Improved Electrical Characteristics of 1200V/20A 4H-SiC Diode by Substrate Thinning and Laser Annealing

In this paper, two kinds of silicon carbide (SiC) backside metallization processes were developed, which were backside thinning combined with laser annealing to form ohmic contact and direct rapid annealing (RTA) to form ohmic contact. The specific contact resistivity obtained by both annealing processes was 3.4E-5 Ω·cm2 to 3.8E-5 Ω·cm2. In order to obtain the effect of thinning combined with laser annealing process on forward conduction characteristics of medium voltage devices,1200V/20A JBS diode was developed, and the backside contact adopted the above two annealing schemes, the thickness of 4H-SiC substrate is 200μm. According to the statistical results of hundreds of JBS diodes, the electrical characteristics of the two types JBS are basically the same. Compared with the JBS diode without substrate thinning, the forward conduction voltage (VF) of the thinned JBS diode is decreased about 0.048V. When the substrate of 1200V SiC JBS diodes is reduced to 80μm, the value of VF can only be reduced by about 0.0868V.

A Two Dimensional Tunneling Resistance Transmission Line Model for Nanoscale Parallel Electrical Contacts

Contact resistance and current crowding are important to nanoscale electrical contacts. In this paper, we present a self-consistent model to characterize partially overlapped parallel contacts with varying specific contact resistivity along the contact length. For parallel tunneling contacts formed between contacting members separated by a thin insulating gap, we examine the local voltage-dependent variation of potential barrier height and tunneling current along the contact length, by solving the lumped circuit transmission line model (TLM) equations coupled with the tunneling current self consistently. The current and voltage distribution along the parallel tunneling contacts and their overall contact resistance are analyzed in detail, for various input voltage, electrical contact dimension, and material properties (i.e. work function, sheet resistance of the contact members, and permittivity of the insulating layer). It is found the existing one-dimensional (1D) tunneling junction models become less reliable when the tunneling layer thickness becomes smaller or the applied voltage becomes larger. In these regimes, the proposed self-consistent model may provide a more accurate evaluation of the parallel tunneling contacts. For the special case of constant ohmic specific contact resistivity along the contact length, our theory has been spot-checked with finite element method (FEM) based numerical simulations. This work provides insights on the design, and potential engineering, of nanoscale electrical contacts with controlled current distribution and contact resistance via engineered spatially varying contact layer properties and geometry.