Physics and Technology of Crystalline Oxide Semiconductor CAAC-IGZO

Application to LSI

Shunpei Yamazaki, Masahiro Fujita, Shunpei Yamazaki, Masahiro Fujita

• Publisher: Wiley
• Year: 2016
• Print ISBN:
  9781119247340
• Edition: 1
• eBook ISBN:
  9781119247432
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Physics and Technology of Crystalline Oxide Semiconductor CAAC-IGZO: Application to LSI

This book describes the application of c-axis aligned crystalline In-Ga-Zn oxide (CAAC-IGZO) technology in large-scale integration (LSI) circuits. The applications include Non-volatile Oxide Semiconductor Random Access Memory (NOSRAM), Dynamic Oxide Semiconductor Random Access Memory (DOSRAM), central processing unit (CPU), field-programmable gate array (FPGA), image sensors, and etc. The book also covers the device physics (e.g., off-state characteristics) of the CAAC-IGZO field effect transistors (FETs) and process technology for a hybrid structure of CAAC-IGZO and Si FETs. It explains an extremely low off-state current technology utilized in the LSI circuits, demonstrating reduced power consumption in LSI prototypes fabricated by the hybrid process. A further two books in the series will describe the fundamentals; and the specific application of CAAC-IGZO to LCD and OLED displays.

Key features:

• Outlines the physics and characteristics of CAAC-IGZO FETs that contribute to favorable operations of LSI devices.
• Explains the application of CAAC-IGZO to LSI devices, highlighting attributes including low off-state current, low power consumption, and excellent charge retention.
• Describes the NOSRAM, DOSRAM, CPU, FPGA, image sensors, and etc., referring to prototype chips fabricated by a hybrid process of CAAC-IGZO and Si FETs.

1
Introduction

1.1 Overview of this Book

The three books in this series deal with c‐axis‐aligned crystalline indium–gallium–zinc oxide (CAAC‐IGZO), an oxide semiconductor (see Figure 1.1): Physics and Technology of Crystalline Oxide Semiconductor CAAC‐IGZO: Fundamentals (hereinafter referred to as Fundamentals) [1], Physics and Technology of Crystalline Oxide Semiconductor CAAC‐IGZO: Application to LSI (this book, hereinafter referred to as Application to LSI), and Physics and Technology of Crystalline Oxide Semiconductor CAAC‐IGZO: Application to Displays (hereinafter referred to as Application to Displays) [2]. Fundamentals describes, for example, the material properties of oxide semiconductors, the formation mechanism and crystal structure analysis of IGZO, the fundamental physical properties of CAAC‐IGZO, the electrical characteristics of field‐effect transistors (FETs) with CAAC‐IGZO active layer (hereinafter referred to as CAAC‐IGZO FETs), and comparisons between CAAC‐IGZO and silicon (Si) FETs. Application to Displays introduces applications of the CAAC‐IGZO FET technology to liquid crystal and organic light‐emitting diode displays, describing the process flows and characteristics of the FETs, the driver circuits for displays, the technologies for high‐definition, low‐power, flexible displays, and so on.

Figure 1.1 Framework and summary of the book series

This volume, Application to LSI, aims to introduce the applications of CAAC‐IGZO FET technology to large‐scale integration (LSI) and broadly and concisely review the device physics of CAAC‐IGZO FETs. On the basis of the distinct material features of these FETs disclosed in Fundamentals, such FETs have an attractive application field in LSIs, in addition to the display applications described in Application to Displays. Not only focusing on oxide semiconductor material aspects, this book will also describe device design and fabrication using such materials, combination with other technologies, and specific applications (see Figure 1.2). Application examples of CAAC‐IGZO FET technologies to LSIs are specifically described in the subsequent chapters.

Figure 1.2 Scope of this book. The symbol F² means the square of the feature size F, used as an index of the memory cell size

1.2 Background

The integrated circuit (IC) has a huge market [3]. As shown in Figure 1.3, the total market size, including analog, micro, logic, and memory applications, is worth approximately 278 billion US dollars. Here, “micro” applications are microprocessor units (MPUs), microcontroller units (MCUs), and digital signal processors (DSPs); “logic” applications include specified logic and custom logic, such as field‐programmable gate arrays (FPGAs) and application‐specific integrated circuits (ASICs). CAAC‐IGZO FETs address this vast IC market.

Figure 1.3 Market size of ICs in 2014.

Source: Adapted from [3]

1.2.1 Typical Characteristics of CAAC‐IGZO FETs

In the LSI field, reduction of power consumption has so far been achieved mainly by scaling down the FETs, employing advanced power management schemes, and more recently, subthreshold driving. Si FETs are currently scaled down to very small technology nodes, for example, gate lengths as small as 14 and 16 nm [4]. Such aggressive downscaling causes an increase in the FET off‐state current (leakage current in the FET in the off state), which poses new obstacles to further reduction of system power [5].

As reported by Kato et al. [6], CAAC‐IGZO FETs exhibit extremely low off‐state current, for example,

A/μm (135 yA/μm, where y stands for yocto) for a FET with channel length/width of 3/50 μm. In contrast, the off‐state current in a single‐crystal Si (sc‐Si) FET of the same structure and dimensions has an off‐state current of

A/μm (1 pA/μm), i.e., 10 orders of magnitude larger. When CAAC‐IGZO FETs are used in LSI devices, such as dynamic random access memory (DRAM), non‐volatile memories, and central processing units (CPUs), their extremely low off‐state current will therefore reduce the system power consumption tremendously.

As reported by Matsubayashi et al. [7], CAAC‐IGZO FETs with a channel node of 20 nm maintain the extremely low off‐state current, despite the aggressive downscaling. Figure 1.4 shows the miniaturization progress of CAAC‐IGZO and Si FETs during the past four to five years [8]. In the graph, the upper gray band corresponds to the achieved scaling values of CAAC‐IGZO FETs, whereas the lower solid line shows the target scaling values of Si FETs disclosed by International Technology Roadmap for Semiconductors [9]. CAAC‐IGZO FETs for processors, memories, and devices are denoted by diamond shapes, squares, and triangles, respectively. The number next to each mark corresponds to the conference shown below the graph where the device was disclosed. As shown, the scaling of CAAC‐IGZO FETs gradually approaches that of Si FETs in recent years, so if the scaling continues to progress at this speed, it will catch up with that of Si FETs later in 2016 or 2017.

Figure 1.4 Comparison of scaling between CAAC‐IGZO FETs and Si FET.

Source: Adapted from [8]

1.2.2 Possible Applications of CAAC‐IGZO FETs

CAAC‐IGZO FETs can be used in various LSIs (hereinafter called CAAC‐IGZO LSIs), for example, in non‐volatile memories [10–13], DRAMs [14], normally‐off CPUs [15–17], FPGAs [18,19], and image sensors [20,21]. Non‐volatile memories and DRAMs employing CAAC‐IGZO FETs are called non‐volatile oxide semiconductor random access memory (NOSRAM) and dynamic oxide semiconductor random access memory (DOSRAM), respectively.

A CAAC‐IGZO FET is an active element with four terminals: source, drain, gate, and back gate, as shown in Figure 1.5. New memory technologies that have recently attracted attention include magnetoresistive random access memory (MRAM), resistive random access memory (ReRAM), phase change random access memory (PCRAM), and ferroelectric random access memory (FeRAM). These are all passive elements with two terminals, whereas CAAC‐IGZO FETs with their four terminals may lead ...

Table of contents

• Cover
• Title Page
• Table of Contents
• About the Editors
• List of Contributors
• Series Editor's Foreword
• Preface
• Acknowledgments
• 1 Introduction
• 2 Device Physics of CAAC‐IGZO FET
• 3 NOSRAM
• 4 DOSRAM
• 5 CPU
• 6 FPGA
• 7 Image Sensor
• 8 Future Applications/Developments
• Appendix
• Index
• End User License Agreement