Current pulse generator for multilevel cell programming of innovative PCM

Multilevel Cell programming, i.e. storing multiple bits per memory cell, is a promising way to increase storage density in Phase Change Memory (PCM). In this paper, it is shown that it is possible to program a PCM device to multiple intermediate resistance states by using a single-pulse programming approach, as opposed to time-consuming iterative write algorithms previously reported in the literature. A circuit that generates current programming pulses with characteristics suitable for the specific target resistance state, is presented and simulated. The programmed resistance variation due to the variations in current is also studied and the programmed resistance states distributions are shown to be adequately spaced from each other, thus providing a viable programming solution for obtaining multiple resistance levels per memory cell.