2017.05.25 SiC Power Device
We have compared the characteristics of SiC-SBDs with those of Si diodes, and have described products that are currently available. This time, while summarizing our discussion thus far, we would like to consider the advantages of SiC-SBDs.
Characteristics of SiC-SBDs, Si SBDs and Si PNDs
In a SiC-SBD, a metal junction with the SiC semiconductor (a Schottky junction) is formed to obtain a Schottky barrier. The structure is essentially the same as that of a Si Schottky barrier diode, and only electrons move to cause current to flow. In contrast, a Si-PND has a structure based on a junction of P-type silicon and N-type silicon, and current flows due to both electrons and holes.
Both SiC-SBDs and Si SBDs feature fast operation, but SiC-SBDs achieve high rated voltages together with fast operation. 200 V is the upper limit to the Si-SBD rated voltages, but SiC has a dielectric breakdown field some ten times higher than that of silicon, and so SiC products with a rated voltage of 1200 V are being mass produced, and products with a voltage of 1700 V are in development.
Si-PNDs have a reduced resistance due to accumulation of minority carrier holes in the n layer, and so can simultaneously realize low resistance and high voltages far beyond those of Si-SBDs, but turn-off speeds are slow.
Among Si-PNDs, FRDs boast faster operation, but even so the trr characteristic is inferior to that of SBDs.
The diagram on the right indicates the rated voltage ranges for Si-SBDs, Si-PNDs/FRDs, and SiC-SBDs. SiC-SBDs extend over a considerable part of the voltage range of Si- PNDs/FRDs, and so improvement on the trr of Si-PNDs/FRDs is possible in this region.
trr Values of SiC-SBDs
In comparisons with Si-FRDs, it was explained that Si-SBDs have excellent trr characteristics, and exhibit almost no dependence on temperature or current.
Forward Characteristics of SiC-SBDs
The forward characteristics of Si-SBDs differ from those of Si-PNDs. This is a consequence of the physical properties and structures. Particularly where temperature characteristics are concerned, as the temperature rises the VF of a Si-FRD declines, and conduction losses decrease, but on the other hand the IF increases, and there is the possibility of a thermal runaway state.
In contrast, as the temperature rises the VF of a SiC-SBD rises, so that thermal runaway does not occur. However, because of the higher VF, IFSM is lower than for a Si-FRD.
Advantages of SiC-SBDs
Because of these features of SiC-SBDs, the advantages gained by using them to replace Si-PNDs/FRDs are due to their fast operation.
1.The trr is fast, so that recovery losses can be
dramatically reduced, for higher efficiency
2.For a similar reason, the reverse current is small so
that noise is low, and noise/surge suppression
components can be eliminated, enabling enhanced
3.High frequency operation enables miniaturization of
inductors and other peripheral components
Below, examples and related images are presented.
Further, due to their very stable operation with respect to temperature, these devices are compatible with automotive applications, and the advantages of SiC-SBDs are being exploited in actual HV/EV/PHV onboard charging circuits.
・The trr is fast, so that recovery losses can be dramatically reduced, for higher efficiency
・For a similar reason, the reverse current is small so that noise is low, and the number of noise/surge suppression components can be reduced, enabling enhanced miniaturization
・High frequency operation enables miniaturization of inductors and other peripheral components