/electro/form6.htm]
5
Basic structures of BJTs
[D. A. Neamen, Semiconductor Physics and Devices, IRWIN, 1997]
[Encyclopedia Americana, http://go.grolier.com:80/]
Conventional IC npn BJT
An oxide-isolated npn BJT
6
3
NPN Bipolar Transistor
Planar junction (Bipolar) transistor
Emitter
p+
n+
Base
p
Collector
n+
Al•Cu•Si
SiO2
n-epi
p+
Electron flow
n+ buried layer
P-substrate
7
Cross sections of BJTs
[R. F. Robert, Semiconductor Device Fundamentals, Addison Wesely, 1996]
A typical discrete,
double-diffused pnp BJT
An IC npn BJT
8
4
典型雙極性接面電晶體結構
[王水進，電子學- 基礎篇，全華科技圖書，1998]
B
垂直型
E
B
n+
p
(縱向型)
n
n+
C
C
p
n+
射極
10
20
n+
基極
p
集極
n
n+
水平型
(橫向型)
n+
p+
n
+
n − 掩埋層
SiO2
+
p
摻雜濃度
-3
B
(cm )
E
10
10
18
16
p − Si 基板
雜質分佈曲線
深度
9
Bipolar junction transistor
[From Wikipedia, the free encyclopedia]
[http://en.wikipedia.org/wiki/Bipolar_junction_transistor]
A bipolar (junction) transistor (BJT) is a type of transistor. It is a three-terminal
device constructed of doped semiconductor material and may be used in
amplifying or switching applications.
Although a small part of the transistor current is due to the flow of majority
carriers, most of the transistor current is due to the flow of minority carriers and
so BJTs are classified as minority-carrier devices.
10
5
The bipolar Junction Transistors
[http://dspace.mit.edu/bitstream/handle/1721.1/36373/6-012Spring-2003/NR/rdonlyres/Electrical-Engineering-and-Computer-Science/6012Microelectronic-Devices-and-CircuitsSpring2003/DD39CE25-C7AA-4503-999C-5E529728AE6A/0/lecture17.pdf]
11
Concept of
Transistor Action
6
雙極性電晶體之基本操作：
典型pn接面於偏壓下多數與少數載子之電通量
[王水進，電子學- 基礎篇，全華科技圖書，1998]
順偏
n+
反偏
p
p
n
Io
I
Io
I
Fp p
>>
Fn p
Fnn
Fpn
多數載子電通量
少數載子電通量
13
雙極性電晶體之基本操作：
不同基極寬度下由射極注入基極電子流之流動方向
[王水進，電子學- 基礎篇，全華科技圖書，1998]
順偏 反偏
+
p
n
n
IE
IC
0
IE = IC + IB >>IB
W
W<<5Ln
IB
順偏
反偏
+
p
n
I + Io
n
Io
0
W
I
W>5Ln
14
7
Current components in a BJT
[From Wikipedia, the free encyclopedia]
[http://en.wikipedia.org/wiki/Bipolar_junction_transistor]
15
Carrier transport in a BJT
[http://dspace.mit.edu/bitstream/handle/1721.1/36373/6-012Spring-2003/NR/rdonlyres/Electrical-Engineering-and-Computer-Science/6-012Microelectronic-Devices-andCircuitsSpring2003/DD39CE25-C7AA-4503-999C-5E529728AE6A/0/lecture17.pdf]
16
8
Typical output characteristics of a BJT
[Kwok K. Ng, Complete Guide to Semiconductor Devices, 2/e, McGraw-Hill, 2002]
共基(CB)組態
共射(CE)組態
17
Transistor (= Transfer Resistor)
Ö
Q1: low resistance
Q2: high resistance
VCC
iC
iB
vI
RC
+
vCE
-
vO
Load line
VCC = iC RC + vCE
18
9
Switching operation of BJT
iC
VCC
iC
iB
vI
RC
vO
5V
0
iB
C
t
0
VCC
¹¡¦X
VCC
RC
vI
B
vO
t
A
0
VCC
Ioff
vCE
19
[http://www.interfacebus.com/FETs.html#a]
Operation Theory of
BJTs
10
雙極性電晶體之基本操作：
由射極注入基極載子流之流動方向
[王水進，電子學- 基礎篇，全華科技圖書，1998]
n
p
n
p
IC
I
E
p
IE
IC
IB
IB
-V +
BE
n
-V +
CB
+V EB
+V BC
21
Definition of BJT operation regions
[S. M. Sze, Modern Semiconductor Device Physics, John Wiley, 1998]
22
11
Minority carrier distribution in an npn BJT
[D. A. Neamen, Semiconductor Physics and Devices, IRWIN, 1997]
23
Carrier profiles in forward-active regime
[http://dspace.mit.edu/bitstream/handle/1721.1/36373/6-012Spring-2003/NR/rdonlyres/Electrical-Engineering-and-Computer-Science/6-012Microelectronic-Devices-andCircuitsSpring2003/DD39CE25-C7AA-4503-999C-5E529728AE6A/0/lecture17.pdf]
24
12
Ideal pn junction current
I = AJ = A[ J p ( xn ) + J n (− x p )]
VA
Dp
D
= qA[( n n po +
p no )(e VT − 1)]
Ln
Lp
Jp(x), Jn(x)
總電流
VA
= I o (e VT − 1)
J p ( xn )
J n (x)
J n (− x p )
J p (x)
D
x
-xp 0 xn
Dp
p ]
L p no
Dp
)]ni2 ]
Lp N A
I o = qA[ L n n po +
n
Dn
nND
= qA[( L
+
Eg
∝ e − kT
Key concept
D
J p = qA L p pno ⋅ eVA / VT ⎫⎪
p
⎬ ⇒
Dn
J n = qA L n po ⋅ eVA / VT ⎪
n
⎭
Jp
Jn
∝
NA
ND
25
Derivation of I-V equations of BJTs
x < −xp
n( x ) = n Eo − Δn( − x p )e
( x + x p )/ LE
P
pn ( x )
x > xn
n( x ) = n Co − Δn ( x n )e − ( x − xn )/ LC
nEo
0 ≤ x ≤ WB
p( x ) = p Bo [(
n
P
Δp(WB ) − Δp(0)e −WB / LB
2 sinh(WB / L B )
) e x / LB − (
nE ( x )
pBo
− xp 0
Δp(WB ) − Δp( 0) e WB / LB
2 sinh(WB / L B )
nC ( x )
pCo
WB − x n
) e − x / LB ]
27
13
Derivation of I-V equations of BJTs
I E = A E ( J pE + J nE ) = A E [ J p ( x = 0 ) + J n ( x = − x p )]
∂ p(x)
∂ n( x)
= A E [( − q D B
x=0 )+ (− q D E
x = − x p )]
∂x
∂x
q D B p Bo
WB
= AE
coth (
)[( e V EB / VT − 1)
LB
LB
1
q D E n EO V / V
−
( e − V BC / VT − 1)] + A E
(e EB T − 1)
W
LE
cosh ( B )
LB
I C = AC ( J pC + J nC ) = AC [ J p ( x = WB ) + J n ( x = xn )]
= ( − qD B
∂ p( x )
∂x
x =WB
) + ( − qDC
∂ n( x )
∂x
x = xn
)
qD B p Bo
W
1
[( e VEB / VT − 1) − coth( B )( e −VBC / VT − 1)]
= AC
LB sinh( WB )
LB
LB
q DC n Co −VBC /VT
− AC
(e
− 1)
LC
28
Minority carrier distribution in an npn BJT
operating in the active mode
[A. S. Sedra and K. C. Smith, Microelectronic Circuits, Oxford Univ. Press, 1998]
Emitter
(n)
E-B
Base
(p )
depletion region
np(0)
In
B-C
depletion region
Collector
(n)
np(x)
(ideal)
pn(0)
pno
0
np(x)
x
W
(with recombination)
n p (0) = n po e vBE / VT
pn (0) = pno e vBE / VT
I n = AE qDn
dn p ( x)
= AE qDn (−
dx
n p (o)
W
)
29
14
Minority carrier distribution in an npn BJT
operating in the active mode
[S. M. Sze, Semiconductor Devices, Physics and Technology, John Wiley, 1985]
30
Minority carrier distribution in an npn BJT
[D. A. Neamen, Semiconductor Physics and Devices, IRWIN, 1997]
Saturation
Cut-off
31
15
熱平衡狀態下BJT之能帶圖
[R. F. Robert, Semiconductor Device Fundamentals, Addison Wesely, 1996]
32
順向作用區工作電晶體之能帶圖
結構示意圖
+
XE
IE
E
p
VEC
−
XB
XC
p
n
+
IC
能帶圖
C
−
VEB
−
IB
+
VBC
B
qVCB qV
CE
Ec
電荷分佈圖
Ev
qVEB
q( N D − N A )
NB
− xp
xn
0 WB
x
NC
NE
33
16
電晶體之能帶圖
p
p
n
n
Ec
Ec
Ev
Ev
qVDo
Ec
熱平衡
狀態
p
n
Ec
EF
Ev
EF
Ev
qVDo
qVD
Ec
順向操作
狀態
qVCB qV
CE
Ec
Ev
qVEB
Ev qV
EB
qVCB qVCE
qVD
34
pnp 電晶體之電流成份
E
IE
+
p
n
IEp
( I Ep − ICp )
ICBOn
-
IB
B
σ W
≈ 1 − σ B WB
E E
Base transport efficiency
αT ≡
I Cp
I Ep
≈1−
WB2
2 L2p
CB SC current gain
α (≡
IC
IE
= γα T )
IC
ICBOp
Emitter efficiency
γ ≡
ICp
IEn
VEB
I Ep
IE
p
+
-
C
VBC
I E = I Ep + I En
I B = I En + ( I Ep − I Cp ) − I CBO
I E = I C + I B I C = αI E + I CBO
I CBO ( = I CBOp + I CBOn )
I C = I Cp + I CBO = γ α T I E + I CBO
35
17
Diffusion currents flowing in
a pnp BJT under active mode biasing
[R. F. Robert, Semiconductor Device Fundamentals, Addison Wesely, 1996]
CB dc current gain αdc
Emitter efficiency
I Cp = α T I Ep = γ α T I E
I C = α dc I E + I CB 0 = I Cp + I Cn
= γ α T I E + I Cn
I
γ = EP
IE
Base transport factor
αT =
I CP
I EP
⇒ α dc = γ α T , I CB 0 = I Cn
CB dc current gain βdc
I C = β dc I B + I CB 0 = α dc I E + I CB 0
= α dc ( I C + I B ) + I CB 0
α dc
1
IB +
I CB 0
1 − α dc
1 − α dc
= β dc I B + (1 + β dc ) I CB 0
α
β dc = dc
1 − α dc
IC =
36
Current-Voltage Characteristics of BJTs
(Gummel plot)
[B. G. Streetman and S. Banerjee, Solid State Electronic Devices, Prentice Hall, 2000]
High level
injection
Base resistance
ideal
ideal
VEB
ideal
log IC
37
18
Gummel plot and dc current gain
[R. F. Robert, Semiconductor Device Fundamentals, Addison Wesely, 1996]
Ideal
High-level injection,
current crowding,
and/or series resistance
βdc
VBC = 5 V
Ideal
VEB
IC (A)
Data derived from a 2N2605 pnp BJT
38
Gummel plot: semilog plot of IC and IB vs. VBE
[http://dspace.mit.edu/bitstream/handle/1721.1/36373/6-012Spring-2003/NR/rdonlyres/Electrical-Engineering-and-Computer-Science/6012Microelectronic-Devices-and-CircuitsSpring2003/DD39CE25-C7AA-4503-999C-5E529728AE6A/0/lecture17.pdf]
39
19
Gummel plot of BJT (VCE = 3 V )
40
[http://dspace.mit.edu/bitstream/handle/1721.1/36373/6-012Spring-2003/NR/rdonlyres/Electrical-Engineering-and-Computer-Science/6-012Microelectronic-Devices-andCircuitsSpring2003/DD39CE25-C7AA-4503-999C-5E529728AE6A/0/lecture17.pdf]
Current-Voltage
Characteristics of BJTs
41
20
BJT應用之三種組態
[王水進，電子學- 基礎篇，全華科技圖書，1998]
IE
IC
IE
+
IB
−
VCE
+
IE
VBE
−
IC
+
VBE
共射(CE)組態
VCE
−
VCB
IB
+
−
−
IB
VCB
−
共基(CB)組態
+
IC
+
共集(CC)組
42
共基(CB)組態電晶體特性
10
8
VCB = 15 V
(mA)
VCB = 10 V
6
VCB = 5 V
C
4
I
IE (mA)
10
8
I E = 8 mA
6
I E = 6 mA
I E = 4 mA
4
I E = 2 mA
2
2
0
0.6
I E = 10 mA
I CBO
0.7
VBE
0.8
0.9
(Volts)
IE
+
IB
1
2
VBE
IC
−
VBE
0
IE
+
+
VCB
VEB
−
−
3
I E = 0 mA
4
5
6
(Volts)
IC
−
IB
VBC
+
43
21
共射(CE)組態電晶體特性
20
3
18
IB=100 uA
2
14
VCE = 15 V
12
IC (mA)
IB (μA)
16
VCE = 5 V
80 uA
60 uA
10
1
8
40 uA
6
20 uA
4
2
0
0.4
0.6
0.8
VBE
1.0
12
.
1.4
0
0.0
(Volts)
0 uA
0.5
1.0
2.0
2.5
3.0
3.5
4.0
VCB(V)
IC
IB
IC
+
VCE
+
VBE
−
1.5
IE
−
IB
−
−
VEB
+
IE
VEC
+
44
Typical output characteristics of a BJT
[Kwok K. Ng, Complete Guide to Semiconductor Devices, 2/e, McGraw-Hill, 2002]
共基(CB)組態
共射(CE)組態
45
22
共集(CC)組態電晶體特性
I B = 100 μA
80 μA
14
IB
13
IE (mA)
15
VCB = 15 V
16
VCB = 10 V
18
18
VCB = 5 V
(mA)
20
20
10
12
60 μA
10
40 μA
8
8
6
5
20 μA
4
3
2
0
0.0
0
0
2
4
6
8
10
12
14
16
0 μA
0.5
1.0
1.5
VCE
VCB (V)
IE
IB
−
VBC
+
2.0
IC
2.5
3.0
3.5
4.0
(V)
IE
IB
−
VCE
+
+
VBC
+
IC
VEC
−
−
46
Figure-of-Merit (FOM) for BJT performance
[S. M. Sze, Modern Semiconductor Device Physics, John Wiley, 1998]
Current gain cutoff frequency, fT
The frequency at which the short-circuit current gain (hfe, or β) drop to
unity.
A key estimator of transistor high-speed performance
w
1
(kT / q)
= τ b + τ e '+ c + ( RE + RC )C BC + (C BE + C BC )
2π fT
2vs
IC
Maximum frequency of oscillation, fmax
The frequency at which the maximum available power gain (MAG) of
the transistor drops to unity.
Fmax is different from (and typically larger than) fT, because in
addition to current gain, fmax takes into account the possibility of
voltage gain.
Gp = (
2
f max 2 1 Re( Z in )
) = [
] h fe
f
4 Re( Z out )
f max = (
fT
)1 / 2
8π RB C BC
Figure of Merit：效益指數 、評量指標
47
23
Figure-of-Merit for BJT performance
[S. M. Sze, Modern Semiconductor Device Physics, John Wiley, 1998]
48
Non-ideal effects of BJTs
49
24
BJT之穿透崩潰
(punch-through breakdown)
WB
E
N+
Depletion
region
VPT ( = qN B WB2 / 2ε s )
B
WB
E
punch-through
breakdown voltage
C
N
P
N+
VB
C
N
P
ΔVB
V bi + V CB
發生穿透崩潰時
B
Ec
Depletion
region
Ec
50
電晶體與兩端間之崩潰曲線(第三端開路)
M=
1
V
1− (
)m
BV CBO
BVCEO = BVCBO (1−α )1/ m
≈
I
BVCBO
β 1/ m
IB = 0
I CEO
I CEO
BVCEO
I CBO
I
= CBO
1−α M
BVCBO
ICEO
ICBO
V
IE = 0
51
25
The avalanche breakdown in a transistor
[B. G. Streetman and S. Banerjee, Solid State Electronic Devices, Prentice Hall, 2000]
52
Carrier multiplication and feedback mechanism
[R. F. Robert, Semiconductor Device Fundamentals, Addison Wesely, 1996]
0: initial hole injection
1: injected hole entering the CB
depletion junction
2: e-h pair generation by impact ionization
3: generated electrons being swept
into the vase
4: excess base electrons injected
into the emitter
5: hole injected from the emitter
into the base in response to the
step 4 electron injection
53
26
Non-ideal I-V characteristics of BJTs
[R. F. Robert, Semiconductor Device Fundamentals, Addison Wesely, 1996]
Non Early effect
no carrier multiplication
With Early effect and
carrier multiplication
With Early effect
no carrier multiplication
54
The Early effect
[B. G. Streetman and S. Banerjee, Solid State Electronic Devices, Prentice Hall, 2000]
55
27
Dependence of iC on the collector voltage –
the Early effect
[A. S. Sedra and K. C. Smith, Microelectronic Circuit, Oxfor Univ. Press, 1998]
iC = I S e vBE / VT (1 +
vCE
)
VA
⎡ ∂i
C
Output resistance ro ≡ ⎢ ∂v
⎣
CE
⎤ −1
vBE =const . ⎥
⎦
56
Geometrical effect-
current crowding
Emitter area ≠ collector area
Bulk and contact resistance
(using thin epilayer or heavily doped buried layer)
57
28
Current crowding
58
Cross section of a BJT under active bias
C-B
space-charge
layer
Collector region
Lines of flow of
majority carriers
The base current is supplied form two side base contact and flows
toward the center of the emitter causing the BE voltage drop to vary
with position.
62
29
Base resistance
Extrinsic base resistance
R1 =
ρ BX L
A
=
ρ BX d
( xE + xB )W
Intrinsic base resistance
R2 =
ρ BI h
3 xBW
Base resistance
Rb = RC + R1 + R2 = rx
63
Effect of Base Resistance
[B. G. Streetman and S. Banerjee, Solid State Electronic Devices, Prentice Hall, 2000]
64
30
An interdigitated geometry
to release the effects of emitter current crowding
[B. G. Streetman and S. Banerjee, Solid State Electronic Devices, Prentice Hall, 2000]
top view of
implanted region
65
Geometry design of power BJTs
66
31
Transistor collector resistance RCS
In active region
the collector junction is reveres biased
and hence represents a rather high
impedance. The collector voltage
drop ICRCS is normally small
compared to the collector junction
resistance and can be neglected.
In saturation region
The collector junction is forward biased, the collector bulk voltage drop
generally even exceeds the potential drop across the junction.
The effect is most pronounced at low CE voltages where the BJT
is in saturation and hence is collecting minority carrier inefficiently
(the collector is back injection to the emitter).
67
Emitter-collector shorts caused by diffusion pipes or spikes
through the base along the dislocations
Diffusion pipes
Diffusion spikes
Dislocations:
oxidation induced stacking faults, epitaxial-growth-induced
slip dislocations, and other process-induced defects
68
32