Resistive Switching in Atomic Layer Deposited HfO2/ZrO2 Nanolayer Stacks

Abstract

Resistive switching materials and devices have received unparalleled recent attention due their potential and demonstrated use as resistive random access memory (RRAM) and neuromorphic applications. Resistive switching or memristive materials can serve as two-terminal electrical components where the resistance is a function of the amount and direction of current previously experienced and therefore they can uniquely emulate biological synapse behavior. HfO2 is a well-known dielectric and memristive material that has been previously explored for RRAM applications. Here, to better understand the resistive switching in harfnia in the presence of insulating interfaces, the electrical properties of HfO2/ZrO2 nanolayer stacks are discussed. The stacks with total thickness of 16 nm were prepared on platinized Si substrates using atomic layer deposition (ALD). A capping layer of TiN (30 nm thick) and a Au top electrode (100 nm thick) were sputtered to complete the device. We will discuss the current-voltage behavior, pulse time mode measurements, retention and endurance tests of the devices. Resistive switching was observed in all multilayer samples, with the set voltage (Vset) decreasing with increasing number of layers (i.e., number of hafnia-zirconia interfaces). We will show that grazing incidence x-ray diffraction (GI-XRD) demonstrated the transition of the hafnia phase from monoclinic to orthorhombic structure during the post metallization annealing, and that shifts in the binding energy of the x-ray photoelectron spectroscopy spectra (XPS) imply the existence of hafnia suboxide (HfO2-δ). More importantly, we will show how memristive/insulating nanostructures like nanolayered HfO2/ZrO2 can help modulate the resistive switching of memristive-based devices, to include for example, a two-step electroforming process, and multistate resistive switching.