RF Characterization of NiO and TiO2 Based Metal-Insulator-Metal (MIM) Diodes on Flexible Substrates

This paper presents the fabrication and characterization of metal-insulator-metal (MIM) diodes on flexible substrates for RF and microwave circuit applications. Diodes using two types of insulators, titanium dioxide (TiO₂) and nickel oxide (NiO), are investigated. These insulators are obtained using different oxidation techniques, i.e., in-situ oxidation for TiO₂ and plasma oxidation for NiO. Asymmetric metal contacts (Ti-TiO₂-Pd and Ni-NiO-Mo) are utilized to achieve nonlinear I-V characteristics. The fabricated diodes show strong non-linearity, high current densities, and low turn-ON voltage. The diodes show RF to dc rectification with near-ideal behavior and rectification sensitivity of 22 V/W (18 GHz) and 46 V/W (18 GHz) for TiO₂ and NiO, respectively. NiO-based diodes barrier shows higher current density and higher cutoff frequency in comparison with TiO₂ as expected diodes due to thinner oxide and lower dielectric constant. The diodes also work well as frequency doublers over a wide frequency range of 1-4 GHz for TiO₂ and 2-10 GHz for NiO-based diodes. Good dc and RF performance of diodes indicate that good quality oxide can be achieved on plastic substrates and MIM devices can provide a perfect solution for RF and microwave circuits on a flexible substrate.