The Effect of Trapped Charge Distributions on Data Retention Characteristics of nand Flash Memory Cells

Abstract

We present this letter on the combining effect of tunnel-oxide degradation and narrow width effect on the data retention characteristics of NAND flash memory cells. Due to severe boron segregation in shallow-trench isolation (STI) corner, the cell transistor suffers from intense V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> shift on STI corner in data retention mode. Independent of enhancing the tunnel-oxide quality, the data retention characteristics are improved by designing a cell transistor that isolates the region where Fowler-Nordheim stress mainly occurs in tunnel oxide away from STI corner. Experimental results show that V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> shift is reduced by 0.3 V or more in retention mode as the tunneling is separated from the isolation edge.