IGBT Modules - Technologies, Driver and Application (Second Edition) - page 39

Approximately three times more bandgap energy E
of 3.26 eV, compared to
1.12eV for silicon. SiCdiodes therefore haveamuch lower reverse current.
Up to nine times as much critical electrical field strength E
compared to
MV 25.0
for silicon. In technical application, this usually leads to
a reduction in specific resistance of SiC diodes compared to Si diodes,
because it makes it possible to increase the doping of the SiC semiconductor
and decrease its gauge, which is directly proportional to its blocking voltage
Increased thermal conductivity of 3.0 to
K cm
compared to
K cm
silicon, which amounts to a reduction of the thermal resistance R
of a
semiconductor chipwith the same surfacearea.
As already mentioned, it does not make a lot of sense to use silicon based Schottky
diodes in voltage ranges above 200V, but when SiC is introduced as a semiconductor
material, it becomes worthwhile to use Schottky diodes in voltage ranges that were
previously reserved for PIN diodes, because of the advantages mentioned. Depending
on theapplication, SiCSchottky diodes have the following advantages over PINdiodes:
Very low reverse recovery charge, caused entirely by capacitive effects. The
reverse current peak that usually occurs with silicon diodes is almost
completely eliminated.
No effect of the change of current
di on the reverse recovery charge, even at
different load currents and temperatures.
High junction temperatureof well over 200
Diodes that use SiC as a semiconductor material are still much more expensive than
those based on silicon, so are not yet in widespread use. Silicon semiconductors are
expected to have a price advantage over SiC semiconductors for the medium to long
term so, at least for the medium term, SiC semiconductors will be used only where
using them is economic because it brings advantages to the whole system in terms of
costs or performance advantages.
shows the layer structures of SiC Schottky diodes. The traditional variant is
shown on the left. In the middle a Merged-PIN-Schottky (MPS) diode is shown, with p-
doped structures added to the Schottky contact. These structures improve the surge
current behaviour and avalanche resistivity of the SiCMPS diode in comparison to the
standardSiCSchottky diode.
shows how an additional n-doped layer has been inserted
between the high n
-doped cathode contact and the weak n
-doped epitaxial layer. The
The high usable temperature in SiC semiconductors results from the high bandgap energy, because of which
the intrinsic charge carrier density of SiC remains well below the doping concentration even at temperatures of
more than 500
C, preventing thermal runaway of the semiconductor. The extent to which it is possible in practice
toexploit these temperatures is determined by the package and the bonding technologyused.
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