In this study, memristors were fabricated on flexible polyethylene terephthalate (PET) substrates with aluminum contacts and a titanium dioxide film formed with a sol-gel of titanium isopropoxide and ethanol. To study the electric field dependence of switching, the TiO2 film thicknesses were varied from ~8.5 nm to ~47 nm by diluting the sol-gel. Memristors with active areas of 4 mm2 ( large area ) and 10,000 μm2 ( small area ) were fabricated to test the area dependence of the switching. Current-voltage (I-V) measurements exhibited switching similar to the signature bow tie memristor curves. Large area memristors generally switched at similar biases (~4 V to 5 V) independent of TiO2 thickness. For small area memristors, the switching bias was significantly higher for the thickest films (~24 V 8 V) than for the other small area memristors, which had consistent switching biases (~8 V to 13 V). The thickness dependence of the switching bias is inconsistent with the trend that would be expected if switching were due to the electric field. Furthermore, the experimentally-observed off state device resistance/thickness dependence is similar to the switching bias/thickness dependence described above, suggesting a current-based switching mechanism. The high resistance thick TiO2 samples have a lower current at a given voltage during the acquisition of I-V; these data can be interpreted as indicating that sweeps to higher voltages are necessary in order to pass sufficient current to cause switching. To further investigate the dependence of switching on total current, i.e. charge, devices were characterized using multiple I-V measurements over the same bias range but with different sweep rates, and switching was induced in only the longer measurements. This observed dependence of the switching bias on the time that the bias was applied further suggests that switching in these TiO2-based devices is induced by charge.
Pub Type: Talks
Titanium Dioxide, TiO2, Memristors, Flexible, Switching, I-V