Thermodynamic origin of nonvolatility in resistive switching

Abstract

Electronic switches based on the migration of high-density point defects, or memristors, are poised to revolutionize post-digital electronics. Despite significant research, key mechanisms for filament formation and oxygen transport remain unresolved, thus hindering our ability to predict and design crucial device properties. For example, predicted retention times based on current models can be 10 orders of magnitude lower than ones experimentally realized. Here, using electrical measurements, chemical spectroscopy, and first-principles calculations on tantalum oxide memristors, we reveal that the formation and stability of conductive filaments crucially depend on the stability of the amorphous oxygen-rich and oxygen-poor compounds, which undergo composition phase separation. Including the previously neglected effects of this amorphous phase separation reconciles unexplained discrepancies and enables predictive design of key performance indicators such as retention stability. This result emphasizes non-ideal thermodynamic interactions as key design criteria in post-digital devices with defect densities substantially exceeding those of today’s covalent semiconductors.

Materials Horizons Emerging Investigator Series: Professor Yiyang Li, University of Michigan, USA

“…Unfortunately, this descriptor does not describe the ionic conductivity in amorphous materials. In this work and our other work, 10 we found that oxygen-deficient metal suboxides have much lower ionic conductivity than near-stoichiometric metal oxides. Instead, amorphous hafnium oxide made through atomic layer deposition has much lower oxygen tracer diffusivity than ones made through reactive sputtering.…”

Oxygen tracer diffusion in amorphous hafnia films for resistive memory

“…It was recently shown that oxygen may undergo ''uphill'' diffusion against the concentration gradient because of spinodal decomposition. 26 However, these devices would fail from the high-resistance to the low-resistance state. Our results show device failure from the low-resistance to the high-resistance state (Fig.…”

“…Next, we investigate oxygen tracer diffusion in amorphous HfO 2 thin films deposited by sputtering and by atomic layer deposition. To study oxygen tracer diffusion in sputtered HfO 2 , we deposited tri-layer samples 26 comprised of an 18 O-enriched HfO 2 layer sandwiched between natural-abundance oxygen HfO 2 oxide layers as shown in Fig. 2a; all three layers are nominally identical chemically (HfO 2 ).…”