Temperature-Dependent Contact Resistance to Nonvolatile Memory Materials

Abstract

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 Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Te <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> (GST), TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , and HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> Ω·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (~1000 times greater than the hexagonal GST) while that to HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is as high as 5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> Ω·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> 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.