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