Electronic Transport in Sub-100 nm Reset Phase Change Memory Line-Cells

Electronic transport in amorphous chalcogenides, such as amorphous Ge2Sb2Te5 (GST), has significant importance for scaling and multi-bit-per-cell implementations of phase change memory (PCM) cells. When the PCM cells are reset, a small volume of a phase change material, such as GST, thermally switches from its crystalline phase (low-resistance state) to its amorphous phase (high-resistance state). The resistance in the high-resistance state spontaneously increases in time, following a power-law trend, known as resistance drift. The cells also show a significant fluctuation in their read-current in the high-resistance state. Both resistance drift and electronic transport in the high-resistance state are poorly understood and are a topic of active research. A substantial effort has been put into understanding the amorphous phase change materials to understand the contribution of the defects in the bulk material.<br/>In our experimental studies, we reset GST line cells with width x length x thickness of ~ 100 nm x ~ 500 nm x ~ 20 nm, in the 80 K – 350 K temperature range and performed slow high-voltage sweeps. The current-voltage (I-V) characteristics of these cells show an initial hysteresis behavior, with a clear hyperbolic sine I-V response in the low-field regime (&lt;20 MV/m) and a much stronger exponential response in the high-field regime (&gt;20 MV/m). Our experiments on cells wider than 100 nm show that the hysteresis behavior disappears in 1-2 sweeps and the resistance drift stops in the 80 K – 250 K range. The cells in the 60 nm – 100 nm regime tend to amorphized shorter segments (~ 100 nm) and can be stabilized with voltage stresses at room temperature (300 K).<br/>In our studies, we construct a low-field and high-field transport model that explains transport in the amorphous phase and a charge-relaxation-based model that describes the acceleration and stoppage of resistance drift [1-3]. In this study, we analyze the cells stabilized at room temperature and show the same low-field and high-field characteristics at lower voltages to extend the research and prove the validity of our models.<br/><br/>1. R. S. Khan, F. Dirisaglik, A. Gokirmak, & H. Silva, Resistance drift in Ge2Sb2Te5 phase change memory line cells at low temperatures and its response to photoexcitation. Appl Phys Lett 116, 253501 (2020).<br/>2. R.S. Khan, A.H. Talukder, F. Dirisaglik, H. Silva, and A. Gokirmak, “Accelerating and Stopping Resistance Drift in Phase Change Memory Cells via High Electric Field Stress,” ArXiv:2002.12487, (2020).<br/>3. A. Talukder, M. Kashem, M. Hafiz, R. Khan, F. Dirisaglik, H. Silva, and A. Gokirmak, “Electronic transport in amorphous Ge2Sb2Te5 phase-change memory line cells and its response to photoexcitation,” Appl Phys Lett 124(26), (2024).