Threshold switching in a-Si and a-Ge based MSM selectors and its implications for device reliability

Next-generation memory technologies utilizing crosspoint-array architecture require a two-terminal selector element with strong non-linearity, to suppress leakage currents. A promising candidate for this role is metal-semiconductor-metal (MSM) device, that relies on rectifying nature of Fowler-Nordheim tunneling process. In this paper, we report a detailed investigation of a breakdown mechanism of a-Si/a-Ge MSM selectors. For devices with integrated current-limiting series resistor it was found to be a non-destructive threshold switching effect, instead of a hard breakdown. The switching is field-triggered and current is area-independent after initial forming pulse, suggesting that it is closely related to ovonic threshold switching (OTS) phenomenon. Triggering current increases for thinner semiconductor and larger series resistance, providing a way to achieve higher maximum ON-current density.