I made Ag/PVDF/Ag type capacitor structure. PVDF thickness is around 300nm and is showing a mixture of alpha and beta phase. Most of the time the films show a resistance of 100 ohm. But when I try measurement like I-V the resistance goes to mega or 100s of kilo ohm range, with a hysteresis. Why this is happening? Is this ferroelectric switching or resistive switching? One of the measaurement is attached
You should check if time-dependent effects exist, as I observed myself in the past with polymer composite films also measured by I-V experiments, using silver paint for making the contacts at the surface. So the system was very similar to yours.
Try a rather high dc electric fiel, and see how the resistance changes with time. In polymer insulators, you can observe low pseudo-currents, corresponding to slow movement of polymer chains which try to orientate in the electric field. If you see this, the resistance changes much (by several orders of magnitude), and these changes may explain the hysteresis you see.
Alain
DC and AC electric conductivity for the capacitor are different. DC one is more intrinsic effect produced by the transportation of charges by their carriers, the current of which is called leakage current. On the other hand, AC current for the capacitor is actually a combination of the leak current and induced current, but they have phase difference of 90 degree. So, the AC conductivity is also the combination.
Check method of measuring resistance, the delta pulse method is suggested to avoid the Joule effect. In addition to the above.
Unpoled ferroelectric films show higher DC current (poling process) for first time switching followed by lower DC leakage current (poled state), if you want to evaluate leakage current you should sweep the voltage in one direction ( +ve or -ve) multiple times till you see a stable/repeatable DC characteristics. Variation could be due to many things including forming a dead layer at the interface, DC stress induced leakage etc.
Thank you very much Amir N. Hanna.
May be you are right. I also thought about the poling process. But, since the film thickness is low, the applied voltage for I-V itself will be enough to orient the dipoles I guess. Actually most of the work on pure 'PVDF' got shifted towards 'PVDF+its copolymer', where they are fully in beta phase. But the clear idea of the intrinsic nature of Pure PVDF thin film is not well understood till date. But I struggled too much to charcterize
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