The document discusses the different modes of operation of a MOS capacitor: 1. Flat band mode occurs when no potential is applied and the energy bands are flat. 2. Accumulation mode occurs when a negative charge is applied to a p-type semiconductor, accumulating a negative charge at the oxide interface. 3. Depletion mode occurs when a positive gate voltage is applied, depleting the p-type semiconductor of its positive charge carriers. 4. Inversion mode occurs at higher positive voltages when the depletion of positive charge leads to an accumulation of negative charge, inverting the type of charge carriers at the interface.

1. P R E S E N T E D B Y
N I H A R I K A G O U R
SGSITS INDORE
Presentation
on
MOS Capacitor

2. MOS Capacitor
 MOS Capacitor is a two terminal MOS device used to
store the charge in integrated circuit .

3. MOS Energy Band diagram

4.  qsi Work Function Energy of Semiconductor
 qm Work Function Energy of metal
 qXsio2 Electron affinity of SiO2
 qXsi Electron affinity of Si
 qF = EFI – EFP = kT ln(p/ni)=kT ln(N A /ni)
 It represent strength of work function
F=Fermi potential

5. Assumptions
1.Oxide = SiO2 a near-perfect insulator.
2. Assume zero charge in the oxide, electric field is
constant and potential is linear in the oxide.
3. n+ polysilicon has a potential which is the
maximum possible in silicon
4.Zero work function difference between metal &
semiconductor

6. Mode of Operation
 Flat Band
 Accumulation
 Depletion
 Inversion
 Strong Inversion

7. Flat Band

8. Flat mode of operation
 When no potential is applied there is no movement
of electron
 So distribution of dopant is uniform and energy band
has a flat band
Thus this mode of operation is known as flat mode of
operation

10. Accumulation

11. • W H E N N E G A T I V E C H A R G E I S A P P L I E D T O P T Y P E
D U E T O E L E C T R I C F I E L D A T G A T E E N D P O S T I V E
C H A R G E I S D E V E L O P E D
• D U E T O W H I C H A T O X I D E I N T E R F A C E N E G A T I V E
C H A R G E I S A C C U M U L A T E D
• T H U S T H I S M O D E O F O P E R A T I O N I S C A L L E D
A C C U M U L A T I O N
Accumulation

12. Accumulation

13. Depletion

14. W H E N P O S I T I V E G A T E V O L T A G E I S A P P L I E D ,
N E G A T I V E C H A R G E I S D E V E L O P E D A T G A T E E N D
D U E T O W H I C H A T I N T E F A C E S I D E P T Y P E I S
D E P L E T E D O F P O S I T I V E C H A R G E
T H U S T H I S M O D E O F O P E R A T I O N I S C A L L E D
D E P L E T I O N M O D E O F O P E R A T I O N
Depletion mode

15. Depletion

17. Inversion

18. 1 . W H E N P O S I T I V E V O L T A G E I S F U R T H E R
I N C R E A S E D
2 . D E P L E T I O N O F P O S I T I V E C H A R G E I N C R E A S E S
A N D B E C O M E A C C U M U L A T I O N O F N E G A T I V E
C H A R G E I N P T Y P E
T H I S I N V E R S I O N O F C H A R G E D U E T O H I G H E R
P O T E N T I A L I S C A L L E D I N V E R S I O N M O D E .
Inversion mode of operation

20. • T H I S P O T E N T I A L A G A I N I F I N C R E A S E S L E A D
T O S T R O N G I N V E R S I O N
• T H I S S T A T E F E R M I L E V E L W H I C H I N P T Y P E
S H O U L D B E N E A R T O V A L E N C E B A N D
D U E T O P O S I T I V E C H A R G E I S N O W B E C O M E
C L O S E T O C O N D U C T I O N
T H U S A T I N T E R F A C E E N D I T S T A R T B E H A V I N G
L I K E N T Y P E
Strong inversion

21. Summary