Tuning of the thermal stability and ovonic threshold switching properties of GeSe with metallic and non-metallic alloying elements

Abstract

In order to make 3D crossbar memory architectures viable, selector elements with highly non-linear current–voltage characteristics are required. Ovonic Threshold Switching (OTS) is a highly non-linear phenomenon observed in amorphous chalcogenides, such as GeSe, that shows promise for application in selectors. In this paper, the impact of alloying with metallic (Zr), metalloid (B, Sb), and non-metallic (C, N) elements as a function of their concentration on the thermal stability and switching properties of alloyed GeSe layers is studied. In the case of the thermal stability analysis, the key parameter that is tracked is the crystallization temperature (Tc) of the as-deposited amorphous films since OTS only occurs in amorphous materials. Using a simple metal–insulator–metal type test structure where the bottom electrode is scaled to 6 μm, the OTS properties of the alloyed layers are also compared. The pristine leakage current (Ipris), the first fire voltage (VFF), and the threshold voltage (Vth) were determined using DC and pulsed (AC) measurements. Results indicate that C alloying in combination with sufficiently high nitrogen incorporation can extend the thermal stability above 600 °C with only low dependence on the C content. Among the metallic and metalloid elements, crystallization temperature is strongly dependent on alloying concentration. In general, larger concentrations are needed to obtain a Tc above 400 °C as compared to CN alloying. Electrical characterization indicates strong dependence of the first fire voltage and the leakage current on the metallicity of the alloying element with only small to moderate concentrations required to influence electrical properties.