Direct observation of nanometer-scale Joule and Peltier effects in phase change memory devices

TL;DR

This study employs scanning Joule expansion microscopy to directly observe and quantify nanometer-scale Joule and Peltier effects in phase change memory devices, revealing critical insights for energy-efficient PCM design.

Contribution

It provides the first direct nanoscale measurements of Joule and Peltier effects in PCM devices, combining experimental imaging with simulations to uncover thermopower and contact resistance.

Findings

Joule heating dominates temperature rise in GST

Peltier effects are significant at GST-TiW contacts

Thermopower of 25 nm thick face-centered cubic GST is ~350 μV/K

Abstract

We measure power dissipation in phase change memory (PCM) devices by scanning Joule ex-pansion microscopy (SJEM) with ~50 nm spatial and 0.2 K temperature resolution. The temperature rise in the Ge2Sb2Te5 (GST) is dominated by Joule heating, but at the GST-TiW contacts it is a combination of Peltier and current crowding effects. Comparison of SJEM and electrical characterization with simulations of the PCM devices uncovers a thermopower ~350 uV/K for 25 nm thick films of face centered-cubic crystallized GST, and contact resistance ~2.0 x 10^-8 Ohm-m2. Knowledge of such nanoscale Joule, Peltier, and current crowding effects is essential for energy-efficient design of future PCM technology.