Is it a must to write a paper in passive third person, for all types of papers in all journals?
Have a look at the style guide of the journal you're targeting. It has the only authoritative answer to your question.

Having said that, passive voice is not a "must" in the sense that active voice were unheard of in academic writing. Here is a paper written in active voice, first person singular.

Common preferences for either active or passive voice differ between disciplines. (I've heard that in mathematics the first person plural is fairly common, i.e. "we".) 

Preferences also differ between authors. I find the first person singular active voice most authentic, simple, and lively. It is often emphasized, however, that passive voice sounds more neutral and objective.

When deciding which voice to use, consider the style guide first, then your discipline's customs (ask your peers!), and your personal preference last.