Contact resistance and current crowding in tunneling type circular nano-contacts

Current transport and contact resistance in nanoscale electrical contacts are important to the overall device properties, especially for devices based on novel one-dimensional and two-dimensional materials or nanostructures. In this paper, we present a self-consistent method to model tunneling type circular thin film contacts. We solve the lumped circuit circular transmission line model (CTLM) with tunneling-induced specific contact resistivity rho(c) which varies along the radial direction. The contacting members are separated by a thin insulating layer, where the radially dependent rho(c) is calculated from local voltage dependent tunneling current density. The current and voltage distributions in such contacts and their overall contact resistance are studied in detail, for various input voltages, contact dimensions, and material properties (i.e. work function, sheet resistance of the contact members, and permittivity of the insulating layer). Our study shows that the contact resistance is voltage dependent, and the radial current distribution is strongly nonhomogeneous. The contact resistance and the current distribution can be controlled by engineering the contact layer properties and geometry radially. Although focused on Schrodinger tunneling type contacts in this work, our modified CTLM equations with radially varying rho(c) are general, and may be readily used for other types of electrical contacts, such as ohmic and Schottky contacts.