Fabrication And Characterization Of Metal-Insulator-metal Tunnel Diodes For Rectenna

Photovoltaic technology is an effective avenue for the alleviation of current energy crisis and environmental pollution. Efficiency improvement and cost reduction are the main issues to achieve the large-scale commercial applications. Present photovoltaic cells rely on the quantum nature of light, which are limited by the semiconductor band-gap energy. An alternative for the photovoltaic cell is the rectenna, which is based on the wave nature of light and can theoretically achieve greater than90%efficiency. The MIM diode is a high frequency rectification device in the rectenna. As the diode’s equivalent-circuit is the parallel combination of a capacitor and a resistor, the presence of parasitic capacitance defines the cut-off frequency limit. Hence, the lower capacitance is required for higher frequency rectification, that is to say the contact area between the metal layers and the insulator layer should be minimized.Herein, we report a readily accessible approach to fabricate the Ni-NiOx-Cu MIM diode with the high frequency rectification characteristic for rectenna. This method is based on that the anodic aluminum oxide (AAO) template’s nano-hole size ensures the small contact area of the diode and that NiOx ultra-thin insulator layer can be prepared by naturally oxidation. The compositional, micro-structural, electrical properties of the MIM diodes as prepared were characterized. We also studied the influence of the thermal oxidation process, the work function difference between the metal electrode and the contact area between the metal layers and the insulator layer to the electrical properties of the MIM diodes. The primary results are summarized as follows:(1) The Ni-NiOx-Cu tunnel diodes were successfully prepared by the electrochemical deposition of metal electrodes and the thermal oxidation of insulation layer. The minimum contact area between the metal and the oxide layer is0.002μm2due to the AAO template pore’s limit, the cut-frequency of64THz for the corresponding MIM diodes can therefore be estimated. The current-voltage (I-V) characteristics of the MIM diodes with the insulator layer of12nm as prepared exhibit the nonlinear behaviors and the best zero bias sensitivity of the diodes is7.3V-1at bias voltage (Vbias) of0.1V.(2) The NiOx insulator films, fabricated with a thermal oxidation time between 12h to96h and at a thermal oxidation temperature between100℃to300℃. are the amorphous phase with the thicknesses between2nm to18nm. And they are the non-stoichiometric ratio compounds with the atomic ratio between Ni and O changing from1:1to0.68:1as the oxidation temperature increases. The Ni-NiOx-Cu diodes’ zero bias resistor and the zero bias sensitivity are significantly increased with a higher oxidation temperature, which is due to the increase in the thickness of the insulating layer and the improvement of the film quality.(3) Devices’asymmetry and nonlinearity increase with the work function difference values (△φ). The Ni-NiOx-Co diodes’nonlinearity isn’t obvious, since the reverse bias current magnitude should be similar to or greater than the forward bias current for Δφ up to κBT (-26meV at room temperature). The Ni-NiOx-Ag diode’s nonlinearity is less than the corresponding value of the Ni-NiOx-Cu diode, which may be led to the formation of MIIM (double insulator layers’structure) as Cu is more easily oxidation than Ag.(4) The Ni-NiOx-Cu diodes’zero bias resistance and the zero bias sensitivity are significantly increased with the increase of the contact area between the metal and oxide, which is caused by the increase of the insulators’defects.