A non-volatile MOSFET memory device based on mobile protons in SiO_2 thin films

摘要

It is shown how mobile H~+ ions can be generated thermally inside the oxide layer of Si/SiO_2/Si structures. The technique involves only standard silicon processing steps: the non-volatile field effect transistor (NVFET) is based on a standard MOSFET with thermally grown SiO_2 capped with a poly-silicon layer. The capped thermal oxide receives an anneal at approx 1100 deg C that enables the incorporation of the mobile protons into the gate oxide. The introduction of the protons is achieved by a subsequent 500-800 deg C anneal in a hydrogen-containing ambient, such as forming-gas (N_2: H_2 95:5). The mobile protons are stable and entrapped inside the oxide layer, and unlike alkali ions, their space-charge distribution can be controlled and rearranged at room temperature by an applied electric field. Using this principle, a standard metal-oxide-semiconductor (MOS) transistor can be converted into a non-volatile memory transistor that can be switched between 'normally on' and 'normally off. Switching speed, retention, endurance, and radiation tolerance data are presented showing that this non-volatile memory technology can be competitive with existing Si-based non-volatile memory technologies such as the floating gate technologies (e.g. Flash memory).