Double Diffusion
MOS transistor.
Use a n-doped semiconductor to build a n-channel-type device.
Make a p-diffusion. Inside, put a n-diffusion.
Put field oxide over p-diffusion, between epi and n-diffusion. Put gate polysilicium.
The drain can be another n-diffusion at the side (lateral DMOS) or a n-buried layer (vertical DMOS).
________________
| <-- field oxide
------------------------
source | | <----- channel
-------- |
|
p-well /
---------------
n epi
--------------------------------------------
buried layer (drain)
Its vertical variant is usually used to take big
voltages as its
drain area can be very long and is usually only doped lightly.