High Breakdown Voltage Diamond Schottky Barrier Diode with HfO₂/ Al₂O₃ Multilayer Field Plate Structure

Diamond Schottky barrier diodes (SBDs) have been studied by many researchers because of its high current, low turn-on voltage and fast switching frequency. However, the edge electric field crowding effect will lead to premature breakdown of SBD under large reverse voltage, which will result in large leakage current. There are some termination structures have been reported to improve the blocking capacitance, such as field plates (FP), junction termination extension (JTE), metal guard rings. Among those structures, FP is the most common structure because it can alleviate the electric crowding without reducing the forward current and increasing the turn-on voltage. Al₂O₃ has been used as FP of diamond SBD because of its large band offset for oxygen-termination diamond. The HfO₂ has a high dielectric constant (k) of 25-30 and can withstand higher voltage than Al₂O₃. However, due to the large positive fixed charge density in the bulk HfO₂, the barrier between HfO₂ and diamond is low.<br/>In order to solve the weak points of single Al₂O₃ and HfO₂ FP, we fabricated a diamond SBD with HfO₂/Al₂O₃ multilayer FP. The k value of the HfO₂/Al₂O₃ multilayer was larger than that for single Al₂O₃. The leakage current of HfO₂/Al₂O₃ multilayer FP diamond SBD was always smaller than that of single oxide FP SBD. Compared with HfO₂ FP, there was a better interface between diamond and HfO₂/Al₂O₃ multilayer FP. And the diamond SBD has higher breakdown voltage than single oxide FP SBD. We also investigated the effect of annealing on this diamond SBD. The breakdown voltage was improved and the leakage current was reduced after annealing. These results show that the HfO₂/Al₂O₃ multilayer FP and annealing can effectively improve the reverse breakdown voltage of the diamond SBD, and the forward characteristics do not decrease significantly.