The semiconductor filled portion of {TAIL ~ each trench} then serves as {HEAD ~ a drain} and source of a field effect transistor 
The semiconductor filled portion of { TAIL ~ each trench } then serves as { HEAD ~ a drain } and source of a field effect transistor
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH