Terminology:

"Miniature Film" refers to small formats used for pictorial photography. In the past it was used for 35mm and smaller. Today for 16mm and smaller.
The emulsions are the same as for larger formats.
This term thus only refers to the size of the film.

"Microfilm" refers to extreme small scale of the image with reference to the needed enlargement.
It uses special emulsions. Often not continous-tone.
The size of the film is of lesser importance.


Important research labs for continuous-tone applications of this films in the past have been Gigabitfilm and SPUR.