Polysilicon n+p-n+structures for memory redundancy

We have studied n⁺p-n⁺structures in polysilicon for possible use as a programmable element in MOS memories with redundancy. The devices are programmed with current limited pulses which cause the formation of a stable molten filament. A decrease in resistance then occurs because of migration of dopant or aluminum through the molten filament. Dopant migration occurs more quickly and only requires a few short pulses; controlled aluminum migration is achieved when a single long pulse is used. In both cases the currents needed for programming are lower than required for a resistor fuse of similar geometry, and removal of the passivation glass is not necessary. The width of the molten filament was directly measured from photographs of programmed devices. We have compared the measured filament widths with the predictions of a previously developed model. Good agreement is obtained.