SEPTEMBER 2008 n IEEE INDUSTRIAL ELECTRONICS MAGAZINE 19

volutionary improvements in silicon (Si) power devices through bet-

ter device designs, processing techniques, and material quality have

led to great advancements in power systems in the last four decades.

However, many commercial power devices are now approaching the

theoretical performance limits offered by the Si material in terms of

the capability to block high voltage, provide low on-state voltage drop,

and switch at a high frequency. Therefore, in the past five to six years,

many power system designers have been looking for alternative solutions in order

to realize advanced commercial and military hardware that requires higher power

density circuits and modules. One of the most promising approaches is to replace

Si as the material of choice for fabrication of power devices with a wider bandgap

Digital Object Identifier 10.1109/MIE.2008.928617

Opportunities and Challenges in Realizing the Full Potential of SiC Power Devices

RANBIR SINGH AND

MICHAEL PECHT

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20 IEEE INDUSTRIAL ELECTRONICS MAGAZINE n SEPTEMBER 2008

material with acceptable bulk mobility

[1]. A strong effort is now underway

to exploit the excellent properties of

silicon carbide (SiC) for the realization

of high-performance, next-generation

power devices. These material prop-

erties include: a) an order of magni-

tude higher breakdown electric field,

b) a ~3X wider bandgap, and c) a ~3X

higher thermal conductivity than Si.

For a properly designed device, a high

breakdown electric field allows the

design of SiC power devices with thin-

ner and higher doped blocking layers.

The large bandgap of SiC results in a

much higher operating temperature

and higher radiation hardness. The

high thermal conductivity for SiC (4.9

C/W) allows dissipated heat to be

more readily extracted from the de-

vice. Hence, a larger power can be

processed with a device for a given

junction temperature.

Power Applications and Devices

The use of more efficient power devic-

es is expected to have a major impact

on the energy use in the United States,

which is estimated to be approximately

BTUs. Approximately 27% of this

is used for transportation, and 40%

through direct use into electrical ap-

plications. By some estimates, hybrid

vehicles may reduce the consumption

of gasoline and result in saving US$16

billion worth of oil imports in the

United States. In the United States to-

day, approximately 15% of electricity

is consumed in the info-tech industry,

approximately 15% in lighting applica-

tions, 15% in heating and cooling ap-

plications, and another 55% in other

motor control applications. For direct

electric use, the voltage and current

ratings of some major areas of elec-

tric power consumption are shown in

Figure 1, with particular emphasis on

some dominant areas of applications.

Although the current and voltage rat-

ings of power supplies are modest,

they consume a large number of power

semiconductor rectifiers and switch-

es, while power transmission and dis-

tribution systems consume fewer pow-

er semiconductors but may provide a

strong impact on system performance

and reliability. By a rough estimation,

motor control applications (including

heating and cooling) consume approx-

imately 60% of all electricity used in

the United States, and lighting applica-

tions cover 15% of electric power.

The ratings of commercial Si power

devices where the bulk of these de-

vices are used are shown in Figure

2. Most state-of-the-art power ap-

plications use power MOSFETs, p-i-n

rectifiers, and insulated gate bipolar

transistors (IGBTs) because the rat-

ings of these devices are in the “sweet

spot” of the power applications. Since

SiC offers much lower on-resistance

than Si, power MOSFETs and various

flavors of Schottky diodes are consid-

ered promising candidates to replace

Si power MOSFETs, Si IGBTs, and Si

PiN rectifiers in the

600-V ratings.

Apart from high ambient temperature

applications like oil drilling, airborne

applications, and high-radiation space

applications, SiC devices may not of-

fer any performance advantage as

compared to Si devices in the com-

mercially significant

600-V market.

For applications that require

8-kV

power semiconductors, bipolar SiC

devices hold a strong promise.

As in Si, SiC power devices may be

broadly classified into majority carrier

devices, which primarily rely on drift

current during on-state conduction; and

minority carrier devices (also called bi-

polar-type devices), which result in con-

ductivity modulation during on-state

operation. Majority carrier devices like

the Schottky diodes, power MOSFETs,

and JFETs offer extremely low switch-

ing power losses because of their high

switching speed. Although the on-state

(forward) voltage drop of majority car-

rier devices can be low, it becomes pro-

hibitively high at high current densities.

This problem exponentially increases

in its severity as the voltage rating on

Power Supplies

and Factory

Automation

HVDC and Power

Transmission

Lamp

Ballast

Motor

Control

Traction

Control

Others

25%

60%

15%

10,000

1,000

100

10 100 1,000 10,000 100,000

Device Current (A)

Device Blocking Voltage (V)

FIGURE 1 — Voltage and current ratings of various power applications.

SiC MOSFET/JFET/Schottky

SiC PiN/IGBT/Thyristor

02 kV 4 kV 6 kV 8 kV 10 kV

Si MOSFET/Schottky Diode

Si IGBT/PiN Diode

Si GTO

Si Thyristor

FIGURE 2 — Power device voltage ratings of Si versus SiC devices.

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