| Summary: | 碩士 === 國立清華大學 === 電子工程研究所 === 100 === Abstract
This thesis investigated the design and the fabrication of high-voltage 4H-SiC vertical diodes, including PiN diodes and Ti-TJBSs (Titanium Trench Junction Barrier Schottky Diode). Conventional PiN diode is fabricated on epitaxial wafers. Its forward voltage drop will degrade after stress due to bipolar degradation. In this work, PiN diodes on the thinned HPSI (High Purity Semi-Insulating) wafer were fabricated, with ion implantations to form the n+ and p+ region. It is expected to feature good forward characteristics and sufficient reverse blocking capability. Unfortunately, the experiment results were not as expected, with a large turn-on voltage of 200V.
TJBS is an improvement of JBS. With the trench structure, the p+ region is deeper and the surface electric field can be reduced. In this case, the barrier lowering effect can be reduced. Therefore, TJBS can adopt low work function metal, such as titanium, as its Schottky metal. As a result, a low forward voltage drop can be achieved without suffering high leakage currents. The effects of trench spacing, trench depth, device size, and edge termination have been simulated and analyzed. When a reverse bias of 900V is applied, the leakage current of TJBS is 100 times smaller than that of JBS. As for a current density of 100A/cm2, the forward voltage drop is 1.35V and the leakage current density is about 1×〖10〗^(-3) 〖A/cm〗^2. The phenomenon of conductivity modulation is also observed when the TJBS diodes are operated at high current density in the PiN mode.
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