Electrical Characterization of Lateral 4H-SiC MOSFETs in the Temperature Range of 25 to 600°C for Harsh Environment Applications

摘要

In this work, we investigated lateral 4H-SiC-based metal oxide field-effect transistors (MOSFET) for the use as transducers in harsh environments. Inversion channel (IC) as well as buried channel (BC) MOSFETs were fabricated by means of different epi-layer doping and ion implantation. Stacked SiO_2/Si_3N_4 dielectrics and a sputtered Ti/TaSi_x/Pt contact metallization were used. The devices were characterized by means of current-voltage and capacitance-voltage testing up to 600°C. The thermal stability of the transistor characteristics and the factors limiting the MOSFET mobility were analyzed and discussed. The effective barrier height for Fowler-Nordheim tunneling extrapolated at high fields (> 7 MV/cm) decreased of about 1 eV between 25 and 500°C. At high temperatures, the Poole-Frenkel contribution to the leakage current became significant already in the mid-field range. The prolonged operation of MOSFETs at 500°C indicated that sufficient MOS reliability can be achieved only by a minimization of the necessary gate bias. The lifetime was ~25 h when a stress field of 3.5 MV/cm was applied at 500°C. When the stress field was reduced to 0.5 MV/cm, a lifetime > 300 h was found. A degradation of the drain current was observed during the prolonged operation independently of the biasing conditions. This was attributed to a degradation of the ohmic contacts.