The improvement of the embedded Ag nanoislands on the performance of Au/Ag/HfO_x/HfO₂/Ag-NIs/Au devices

To search for ways to improve the performance of selectors, crossbar-structured Au/Ag/HfOx(2 nm)/HfO2(4 nm)/Ag-NIs/Au devices with embedded Ag nanoislands (Ag-NIs) and dual hafnium oxide layers with different Hf:O ratios were prepared. Highly ordered Ag-NIs were prepared by electron beam evaporation with the help of an ultrathin anodic aluminum oxide (AAO) template. A 4-nm HfO2 layer was deposited by plasma-enhanced atomic layer deposition (PEALD) with tetrakis-ethyl methylaminohafnium (TEMAHf) as the precursor and O-plasma as the oxygen source (PEALD-HfO2), and a 2-nm HfOx (x = 1.60) layer was deposited by atomic layer deposition (ALD) with TEMAHf as the precursor and H2O as the oxygen source (ALD-HfOx). Au/Ag/HfOx(2 nm)/HfO2(4 nm)/Ag/Au, Au/Ag/HfOx(6 nm)/Ag-NIs/Au, and Au/Ag/HfO2(6 nm)/Ag-NIs/Au devices were also prepared for comparison. For the Au/Ag/HfOx/HfO2/Ag-NIs/Au device, the embedded Ag-NIs could effectively eliminate the need for an electroforming process, improve the volatile threshold switching (TS) endurance, and decrease the variation in the threshold voltages. The device could maintain volatile TS behavior under a high working current due to the dual-layer structure. By combining XPS characterization and measurements of the electrical properties of devices, we have proposed a phenomenological mechanism model that can be used to well explain the TS behavior of the Au/Ag/HfOx/HfO2/Ag-NIs/Au device. This work demonstrates that the introduction of Ag-NIs and a dual-layer structure is the effective way to improve the performance of selectors.