Download
1 / 79

Memory Aid “a hairpin is lighter than a frying pan” - PowerPoint PPT Presentation


  • 58 Views
  • Uploaded on

light m * (larger d 2 E/dK 2 ). heavy m * (smaller d 2 E/dK 2 ). Memory Aid “a hairpin is lighter than a frying pan”. 1. T=0 o K. T 1 >0. f (E). T 2 >T 1. 0.5. 0. E. E F. f (E) = 1/{1+exp[(E- E F )/ kT ]}. All energy levels are filled with e - ’s below the Fermi Energy at 0 o K.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Memory Aid “a hairpin is lighter than a frying pan”' - hilary-crawford


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Memory aid a hairpin is lighter than a frying pan

light m*

(larger d2E/dK2)

heavy m*

(smaller d2E/dK2)

Memory Aid“a hairpin is lighter than a frying pan”


F e 1 1 exp e e f kt

1

T=0 oK

T1>0

f(E)

T2>T1

0.5

0

E

EF

f(E) = 1/{1+exp[(E-EF)/kT]}

All energy levels are filled with e-’s below the Fermi Energy at 0 oK


Putting the pieces together for electrons n e

f(E)

1

T=0 oK

T1>0

T2>T1

S(E)

0.5

0

E

EV

EF

EC

n(E)=S(E)f(E)

E

Putting the pieces together:for electrons, n(E)


S(E)

Putting the pieces together:

for holes, p(E)

fp(E)

T=0 oK

1

T1>0

T2>T1

0.5

0

E

EV

EF

EC

p(E)=S(E)f(E)

hole energy


Finding n o and p o
Finding no and po

the effective density of states

in the conduction band


NA -> NA-ND = NA’ = ppo

ND -> ND-NA = ND’ = nno


w=(2εV/qNB)1/2



n++

p

n+

n+

W

L

(x)

Ec(y) with VDS=0


Increasing v gs decreases e b
Increasing VGS decreases EB

EB

EF ~ EC

y

0

L


Band diagram of triode and saturation
Band diagram of triode and saturation


Threshold voltage definition
Threshold Voltage Definition

VGS = VT when the carrier concentration in the channel is equal to the carrier concentration in the bulk silicon.

Mathematically, this occurs when fs=2ff ,

where fsis called the surface potential


Quantum Effects

on Threshold Voltage


(Maybe not so good for GaAs!)

This is very confusing, because this effective mobility is being used to describe the velocity of carriers when the concept of mobility is not applicable!


Most simple model constant field scaling

next

Most Simple Model: Constant Field Scaling

E = VDD/L

after scaling becomes

E = (VDD/a)/(L/a)

…where a>1


Subthreshold current revisited v dd scaling v t scaling
Subthreshold Current (revisited)VDD scaling  VT scaling



Junction leakage current tunneling current due to highly doped drain body junctions

E a thicker insulatorC

EV

W

Junction Leakage CurrentTunneling current due to highly doped Drain-Body junctions

B

D

IJE

Recall: tunneling

T = Kexp(-2kW)


Total stand by power p off v dd i g i je i off
Total Stand-by Power a thicker insulatorPoff = VDD(Ig + IJE + Ioff)


Scaling directions i soi dst depleted substrate transistor
Scaling Directions (I) a thicker insulatorSOI (DST, depleted substrate transistor)

Very thin body region (Tsi = L/3) makes the source and drain spreading resistance (RS) large.

Raised S/D improves ID (next)

Improves subthreshold slope, S

and decreases Ioff

Also decreases CjE

…and IJE


Scaling Directions (II) a thicker insulatorThe “FinFET” moves from a single gate to double and triple gate structures and also multiple channels.


(Equation 2.111) a thicker insulator



General behavior of a thicker insulatorβ (hFE) as a function of collector current (from Sze).

  • Low currents: Recombination currents dominate (just as in diode).

  • High currents: High injection effects (increases effective base doping) and series resistance effects increase.


ad