iFixit

Chipworks has confirmed that the MEMS gyroscope found inside the iPhone 4 is nearly identical to an off-the-shelf STMicroelectronics L3G4200D gyroscope.

The picture of the die you see on the left is that of the GK10A MEMS die, found in the L3G4200D.

The GK10A is comprised of a plate, called the "proof mass," that vibrates (oscillates) when a drive signal is applied to set of drive capacitor plates.

When a user rotates the phone, the proof mass gets displaced in the X, Y, and Z directions by Coriolis forces. An ASIC processor senses the proof mass' displacement through capacitor plates located underneath the proof mass, as well as finger capacitors at the edges of the package.