Bande piatte =0 n p =n po (p p =p po ) 2)Accumulazione Q s ≈exp( s| /2) 3)Svuotamento

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 )


Applicazioni

“Tuning” del numero e tipo portatori vicino alla superficie del semiconduttore ( appl. CCD -1969 Boyle-Smith )


Regime di deep depletion

Con sequenza clock si ha immagazzinamento e trasferimento carica

1 2

3


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


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.


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.


Giunzione np


n

p

n

p

Giunzione np


Corrente giunzione pn


n

p

n

Due giunzioni separate con polarizzazione opposta

Forward

Reverse


Due giunzioni vicine

n

p

n

http://it.wikipedia.org/wiki/File:BJT_symbol_NPN.svg


Nobel 1956


PNPNPN

Transistor

In genere la regione di emettitore ha drogaggio più alto rispetto al collettore

http://it.wikipedia.org/wiki/File:BJT_symbol_NPN.svg

http://it.wikipedia.org/wiki/File:BJT_symbol_PNP.svg


x

-xE

WxC

p n p

VEB VBC

Emettitore Base Collettore


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


Transistor


5 e 6 sonocorrenti trascurabili


N-P-N


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


⎥⎥⎦⎤

⎢⎢⎣⎡

⎟⎟⎠⎞

⎜⎜⎝⎛

−⎟⎟⎠⎞

⎜⎜⎝⎛ −

⎟⎟⎠⎞

⎜⎜⎝⎛

−

⎟⎟⎠⎞

⎜⎜⎝⎛=Δ

hh

KTqV

h

B

Lx

LxWe

LW

pxp

BE

sinhsinh1sinh

)( 0,

Lacune nella base


Distribuzione portatori minoritari


€

γ≡IE ,pIE=

IE ,pIE ,p + IE ,n

(n − p− n)γ ≡IE ,nIE

Efficienza di emettitore

Parametri


€

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


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


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


Parametri

BBBC

CCCEB

IIII

IIIII

1661

006.011

0

0

0

==⎟⎟⎠⎞

⎜⎜⎝⎛

−=

=⎟⎟⎠⎞

⎜⎜⎝⎛

−=−=

α

α

α

Bande piatte =0 n p =n po (p p =p po ) 2)Accumulazione Q s ≈exp( s| /2) 3)Svuotamento

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