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EE151 Class Notes: Diode  Spice Models
S.K. Tewksbury
Sept. 29, 1997
Contents
1 Introduction
1
2 IS: Saturation Current
1
3 RS: Parasitic Series Resistance of Neutral Regions
2
4 N: Emission Coeﬃcient (or Ideality Factor
3
5 TT: Transit Time
4
6 CJ0: The Zero Bias pn Capacitance
7
7 VJ: Junction Potential
8
8 M: JunctionGradient Coeﬃcient
8
9 XTF: IS Temperature Coeﬃcient
9
1
Introduction
This handout summarizes the Spice modeling of a silicon PN diode. Table 1 lists the Spice parameters,
which are described individually in the sections below.
2
IS: Saturation Current
The total DC diode current density
J
d
(Amps/cm
2
) and current
I
d
=
AJ
d
(Amps) is related to the voltage
V
across the diode and the saturation current
J
s
under reverse bias by
J
d
=
q
±
D
p
p
n
0
L
p
+
D
n
n
p
0
L
n
¶
·
e
q
(
V
bi

V
)
/kT
(1)
=
J
s
·
e
q
(
V
bi

V
)
/kT
(2)
where
J
s
=
q
±
D
p
p
n
0
L
p
+
D
n
n
p
0
L
n
¶
(3)
1
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View Full Document Table 1: Spice parameters for silicon PN diode. Parameters marked with a ”*” in column 2 are proportional
to the area (endface) of the diode.
Name
Area
Model parameter
Units
Default
Typical
IS
*
Reverse saturation current
Amps
1E14
114
RS
*
Parasitic resistance of neutral regions
Ohms
0
10
N
Emission Coeﬃcient
1
0.5 to 1
(also called ideality factor)
TT
Transit time
seconds
0
0.1NS
CJO
*
Zero bias pn capacitance
Farads
0
2pF
VJ
Junction potential
Volts
1
0.6
M
Junctiongradient coeﬃcient
0.5
0.5
EG
Activation energy
Electron Volts
1.11
1.11
(same as energy gap)
XTF
IS temperature coeﬃcient
3
3
KF
Flicker noise coeﬃcient
0
AF
Flicker noise exponent
1
FC
Forward bias depletion
0.5
capacitance coeﬃcient
BV
Reverse breakdown voltage
Volts
∞
50
IBV
*
Reverse breakdown current
Amps
1E10
J
d
and
J
s
are current densities, with the total currents
I
d
and
I
s
determined by the cross sectional area
A
through which the current enters and leaves the diode, i.e.,
I
s
=
J
s
·
A
(4)
I
d
=
I
s
·
e
q
(
V
bi

V
)
/kT
(5)
The Spice parameter
IS
is
I
s
. Three cases arise in obtaining
I
s
.
1. An estimate of
J
s
can be obtained if you know the physical parameters used in (3). This “physics
model” also allows you to explore the eﬀect of various variations in fabrication (e.g., doping densities
in the N and Ptype regions, minority carrier lifetimes, etc.).
I
s
is then obtained by multiplying by
the area of the device.
2. The saturation current density
J
s
(or the saturation current
I
s
) may be speciﬁed directly, either on a
data sheet for a commercial diode or as a speciﬁcation for diodes in a given VLSI circuit.
3. The saturation current may be estimated from current voltage characteristics (either data sheets or
experimental measurement).
3
RS: Parasitic Series Resistance of Neutral Regions
The neutral regions of the diode are the regions between the depletion layer edges and the contacts to the
diode. There is a nonzero resistance in these regions, which lead to a voltage drop between the external
2
voltage applied
V
appl
and the voltage
V
across the diode in (2). If the distance between the junction (point
where Ntype region changes to Ptype region) and the Nside contact is
l
n
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This note was uploaded on 10/27/2009 for the course ECE 5 taught by Professor Chavez during the Spring '09 term at Stevens.
 Spring '09
 chavez

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