These two images represent equipotentials in two metallic films separated by a tunneling barrier in cross geometry. The current is injected by the bottom of the left electrode and collected at the left part of the right one. However, due to the intrinsic sheet resistivity of the metallic electrodes, a significant voltage drop occurs in the plane of the junction. In the extreme case presented here, the junction resistance, measured as the voltage difference between V+ and V- divided by the intensity is NEGATIVE!

Such spurious effects are currently observed in real devices. We have used the Laplace equation:

with the finite elements approximation to determine the value of the electric potential in a meshed model. The calculations were performed in C++ and loaded into the Igor experiment as Z-matrices.

Submitted by J-F Bobo and Ch. Fery.