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Overview
This article compares traditional SiC MOSFETs with Qorvo's integrated SiC FETs based on a common-source common-gate structure. SiC has become widely used in power electronics for applications such as electric vehicles (EVs), data centers, and solar or other renewable-energy systems due to its material advantages over silicon.
Qorvo common-source common-gate SiC FET architecture
Qorvo's integrated SiC FET combines a normally-on SiC JFET with a silicon MOSFET in a co-packaged configuration to create an integrated normally-off SiC FET. The resulting device topology differs from a discrete SiC MOSFET and is intended to address specific limitations of MOS-based SiC devices.
Advantages of SiC over silicon
Compared with silicon-based devices, SiC as a wide-bandgap material provides several technical benefits:
- Higher breakdown field strength permits thinner devices to support higher voltages.
- For a given voltage and resistance class, SiC enables higher switching frequencies, allowing reductions in passive component size and overall system volume and cost.
- At higher voltage ratings (for example, 1200 V and above), SiC can achieve high-frequency switching with lower losses; comparable silicon devices at these voltage levels are limited.
- Within equivalent packages, SiC devices typically exhibit lower on-resistance and switching losses than silicon counterparts.
- Using SiC in designs often yields higher system efficiency, improved thermal performance, and higher power ratings for the same form factor.
Additional attributes of Qorvo SiC FETs
The integrated SiC FET architecture introduces several design-level characteristics relevant to system designers:
- Compatibility with standard silicon gate drivers, which can simplify migration from silicon MOSFETs to SiC-based designs.
- Low drain-source on-resistance RDS(ON) within a given package to help improve system efficiency.
- Lower capacitances that support faster switching and higher operating frequencies, enabling smaller inductors and capacitors.
- At high voltage levels (1200 V and above), SiC FETs can operate at higher switching frequencies than typical silicon IGBTs, which are usually used at lower frequencies and exhibit higher switching losses.
- The integrated approach can reduce die area for a given RDS(ON) and avoid some gate-oxide reliability issues associated with SiC MOSFETs.
Technical comparison: SiC MOSFET vs integrated SiC FET
The integrated common-source common-gate SiC FET differs from SiC MOSFETs in several key ways. By using a SiC JFET element, the integrated device removes the MOS gate oxide from the primary conduction path, which eliminates MOS channel resistance and allows for a more compact die area for the same conduction performance.
The integrated SiC FET typically exhibits lower output capacitance Coss than comparable SiC MOSFETs. Lower Coss reduces charge and discharge delay under low-load conditions, enabling faster switching speeds and reducing the need for large passive components. This can lead to smaller, lighter, and potentially lower-cost end products with higher power density.
Challenges with SiC MOSFETs
- High channel resistance in SiC MOS structures, which limits electron mobility.
- Threshold voltage (Vth) drift under elevated gate bias, constraining gate-to-source drive range.
- Body diode characteristics that produce relatively high knee voltage, often necessitating synchronous rectification.
How the integrated SiC FET addresses these issues
- The SiC JFET-based element avoids the MOS gate oxide, reducing gate-oxide-related reliability concerns.
- For the same chip area, the integrated device can achieve lower drain-source resistance.
- Lower device capacitances enable faster switching transitions and higher switching frequencies.
Applications
Devices combining low RDS(ON), low output capacitance, and reduced gate-oxide exposure are suitable for high-efficiency power conversion. Such integrated SiC FETs are relevant for AC/DC power supplies, DC/DC converters for energy storage and renewable-energy systems, and electric vehicle fast chargers, where higher switching frequency and improved thermal or efficiency characteristics are beneficial.
