Do domain pinning results in high leakage current in BiFeO3? in divalent doped BiFeO3 at high concentration of divalent ions conductivity become dominant? As a result it is very difficult to get P-E loop.
You might like to read this paper:
http://onlinelibrary.wiley.com/doi/10.1002/adma.201402558/abstract
BFO has large leakage currents independent of the existence of domain walls. There are many issues, e.g., how thick is the sample?
Assuming a thick enough sample, let us say 100 nm, and proper annealing and topography, I would like to answer you in a different way. My experience is that leakage is not directly related to domains pinning. But it really depends on the type of material. For example, in PZT, domain pinning leads to reduced leakage- a fatigued sample with Pt electrodes leak less. In other Bi based materials, it is the reverse. There are two things to look at: surface and grain boundary passivation. Also, when you start doping with certain types of ions, the lectron density may vary a lot, and electrons can populate grain boundaries in such a way that they easily de trap and conduct. If domains are pinning because the charged grain boundaries are already the source of pinning, that is, a large charge sheet is in the grain boundary will pin the domain laterally (- in the grain and + in the polarization direction). So, when you apply a voltage, the conduction current will go through the grain but at steady state will not depin the domain as the field is to small to flip the dipoles. To solve this problem, the best way is to increase iron by about 10% so that grain boundary oxidation is increased. Then, make sure the BiO is about 5% higher in everything! as BiO reacts with the Pt electrode and reduce the surface layer. Them, oxidize this well. Another point is to make sure that the bottom electrode has a TiO glue layer by optimizing the bottom electrode process in such a way that SiO2 and TiO will not create hillock. So, the trick is to put down Ti and multiply by 10 the Pt thickness, so that the oxidation of the Ti below is hillock free. The top electrode thickness can be half that thickness. Now, the thermal history of multiple annealings, et. Is the killer. So, it is good to anneal the bottom electrode stack before you put down the BFO. This should be done at a temperature slightly higher than the BFO annealing temp. So that, at the annealing temperature, the electrode stack is already passivated. Finally, anneal a little before top electrode and longer after final electrode. Test using TVS so that you can separate leakage and displacement currents.good luck. This is all fun stuff.
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