Do the RAM modules use Flash as the USB keys and SSD?
No, they don't.

DRAM cells are real tiny capacitators directly connected to the addressing logic, which makes them really really fast, but make them leak much, so they have to be refreshed thousands of times in a second. This is done by reading out data and rewrite the full load. Today's DRAM chips do that internally and fully automatical.

Flash ROM cells in contrary are somewhat bigger capacitators which are indirectly connected to the addressing logic. Their floating gate, which stores the information in the cell, is embedded into an isolating patch. So a Flash ROM cell leaks much less than a DRAM cell, it needs years until the information is jumbled by the leak. However, it's hard to empty or refill the cell through the isolator as needed to write a 0 or 1 into it. that's the reason why Flash ROM is much much slower to write than a DRAM cell. Reading speed is similar.

Analogy:


DRAM cell: glass of water (or no water)
Flash ROM cell: glass of water (or no water) with a lid and a very tiny hole in it.