Filament LED bulbs use very narrow strips containing the LED, which look similar to filaments of an old incandescent bulb.

Here's a good picture: http://www.aruana-led.de/

How are these filaments build? I could imagine the it's "pretty normal" LEDs, but lots of them, directly bonded to something? (There are references to COB)

And how does the driver look like?

Update:

Found some really detailed images at alibaba.com