bande piatte =0 n p =n po (p p =p po ) 2)accumulazione q s ≈exp( s| /2) 3)svuotamento
DESCRIPTION
Bande piatte =0 n p =n po (p p =p po ) 2)Accumulazione Q s ≈exp( s| /2) 3)Svuotamento Q s ≈sqrt( s ) 4)Inversione debole n p cresce 5)inversione forte Q s ≈exp( s /2). Applicazioni. - PowerPoint PPT PresentationTRANSCRIPT
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Dispositivi a semiconduttore 1
1)Bande piatte =0
np=npo (pp=ppo)
2)Accumulazione
Qs≈exp(s|/2)
3)SvuotamentoQs≈sqrt(s)
4)Inversione debole
np cresce
5)inversione forte
Qs≈exp(s/2)
€
np = np0 exp(βψ )
pp = pp0 exp(−βψ )
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Dispositivi a semiconduttore 2
Applicazioni
“Tuning” del numero e tipo portatori vicino alla superficie del semiconduttore ( appl. CCD -1969 Boyle-Smith )
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Dispositivi a semiconduttore 3
Regime di deep depletion
Con sequenza clock si ha immagazzinamento e trasferimento carica
1 2
3
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Dispositivi a semiconduttore 4
Transistor bipolare
Transfer resistor:dispositivo a 3 terminali in cui la resistenza fra 2 terminali è controllata dal terzo terminaleE’ un dispositivo bipolare perchè la corrente è trasportata da due tipi di portatori
Bell Labs 1947: Bardeen & Brittain point contact transistor1949: Teoria di Shockley per giunzioni p-n1951:I dimostrazione di un transistor bipolare1956: Nobel a Bardeen & Brittain e Shockley
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Dispositivi a semiconduttore 5
An amazingly simple device, capable of performing efficiently nearly all the functions of an ordinary vacuum tube, was demonstrated for the first time yesterday at Bell Telephone Laboratories where it was invented. Known as the Transistor, the device works on an entirely new physical principle discovered by the Laboratories in the course of fundamental research into the electrical propertiesof solids. Although the device is still in the laboratory stage, Bell scientists and engineers expect it may have far-reaching significance in electronics and electrical communication.The whole apparatus is housed in a tiny cylinder less than an inch long. It will serve as an amplifier or an oscillator -- yet it bears almost no resemblance to the vacuum tube now used to do these basic jobs. It has no vacuum, no glass envelope, no grid, no plate, no cathode and therefore no warm-up delay. Two hair-thin wires touching a pinhead of a solid semi- conductive material soldered to a metal base, are the principal parts of the Transistor. These are enclosed in a simple, metal cylinder not much larger than a shoe-lace tip. More than a hundred of them can easily be held in the palm of the hand. Since the device is still in the experimental stage, no data on cost are available. Its essential simplicity, however, indicates the possibility of widespread use, with resultant mass- production economies. When fully developed, the Transistor is also expected to find new applications in electronics where vacuum tubes have not proved suitable. Tests have shown that the Transistor will amplify at least I00 times (20 decibels). Some test models have been operated as amplifiers at frequencies up to ten million cycles per second. Because of the basically simple structure of the new units, stability and long life are expected.
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Dispositivi a semiconduttore 6
La definizione di lacuna….
Transistor action depends upon the fact that electrons in a semi-conductor can carry current in two distinctly different ways. This is because most of the electrons in a semiconductor do not contribute to carrying the current at all. Instead they are held in fixed positions and act as a rigid cement to bind together the atoms in a solid. Only if one of these electrons gets out of place, or if another electron is introduced in one of a number of ways, can current be carried. If, on the other hand, one of the electrons normally present in the cement is removed, then the "hole" left behind it can move like a bubble in a liquid and thus carry current.
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Dispositivi a semiconduttore 7
Giunzione np
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Dispositivi a semiconduttore 8
n
p
n
p
Giunzione np
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Dispositivi a semiconduttore 9
Corrente giunzione pn
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Dispositivi a semiconduttore 10
n
p
n
Due giunzioni separate con polarizzazione opposta
Forward
Reverse
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Dispositivi a semiconduttore 11
Due giunzioni vicine
n
p
n
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Dispositivi a semiconduttore 12
Nobel 1956
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Dispositivi a semiconduttore 13
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Dispositivi a semiconduttore 14
PNPNPN
Transistor
In genere la regione di emettitore ha drogaggio più alto rispetto al collettore
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Dispositivi a semiconduttore 15
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Dispositivi a semiconduttore 16
x
-xE
WxC
p n p
VEB VBC
Emettitore Base Collettore
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Dispositivi a semiconduttore 17
x
-xE
WxC
p n p
VEB VBC
Emettitore Base Collettore
⎟⎟⎠⎞
⎜⎜⎝⎛
−=−Δ
−Δ=Δ+
1)(
)()(
0,KTqV
EE
Lxx
E
EB
e
E
enxn
exnxn
⎟⎟⎠⎞
⎜⎜⎝⎛
−=Δ
Δ=Δ
−
−−
1)(
)()(
0,KTqV
CC
Lxx
C
BC
e
C
enxn
exnxn
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Dispositivi a semiconduttore 18
Transistor
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Dispositivi a semiconduttore 19
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Dispositivi a semiconduttore 20
5 e 6 sonocorrenti trascurabili
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Dispositivi a semiconduttore 21
N-P-N
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Dispositivi a semiconduttore 22
N-P-N
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Dispositivi a semiconduttore 23
Componenti corrente N-P-N
Giunzione E-B: corrente di diffusione di elettroni e lacune
Nella base: Ricombinazione e se base sottile transito elettroni
Nel collettore: raccolta elettroni
InE: corrente diffusione elettroniInC: corrente diffusione elettroni raccolti al collettoreIrB= InE-InC: ricombinazione in baseIpE: corrente di diffusione lacune E-BIrE: ricombinazione E-BICO: corrente inversa C-B
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Dispositivi a semiconduttore 24
⎥⎥⎦⎤
⎢⎢⎣⎡
⎟⎟⎠⎞
⎜⎜⎝⎛
−⎟⎟⎠⎞
⎜⎜⎝⎛ −
⎟⎟⎠⎞
⎜⎜⎝⎛
−
⎟⎟⎠⎞
⎜⎜⎝⎛=Δ
hh
KTqV
h
B
Lx
LxWe
LW
pxp
BE
sinhsinh1sinh
)( 0,
Lacune nella base
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Dispositivi a semiconduttore 25
Distribuzione portatori minoritari
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Dispositivi a semiconduttore 26
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Dispositivi a semiconduttore 27
€
γ≡IE ,pIE=
IE ,pIE ,p + IE ,n
(n − p− n)γ ≡IE ,nIE
Efficienza di emettitore
Parametri
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Dispositivi a semiconduttore 28
€
αT ≡IC ,pIE ,p
(n − p− n)α T ≡IC ,nIE ,n
Fattore di trasporto nella base
€
α0 ≡IC ,p
IE ,p + IE ,n= γα T = hFB ≈
ICIE
(n − p− n)α 0 ≡IC ,n
IE ,p + IE ,n
Guadagno a base comune
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Dispositivi a semiconduttore 29
EA
BD
eh
enEpE
pE
NN
LW
DDII
I
,
,,,
,
1
1
+=
+=γ
2
2
,
,
21
hpE
pCT L
WII
−==α
TnEpE
pC
III
γαα =+
=,,
,0
Parametri
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Dispositivi a semiconduttore 30
999.0
1001
505
111
1
1
1
,
,,,
, =+
=+
=+
=
EA
BΔ
eh
enEpE
pE
NN
LW
ΔΔII
Iγ
995.0101
211
21
2
2
2
,
, =⎟⎠⎞⎜⎝
⎛−=−==hpE
pCT L
WII
α
994.0,,
,0 ==
+= T
nEpE
pC
III
γαα
Parametri
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Dispositivi a semiconduttore 31
Parametri
BBBC
CCCEB
IIII
IIIII
1661
006.011
0
0
0
==⎟⎟⎠⎞
⎜⎜⎝⎛
−=
=⎟⎟⎠⎞
⎜⎜⎝⎛
−=−=
α
α
α
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Dispositivi a semiconduttore 32
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Dispositivi a semiconduttore 33
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Dispositivi a semiconduttore 34
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Dispositivi a semiconduttore 35
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Dispositivi a semiconduttore 36
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Dispositivi a semiconduttore 37