Skip to main content
main-content
Top

About this book

Oxide materials are good candidates for replacing Si devices, which are increasingly reaching their performance limits, since the former offer a range of unique properties, due to their composition, design and/or doping techniques.

The author introduces a means of selecting oxide materials according to their functions and explains metal/oxide interface physics. As he demonstrates, material development is the key to matching oxide materials to specific practical applications.

In this book, the investigation and intentional control of metal/oxide interface structure and electrical properties using data obtained with non-destructive methods such as x-ray photoelectron spectroscopy (XPS) and x-ray reflectometry (XRR) are discussed. Further, it shows how oxide materials can be used to support the development of future functional devices with high-k, ferroelectric, magnetic and optical properties. In closing, it explains optical sensors as an application of metal Schottky contact and metal/oxide resistive random access memory structure.

Table of Contents

Frontmatter

Chapter 1. General Introduction

Abstract
The integrated circuit technologies stand at a crucial turning point in establishing the fundamentals for further advancement. To overcome the performance limits of conventional materials such as SiO2 gate, polycrystalline Si gate, and Al wiring, it is necessary to develop a new material with a new functionality that is not found in Si devices up to now, such as nonvolatile memory function.
Takahiro Nagata

Chapter 2. Changes in Schottky Barrier Height Behavior of Pt–Ru Alloy Contacts on Single-Crystal ZnO

Abstract
In this chapter, the Schottky contact formation and changes in Schottky barrier height (SBH) behavior of binary alloy contacts on n-type zinc oxide (n-ZnO) single crystals are shown. Pt–Ru alloy electrodes were deposited on the Zn-polar and O-polar faces of ZnO substrates by combinatorial ion-beam deposition under identical conditions. The crystal structures of the Pt–Ru alloy film changed from the Pt phase (cubic structure) to the Ru phase (hexagonal structure) in the Pt–Ru alloy phase diagram with decreasing Pt content. The SBH, determined from current–voltage measurements, decreased with decreasing Pt content, indicating that the SBH behavior also followed the Pt–Ru alloy phase diagram. The alloy electrodes on the Zn-polar face showed better Schottky properties than those on the O-polar face. Hard X-ray photoelectron spectroscopy revealed a difference in the interface oxidization of the Pt–Ru alloy: the interface of the O-polar face and Pt–Ru mixed phase with poor crystallinity had a more oxidized layer than that of the Zn-polar face. As a result of this oxidization, the O-polar face, Pt–Ru mixed phase, and Ru phase showed poor Schottky properties.
Takahiro Nagata

Chapter 3. Surface Passivation Effect on Schottky Contact Formation of Oxide Semiconductors

Abstract
In this chapter, the passivation of an oxide surface by atmospheric-pressure nitrogen plasma (NAP) method to eliminate the intermediate layer effect on a metal/oxide interface is described. NAP can nitride the oxide surface even at room temperature. Hard X-ray photoelectron spectroscopy revealed that NAP treatment reduced the electron accumulation on a ZnO surface and inhibited Zn diffusion into a Pt electrode, both of which are critical issues affecting the Schottky barrier height and ideality factor of a Pt/ZnO structure. After NAP treatment, the Pt Schottky contact showed an improvement of electrical properties.
Takahiro Nagata

Chapter 4. Bias-Induced Interfacial Redox Reaction in Oxide-Based Resistive Random-Access Memory Structure

Abstract
In this chapter, we report on the investigation of the filament formation process in a resistive random-access memory (ReRAM) structure by performing hard X-ray photoelectron spectroscopy under bias operation. We demonstrated resistance switching for nonvolatile memory applications using a polycrystalline HfO2 film with a Cu top electrode, and revealed the diffusion of Cu into the HfO2 layer during the filament formation process. Resistive switching was clearly observed in the Cu/HfO2/Pt structure by performing current–voltage measurements. The current step from a high-resistivity state to a low-resistivity state was on the order of 103–104 Ω, which provided a sufficient on/off ratio for use as a switching device. The application of a bias to the structure reduced the Cu2O at the interface and the intensity ratio of Cu 2p3/2/Hf 3d5/2, providing evidence of Cu2O reduction and Cu diffusion into the HfO2 layer. These results also provide evidence that the resistance switching of the Cu/HfO2/Pt structure originates in a solid electrolyte (nanoionics model) containing Cu ions.
Takahiro Nagata

Chapter 5. Switching Control of Oxide-Based Resistive Random-Access Memory by Valence State Control of Oxide

Abstract
Controlling the switching voltage and initial conductive filament formation of resistive random-access memory (ReRAM) is beneficial for actual applications. As summarized in Chap. 4, the density of oxygen vacancies is important in terms of controlling the conductive filament formation and switching of a nanoionic-type ReRAM structure. In this chapter, as an example of the control of oxygen vacancies and switching properties of the ReRAM structure, the intentional change in the valence state of an oxide layer is described. We investigated the Ta-Nb binary oxide ((TaxNb1-x)2O5) system as a dielectric oxide layer by a combinatorial method. A combinatorial pulsed laser deposition method was used to fabricate the (TaxNb1-x)2O5 system systematically. X-ray photoelectron spectroscopy revealed defect formation relating to Ta and the compensation of oxygen vacancies caused by a change in the valence of Nb. As the Ta content decreased, a decrease in the threshold voltage of the low-resistance state and an enhancement of the leakage current were observed, meaning that the switching properties can be controlled by controlling the (TaxNb1-x)2O5 system.
Takahiro Nagata

Chapter 6. Combinatorial Thin-Film Synthesis for New Nanoelectronics Materials

Abstract
In this chapter, the combinatorial synthesis techniques for the development of new thin-film materials for nanoelectronics are briefly introduced. Although this topic is not relating to the oxide thin-film materials directory, for the high-throughput material synthesis and systematic investigation, the combinatorial synthesis technique is effective. In former chapters, these techniques are used and have been effective. In the thin-film synthesis, technically, by combining a moving mask system and a target exchange system with physical thin-film growth methods, a ternary or binary composition spread thin-film sample can be obtained. In particular, in this chapter, combinatorial focused Ar ion-beam sputtering (FIBS), which is optimized for material research on new metal thin films and developed in NIMS, is mainly introduced.
Takahiro Nagata

Chapter 7. General Summary

Abstract
In this book, the research topics concerns the oxide thin-film materials for the electronics device applications, which were performed by author’s grouped at NIMS.
Takahiro Nagata
Additional information

Premium Partner

    Image Credits