Two-dimensional (2-D) device simulation is used to investigate the tunneling current of metal ultra-thin-oxide silicon tunneling diodes with different oxide roughness. With the conformal nature of ultrathin oxide, the tunneling current density is simulated in both direct tunneling and Fowler-Nordheim (FN) tunneling regimes with different oxide roughness. The results show that oxide roughness dramatically enhances the tunneling current density and the 2-D electrical effect is responsible for

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... increment of tunneling current density. Furthermore, a set of devices with controlled oxide roughness is fabricated to verify the simulation results and our model qualitatively agrees with the experiment results.