Silicon Carbide Technology:Applications and Benefits of SiC Electronics

Applications and Benefits of SiC Electronics

Two of the most beneficial advantages that SiC-based electronics offer are in the areas of high-temperature and high-power device operation. The specific SiC device physics that enables high-temperature and high-power capabilities will be examined first, followed by several examples of revolutionary system-level performance improvements these enhanced capabilities enable.

High-Temperature Device Operation

The wide bandgap energy and low intrinsic carrier concentration of SiC allow SiC to maintain semiconductor behavior at much higher temperatures than silicon, which in turn permits SiC semi- conductor device functionality at much higher temperatures than silicon [7]. As discussed in basic semiconductor electronic device physics textbooks [14,15], semiconductor electronic devices function in the temperature range where intrinsic carriers are negligible so that conductivity is controlled by intentionally introduced dopant impurities. Furthermore, the intrinsic carrier concentration ni is a fundamental prefactor to well-known equations governing undesired junction reverse-bias leakage currents. As temperature increases, intrinsic carriers increase exponentially so that undesired leakage

currents grow unacceptably large, and eventually at still higher temperatures, the semiconductor device operation is overcome by uncontrolled conductivity as intrinsic carriers exceed intentional device dopings. Depending upon specific device design, the intrinsic carrier concentration of silicon generally confines silicon device operation to junction temperatures <300°C. SiC’s much smaller intrinsic carrier concentration theoretically permits device operation at junction temperatures exceeding 800°C. 600°C SiC device operation has been experimentally demonstrated on a variety of SiC devices (Section 5.6.3).

The ability to place uncooled high-temperature semiconductor electronics directly into hot environments would enable important benefits to automotive, aerospace, and deep-well drilling industries [7,16]. In the case of automotive and aerospace engines, improved electronic telemetry and control from high-temperature engine regions are necessary to more precisely control the combustion process to improve fuel efficiency while reducing polluting emissions. High-temperature capability eliminates performance, reliability, and weight penalties associated with liquid cooling, fans, thermal shielding, and longer wire runs needed to realize similar functionality in engines using conventional silicon semiconductor electronics.

High-Power Device Operation

The high breakdown field and high thermal conductivity of SiC coupled with high operational junction temperatures theoretically permit extremely high-power densities and efficiencies to be realized in SiC devices. The high breakdown field of SiC relative to silicon enables the blocking voltage region of a power device to be roughly 10× thinner and 10× heavier doped, permitting a roughly 100-fold beneficial decrease in the blocking region resistance at the same voltage rating [8]. Significant energy losses in many silicon high-power system circuits, particularly hard-switching motor drive and power conversion circuits, arise from semiconductor switching energy loss [1,3,17]. While the physics of semiconductor device switching loss are discussed in detail elsewhere [18], switching energy loss is often a function of the turn-off time of the semiconductor switching device, generally defined as the time lapse between application of a turn-off bias and the time when the device actually cuts off most of the current flow. In general, the faster a device turns off, the smaller its energy loss in a switched power conversion circuit. For device-topology reasons discussed in References 3,8, and 19–21, SiC’s high breakdown field and wide energy bandgap enable much faster power switching than is possible in comparably volt–ampere-rated silicon power-switching devices. The fact that high-voltage operation is achieved with much thinner blocking regions using SiC enables much faster switching (for compa- rable voltage rating) in both unipolar and bipolar power device structures. Therefore, SiC-based power converters could operate at higher switching frequencies with much greater efficiency (i.e., less switch- ing energy loss) [1,22]. Higher switching frequency in power converters is highly desirable because it permits use of smaller capacitors, inductors, and transformers, which in turn can greatly reduce overall power converter size, weight, and cost [3,22,23].

While SiC’s smaller on-resistance and faster switching helps minimize energy loss and heat generation, SiC’s higher thermal conductivity enables more efficient removal of waste heat energy from the active device. Because heat energy radiation efficiency increases greatly with increasing temperature difference between the device and the cooling ambient, SiC’s ability to operate at high junction temperatures permits much more efficient cooling to take place, so that heat sinks and other device-cooling hardware (i.e., fan cooling, liquid cooling, air conditioning, heat radiators, etc.) typically needed to keep high-power devices from overheating can be made much smaller or even eliminated.

While the preceding discussion focused on high-power switching for power conversion, many of the same arguments can be applied to devices used to generate and amplify RF signals used in radar and communications applications. In particular, the high breakdown voltage and high thermal conductivity coupled with high carrier saturation velocity allow SiC microwave devices to handle much higher power densities than their silicon or GaAs RF counterparts, despite SiC’s disadvantage in low-field carrier mobility [5,6,24–26].

System Benefits of High-Power High-Temperature SiC Devices Uncooled operation of high-temperature and high-power SiC electronics would enable revolutionary improvements to aerospace systems. Replacement of hydraulic controls and auxiliary power units with distributed “smart” electromechanical controls capable of harsh ambient operation will enable substantial jet-aircraft weight savings, reduced maintenance, reduced pollution, higher fuel efficiency, and increased operational reliability [7]. SiC high-power solid-state switches will also enable large efficiency gains in electric power management and control [1,4,27–31]. Performance gains from SiC electronics could enable the public power grid to provide increased consumer electricity demand without building additional generation plants, and improve power quality and operational reliability through “smart” power man- agement. More efficient electric motor drives enabled by SiC will also benefit industrial production systems as well as transportation systems such as diesel-electric railroad locomotives, electric mass-transit systems, nuclear-powered ships, and electric automobiles and buses.

From the above discussions it should be apparent that SiC high-power and high-temperature solid- state electronics promise tremendous advantages that could significantly impact transportation systems and power usage on a global scale. By improving the way in which electricity is distributed and used, improving electric vehicles so that they become more viable replacements for internal combustion-engine vehicles, and improving the fuel efficiency and reducing pollution of the remaining fuel-burning engines and generation plants, SiC electronics promises the potential to better the daily lives of all citizens of planet Earth.