Single power supply operated and highly reliable SONOS EEPROMs

Abstract

Two kinds of polysilicon-oxide-nitride-oxide-silicon (SONOS) transistors were fabricated, whose nitride thicknesses were 40 ? and 70 ?, to investigate the scaling effects. The blocking oxide and the tunnel oxide were 25 ? and 24 ?, respectively, for both devices. The SONOS device with the 40-? nitride layer had a larger memory window and a lower decay rate of programmed charges than the device with a 70-? nitride layer, that means that, for a scaled device, the electrons injected in the nitride layer fill the blocking oxide-nitride interface, as well as the nitride layer, while the injected electrons for the device with a nitride thickness of 70 ? fill part of the nitride bulk. A new programming method, a source/drain program and a channel erase, to operate with only a single power supply of 3 V and to realize high reliability has been proposed. After 1 × 106 program/erase cycles, the interface trap density of the channel region showed only a small increase from the initial density of 8.73 × 1010 cm2 to 1.62 × 1011/cm2 for the proposed programming method.