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