A new buried-channel EEPROM device

Summary form only given. A buried-channel polysilicon-oxide-nitride-oxide-silicon (BC SONOS) device structure is described with improved electrical characteristics for high-density nonvolatile semiconductor memories (NVSMs). Compared to the conventional SONOS device the WRITE is performed from an accumulation layer where, for the same oxide electric field, there is a large number of carriers available for the tunneling current. The WRITE speed is improved by an order of magnitude in this new device structure over the conventional SONOS device due to the increase in the supply of carriers. The BC SONOS NVSM provides a reduced oxide electric field in the retention mode to suppress the back-tunneling of stored charge, thereby improving the memory retention. Other interesting features of this device include the minimization of Si/SiO₂ interface trap formation, which improves the endurance due to the extended ERASE/WRITE cycling