Low resistance-drift characteristics in Cr2Ge2Te6-based phase change memory devices with a high-resistance crystalline phase

Abstract

Resistance drift affects the reliability of data reading in phase change material (PCM)-based memory devices. In general, resistance drift occurs in high-resistance amorphous state in the PCM-based memory devices. The conduction mechanism such as Poole-Frenkel conduction (PF) in amorphous PCMs causes severe resistance drift in the device. Cr2Ge2Te6 (CrGT) exhibiting a phase transition between low-resistance amorphous and high-resistance crystalline phases demonstrates band conduction in the amorphous phase and mixed conduction with band conduction and nearest-neighbor hopping conduction in the crystalline phase. Since the conduction mechanisms of both phases in the CrGT are not governed by PF, the resistance-drift characteristics are expected to be different from that in conventional PCMs. In this study, the resistance-drift characteristics of the CrGT-based devices were investigated. The fabricated CrGT-based devices exhibited a cyclic endurance of ~7 × 105 times with a clear difference in resistance between the high- and low-resistance states. The drift coefficient, v, at 40 °C was evaluated for the CrGT- and Ge-Sb-Te (GST)-based devices; the value of v for the CrGT-based device was smaller than that for the GST-based device in both high- and low-resistance states. The current–voltage analysis revealed that mixed-conduction mechanism plays an important role to suppress the resistance drift in the high-resistance state of the CrGT-based devices. These findings provide new insights to realize a low resistance-drift PCM-based memory device.