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