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# EE 434 Lecture 12 - PowerPoint PPT Presentation

EE 434 Lecture 12. Devices in Semiconductor Processes Diodes Capacitors MOS Transistors. Quiz 10. A “10K” resistor has a temperature coefficient of +80ppm/ o C If the resistor was measured to be 9.83K at 20 o C, what would be the resistor value at 80 o C? . And the number is ….

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Presentation Transcript
EE 434Lecture 12

Devices in Semiconductor Processes

Diodes

Capacitors

MOS Transistors

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?

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?

Solution

• 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

• Resistor

• Diode

• Capacitor

• MOSFET

• BJT

N

P

Depletion region created that is ionized but void of carriers

N

P

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-

Physical Boundary Separating n-type and p-type regions

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

N-

P+

Physical Boundary Separating n-type and p-type regions

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

N

P

I

V

I

N

P

V

I

V

Diode Equation:

JS= Sat Current Density

A= Junction Cross Section Area

VT=kT/q

n is approximately 1

• Resistor

• Diode

• Capacitor

• MOSFET

• BJT

• Types

• Parallel Plate

• Fringe

• Junction

A2

C

A1

cond1

cond2

d

insulator

A = area of intersection of A1 & A2

One (top) plate intentionally sized smaller to determine C

: Dielectric constant

C

d

A is the area where the two plates are parallel

Only a single layer is needed to make fringe capacitors

Junction Capacitor

C

VD

p

d

d

n

depletion

region

• Note: d is voltage dependent

• capacitance is voltage dependent

• usually parasitic caps

• varicaps or varactor diodes exploit

• voltage dep. of C

Cj0: junction capacitance at VD = 0V

B: barrier or built-in potential

• Resistor

• Diode

• Capacitor

• MOSFET

• BJT

Poly

Gate oxide

n-active

p-sub

Gate

Drain

Source

L

W

LEFF

Bulk

Poly

Gate oxide

n-active

p-sub

depletion region (electrically induced)

VDS

ID

VGS

IG

VBS

IB

Apply small VGS

(VDS and VBS assumed to be small)

ID=0

IG=0

IB=0

Depletion region electrically induced in channel

Termed “cutoff” region of operation

VDS

ID

VGS

IG

VBS

IB

Increase VGS

(VDS and VBS assumed to be small)

ID=0

IG=0

IB=0

Depletion region in channel becomes larger

VDS

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

ID

VGS

IG

VBS

IB

(VDS and VBS small)

Increase VGS more

IDRCH=VDS

IG=0

IB=0

Inversion layer forms in channel

Inversion layer will support current flow from D to S

Channel behaves as thin-film resistor

VDS

ID

VGS

IG

VBS

IB

(VDS and VBS small)

Increase VGS more

IDRCH=VDS

IG=0

IB=0

Inversion layer in channel thickens

RCH will decrease

Termed “ohmic” or “triode” region of operation

For VDS small

VDS

ID

VGS

IG

VBS

IB

(VBS small)

Increase VDS

ID=?

IG=0

IB=0

Inversion layer thins near drain

ID no longer linearly dependent upon VDS

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

For VDS larger

VDS

ID

VGS

IG

VBS

IB

(VBS small)

Increase VDS even more

ID=?

IG=0

IB=0

Inversion layer disappears near drain

Termed “saturation”region of operation

Saturation first occurs when VDS=VGS-VT

For VDS at saturation

VDS

ID

VGS

IG

VBS

IB

(VBS small)

Increase VDS even more (beyond VGS-VT)

ID=?

IG=0

IB=0

Nothing much changes !!

Termed “saturation”region of operation

For VDS in Saturation

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