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High-quality Al2O3 and Si3N4 dielectrics synthesized in a molecular/atomic deposition system were developed and adopted as blocking oxide and tunnel dielectric, respectively in a SONOS-type NAND flash memory cell. In particular, the use of trap-free Si3N4 as tunnel dielectric enables low-voltage erase operation due to its low barrier height for holes, and the relatively high-k value of Al2O3 enhances the low-voltage and high-speed program/erase (P/E) operations. We fabricated and investigated NAND flash memory cells with metal/Al2O3/SiN/Si3N4/Si structure. The fabricated cell shows 3.8-V memory window with P/E conditions of +15 V for 100 mus and -10 V for 10 ms. It also shows good endurance up to 10 000 cycles and more than 1.5-V memory window after ten years.
Date of Publication: May 2008