The memory circuit 6, wherein {HEAD ~ the third impurity concentration} is identical to {TAIL ~ the first impurity concentration}, and the fourth impurity concentration is identical to the second impurity concentration 
is identical to
The memory circuit 6 , wherein { HEAD ~ the third impurity concentration } is identical to { TAIL ~ the first impurity concentration } , and the fourth impurity concentration is identical to the second impurity concentration
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH