A novel MONOS nonvolatile memory device ensuring 10-year data retention after 107 erase/write cycles

A highly reliable nonvolatile memory device suitable for high-density electrically erasable and programmable read only memories (EEPROMs) is described. A metal-oxide-nitride-oxide-semiconductor (MONOS) structure whose top oxide is fabricated by chemical vapor deposition (CVD) on the nitride is proposed. This CVD oxide is densified by pyrogenic annealing and has stoichiometric SiO₂ characteristics. Its potential barrier, which prevents stored charges from decaying through the top oxide to the gate, thus becomes sharper than that of the thermally grown top oxide used in the conventional MONOS structure. For comparison between the proposed MONOS, conventional MONOS, and MNOS structures, three devices were fabricated on the same process line. The 16.7-nm nitride thickness in combination with a top oxide thickness of 4.0 nm results in a gate capacitance equivalent to that of the conventional NMOS structure with a 23.5-nm nitride thickness. Moreover, an asymmetric erase/write programming voltage has been adapted to the MONOS device operation by considering both erased-state degradation and written-state retention. At 85 °C, the proposed MONOS device has 10⁷-cycle endurance with 10-year data retention