Light-activated storage device (LASD)

Abstract

A novel nonvolatile semiconductor memory called the light-activated storage device (LASD) is reported. It consists of a thin metal-silicon-dioxide-silicon (MOS) structure with the SiO2 layer ion implanted with impurities such as As or P which create light-sensitive traps. The sites resulting from the implantation are charged ("write" operation) by using light and a moderate-voltage bias to photoinject carriers from the metal or silicon contacts into the SiO2 where some of the carriers are trapped on these sites as they traverse the oxide layer. It is discharged ("erase" operation) by using light and a low-voltage bias to photoionize these trapped charges while blocking photoinjection from the contacts with the internal field of the trapped charges. The "write" and "erase" properties of this structure are investigated as a function of the ion used (As or P), ion fluence, ion energy, and oxide thickness. The LASD is shown to have reproducible cycling properties and excellent charge retention.