Filamentary Transport and Thermoelectric Effects in Mushroom Phase Change Memory Cells

Md Samzid Bin Hafiz; Helena Silva; Ali Gokirmak

paper

Filamentary Transport and Thermoelectric Effects in Mushroom Phase Change Memory Cells

arXiv:2606.10262

Abstract

We performed a 2D finite-element electrothermal computational study of thermoelectric effects and filamentary electronic transport in Ge $_{2}$ Sb $_{2}$ Te $_{5}$ mushroom phase change memory cells during Reset and Set operations, accounting for spatial activation energy variations in amorphous Ge $_{2}$ Sb $_{2}$ Te $_{5}$ and phase-change dynamics. Reset operations with current going from the top electrode to the narrow 4 nm bottom electrode require $\sim$ 3x less energy and power, and $\sim$ 2x lower current to achieve the same Reset resistance, compared to the opposite polarity, due to thermoelectric effects. Filamentary conduction, electrical breakdown, thermal runaway, and local crystallization of amorphous Ge $_{2}$ Sb $_{2}$ Te $_{5}$ depend on current polarity and thermal boundary conditions, and determine the location, shape, and volume of the programming region, which may be significantly smaller than the semi-cylindrical mushroom region. The programming volume does not scale with contact dimensions larger than 10 nm. Larger contact areas introduce increased device-to-device and cycle-to-cycle variability due to filamentary conduction but are expected to lead to higher reliability and endurance.