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FIGURE 3: GENERATIONAL IMPROVEMENTS IN SiC MOSFET STRUCTURE
cell pitch and novel trench structures is an increase in local current density. This results in faster device heating during overcurrent conditions and a reduction when a SiC MOSFET can with- stand short-circuit conditions. Special cell structures are implemented in the new trench MOSFET that suppress short-circuit current levels and help improve the ability to safely withstand the same kinds of short-circuit events to which the previous generation was exposed. More importantly, dedicated gate driver ICs have been developed to complement SiC MOSFETs by detecting and eliminating short-circuit current.
One example is Rohm’s BM60060FV-C isolated gate driver, which offers many of the same features seen in IGBT driv- ers, including high-voltage isolation, fast propagation time, fault signal out- put functions, and undervoltage lock- out. Specific to driving SiC MOSFETs, this driver IC includes a short-circuit– detection path, as shown in Figure 5. A current-sense resistor is added to the SiC MOSFET source terminal and monitored by the SCPIN terminal. When excessive current is detected, the gate drive is immediately disabled, and the SiC device is protected from thermal damage.
Physical device structure and special-
continue to mature in complex- ity, demanding higher performance from power electronics, SiC devices are quickly becoming the key components to their success.
State of the art in SiC
MOSFETs
SiC MOSFETs are now in their fourth generation of development at Rohm, with fifth-generation advanced research already in progress. The primary goal of improving device performance centers on the reduction of RDS(on) while main- taining short-circuit current suppres- sion. This has been accomplished by
developing an advanced trench struc- ture for the MOSFET active area, as shown in Figure 3.
An additional benefit of the new trench structure is reduced parasitic capaci- tance, improved switching speeds, and minimized energy loss in high- frequency switching. As shown in Figure 4, the reduction in switching energy from third- to fourth-generation structures is significant. This directly enables higher switching frequencies in power-conversion circuits without exceeding thermal dissipation limits.
One concern that arises with reduced
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ASPENCORE GUIDE TO SILICON CARBIDE
FIGURE 4: SWITCHING LOSS IMPROVEMENT FROM THIRD- TO FOURTH-GENERATION SiC MOSFET