Effect of Ag and Ti electrodes on capacitance tunability of oxygen - deficient SrTiO₃ based MIM varactors prepared by plasma sputtering

The role of oxygen deficiencies on the electrical performance of SrTiO₃ films is investigated by depositing on the stack of TiN/Ti/SiO₂/Si films using radio-frequency (RF) and direct current (DC) magnetron sputtering systems operating in oxygen-deficient plasma environment. Electrodes of silver (Ag) and titanium (Ti) are used to observe the effects of their sizes on the electrical properties of the SrTiO₃ films. It is found that the nonlinearity in capacitance-voltage graphs (capacitance tunability) of the varactor can be controlled by varying the electrode area. In addition, the material of the electrode plays a vital role in controlling the non-linearity in the capacitance of the oxygendeficient SrTiO₃ dielectric films with varying voltage. It is found that the silver top electrode instead of titanium, delivers better performance with high capacitance tunability, low leakage current and good quality factor. Post deposition annealing at 550 °C in nitrogen ambient, creates more oxygen deficiencies in SrTiO₃ film thereby increasing the linearity of the capacitance-voltage graph and decreasing the capacitance tunability.