6.3.3
Proceedings of 1990 International Symposium on Power Semiconductor Devices & ICs, Tokyo, pp. 277-282
ULTRA HIGH di/dt PULSE SMTCHING
OF 2500 V MO5 ASSISTED GATE-TRIGGERED THYRISTORS (MAGTs)
Takashi Shinohe, Akio Nakagawa, Yoshihiro Minami, Masaki Atsuta,
Yoshio Kamei and Hiromichi Ohashi
Research & Development Center, Toshiba Corporation
1. Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi 210, Japan
Phone:044-549-2138, Fax:044-555-2074
ABSTRACT
INTRODUCTION
An ultra high difdt 2500 V MOS Assisted
Thyristor
(MAGT)
was
developed to replace a thyratron in pulsed
power applications, such as high repetition
(>f
kpps)
excimer
lasers.
The main
objective in developing such devices is to
realize extremely low transient turn-on
power losses, while still retaining high
breakdown voltages. The MAGT exhibits the
much higher turn-on characteristics than
that for IGBTs.
It is shown that 40
kAfgsfcm' for difdt can be attained for a
turn-on from 1500 V anode voltage, 9090
Afcm' peak anode current, and 0.7 ,us pulse
width, with an extremely low turn-on power
loss.
Gate-triggered
k
A part of this work was accomplished under
the Research and Development Program on
"Advanced Material Processing and Machining
System," conducted under a program set up by
the New Energy and Industrial Technology
Development Organization.
Gate
Base Cathode
Much progress has been made in achieving
functionally integrated MOS-bipolar devices,
in regard to their maximum controllable
power. Especially, IGBTs have attained a
high forward blocking voltage (-1800 V) ( I ) ,
and a large current handling capability
(-400 A ) (2). Now, they are widely used for
many
applications, such
as
replacing
conventional bipolar transistors, to take
advantage of their easy driving and fast
switching capabilities.
However, higher
forward blocking voltages (>2000 V) lead to
unacceptable high on-state voltages, even in
IGBTs. Therefore, a new class of integrated
MOS-bipolar devices, based on the thyristor
mode operation, has been actively studied
(3)-(8).
Their application range has now been
extended to new fields, including pulsed
power applications, such as high repetition
Although
excimer lasers (>1 kpps) (9).
thyratrons are commonly used to generate
very short high current pulses f o r this
Gate
Source
P
9
Lfd7-l
n- channel
NE+/
I
n-channel
N
;
PE+
MAGT
b
I GBT
Anode
b
Drain
Fig.1 Basic structures for MAGT (left) and IGBT (right).
277
field, their lifetime (IO8 shots) and
reliability are not adequate for use in high
repetition excimer lasers. Although many
efforts
to
replace
thyratrons
with
conventional
high
power
semiconductor
devices have been made recently (10)-(12),
their large turn-on power losses prevent
them from being applied to high repetition
excimer lasers. The investigation on IGBT
switches applied for this objective started
recently (9). However, its application area
is limited to small power lasers, because of
their current saturation characteristics.
Therefore, power semiconductor devices,
which can switch pulsive high current at
high repetition rate, are urgently required.
This paper proposes an MOS Assisted
-Gate-triggered Thyristor (MAGT) for pulsed
power applications. It is shown that the
loss can be
transient turn-on power
extremely reduced, even in the high di/dt
ratio.
( a ) Pulse width
3ps
0.4 400
0.3 300
0.2 200
0.1 100
0.0
0
0
1
TIME
2
3
(PSI
( b 1 Pulse width 0 . 7 ~
DEVICE STRUCTURE
The MAGT basic device structure is shown
in Fig.1, compared with the IGBT device
structure. The MOS gate electrode is placed
on the edge of the p-base layer (PB) to
turn-on this thyristor with a high dildt
ratio. A base electrode is placed on the
p-base layer (PB ) , to ensure constant p-base
potential and high dv/dt immunity, while the
source el+ectrode contacts both the source
layer (Ns ) and the p-base layer(PB) in the
IGBT structure.
is
minimized,
The
n-base
width
contingent upon the forward blocking voltage
being maintained, in order to rapidly
increase the n-base carrier density. The
impurity profile is designed to attain high
trigger sensitivity.
The gate electrode
length and
the n-emitter length are
optimized, considering on-state voltages and
dildt characteristics.
When a positive bias is applied to the
gate electrode, electrons are directly
injected from the cathode electrode toward
the n-base layer (N ) through the n-channel.
resulting in a rapi% increase in the n-base
electron density.
This rapid electron
injection urges hole injection from the
anode electrode.
Then, electrons are
injected from the emitter junction, and the
MAGT is latched up within some tens of nano
seconds.
This is because the p-base
potential is fixed by the base electrode,
instead of the emitter short, to rise the
emitter injection efficiency.
When the MAGT must be in its off-state,
a negative bias is applied to the base
electrode.
The leakage current in the
off-state, and the displacement current
caused by a high dv/dt are extracted from
the base electrode.
It prevents the
sensitive MAGT from being mis-triggered.
0.4 1.6
0.3 1.2
0.2 0.8
0.1 0.4
0.0 0
I
3
0.25
TIME
0.50
0.75
(PSI
Fig.2 Calculated turn-on waveforms for anode
current (IA). anode voltage (V,) and power
loss (P).
CALCULATION
Numerical calculations were carried out
to estimate the turn-on power loss for an
approximate
model,
while
making
the
following simple assumptions.
1) The n-base resistance is in inverse
proportion to the average n-base carrier
density .
2) Carrier recombination is negligible, and
the whole anode current contributes to
the carrier accumulation in the n-base.
3 ) The average n-base carrier density does
not exceed lxlO” cm-*.
4 ) The whole device area turns on
uniformly, by adopting a VLSI fine
process technology.
Figure 2 shows the calculated turn-on
waveforms f o r an ideal condition in the two
different excimer laser power unit circuits.
278
Figure 2 (a) indicates that turn-on power
loss consists of two peaks, when pulse width
is 3 p s .
One is the small peak caused by
high di/dt. The other is the large peak
caused by the following high anode current.
On the contrary, turn-on power loss is
caused by only high dildt, when pulse width
j ~ s , as shown in Fig.2 (b).
is 0 .7
Consequently, it is understood that the
on-state voltage is the primary concern f o r
the 3 p s pulse width case, while the rapid
turn-on has to be attained for the 0.7 p s
pulse
width
case.
In
other
words,
conventional slow discrete power devices are
suitable for the 3 p s pulse width case,
while high di/dt triggered power devices,
like MAGTs, are suitable for the 0 . 7 .ifs
pulse
width
case.
From
the
laser
application point of view, the shorter pulse
width is desirable, because the higher
circuit efficiency is attained by the
reduction in additional magnetic pulse
compression circuit.
~ ~ i i i i i ~ /i /~i /i/I~ili!lli
i li~i
//I
Fig.3 Fabr cated MAG7
FABRICATION
Small sized devices (3.3, mm x 4 . 9 mm
chips)
were
fabricated
in
order
to
demonstrate the high di/dt , high power pulse
Figure 3 shows the
switching for MAGTs.
fabricated device mounted onto a stem.
The process steps are similar to those
for a conventional IGBT.
The starting
material is a high resistivity neutron doped
FZ-Si wafer, whose resistivity and thickness
are determined f o r the requested forward
blocking voltage. The base electrode was
separated from the cathode electrode, to
form the MAGT device structure.
IGBT
pellets were fabricated under identical
processes for comparison. Some of these
chips were subjected to a lifetime reduction
by electron beam irradiation, in order to
gain a high dv/dt immunity.
Fig.4
Fabricated MAGT forward blocking
voltage. (VA:500 V/div., IA:lOO @/div.)
RESULTS
/'
Forward blocking voltage
A 2500 V forward blocking voltage was
realized by a resistive field plate junction
termination structure (1),(13), as is shown
in Fig.4.
On-state voltage
Figure 5 shows the V - I characteristics
for a fabricated MAGT and IGBT. The MAGT
can handle 10 kA/cmz at 7 V for the on-state
voltage, taking advantage of the t h y r i s t o r
mode operation, while the IGBT is saturated
at
300 A/cm'.
Therefore, the
IGBT
application area is limited to small power
lasers, because the peak of pulsive current
must be smaller than the saturation current.
High power handling capability is an
indispensable feature f o r pulsed power
switches.
279
I
I
/
I
I
I
I
I
I
I
l
l
1
1
1
1
1
I2 3 4 5 6 7 0
ON-STATE VOLTAGE ( V I
Fig.5 V-I characteristics
MAGT and IGBT.
for
fabricated
Turn-on c h a r a c t e r i s t i c s
F i g u r e 6 shows t h e t e s t c i r c u i t f o r
measuring
turn-on
waveforms.
The
a p p r o p r i a t e v a l u e s f o r c a p a c i t a n c e ( C) and
each
inductance
(L) were s e l e c t e d f o r
c o n d i t i o n i n t h e peak anode c u r r e n t and t h e
anode c u r r e n t r i s i n g r a t e d i / d t .
F i g u r e 7 shows t h e t u r n - o n waveform f o r
A steep increase i n t h e drain
an IGBT.
v o l t a g e was observed c o r r e s p o n d i n g t o t h e
peak d r a i n c u r r e n t (IDp), because o f t h e
drain current saturation.
The turn-on waveforms f o r 0 . 1 , 0 . 7 , and
3 p s p u l s e w i d t h s a r e shown i n F i g . 8 . I t i s
a p p a r e n t t h a t t h e t r a n s i e n t anode v o l t a g e is
s i g n i f i c a n t l y reduced f o r an MAGT. No s t e e p
i n c r e a s e i n t h e anode c u r r e n t is o b s e r v e d .
L i t t l e anode v o l t a g e i n c r e a s e is o b s e r v e d ,
f o r 3 p s p u l s e width c a s e . For 0 . 7 p s p u l s e
width c a s e , t h e t r a n s i e n t anode v o l t a g e ,
caused by h i g h d i / d t , is l e s s t h a n 100 V ,
even i n t h e c a s e o f 9090 A/cm' f o r t h e peak
anode c u r r e n t d e n s i t y ( I ) , and up t o 40
kA/ps/cm'
o f d i / d t can A t e o b t a i n e d .
No
anode v o l t a g e peak i s observed a t t h e peak
anode
current,
which
agrees
with
the
calculation
result
for
the
approximate
model.
I t is a l s o shown t h a t t h e t u r n - o n
power l o s s is h i g h e r t h a n t h a t f o r t h e o t h e r
c a s e s , because t h e anode v o l t a g e d e c r e a s e s
d u r i n g t h e s t e e p i n c r e a s e o f t h e anode
c u r r e n t , f o r t h e 0 . 1 p s p u l s e width c a s e .
F i g u r e 9 shows turn-on
power
loss
dependence on t h e p u l s e width f o r a 5 kpps
o p e r a t i o n , when t h e product o f t h e peak
anode c u r r e n t ( I ) and t h e p u l s e width ( t w )
is c o n s t a n t , whk% c o r r e s p o n d s t o t h e p u l s e
width adjustment i n t h e a c t u a l l a s e r power
s u p p l y . I n t h i s f i g u r e , t h e 1st p a r t is t h e
power l o s s g e n e r a t e d d u r i n g t h e r i s i n g t i m e .
The 2nd p a r t is t h e r e s i d u a l p a r t of t h e
1st
part
total
power
loss.
The
m o n o t o n i c a l l y d e c r e a s e s a s t h e p u l s e width
i n c r e a s e s , which c o r r e s p o n d s t o t h e d i / d t
decrease.
On t h e c o n t r a r y , t h e 2nd p a r t
i n c r e a s e s below 0 . 4 p s p u l s e w i d t h , and
slowly decreases a f t e r t h a t . Therefore, t h e
t o t a l power l o s s is not s o h i g h , when more
I t is
t h a n 0 . 5 fis p u l s e width is chosen.
a l s o understood
that
a threefold
large
d e v i c e a r e a is needed f o r t h e 0 . 1 p s p u l s e
width o p e r a t i o n , which c o r r e s p o n d s t o t h e
d i r e c t d r i v e f o r a l a s e r head without any
additional
magnetic
pulse
compression
circuit.
F i g u r e 10 shows t u r n - o n
power l o s s
dependence on I * t w f o r a 5 kpps o p e r a t i o n .
A s mentioned b t f o r e , t h e t u r n - o n power l o s s
f o r t h e 0 . 7 ps p u l s e width c a s e is s l i g h t l y
l a r g e r t h a n t h a t f o r t h e 3 p s p u l s e width
case.
T h e r e f o r e , t h e t u r n - o n power l o s s
v a l u e can be determined f o r t h e r e q u e s t e d
l a s e r power, when more t h a n 0 . 5 p s p u l s e
width is u s e d .
The designed d e v i c e a r e a
depends on t h e t h e r m a l r e s i s t a n c e f o r t h e
package, and t h e r e q u e s t e d IAp*tw.
R-600kn
AI4
"V
L- 0.5-25pH
-
1
V-1500 V
F i g .6 T e s t c i r c u i t
behavior.
f o r measuring t h e d i
IDp=19 A (400 A/cm' )
I D : 1 0 A/div.
VD:200 V/div.
t : 0 . 5 ps/div.
Pulse width 0.7 f i
F i g . 7 Turn-on waveform f o r d r a i n c u r r e n t
( I D ) and d r a i n v o l t a g e (V,) f o r t h e IGBT:
IAp=45 A ( 2 . 0 kA/cm*)
dIA/dt=1.2 kA/ps
(55 kA/pslcm' )
IA:10 A/div.
VA:500 V l d i v .
t :0.1 W l d i v .
( a ) P u l s e width 0.1 ps
IAp=200 A ( 9 . 1 kA/cm* )
d I / d t = 0 . 8 6 kA/W
A
( 4 0 kA/ps/cm' )
I A : 5 0 A/div.
VA:500 V/div.
VG:20 V/div.
(b)Pulse width 0 . 7 p s
t : 1 ps/div.
IAp=125 A ( 5 . 7 kA/cm* )
dIA/dt=0.13 kA/ps
( 5 . 7 kA/ps/cm')
IA:50 A / d i v .
VA:500 Vfdiv.
VG:20 V/div.
( c ) P u l s e width 3 ps
t :1 p s l d i v .
F i g . 8 Turn-on waveforms f o r anode c u r r e n t
( I ) , anode v o l t a g e (VA), g a t e v o l t a g e (V,)
fo$ a f a b r i c a t e d 2500 V MAGT.
280
U--- total loss
A---lst part
0---2nd part
A ' M A G T with E.B.
B I MAGT without E.B.
PULSE WIDTH (PSI
Fig.9 Turn-on power loss dependence on pulse
width.
(U
20-
E
B
? 15 -
n
-A--
3 . 0 ~ ~
--O--
0*7Ps
Fia.11 V-I characteristics for fabricated
MAGTs (A) with and (B) without electron
irradiation.
Y
v)
v)
0 '0-
-I
I .4
U
ga
A * MAGT with E.B.
5-
1.2 - B MAGT without E.B.
I
h
O6
5
I
I
IO
15
(U
6 1.0-
Iw*tw (kA*ps /cm2 I
\
3
5 0.8Fig.10 Turn-on power
IAP*tW.
loss
dependence
on
tn
-I
0.60.4 -
dv/dt immunity
The MAGT shows excellent dvfdt immunity,
when a negative bias is applied to the base
electrode.
However,
the
displacement
current, flowing from the base electrode,
leads to a large power dissipation, when
high dv/dt is applied soon after a large
pulsive
current.
Therefore,
lifetime
reduction by electron beam irradiation was
examined.
Figures 11 and
12 show the V-I
characteristics and the turn-on power l o s s
dependence
on
peak
anode
current,
respectively, for the 0.7 ps pulse width
case. Although the on-state voltage for
MAGT with electron beam irradiation was
higher than that for the other, as shown in
Fig.11, the turn-on power loss difference
between them is very small, as shown in
Fig.12. This is because the turn-on power
loss is mainly determined by the initial
0
a 0.2 -
i
h i 4 b
O o
PEAK ANODE CURRENT (kA/cm 1
Fig.12 Turn-on power loss dependence on peak
anode current f o r MAGTs (A) with and (B)
without electron beam irradiation.
,
di/dt, and the peak anode current does not
exceed the saturation current f o r MAGTs in
the range of this figure.
The extracted base current was much
reduced f o r the MAGT with electron beam
irradiation, even when 1000 VIps of dv/dt
was applied.
281
CONCLUSION
An O
!S
Assisted Gate-triggered Thyristor
(MAGT) was developed, incorporating a power
thyristor with the MOS gate electrode, as
well as a base electrode. This device
showed extremely high di/dt characteristics,
while retaining high breakdown voltage (2500
V). The transient anode voltage, caused by
high di/dt, is less than 100 V, even in the
case of 9090 A/cm' for the anode current
density, in the 0.7 ,us pulse width case.
Therefore, MAGTs are very promising for
application to a high repetition excimer
laser system.
(12)S.Sugawara and K.Yoshioka, "Regarding t o
the capability endurable to di/dt of
static induction thyristor,"
Toyo Denki Giho, vo1.69. pp.2-6, 1987.
(lJ)K.Watanabe, A.Nakagawa, and H.Ohashi,
"Design optimization of 1000 V resistive
field plate," Trans. IECE of Japan,
vol.E69, pp.246-247,April 1986.
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