Theory and Design of Novel Power Poly-Si/SiC Heterojunction Tunneling Transistor Structure

A novel 4H-silicon carbide power heterojunction tunneling transistor (4H-SiC power HETT) structure is proposed and demonstrated by the calibrated process and characteristic simulation, featuring a low specific ON-resistance ( ${R} _{ \mathrm{\scriptscriptstyle ON},\text {sp}}$ ) of 1.56 $\text{m}\Omega \cdot \text { cm}^{{2}}$ , 1460 V breakdown voltage (BV), and a low forward voltage drop ( ${V} _{\text {F}}$ ) of 1.4 V reaching the level of the junction barrier Schottky barrier diode (JBS) diode. The N+ type polycrystalline silicon (Poly-Si) is utilized to form the heterojunction with the 4H-SiC epi-layer. Owing to the unique cell structure of 4H-SiC power HETT, the cell pitch is reduced to $3~\mu \text{m}$ for significantly improving the tunneling current density. Moreover, the 0.3- $\mu \text{m}$ shallow gate trench and the Al2O3 high- ${k}$ dielectric further enhance the gate-controlled heterojunction tunneling characteristic. The parasitic heterojunction body diode with a heterojunction barrier of 0.7 eV provides a ${V} _{\text {F}}$ of 1.4 V and the unipolar freewheeling current without bipolar degradation issues. The P region sustains a high avalanche breakdown and effectively shields the electric field ( ${E}$ ) under the shallow gate trench and the heterojunction interface, leading to good gate reliability and low reverse leakage current. The simulation results show that the 4H-SiC power HETT has potential to approach the ideal performances of the SiC material and replace the conventional SiC power MOSFETs.