Accelerating and Stopping Resistance Drift in Phase Change Memory Cells via High Electric Field Stress

Abstract

We observed resistance drift in 125 K - 300 K temperature range in melt quenched amorphous Ge2Sb2Te5 line-cells with length x width x thickness = ~500 nm x ~100 nm x ~ 50 nm. Drift coefficients measured using small voltage sweeps appear to decrease from 0.12 +/- 0.029 at 300 K to 0.075 +/- 0.006 at 125 K. The current-voltage characteristics of the amorphized cells measured in the 85 K - 300 K using high-voltage sweeps (0 to ~25 V) show a combination of a linear, low-field exponential and high-field exponential conduction mechanisms, all of which are strong functions of temperature. The very first high-voltage sweep after amorphization (with electric fields up to ~70% of the breakdown field) shows clear hysteresis in the current-voltage characteristics due to accelerated drift, while the consecutive sweeps show stable characteristics. Stabilization was achieved with 50 nA compliance current (current densities ~104 A/cm^2), preventing appreciable self-heating in the cells. The observed acceleration and stoppage of the resistance drift with the application of high electric fields is attributed to changes in the electrostatic potential profile within amorphous Ge2Sb2Te5 due to trapped charges, reducing tunneling current. Stable current-voltage characteristics are used to extract carrier activation energies for the conduction mechanisms in 85 K - 300 K temperature range. The carrier activation energy associated with linear current-voltage response is extracted to be 331 +/- 5 meV in 200 - 300 K range, while carrier activation energies of 233 +/- 2 meV and 109 +/- 5 meV are extracted in 85 K to 300 K range for the mechanisms that give exponential current-voltage responses.