mosfet characteristics

7/29/2019 MOSFET CHARACTERISTICS

1/6

1

BASICS OF VLSI LAB-1 REPORT

Submitted by,

Richu Jose Cyriac (M120128EC)Davis Oommen Abraham (M120133EC)

Aim1. To plot current-voltage characteristics of NMOSFET and PMOSFET.

2. To measure MOS model parameters.

1. CURRENT VOLTAGE CHARACTERISTICSCurrent-Voltage equations for the n-channel MOSFET

0DI f o r TGS VV

])().(2[2

)(2

...

DSTGSoxn

D VVVLWC

linI

fo r TGS VV an d TGSDS VVV

for TGS VV and TGSDS VVV

Current-Voltage equations for the p-channel MOSFET

0DI f o r TGS VV

])().(2[2

)( 2...

DSTGSoxp

D VVVLWC

linI for TGS VV an d TGSDS VVV

)1()(2

)( 2... DSTGSoxpD VVVLWCsatI f o r TGS VV an d TGSDS VVV

Figure 1.1 : Drain current vs gate voltage characteristics for NMOS and PMOS

-1.00E-04

-5.00E-05

0.00E+00

5.00E-05

1.00E-04

1.50E-04

2.00E-04

-2 -1 0 1 2

Id(A),D

rain

current

Vgs(V),Gate to source volt age

NMOSVds=-1.8V

Vds=-1.35V

Vds=-0.9V

Vds=-.45V

Vds=0V

Vds=1.80V

Vds=1.35V

Vds=0.90V

Vds=0.45V

Vds=0.00V

PMOS

)1()(2

)( 2...

DSTGSoxn

D VVVLWC

satI )1()(2

)( 2...

DSTGSoxn

D VVVLWC

satI


2/6

2

Figure 1.2: Drain current vs Drain to source voltage characteristics for NMOS and PMOS

2. MOS MODEL PARAMETER EXTRACTION

2.1THRESHOLD VOLTAGE TV

Fig2.1: Gate to Source Voltage vs Drain current and its second derivative

TV =478.74 mV

-0.0001

-0.00005

0

0.00005

0.0001

0.00015

0.0002

-2 -1.5 -1 -0.5 0 0 .5 1 1.5 2

Id,D

rain

Current(A)

Vds,Drain to source Voltage(V)

Vgs=1.80

Vgs=1.44V

Vgs=1.08

Vgs=0.72V

Vgs=0.00V

Vgs=-0.36V

Vgs=-0.72V

Vgs=-1.08V

Vgs=-1.44V

Vgs=-1.8V

N M O SPM O S

-5.00E-05

0.00E+00

5.00E-05

1.00E-04

1.50E-04

2.00E-04

2.50E-04

3.00E-04

3.50E-04

4.00E-04

4.50E-04

0 0.5 1 1 .5 2

Drain

current(A)

Vgs(V)

Threshold Voltage

second derivat ive

Ids(A)


3/6

3

2.2 DRAIN-INDUCED BARRIER LOWERING

THEORY

A part of the region below gate is already depleted a smaller threshold suffices to cause strong inversion in short

channel devices. By increasing the drain-source voltage the width of drain-junction depletion region increases

consequently threshold decreases with increasing DSV .This effect is known as drain-induced barrier

lowering(DIBL).

It can be estimated asDS

T

V

V

Fig 2.2.: Gate to Source Voltage vs Drain current and its second derivative at differentvalues of Vds

CALCULATIONS

2THV =0.48V, 1THV =0.52V ,Vds2=1.8V,Vds1=1.0V, DIBL= -0.05

-1.00E-04

-5.00E-05

0.00E+00

5.00E-05

1.00E-04

1.50E-04

2.00E-04

2.50E-04

3.00E-04

3.50E-04

4.00E-04

4.50E-04

0 0.5 1 1.5 2

Id

(A)

Vgs(V)

DIBL

Vds =1.0V

Vds =1.8V

2n d

der ivat iveat Vds=1.8V

2n d

der ivat iveat Vds=1.0V


4/6

4

2.3 EFFECT OF CHANNEL LENGTH MODULATION

Figure 2.3: Drain current vs Drain to source voltage characteristics for NMOS at

Vgs=1.8V

THEORY

If DSV is increased beyond )(satDSV the additional voltage applied to the drain appears across the end of the channel and

drain region. This voltage accelerates the electrons that reach the drain end of the channel and sweeps them across the

depletion region into drain. Channel length in effect is reduced since DI is inversely proportional to channel length

current increases with DSV after )(satDSV

1

2

1

2

1

1

)(

)(

DS

DS

satD

satD

V

V

I

I

CALCULATION

Selecting values

2DSV =1.8V and 1DSV =1.7V ,both greater than )(satDSV

2)(satDI = 0.0001747 A and 1)(satDI = 0.0001731 A

=0.109661

V

0

0.00002

0.00004

0.00006

0.000080.0001

0.00012

0.00014

0.00016

0.00018

0.0002

0 0.5 1 1.5 2

Ids(A),D

rain

current

Vds(V),Drain to Source Volt age

Channe l length m odulat ion

Vgs=1.8V


5/6

5

2.4 BODY EFFECT COEFFICIENT

THEORY

The effect of substrate bias is to widen the depletion region and raise the threshold voltage.

CALCULATION

0TV =478.74mV, TV =542.96M v, SBV =0.4V, typically F2 =0.8V

=0.319 21

V

RESULTS AND INFERENCES

1. The difference in amount of drain currents in NMOS and PMOS is due to the difference in electron hole

mobility. For electron mobility is higher therefore NMOS structures provides higher currents.

2. Threshold voltage at Vsb=0 is 478.74Mv.

3. DIBL= -0.05V .As Vds increases threshold voltage lowers.

4. = 0.10966 1

V In saturation region current increases as Vds increases.

5. =0.3192

1

V .As Vsb increases threshold voltage also increases

-5.00E-05

0.00E+00

5.00E-05

1.00E-04

1.50E-04

2.00E-04

2.50E-04

3.00E-04

3.50E-04

4.00E-04

4.50E-04

0 0.5 1 1.5 2

Id(A)

Vgs(V)

Body effect coefficient secondder ivat iveat Vsb=0

Ids(A) at

Vsb=0

second

der ivat ive

at Vsb=0.4V

Ids at

Vsb=0.4V

)22(0 FSBFTT VVV


6/6

6

.

mosfet characteristics

Documents