Metal-based asymmetric field emission diodes operated in the air

In this study, metal-based asymmetric electrodes for field emission (FE) diodes were fabricated. E-beam lithography generated a minimal anode-cathode distance of approximately 24 nm. Measurements in the air displayed Fowler-Nordheim tunneling under a potential less than 0.5 V. The design enabled the maximal electric field at acute terminals made of multiple triangles as cathode, thus generating high acceleration for the forward current. By contrast, the maximal electric field occurred at blunt terminals made of multiple semicircles as cathode, thus generating low acceleration in reverse bias. Furthermore, the reverse bias could be subject to electron scattering because of the operation in the air, leading to a lower electric current than the forward bias. The forward/reverse current ratio increased with increasing applied voltage. Compared with other asymmetric FE devices, the FE diodes developed in this work can effectively enhance the forward/reverse current ratio, suggesting that asymmetric cathode and anode design can serve as an FE diode. Finite element modeling showed that the electric field and speed were maximal at apices of the multiple triangular electrodes used as cathode and minimal on flat edges of the multiple semicircular electrodes used as cathode, thereby resulting in asymmetric electron flow. The results supported the potential application of metal-based asymmetric electrodes to FE diodes.