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MOSFET

The document summarizes the operation of MOSFET transistors. It describes the different regions of operation including flat band, depletion, weak inversion, moderate inversion, and strong inversion. It examines how varying the gate-source voltage (VGS) and drain-source voltage (VDS) affects the characteristics curves and pinch-off point. It also discusses factors that affect the threshold voltage and drain current, as well as short channel effects that occur as transistors continue to shrink in size.

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Parul Trivedi
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545 views21 pages

MOSFET

The document summarizes the operation of MOSFET transistors. It describes the different regions of operation including flat band, depletion, weak inversion, moderate inversion, and strong inversion. It examines how varying the gate-source voltage (VGS) and drain-source voltage (VDS) affects the characteristics curves and pinch-off point. It also discusses factors that affect the threshold voltage and drain current, as well as short channel effects that occur as transistors continue to shrink in size.

Uploaded by

Parul Trivedi
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PPT, PDF, TXT or read online on Scribd
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Qualitative analysis of MOSFET Operation

Introduction
MOSFET operation regions Conduction phenomenon I-V Characteristics Pinch-off Fluid dynamic analogy Complete set of Characteristics Factors Affecting VT Factors Affecting Drain current Short channel effect

MOSFET OPERATION REGIONS


FLAT-BAND DEPLETION WEAK INVERSION MODERATE INVERSION

STRONG INVERSION

MOSFET OPERATION REGIONS

Flat Band

Depletion

MOSFET OPERATION REGIONS


WEAK INVERSION MODERATE INVERSION

STRONG INVERSION

Effect of VSB : The Body Effect


Original Bias

Effect of an increase in VSB

Effect of an increase in VGS


,

Effect of VDS : Drain current


FLAT BAND DEPLETION

Weak Inversion

Moderate Inversion

Strong Inversion

PINCHOFF

Pinch off

ID versus VDS, for fixed VSB and VGS

V-I CHARACTERISTIC

When VSB = 0V

When VSB = 2V

V-I CHARACTERISTIC

ID versus VDS, for VGS as parameter and fixed VSB

ID versus VGS as obtained from (a) with VDS = VDS1

V-I CHARACTERISTIC

a.) ID versus VDS, for VGS as parameter

b.) ID versus VGS as obtained from (a) with VDS = VDS1

c.) ID versus VGS obtained from part (b)

V-I CHARACTERISTIC
In moderate inversion, ID is neither exponential nor square-law with VGS

SHORT CHANNEL EFFECTS


Now MOSFETs are small in order to increase their operation speed. Pushing the dimensions of the gate length down influences the electrostatics of the devices. In order to preserve the electrostatic integrity of the MOSFET scaling has proceeded in a controlled way: Lg has to go together with tox , NA , tJ ,VDD and W But reducing these geometrical parameters not only increases fabrication complexity but also change the physical processes in the device

Leakage Mechanism
I1 is the reverse-bias pn junction leakage I2 is the subthreshold leakage I3 Is the oxide tunneling current I4 is the gate current due to hot-carrier injection I5 is the GIDL I6 is the channel punchthrough current

Thank You

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