Mike Harrison has build what he claims the “world’s smallest” led blinky. Likely it is based on the CPH3225A supercapacitor giving the blinky a footprint of 3.2 x 2.5 mm. With that in hand he added a PIC 10f322 microcontroller in a SOT23 package, an 0603 smoothing capacitor, and an SMD LED. The tiny structure is charged using a CR2032 battery and it blinks for 6 minutes.
World’s smallest LED blinky – [Link]