Temperature-Dependent Contact Resistance to Nonvolatile Memory Materials

Emerging nonvolatile memories store data by reversible resistive switching in phase-change materials or metal oxides. As memory cell dimensions are reduced to 10-nm scale or below, electrical contacts can dominate the device behavior, yet are often poorly understood. Here, we study the contact resistance to memory materials Ge₂Sb₂Te₅ (GST), TiO₂, and HfO₂ with low-current and temperature-dependent measurements. We find that the contact resistivity varies over ten orders of magnitude depending on the material; contact resistivity to cubic GST is near 10^-2Ω · cm² (1000 times greater than the hexagonal GST) while that to HfO₂ is as high as 5 × 10^{{5}} Ω · cm² at room temperature. Contact resistivity decreases with increasing temperature and with increasing current density, the latter due to the non-Ohmic nature of the contacts. These results are important to understand the design, scaling, and behavior of nanoscale data storage devices.