A Review on Resistive Switching in High-k Dielectrics: A Nanoscale Point of View Using Conductive Atomic Force Microscope.

Mario Lanza

doi:10.3390/ma7032155

Abstract

Metal-Insulator-Metal (MIM) structures have raised as the most promising configuration for next generation information storage, leading to great performance and fabrication-friendly Resistive Random Access Memories (RRAM). In these cells, the memory concept is no more based on the charge storage, but on tuning the electrical resistance of the insulating layer by applying electrical stresses to reach a high resistive state (HRS or “0”) and a low resistive state (LRS or “1”), which makes the memory point. Some high-k dielectrics show this unusual property and in the last years high-k based RRAM have been extensively analyzed, especially at the device level. However, as resistance switching (in the most promising cells) is a local phenomenon that takes place in areas of ~100 nm2, the use of characterization tools with high lateral spatial resolution is necessary. In this paper the status of resistive switching in high-k materials is reviewed from a nanoscale point of view by means of conductive atomic force microscope analyses.

Highlights

High-k materials were initially used in the semiconductors industry as gate oxide inMetal-Oxide-Semiconductor Field Effect Transistors (MOSFET) [1,2,3], but with time, the electrical tests to which high-k materials were subjected revealed unexpected properties that extended their use Materials 2014, 7 to other applications
Unlike NAND Flash RAM, which stores data in a little cloud of electrons in a quantum well, Resistive Random Access Memories (RRAM) stores information through changes in the resistance of a cell
First the HRS and LRS were written at the device level, and the top electrode was etched and the surface of the TiO2 layer was scanned with the Conductive Atomic Force Microscope (CAFM)

Summary

Introduction

High-k materials were initially used in the semiconductors industry as gate oxide in. Avoiding charge storage is necessary to minimize the power consumption of the entire device due to leakage currents In this novel cell the memory concept is based on the resistance change of a relatively simple Metal-Insulator-Metal (MIM) structure [9]. The electronic signals collected with the probestation are related to the whole area under test and, despite the fact that they give an excellent picture of the device performance, nanoscale analyses are necessary to fully understand the switching mechanisms involved In this sense, the electrical modes of an atomic force microscope are very powerful tools to in situ analyze RS, from localized spectroscopic measurements, and from current maps. The state-of-the-art on nanoscale observation of resistive switching in high-k materials using AFM related techniques is reviewed, and the correct habits for a reliable characterization using electrical modes of AFM are presented

Resistive Switching in High-k Materials

In Situ Observations of Bipolar Resistive Switching

Physical Origin of Resistive Switching in Hafnium Dioxide

Findings

Conclusions