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