EE 434Lecture 12

Devices in Semiconductor ProcessesDiodes

Capacitors

MOS Transistors

Quiz 10 A “10K” resistor has a temperature coefficient of +80ppm/oC If the resistor was measured to be 9.83K at 20oC, what would be the resistor value at 80oC?

And the number is ….

631

24578

9

3

Quiz 10

Solution

61212 10

TCRTT1 TRTR

A “10K” resistor has a temperature coefficient of +80ppm/oC If the resistor was measured to be 9.83K at 20oC, what would be the resistor value at 80oC?

9.877184K9.83K1.004810

8020-80 TR

62

183.9 K

• Process Flow is a “recipe” for the process– Shows what can and can not be made – Gives insight into performance capabilities and limitations

• Back-End Processes– Die attach options (eutectic, preform,conductive epoxy)

• Stresses the die

– Bonding• Wire bonding• Bump bonding

– Packaging• Many packaging options• Package Costs can be large so defective die should be

eliminated before packaging

Review from Last Time

Basic Devices and Device Models

• Resistor

• Diode

• Capacitor

• MOSFET

• BJT

Diodes (pn junctions)

Depletion region created that is ionized but void of carriers

N P

pn Junctions

Physical Boundary Separating n-type and p-type regions

If doping levels identical, depletion region extends equally into n-type and p-type regions

N P

pn Junctions

Physical Boundary Separating n-type and p-type regions

Extends farther into p-type region if p-doping lower than n-doping

N+P-

pn Junctions

Physical Boundary Separating n-type and p-type regions

Extends farther into n-type region if n-doping lower than p-doping

N- P+

pn Junctions

VI

N P

pn Junctions

VI

0V0

0VAeJITnV

V

S

I

V

Diode Equation:

JS= Sat Current DensityA= Junction Cross Section AreaVT=kT/qn is approximately 1

N P

Basic Devices and Device Models

• Resistor

• Diode

• Capacitor

• MOSFET

• BJT

Capacitors

• Types– Parallel Plate– Fringe– Junction

Parallel Plate Capacitors

C

d

A1

A2

cond1

cond2

insulator

A = area of intersection of A1 & A2

d

AC

One (top) plate intentionally sized smaller to determine C

: Dielectric constant

Parallel Plate Capacitors

ACC dd

AεC

areaunit

CapC If d

d

εCd

where

Fringe Capacitors

d

C

d

AεC

A is the area where the two plates are parallel

Only a single layer is needed to make fringe capacitors

Fringe Capacitors

C

Capacitance

2

φV

φV

1

ACC B

FBn

B

D

jo

for

ddepletionregion

C

Junction Capacitor

d

AC

Note: d is voltage dependent-capacitance is voltage dependent-usually parasitic caps-varicaps or varactor diodes exploit voltage dep. of C

dp

n

VD

0.6VφB Cj0: junction capacitance at VD = 0V

B: barrier or built-in potential

Basic Devices and Device Models

• Resistor

• Diode

• Capacitor

• MOSFET

• BJT

n-Channel MOSFET

Polyn-active

Gate oxide

p-sub

n-Channel MOSFET

LEFF

L

W

Source

DrainGate

Bulk

n-Channel MOSFET

Polyn-active

Gate oxide

p-subdepletion region (electrically induced)

n-Channel MOSFET Operation and Model

VBS

VGS

VDS

Apply small VGS

(VDS and VBS assumed to be small) ID=0IG=0IB=0

Depletion region electrically induced in channel

ID

IGIB

Termed “cutoff” region of operation

n-Channel MOSFET Operation and Model

VBS

VGS

VDS

Increase VGS

(VDS and VBS assumed to be small) ID=0IG=0IB=0

Depletion region in channel becomes larger

ID

IGIB

n-Channel MOSFET Operation and Model

VBS

VGS

VDS

Increase VGS moreIDRCH=VDS

IG=0IB=0

Inversion layer forms in channel

ID

IGIB

(VDS and VBS small)

Inversion layer will support current flow from D to SChannel behaves as thin-film resistor

Critical value of VGS that creates inversion layer termed threshold voltage, VT)

n-Channel MOSFET Operation and Model

VBS

VGS

VDS

Increase VGS moreIDRCH=VDS

IG=0IB=0

Inversion layer in channel thickens

ID

IGIB

(VDS and VBS small)

RCH will decreaseTermed “ohmic” or “triode” region of operation

Triode Region of Operation

VDS

VBS = 0

VGS

ID

IG

IB

OX

TGSCH C1

VVWL

R

0II

VVVL

WμCI

BG

DSTGSOXD

For VDS small

n-Channel MOSFET Operation and Model

VBS

VGS

VDS

Increase VDS

ID=?IG=0IB=0

Inversion layer thins near drain

ID

IGIB

(VBS small)

ID no longer linearly dependent upon VDS

Still termed “ohmic” or “triode” region of operation

Triode Region of Operation

VDS

VBS = 0

VGS

ID

IG

IB

OX

TGSCH C1

VVWL

R

0II

V2

VVV

L

WμCI

BG

DSDS

TGSOXD

For VDS larger

n-Channel MOSFET Operation and Model

VBS

VGS

VDS

Increase VDS even moreID=?IG=0IB=0

Inversion layer disappears near drain

ID

IGIB

(VBS small)

Termed “saturation”region of operationSaturation first occurs when VDS=VGS-VT

Saturation Region of Operation

VDS

VBS = 0

VGS

ID

IG

IB

0II

VV2L

WμCI

VV2

VVVV

L

WμCI

V2

VVV

L

WμCI

BG

2TGS

OXD

TGSTGS

TGSOXD

DSDS

TGSOXD

lyequivalentor

lyequivalentorFor VDS at saturation

n-Channel MOSFET Operation and Model

VBS

VGS

VDS

Increase VDS even more (beyond VGS-VT)ID=?IG=0IB=0

Nothing much changes !!

ID

IGIB

(VBS small)

Termed “saturation”region of operation

Saturation Region of Operation

VDS

VBS = 0

VGS

ID

IG

IB

0II

VV2L

WμCI

BG

2TGS

OXD

For VDS in Saturation

Model Summary

VDS

VBS = 0

VGS

ID

IG

IB

TGSDSTGS2

TGSOX

TGSDSGSDSDS

TGSOX

TGS

D

VVVVVVV2LW

μC

VVVVVV2

VVV

LW

μC

VV0

I T

Note: This is the third model we have introduced for the MOSFET