Currently, the primary applications driving high temperature electronics development include vehicles, space and aviation, and deep well drilling。

5。3 High Voltage(High Power)

Higher breakdown voltage is another consequence of wide band-gap material and leads directly

to much Higher-voltage devices。 The prospect of single devices that can withstand 5, 000 to

40, 000 V is very appealing in high power systems。 Currently, achieving medium voltage in

silicon IGBTs requires multilateral converters, or the stacking or cascading of multiple inverter

modules。 A simple 6-device inverter that operates with high switching frequency at 4, i60 VAC

(requires a 10,000 V device) would male serious impact on size, cost and reliability。

In the 400 to 690 V range。 some SIC reduction in conduction losses may occur, but it will not t

dramatically lower compared to its silicon counterpart。 The results so far do not show a

significant reduction in conduction losses。 However, higher voltage leads to significant lower

conduction losses no matter what device is use¢ and SIC makes the higher voltage possible。 A

significant forward conduction loss at 690V might be insignificant at 4, 160 V。

Theoretically, the resistance other blocking layer in a power semiconductor increases as the

voltage blocking capability is increased。 In fact for most devices, the resistance increases with

the square of the voltage。 However, this is quite misleading in predicting the practical result。 11

conduction loss is proportional to the square of the current which decreases inversely with the

increase in voltage。 The conduction loss determined by this simple analysis would thus remain

the same。 However, the device has regions other than the blocking layer where the resistance

does not increase commensurately with the voltage。 The practical outcome of increasing voltage

is usually quite favorable。

Some examples of what happens to forward voltage drop when the voltage is increased will be

Enlighten。 A major supplier of IGBTs reports the forward voltage drop to be 3。 4 V in one of its 1,200 V devices and 5。3 V in its 6,500 V device。 Another supplier reports the forward voltage drop to be 2。4 V in a 1,200 V IGBT and 3。3 V in a 4,500 V IGBT。 The higher-voltage devices obviously must be thicker, causing more forward resistance, but the conduction loss is not commensurate with the increase in voltage。 One can readily project substantial reductions in

conduction loss when operating at 4, 160 V rather than 480 V。 A similar reduction in forward

voltage drop should occur with SIC。 In extremely high-voltage situations (for example, over 500

kV), converters using strings of thyristors have efficiencies nearing 1oo%。 The primary benefit

from SIC may not be a reduction in conduction losses relative to a comparable silicon device, but

rather the capability of using a higher voltage that reduces conduction losses。

One of the major negative implications of targeting SIC at higher voltages is longer development

time。 If a commercial, 200 V MOSFET wiJ1be available in 2years。 a commercial 10, 000V SIC

MOSFET would surely require 2 more years。 However, there is considerable work being carried

out in this area today by the Office of Naval Research and DARPA。

5。4 High Switching Frequency

Higher switching speeds are achieved with SIC for two reasons (1) the higher speed,  lower loss,

switching properties of SIC devices, and (2) the ability to use faster switching types of devices at

higher voltages。 Silicon MOSFETs have excellent switching characteristics but are limited to

lower voltages and currents。 With SIC, the MOSEET might be designed for operation up to