SiC and GaN: Real-World Solutions

BY MURRAY SLOVICK

Advanced wide-band-gap (WBG) materials–semiconductor compounds such as SiC and GaN with bandgap energies larger than that of Si — certainly have the lab specs right. According to development engineers, when used in power electronics they can significantly reduce switching and conduction losses, provide lower on-resistance than is possible in Si, allow for increased switching frequency and make possible a substantial cut in the size of the power supply unit.

The singular question then is whether commercially available WBG products will back up all that promise.

Happily, after a lot of fits and starts the answer now seems to be an unequivocal “Yes!” As evidence, let’s take a look at some recently announced products using SiC and GaN materials.
Cree has introduced the first commercially available all-SiC Cree power module (part # CAS100H12AM1). The new high frequency module, rated at 100-A current handling and 1,200-V blocking includes SiC MOSFETs and SiC Schottky diodes in a 50-mm half-bridge configuration rated to 150°C maximum junction temperature.

Cree module includes SiC MOSFETs and SiC Schottky diodes  

The CAS100H12AM1 takes advantage of the reduced switch losses of SiC MOSFETs, compared with silicon MOSFETs and IGBTs. Also, the SiC MOSFET's high current density and small die size results in lower capacitance than with silicon MOSFETs. Module size is 50 x 87.5 mm.

The SiC components enable the Cree module to be operated at very high switching frequencies (the module has demonstrated up to 100 kHz switching frequency) that can reduce the size, weight and cost of a power conversion system. Target applications include high-power converters, industrial motor drives, solar inverters and uninterruptible power supplies.

iC bipolar junction transistors promise very fast switching speed, low conduction losses, high-temperature operation and relative ease of manufacturing. Among the first products to be released in Fairchild Semiconductor’s SiC portfolio is a family of SiC BJTs. By leveraging efficient transistors, Fairchild’s SiC BJTs enable higher switching frequencies due to lower conduction and switching losses (ranging from 30% to 50%) that provide up to 40% higher output power in the same system form factor, according to Fairchild.

Working in conjunction with a properly designed gate driver, SiC BJTs are suitable for industrial applications, including high-power converters, motor drives, solar inverters, UPS and SMPS, and induction heating.. Enabling the use of smaller inductors, capacitors, and heat sinks, these BJTs can lower overall system costs up to 20%, according to Fairchild. The company’s SiC BJTs are available in a TO-247 package. (Engineering samples are available.)

While GaN power electronics and related controller technology has come of age for lower voltage applications – below about 200 V–leading suppliers are working on 600-V-and-higher devices, with International Rectifier, for example, last fall demonstrating a 600-V GaNpowIR-based motor controller. When compared to state-of-the-art silicon trench IGBTs in terms of conduction × switching loss figure of merit, the 600 V rated GaNpowIR device performs 6 times better, according to IR.

For its part, Freescale, known mostly for LDMOS RF parts, is developing gallium nitride hetero-junction field effect transistors (GaN HFETs) to address emerging high-power, high-efficiency RF applications. With higher breakdown field strength than Si and higher electron density than GaA devices at equivalent speeds, GaN HFET devices are said to allow order of magnitude higher power densities, higher breakdown voltages and lower on-resistances than conventional SI or GaAs solutions. Freescale’s first part, designated AFG25HW355S, is a 48-V 350-W GaN transistor, designed exclusively for W-CDMA and LTE macro cell applications, operating in the 2,300 to 2,700 MHz frequency band.

Going forward, look for SiC products to include devices operating at 1,700 V and above, plus GaN diodes and transistors at 1,200 V and higher. In particular, exciting opportunities for wide-band-gap power devices exist in the hybrid and electric vehicle market. Adoption of these devices could increase inverter efficiency, leading to a longer vehicle range between battery recharging.