Effects of a series resistor on quantum tunneling current in dissimilar metal–insulator–metal nanogap

This study analyzes tunneling current in nanoscale asymmetric metal–insulator–metal junctions connected with a series resistor, where the two electrodes separated by the insulator generally possess different work functions. To delineate the conditions under which resistor values significantly influence device performance, a comprehensive analysis is provided to predict tunneling current across a wide range of input parameters. We found that the impact of the series resistor becomes pronounced in configurations with small insulator thicknesses and high voltages, where the junction impedance is comparable to the resistor value, and the system transitions from quantum tunneling-limited to Ohmic-limited transport. The series resistor not only acts as a current limiter but also suppresses nonlinearity and directional asymmetry in the tunneling response under large bias. To quantitatively characterize these effects, we introduce current reduction ratios and forward/reverse bias asymmetry indices, revealing how the series resistance affects current magnitude and polarity dependence. Contour plots of impedance/resistor ratio Z/R as a function of barrier height and voltage reveal a clear transition boundary, whose position shifts with barrier height and material asymmetry—highlighting their exponential influence on electron transport. The effects of insulator properties, electrode work functions, and bias voltage, which are critical in determining the forward and reverse bias tunneling currents, are also examined comprehensibly under the influence of the series resistor. These results demonstrate that the resistor fundamentally reshapes the tunneling landscape and can serve as an active symmetry modulator, enabling design strategies for stable and tunable nanoelectronic and molecular devices.