We are fabricating a tandem structure where a ~50 nm thick WO3 film is deposited between two metal films using DC sputtering. We use a mixture of Ar and O2 gases at different flow rates while purging the chamber. However, the final resistance measured between the top and bottom electrodes is very low (1-10 ohms). When we replace the top electrode deposition with simple copper tape adhesion, the resistance becomes very high (Mohms). This suggests that the WO3 film is exhibiting a highly porous nature. What strategies can we employ to reduce the porosity of the WO3 film?
Typically increasing substrate temperature or using IBAD (ion beam assisted deposition) are the ways to increase density. Using maximum possible voltage to provide more energy to at least some of the sputtered atoms should also help.
But I'm confused - "tandem structure ... between two metal films" - so a 2-something structure with 3 layers. I don't understand.
Are you picturing porosity that extends in straight lines all the way through the film, so the next metal layer fills in the pores, thus making the oxide layer conductive? I find that far-fetched. Really tough to picture that. Maybe you have a different rationale?
Are you sure the adhesive layer when you use adhesive Cu is not the insulator?
Are you sure the "WO3" film is really that? e.g., by XRD or RBS etc.?
Thanks for your answer w.s.l. Boyer.
- In this context, I use the "tandem structure," which means Metal/WO3/Metal.
- Yes, the explanation you provided is the same as what I believe.
- Yes, I have tested the copper tape, which is conductive.
- I am currently investigating the XRD of the deposited film.
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