Simulation, modeling and characterization of SiC devices

With superior material properties, Silicon carbide (SiC) power devices show great potential for high-power density, high temperature switching applications. Among all the power device structures, SiC MOSFET attracts the most attention because of its high gate input impedance, simple gate control and fast switching speed. However, low inversion channel mobility, high near-interface state density close to the conduction band edge, questionable oxide reliability as well as theoretical limit on the device figure-of-merit still remain to be significant challenges to the development of SiC power MOSFETs. In this dissertation, all of the above challenges are addressed from various approaches. First, simulations on the super-junction structure show that the unipolar theoretical limit of SiC can be broken even with the state-of-the-art processing technologies. An easy-to-implement analytical model is developed for calculations of the blocking voltage, specific on-resistance and charge imbalance effects of 4H-SiC super-junction devices. This model is validated by extensive numerical simulations with a large variety of device parameters. Device design and optimization using this model are also presented. Second, a wafer-level Hall mobility measurement technique is developed to measure channel mobility more accurately, more efficiently and more cost-effectively. Device characterization and development are much more convenient by using this technique. With this method, further explorations of interactions between interface traps and channel carriers as well as device degradation mechanisms become possible. Third, reliability of SiO2 on 4H-SiC is characterized with time dependent dielectric breakdown (TDDB) measurements at various temperatures and electric fields. Lifetime prediction to normal operation conditions suggests that the oxide on SiC has a characteristic lifetime of 10 years at 375° C if the oxide electric field is kept below 4.6 MV/cm. The observed excellent reliability data contradict the widespread belief that the oxide on SiC is intrinsically limited by its physical properties. Detailed discussions are provided to re-examine the arguments leading to the misconception.Ph.D.Includes abstractVitaIncludes bibliographical referencesby Liangchun Y