In this paper we report the resistance switching characteristics in Au/V2O5/SiO2/Si structures feasible for the application as nonvolatile memory cells with nondestructive read out operation.
Two terminal devices were fabricated on p-Si wafers with amorphous 70 nm thick thermally grown SiO2 buffer layer. First, thin films of amorphous 300 nm thick V2O5 and 250 nm thick Au were deposited at room temperature using thermal evaporation. Then, the array of Au/V2O5 100Χ100µm junctions was fabricated on SiO2/Si substrate using photolithography and lift-off technique.
In virgin state junctions demonstrate insulator properties. The electrical forming was performed by increasing bias above 70-80 V with a positive polarity on Au electrode and compliance current of 50 µA. This happens as a 'soft breakdown' of V2O5/SiO2 bilayer accompanied with a switching of junction resistance from high resistive (HRS) to low resistive state (LRS) with the resistance ratio as high as 105. Too high current compliance settled at the process of electrical forming may lead to a 'hard' V2O5/SiO2 breakdown with nonreversible HRS-to-LRS transition.
LRS conserves after switching bias voltage off and can be read out nondestructively applying low probing voltage. In properly electrically formed junctions reproducible switching between LRS and HRS can be performed by continuous sweeping or pulsing bias voltage of opposite polarity. LRS is switched back to HRS under negative voltage around 10 V. Positive voltage about 5 V causes switching of HRS again to LRS.
Qualitatively, the mechanism of reversible resistance switching we rely upon electric field promoted nucleation of conducting VOx (x < 2) channel in isolating V2O5 matrix. Metal-to-insulator phase transition in V2O5 matrix occurs through electric field driven redistribution of oxygen vacancies and consequent reduction of V2O5 to VOx in nanosize filament perforating V2O5 isolator. It is worthy to note, that nonvolatile resistance switching we also observed in Au/V2O5/SiO2/Si structure.
This work was supported by Svenska Institutet (Dnr:01370/2006), US CRDF grant (award No. RUX0-000013-PZ-06) and by Ministry of Education of Russian Federation. |