Revolutionary Innovation in SiC Power Devices
Technical Report,16 Jul 2015,16 Jul 2019
Sonrisa Research, Inc. Santa Fe United States
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Silicon carbide SiC is a wide bandgap semiconductor with a power figure-of-merit --400x higher than silicon, SiC power MOSFETs have beers in commercial production since 2011, but they are still far from their ultimate limits of performance. The main limitations are the resistances of the MOS channel, the drift region, and the substrate, tn this program we address all three resistances. To reduce the channel resistance, we Introduce two new trench MOSFET structures. The tri-gate 3G MOSFET applies FinFET geometry to vertical power devices for the first time, and the IMOSFET implements a deeply-scaled trench MOSFET using a fully-self-aligned approach. Both structures can reduce the channel resistance by 5 - IQx, To reduce the substrate resistance we etch a waffle pattern of depressions that penetrate 90 of the way through a thinned 200 pm substrate, and back-fill with electroplated copper for low thermal and electrical resistance. We have demonstrated substrate resistances 3x lower than that of a substrate uniformly thinned to 110 pm, the process currently used in industry. To reduce the drift layer resistance we first evaluated superjunction structures, but the benefit in the presence of realistic charge imbalance was insufficient to justify the complexity of fabrication. Instead, we elected to use conductivity modulation by implementing an n-channel IGBT on an n substrate, where the buried p anode layer is contacted using our waffle substrate technology. In addition, we addressed the problem of limited short-circuit withstand time SCWT by introducing the concept of gate-charge scaling, wherein we reduce the oxide thickness and gate drive by the same factor. This increases the SCWT by that factor, with no impact on the on-state or blocking operation. At the time of this writing, the waffle substrate development has been completed, the first 3G-MOSFETs are being tested, and the IMOSFET and n-IGBT devices are still in fabrication.
- Electricity and Magnetism