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Second breakdown in high voltage MOS transistors
Solid-State Elecmnics.
1977, Vol. 20, pp. 875478.
Pergamon Press. Printed in Great
SECOND BREAKDOWN
Britain
IN HIGH VOLTAGE
Surinder General
Electric (Received
The characteristics it an attractive interest
in this device
In many cases,
has centered
conditions
description
conditions
conditioning
systems
cy and light weight
may be of a nature
Usually,
will be discussed current
regulators,
investigations
injection
is determined
of this phenomenon
process.
field that triggers
by the high concentration
of mobile
The conditions
current density,
jcrit and associated
is a
to
as
transisand
of the electric in the drain
for second breakdown
(1, 3).
To a first order
space charge necessary
to
is given by (1, 2):
ND and WD are the donor concentration la, EC is the critical velocity
described
space charge
necessary
approximation,
injection
efficien-
impact ionization,
The spatial distribution
and experimentally
the critical
power
the full voltage
in diodes and bipolar
both analytically
vs is the saturated
In numerous
the path is not long enough
to occur have been verified
trigger avalanche
of the MOSFET under
Even so, the device may fail due to a mechanism
by an avalanche
locus, the
from an "on" to "off" state that
the time taken to traverse
space, and the voltage drop in this region.
mences
switch.
in three parts,
etc., high operating
the full current, while maintaining
that it is an intense electric
seen in Figure
More recent
such that it
voltage
and a high voltage.
the transition
tors (2), suggest,
where
make
The V-I locus of the power switch in such circuits
It is during
to conduct
heat.
choppers,
Recent
field intensity
as a high voltage
and, the physics
process,
second breakdown.
is followed
usefulness
the necessary
of a high current density
are necessary.
is required
substantial
to produce
such as inverters,
its terminals.
produce
applications.
in MOS transistors
required
loop as given in (1).
across
and memory
locus of the transistor
of the second breakdown
simultaneous
the device
(MOS) transistor
of the device due to second breakdown.
viz., the circuit
square
Semiconductor
on its potential
The subject of second breakdown
physical
Metal-Oxide
for use in linear, digital
the voltage-current
leads to failure
Krishna
Company - Corporate Research & Development Schenectady, NY 12301 20 May 1977; in revised form 28 July 1977)
of a conventional
component
MOS TRANSISTORS
electric
of electrons
and the rise in current
through
and width
of the drain
space respectively,
field for impact ionization
in the high field.
the device 875
Once avalanche
is not controlled,
as
( w LO5 V/cm), and injection
it inevitably
com-
results
876
Communications
INVERSION LAYER
,lNVERSION LAYER
I
) REPLETION LAYER
Figure
la:
ELECTRON SPACE CHARGE
sistor,
+
DEPLETION LAYER
"V;
Figure
tran-
Cross section of a D-MOS
tor for superior capability,
0.1 pm (9)
the drain
adequately,
but were
the saturation
between drain
electric
interface
now repels
include
two dimensions,
(10).
In an effort
grated
circuits,
MOS structure Depletion
with a wide drain such structures, To account
Studies
in an increase D'
for mobile
the electric
space charge
current
=
"C e(y)
The current
in the bulk.
The
in
has been extended
the density
tc
effects in inteThe D-
of an Enhancement
and a
that, the short channel
capability,
may also be combined
The breakdown
been reported
the expression
to the
layer of the
been developed.
indicate
has recently
21 2L
region and
(8, 9), and hot electron
connection
in source drain current
PC ojds
(1).
(SCL) flow which
the analysis
have recently
of the E/D structure
space charge, we modify
carried
and increase
performance,
conditions
ir
(6, 7) by the
in the drain region.
Further,
as a hybrid
density
field normal
in the inversion
that could support a high voltage.
under electrostatic
the pinch-off
is, therefore,
transistor
la may be considered
region W
surface
field.
for mobile
(11) and V-MOS
(E/D) device.
length that results
electric
given by Eq.
region was described
as having Space-Charge-Limited
to account
the D-MOS
to explain
charge
terminal
to raise the power-speed
of Figure
mode
mobile
from the silicon
the longitudinal
second breakdown
the source region of the channel
In this situation,
region and the drain
space has been analyzed
turn influences
field.
in attempts
the pinch-off
that accumulates
the charge
the pinch-off
Later,
of a MOS transis-
d FJ 1 to 10 pm
the critical value
(4, 5) described
successful
(VD > VC).
of transverse
can exceed
physics
not quite
stage
silicon dioxide channel,
in MOS device
ELECTRON SPACE CHARGE
It will be shown that the current
of the transistor.
space of the MOS transistor
Early works
reversal
failure
I
Cross section
lb:
e(y) varies from 0.01 to
in the catastrophic
,
I
voltage
of
(12).
for channel
current
(2)
(5):
877
Communications
C ox
is the capacitance per unit area, L the length of the channel, and 6(y) accounts for any
spreading of the space charge as it is transported across the drain space. Investigations of Popa (9) show that the space charge density is only a function of gate voltage, and independent of drain voltage VD, and drain space length WD.
Choosing the minimum current den-
sity (which actually occurs at the drain contact) as prevailing over the entire length WD, reduces the problem to one dimension, and provides a conservative estimate of j,s. In the in the structure given with a lightly doped drain region, the breakdown voltage, V BR' absence of mobile charge:
'SBR "
(3)
Ec 'D
Combining Eqs. (1) and (2) where jds"
jcrit gives the breakdown voltage, VSBR, in the
presence of mobile charge:
V SBR "
If 'SBR < 'BR'
EL 6 c sivs jds -qvs%
the voltage switching of the MOS transistor is limited by second breakdown.
Consider a MOS transistor with the following parameters: SiO2 thickness = 0.6 pm, L = 10 pm, wD
14 = 50 pm, ND s 10 cmw3, VG = 10 volts, B(y) r 700 12 (9), pn
= 200 cm2/volt-sec. From
Eq. (2), jds z 7900 A/cm2, from Eq. (3) VBR = 500 V, and from Eq. (4) VSBR?
14V. Clearly
such a device would be severely limited in its ability to switch voltage (in the presence of full current) by second breakdown. In spite of the gross assumptions that, Ec is independent of the charge concentration,and the unmodulated drain resistivity is nearly intrinsic; it would take significant deviations from the value of B(y) used in the above example, before VSBR-+VBR' A large divergence of the current density jds, appears unlikely in the D-MOS and V-MOS structures because even though the mobile charge is repelled from the interface, as mentioned earlier, conduction is at or very near the silicon/silicondioxide surface. A superior structure, for the reduction in jds, and therefore an increase in the second breakdown voltage VSBR, is given in Figure lb. The voltage and the electric field are now present in the bulk, the distance 'd' determines the punch-throughvoltage between gate and drain, and also determines the drain current density jds. The dimensions of 'd' are of the order of microns compared to 0(y) w 0.01 to 0.1 microns in the conventional MOS transistor, and one may therefore expect a considerable improvement in the threshold for second breakdown.
The structure of Figure lb should have a power-speed performance comparable to the
D-MOS/V-MOS devices, with significant improvements, however, in packing density and second breakdown capability.
878
Communications References
(1) S. Krishna and P. L. Hower, Proc. IEEE, 6l, 393 (1973). (2) P. L. Hower and V.G.K. Reddi, IEEE Trans. Electron Dev.,ED_17, 322 (1970). (3) B. A. Beatty, S. Krishna and M. S. Adler, IEEE Trans. Electron Dev.,ED_23, 851 (1976) (4) H.K.J. Ihantola and J. L. Mall, Solid State Electronics, 1, 423 (1964). (5) S. R. Hofstein and F. P. Heiman, Proc. IEEE, 5l, 1190 (1963). (6) J. E. Schroeder and R. S. Muller, IEEE Trans. Electron Dev., ED_15, 954 (1968). (7) H. W. Loeb, R. Andrew and W. Love, Electronics Letters, 5, 352 (1968). (8) G. Merckel, J. Bore1 and N. Cupcia, IEEE Trans. Electron Dev., ED-19, 681 (1972). (9) A. Popa, IEEE Trans. Electron Dev., ED_19, 774 (1972). (10) G. A. Armstrong and J. A. Magowan, Solid State Electronics, 14, 723 (1971). (11) H. Masuda, T. Masuhara, M. Nagata and N. Hashmito, Proc. 4th Conf. on Solid State Devices, Tokyo, 1972. (12) M. J. Declercq and J. D. Plumner, IEEE Trans. Electron Dev., ED-23, 1 (1976).
1977, Vol. 20, pp. 875478.
Pergamon Press. Printed in Great
SECOND BREAKDOWN
Britain
IN HIGH VOLTAGE
Surinder General
Electric (Received
The characteristics it an attractive interest
in this device
In many cases,
has centered
conditions
description
conditions
conditioning
systems
cy and light weight
may be of a nature
Usually,
will be discussed current
regulators,
investigations
injection
is determined
of this phenomenon
process.
field that triggers
by the high concentration
of mobile
The conditions
current density,
jcrit and associated
is a
to
as
transisand
of the electric in the drain
for second breakdown
(1, 3).
To a first order
space charge necessary
to
is given by (1, 2):
ND and WD are the donor concentration la, EC is the critical velocity
described
space charge
necessary
approximation,
injection
efficien-
impact ionization,
The spatial distribution
and experimentally
the critical
power
the full voltage
in diodes and bipolar
both analytically
vs is the saturated
In numerous
the path is not long enough
to occur have been verified
trigger avalanche
of the MOSFET under
Even so, the device may fail due to a mechanism
by an avalanche
locus, the
from an "on" to "off" state that
the time taken to traverse
space, and the voltage drop in this region.
mences
switch.
in three parts,
etc., high operating
the full current, while maintaining
that it is an intense electric
seen in Figure
More recent
such that it
voltage
and a high voltage.
the transition
tors (2), suggest,
where
make
The V-I locus of the power switch in such circuits
It is during
to conduct
heat.
choppers,
Recent
field intensity
as a high voltage
and, the physics
process,
second breakdown.
is followed
usefulness
the necessary
of a high current density
are necessary.
is required
substantial
to produce
such as inverters,
its terminals.
produce
applications.
in MOS transistors
required
loop as given in (1).
across
and memory
locus of the transistor
of the second breakdown
simultaneous
the device
(MOS) transistor
of the device due to second breakdown.
viz., the circuit
square
Semiconductor
on its potential
The subject of second breakdown
physical
Metal-Oxide
for use in linear, digital
the voltage-current
leads to failure
Krishna
Company - Corporate Research & Development Schenectady, NY 12301 20 May 1977; in revised form 28 July 1977)
of a conventional
component
MOS TRANSISTORS
electric
of electrons
and the rise in current
through
and width
of the drain
space respectively,
field for impact ionization
in the high field.
the device 875
Once avalanche
is not controlled,
as
( w LO5 V/cm), and injection
it inevitably
com-
results
876
Communications
INVERSION LAYER
,lNVERSION LAYER
I
) REPLETION LAYER
Figure
la:
ELECTRON SPACE CHARGE
sistor,
+
DEPLETION LAYER
"V;
Figure
tran-
Cross section of a D-MOS
tor for superior capability,
0.1 pm (9)
the drain
adequately,
but were
the saturation
between drain
electric
interface
now repels
include
two dimensions,
(10).
In an effort
grated
circuits,
MOS structure Depletion
with a wide drain such structures, To account
Studies
in an increase D'
for mobile
the electric
space charge
current
=
"C e(y)
The current
in the bulk.
The
in
has been extended
the density
tc
effects in inteThe D-
of an Enhancement
and a
that, the short channel
capability,
may also be combined
The breakdown
been reported
the expression
to the
layer of the
been developed.
indicate
has recently
21 2L
region and
(8, 9), and hot electron
connection
in source drain current
PC ojds
(1).
(SCL) flow which
the analysis
have recently
of the E/D structure
space charge, we modify
carried
and increase
performance,
conditions
ir
(6, 7) by the
in the drain region.
Further,
as a hybrid
density
field normal
in the inversion
that could support a high voltage.
under electrostatic
the pinch-off
is, therefore,
transistor
la may be considered
region W
surface
field.
for mobile
(11) and V-MOS
(E/D) device.
length that results
electric
given by Eq.
region was described
as having Space-Charge-Limited
to account
the D-MOS
to explain
charge
terminal
to raise the power-speed
of Figure
mode
mobile
from the silicon
the longitudinal
second breakdown
the source region of the channel
In this situation,
region and the drain
space has been analyzed
turn influences
field.
in attempts
the pinch-off
that accumulates
the charge
the pinch-off
Later,
of a MOS transis-
d FJ 1 to 10 pm
the critical value
(4, 5) described
successful
(VD > VC).
of transverse
can exceed
physics
not quite
stage
silicon dioxide channel,
in MOS device
ELECTRON SPACE CHARGE
It will be shown that the current
of the transistor.
space of the MOS transistor
Early works
reversal
failure
I
Cross section
lb:
e(y) varies from 0.01 to
in the catastrophic
,
I
voltage
of
(12).
for channel
current
(2)
(5):
877
Communications
C ox
is the capacitance per unit area, L the length of the channel, and 6(y) accounts for any
spreading of the space charge as it is transported across the drain space. Investigations of Popa (9) show that the space charge density is only a function of gate voltage, and independent of drain voltage VD, and drain space length WD.
Choosing the minimum current den-
sity (which actually occurs at the drain contact) as prevailing over the entire length WD, reduces the problem to one dimension, and provides a conservative estimate of j,s. In the in the structure given with a lightly doped drain region, the breakdown voltage, V BR' absence of mobile charge:
'SBR "
(3)
Ec 'D
Combining Eqs. (1) and (2) where jds"
jcrit gives the breakdown voltage, VSBR, in the
presence of mobile charge:
V SBR "
If 'SBR < 'BR'
EL 6 c sivs jds -qvs%
the voltage switching of the MOS transistor is limited by second breakdown.
Consider a MOS transistor with the following parameters: SiO2 thickness = 0.6 pm, L = 10 pm, wD
14 = 50 pm, ND s 10 cmw3, VG = 10 volts, B(y) r 700 12 (9), pn
= 200 cm2/volt-sec. From
Eq. (2), jds z 7900 A/cm2, from Eq. (3) VBR = 500 V, and from Eq. (4) VSBR?
14V. Clearly
such a device would be severely limited in its ability to switch voltage (in the presence of full current) by second breakdown. In spite of the gross assumptions that, Ec is independent of the charge concentration,and the unmodulated drain resistivity is nearly intrinsic; it would take significant deviations from the value of B(y) used in the above example, before VSBR-+VBR' A large divergence of the current density jds, appears unlikely in the D-MOS and V-MOS structures because even though the mobile charge is repelled from the interface, as mentioned earlier, conduction is at or very near the silicon/silicondioxide surface. A superior structure, for the reduction in jds, and therefore an increase in the second breakdown voltage VSBR, is given in Figure lb. The voltage and the electric field are now present in the bulk, the distance 'd' determines the punch-throughvoltage between gate and drain, and also determines the drain current density jds. The dimensions of 'd' are of the order of microns compared to 0(y) w 0.01 to 0.1 microns in the conventional MOS transistor, and one may therefore expect a considerable improvement in the threshold for second breakdown.
The structure of Figure lb should have a power-speed performance comparable to the
D-MOS/V-MOS devices, with significant improvements, however, in packing density and second breakdown capability.
878
Communications References
(1) S. Krishna and P. L. Hower, Proc. IEEE, 6l, 393 (1973). (2) P. L. Hower and V.G.K. Reddi, IEEE Trans. Electron Dev.,ED_17, 322 (1970). (3) B. A. Beatty, S. Krishna and M. S. Adler, IEEE Trans. Electron Dev.,ED_23, 851 (1976) (4) H.K.J. Ihantola and J. L. Mall, Solid State Electronics, 1, 423 (1964). (5) S. R. Hofstein and F. P. Heiman, Proc. IEEE, 5l, 1190 (1963). (6) J. E. Schroeder and R. S. Muller, IEEE Trans. Electron Dev., ED_15, 954 (1968). (7) H. W. Loeb, R. Andrew and W. Love, Electronics Letters, 5, 352 (1968). (8) G. Merckel, J. Bore1 and N. Cupcia, IEEE Trans. Electron Dev., ED-19, 681 (1972). (9) A. Popa, IEEE Trans. Electron Dev., ED_19, 774 (1972). (10) G. A. Armstrong and J. A. Magowan, Solid State Electronics, 14, 723 (1971). (11) H. Masuda, T. Masuhara, M. Nagata and N. Hashmito, Proc. 4th Conf. on Solid State Devices, Tokyo, 1972. (12) M. J. Declercq and J. D. Plumner, IEEE Trans. Electron Dev., ED-23, 1 (1976).