The first Transistor

[ 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

The discovery of the point
contact transistor in 1947
This work resulted in their
receiving the Nobel Prize
for Physics in 1956.
雙 極 性 電 晶 體 發 明 人
[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
Base
Collector
Al•Cu•Si
SiO 2
n p n
p +
+
+ n-epi
Electron flow
n + buried layer
P-substrate
p +
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
E
B
垂 直 型
( 縱 向 型 )
n +
p
n
n +
E
C
B
C
10 20
射 極
n +
基 極
p
集 極
n n +
水 平 型
( 橫 向 型 )
p +
n+
p n +
n
p +
n + − 掩 埋 層
SiO 2
-3
摻 雜 濃 度 (cm )
10 18
10 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/6-
012Microelectronic-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
反 偏
I
n +
p
I o
p
n
I o
I
F pp
>>
F nn
F np
F pn
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
順 偏 反 偏
n +
p
n
[ 王 水 進 , 電 子 學 - 基 礎 篇 , 全 華 科 技 圖 書 ,1998]
I E
I C
IE= IC+ IB>>
IB
0 W
I B
W

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-and-
CircuitsSpring2003/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)
v I
i C
V CC
RC
i B +
v CE
-
v O
Load line
V
CC
= i
Q 1 : low resistance
Q 2 : high resistance
C
R
C
+ v
CE
18
9

Switching operation of BJT
V CC
i C RC
i B v O
v I
5V
0
V CC
0
v I
v O
t
t
V
R
CC
C
C
¹¡¦X
B
A
i B
I off
i C
V CC
v CE
0
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 n p
I E
I C
I E
I C
I B
I B
- V BE
+ -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-and-
CircuitsSpring2003/DD39CE25-C7AA-4503-999C-5E529728AE6A/0/lecture17.pdf]
24
12

Ideal pn junction current
J
J
p
n
J p
(x), J n
(x)
-x p
0
x n
總 電 流
J p ( x n )
J n (x)
Jn( −xp)
J p (x)
Key concept
= qA
= qA
Dp
Lp
Dn
Ln
p
n
no
po
⋅e
⋅e
VA
/ VT
VA
/ VT
⎫
⎪
⎬
⎪
⎭
⇒
J
J
p
n
N
∝
N
A
D
x
I = AJ = A[
J
Dn
= qA[(
n
L
I
= I
o
o
( e
= qA[
= qA[(
∝ e
n
VA
V T
−
−1)
D
L
Eg
kT
p
po
n
n
n
D
L
( xn)
+ J
Dp
+ p
L
po
n
nND
p
+
+
n
( −x
no
Dp
Lp
Dp
L N
p
)( e
A
p
p
)]
V A
V T
−1)]
no
]
)] n ]
2
i
25
Derivation of I-V equations of BJTs
x
x n
Eo
p
x x LE
P n P
pn( x)
nx ( ) = n −Δnx ( ) e
Co
0 ≤ x ≤W B
n
−( x−xn)/
LC
nE ( x)
n Eo
− x p
p Bo
0
W B
nC ( x )
− x n
p Co
−W
/ L
B B
B
ΔpW ( B ) − Δp( 0)
e
x/
L ΔpW ( B ) − Δp( 0)
e
B
px ( ) = pBo[(
) e − (
2 sinh( W / L )
2 sinh( W / L )
B
B
B
W / LB
B
− x/
L
B
) e ]
27
13

Derivation of I-V equations of BJTs
I E = AE
( J pE + J nE ) = AE
[ J p ( x = 0) + J n ( x = − x p )]
∂ p ( x )
∂ n(
x)
= AE
[( − q D B
x = 0 ) + ( − q D E
x = − x )]
p
∂ x
∂ x
q D B p Bo W
= A
coth ( B )[( V EB / VT
E
e − 1)
L B L B
1
− ( −V
BC / V
q D E n EO
e
T − 1)] + A
( V EB / VT
E e − 1)
W B
cosh ( )
L
L
E
B
I C = AC
( J pC + JnC
) = AC
[ J p(
x = WB
) + Jn(
x = xn)]
∂ px ( )
∂ nx ( )
= ( − qDB x= W ) + ( −qDC x=
x )
∂x
B
∂x
n
−
= A qD B p Bo 1 V W
EB VT B VBC VT
C
[( e
−1) −coth( )( e
W
L
B
B sinh( ) L
L
B
B
−1)]
−
−A C n Co VBC
/ VT
C ( e
LC
−1)
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
depletion region
Base
(p)
B-C
depletion region
Collector
(n)
n p (0)
p n (0)
p no
n (0) = n
p
p (0) = p
n
e
vBE
/ VT
po
vBE
VT
noe
/
0
I n
n p (x)
(ideal)
n p (x)
W
(with recombination)
I
n
dnp(
x)
= AE
qDn
dx
np
( o)
= AE
qDn
( − )
W
x
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
+ −
E
+
X E
p
X B
n
X C
p
I C
−
C
能 帶 圖
I E
V EB
電 荷 分 佈 圖
V EC
I B
− +
B
V BC
qV
E CB qV c CE
qV EB
E v
qN ( D − NA)
N B
x n
− x p
0 W B
x
N C
N E
33
16

電 晶 體 之 能 帶 圖
p
n
p
n
p
n
E c
E c
E v
E v
熱 平 衡
狀 態
E c
E v
E F
E c
E v
E v
qV Do
E F
qV Do
qV D
順 向 操 作
狀 態
E c
E v
E c
qV CB qV CE qV qVCB
EB
qV CE
qV EB
qV D
34
E
I B
pnp 電 晶 體 之 電 流 成 份
p n p
I E
I Ep
( Ep − ICp)
I Cp I C
+
I CBOp
I En
I CBOn
-
C
I
I
Ep
γ ≡ ≈1−
E
σ BW
σ W
E
V EB
Emitter efficiency
α T
I
I
Cp
≡ ≈1
−
Ep
W
B
E
2
B
2
p
2 L
-
B
Base transport efficiency
CB SC current gain
I
I
C
α( ≡ = γα )
E
T
+
V BC
IE = IEp + I En
I = I + ( I − I ) − I
B En Ep Cp CBO
I E = I C + I B
I ( = I + I )
CBO CBOp CBOn
I = αI + I
C E CBO
I = I + I = γ α I + I
C Cp CBO T E 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 α dc
I Cp = αT
I Ep = γ αT
I
Emitter efficiency Base transport factor
E
I
I
γ = EP
ICP
C = α dcIE
+ ICB0
= ICp
+ ICn
α T =
IE
I
= γ α I + I
EP
T
E
Cn
⇒
α
dc
= γ α ,
T
I
CB0
= I
Cn
I
C
= β
= α
CB dc current gain β dc
dc
dc
IB
+ I
( I + I
C
CB0
B
= α
) + I
I
dc E
CB0
+ I
CB0
α dc 1
IC
= IB
+ I
1−α
dc 1−α
dc
= β dcIB
+ (1 + β dc)
I
α dc
β dc
−α
dc
CB0
CB0
36
= 1
37
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
V EB
log I C
ideal
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
β dc
V BC = 5V
Ideal
V EB
I C
(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/6-
012Microelectronic-Devices-and-CircuitsSpring2003/DD39CE25-C7AA-4503-999C-5E529728AE6A/0/lecture17.pdf]
39
19

Gummel plot of BJT (VCE = 3 V )
[http://dspace.mit.edu/bitstream/handle/1721.1/36373/6-012Spring-2003/NR/rdonlyres/Electrical-Engineering-and-Computer-Science/6-012Microelectronic-Devices-and- 40
CircuitsSpring2003/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]
+
I B
V
+
CE
V BE
−
I E
I C
−
V BE
+ I B
−
V CB
V
−
CB
I
+
C
I E I C
−
+
I B
I E
−
V CE
+
共 射 (CE) 組 態
共 基 (CB) 組 態
共 集 (CC) 組
42
共 基 (CB) 組 態 電 晶 體 特 性
I E
(mA)
10
8
6
VCB = 15V
VCB = 10V
VCB = 5V
4
2
0
0.6 0.7 0.8 0.9
V BE
(Volts)
I C
(mA)
10
8
6
4
2
IE = 10 mA
IE = 8 mA
IE = 6 mA
IE = 4 mA
IE = 2 mA
I CBO
IE = 0 mA
0 1 2 3 4 5 6
VBE ( Volts)
I E I C
I B I B
I E I C
−
V BE
+
+
V CB
−
+
V EB
−
−
V BC
+
43
21

共 射 (CE) 組 態 電 晶 體 特 性
3
20
18
16
I B =100 uA
I B
(μA)
2
1
VCE = 5V
VCE = 15V
I C (mA)
14
12
10
8
6
80 uA
60 uA
40 uA
4
20 uA
0 04 . 06 . 08 . 10 . 12 . 14 .
VBE ( Volts)
2
0 uA
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
V CB (V)
I C
I C
I B
+
+
V CE
V BE −
I
−
E
−
V EB
+
I B
I E
−
V EC
+
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 (mA)
20
18
15
13
V CB = 5 V
V CB = 10 V
V CB = 15 V
10
8
5
3
0
0 2 4 6 8 10 12 14 16
V CB (V)
I E (mA)
20
18
16
14
12
10
8
6
4
2
IB = 100 μ A
80 μA
60 μA
40 μA
20 μA
0 μA
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
V CE (V)
I E
I E
−
V BC
+
I B
I C
−
V CE
+
+
I B
V BC I −
+
−
C
V EC
46
Figure-of-Merit (FOM) for BJT performance
[S. M. Sze, Modern Semiconductor Device Physics, John Wiley, 1998]
Current gain cutoff frequency, f T
The frequency at which the short-circuit current gain (h fe
, or β) drop to
unity.
A key estimator of transistor high-speed performance
1
wc
( kT / q)
= τ b + τ e'
+ + ( RE
+ RC
) CBC
+ ( CBE
+ CBC
)
2π fT
2vs
IC
Maximum frequency of oscillation, f max
The frequency at which the maximum available power gain (MAG) of
the transistor drops to unity.
F max
is different from (and typically larger than) f T
, because in
addition to current gain, f max
takes into account the possibility of
voltage gain.
fmax 2 1 Re( Zin)
2
G p = ( ) = [ ] h fe
f 4 Re( Zout
)
T 1/ 2
max ( )
8π RBCBC
f =
f
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)
W B
E
N + P N
C
punch-through
breakdown voltage
Depletion
region
B
V
2
PT B B s
( = qN W / 2ε )
W B
V B
E
N + P N
B
Depletion
region
C
ΔV B
發 生 穿 透 崩 潰 時
V + V
bi CB
E c
E c
50
電 晶 體 與 兩 端 間 之 崩 潰 曲 線 ( 第 三 端 開 路 )
I
1
M =
V
1 − ( )
I CEO
BV CBO
m
I
CEO
BV CEO
I CBO
BV CBO
1/ m
β
I CBO
=
1−α
M
V
BV
CEO
= BV
BV
≈
CBO
CBO
(1−
α)
I B = 0
I CEO
I CBO
I E = 0
1/ m
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 i C on the collector voltage –
the Early effect
[A. S. Sedra and K. C. Smith, Microelectronic Circuit, Oxfor Univ. Press, 1998]
i
C
v
/ CE
= I v V
Se
BE T (1 + ) Output resistance
V
A
⎡ ∂i
ro
≡ ⎢
⎣∂v
C
CE
vBE
=const.
⎤
⎥
⎦
−1
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
ρBX
L ρBX
d
R1
= =
A ( x + x ) W
E
B
Intrinsic base resistance
R
2
ρBIh
=
3x
W
B
Base resistance
R = r
b
= RC
+ R1
+ R2
x
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 R CS
In active region
the collector junction is reveres biased
and hence represents a rather high
impedance. The collector voltage
drop I C
R CS
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