Electrical Memory Materials and Devices

406 Pages·2015·18.41 MB·English

by  Wen-Chang Chen (ed.)

Electrical Memory Materials and Devices
RSC Polymer Chemistry Series
Editor-in-Chief:
Professor Ben Zhong Tang, The Hong Kong University of Science and
Technology, Hong Kong, China
Series Editors:
Professor Alaa S. Abd-El-Aziz, University of Prince Edward Island, Canada
Professor Stephen Craig, Duke University, USA
Professor Jianhua Dong, National Natural Science Foundation of China, China
Professor Toshio Masuda, Shanghai University, China
Professor Christoph Weder, University of Fribourg, Switzerland
Titles in the Series:
1: Renewable Resources for Functional Polymers and Biomaterials
2: M olecular Design and Applications of Photofunctional Polymers and
Materials
3: Functional Polymers for Nanomedicine
4: Fundamentals of Controlled/Living Radical Polymerization
5: Healable Polymer Systems
6: Thiol-X Chemistries in Polymer and Materials Science
7: Natural Rubber Materials: Volume 1: Blends and IPNs
8: Natural Rubber Materials: Volume 2: Composites and Nanocomposites
9: Conjugated Polymers: A Practical Guide to Synthesis
10: Polymeric Materials with Antimicrobial Activity: From Synthesis to
Applications
11: Phosphorus-Based Polymers: From Synthesis to Applications
12: Poly(lactic acid) Science and Technology: Processing, Properties,
Additives and Applications
13: Cationic Polymers in Regenerative Medicine
14: Electrospinning: Principles, Practice and Possibilities
15: Glycopolymer Code: Synthesis of Glycopolymers and their Applications
16: Hyperbranched Polymers: Macromolecules in-between of Deterministic
Linear Chains and Dendrimer Structures
17: Polymer Photovoltaics: Materials, Physics, and Device Engineering
18: Electrical Memory Materials and Devices
How to obtain future titles on publication:
A standing order plan is available for this series. A standing order will bring
delivery of each new volume immediately on publication.
For further information please contact:
Book Sales Department, Royal Society of Chemistry, Thomas Graham
House, Science Park, Milton Road, Cambridge, CB4 0WF, UK
Telephone: [phone], Fax: [phone]
Email: [email protected]
Visit our website at www.rsc.org/books
Electrical Memory Materials
and Devices
Edited by
Wen-Chang Chen
National Taiwan University, Taipei, Taiwan
Email: [email protected]
RSC Polymer Chemistry Series No. 18
Print ISBN: 978-1-78262-116-4
PDF eISBN: 978-1-78262-250-5
ISSN: 2044-0790
A catalogue record for this book is available from the British Library
© The Royal Society of Chemistry 2016
All rights reserved
Apart from fair dealing for the purposes of research for non-commercial purposes or for
private study, criticism or review, as permitted under the Copyright, Designs and Patents
Act 1988 and the Copyright and Related Rights Regulations 2003, this publication may
not be reproduced, stored or transmitted, in any form or by any means, without the prior
permission in writing of The Royal Society of Chemistry, or in the case of reproduction in
accordance with the terms of licences issued by the Copyright Licensing Agency in the UK,
or in accordance with the terms of the licences issued by the appropriate Reproduction
Rights Organization outside the UK. Enquiries concerning reproduction outside the terms
stated here should be sent to The Royal Society of Chemistry at the address printed on
this page.
The RSC is not responsible for individual opinions expressed in this work.
The authors have sought to locate owners of all reproduced material not in their
own possession and trust that no copyrights have been inadvertently infringed.
Published by The Royal Society of Chemistry,
Thomas Graham House, Science Park, Milton Road,
Cambridge CB4 0WF, UK
Registered Charity Number 207890
For further information see our web site at www.rsc.org
Printed in the United Kingdom by CPI Group (UK) Ltd, Croydon, CR0 4YY, UK
Foreword: Introduction to
Organic Memory Technologies
SEBASTIAN NAUa AND EMIL J. W. LIST-KRATOCHVIL*a,b
aNanoTecCenter Weiz Forschungsgesellschaft mbH, A-8160 Weiz,
Austria; bInstitute of Solid State Physics, Graz University of Technology,
A-8010 Graz, Austria
*E-mail: [email protected]
The discovery of how to store information in the form of numbers and letters
is generally considered as one of the most important steps of social evolution
in human history as it allowed passing of information from generation to
generation. The simplest forms appeared at least forty thousand years ago in
the form of unary numeral systems (tally marks). Real alphabets developed,
however, much later around 4000 BC in Mesopotamia. The invention of a
moveable metal type printing press by Johannes Gutenberg (1450) is consid-
ered as another big leap since it enabled a relatively cheap, large scale dupli-
cation of information. Nowadays, information is stored digitally encoded in
a binary language consisting of zeros and ones, i.e. binary logical states. The
origin of the rapid development in this field dates back to the 1940s, starting
from the first computer prototypes with an implemented memory – Zuse3
(1942, Germany) and ENIAC (1946, USA) – via the launch of the first per-
sonal computers (1970s) to the present state where digital memory is found
in nearly every electronic device. Recent calculations showed that approxi-
mately 300 exabytes (1018 bytes) of information is stored worldwide.1
RSC Polymer Chemistry Series No. 18
Electrical Memory Materials and Devices
Edited by Wen-Chang Chen
© The Royal Society of Chemistry 2016
Published by the Royal Society of Chemistry, www.rsc.org
v
vi Foreword: Introduction to Organic Memory Technologies
As predicted 50 years ago memory capacity develops according to Moore’s
law,2 meaning that roughly every 18 months a doubling of the number of
transistors per chip at approximately equal cost is found. Although this
observation has been doubtlessly valid for the past decades, a strong conver-
gence to an upper integration density is predicted. It is expected that within
the next 10 to 20 years it will not be possible to further downsize the tradi-
tional complementary metal-oxide-semiconductor (CMOS) architecture due
to physical restrictions at such small dimensions. In order to overcome this
fact, two parallel strategies are usually presented. First, more Moore, deal-
ing with the continuous miniaturization of classical CMOS building blocks
as well as post-CMOS materials and devices. Second, the more-than-Moore
approach which targets system integration and functional diversification
rather than scaling issues: the inclusion of non-digital functionalities like
sensors and actuators, bio-chips, photonic applications, etc. interfaces the
integrated circuit to the outside world. Materials and devices presented in
this book actually address both approaches by investigating organic and
hybrid material memory technologies based on capacitors, transistors and
resistive switching elements and their advantages (more Moore) and secondly
demonstrating how organic and hybrid memory devices may be integrated
into flexible electronic applications (more-than-Moore).
However, there are numerous prerequisites that novel materials, device
concepts and memory elements based on these materials should fulfil to
outperform established technologies. The most important ones are listed in
the following:
● Non-volatility: state should be preserved at least for several years even if
the supply voltage is turned off
● Fast read, write and erase times in the range of the CPU clock (∼GHz):
this prevents a bottleneck effect in the communication between the
individual components in an electronic application
● Cyclability: 1012–1015 write–read–erase–read cycles should be possible
● CMOS compatibility
● Operation temperature not higher than 85 °C
● ON/OFF ratio: clear difference between ‘0’ (OFF) and ‘1’ (ON) state which
enables for simple peripheral electronics and a reliable read-out
● High integration density (down to 4F², where F denotes the smallest
lithographically obtainable feature size)
● Low power consumption
● Compatibility with existing semiconductor fabrication plants
● Non-destructive read-out
● 3D-integration on multiple layers, multiple bits per cell
● Random Access: each bit cell should be accessible directly and sequen-
tial read-out is necessary.
As discussed in Chapter 1 in detail, today’s dominant memory technolo-
gies do not meet all of these criteria simultaneously and the decision about
Foreword: Introduction to Organic Memory Technologies vii
Figure 1 Memory-storage hierarchy. Costs and speed are increasing from bottom
to top whereas information capacity is decreasing.
which memory or storage technology is used strongly depends on its actual
application case. Figure 1 depicts the memory-storage hierarchy. Usually
storage and memory are considered separately, where the first term includes
non-volatile, high capacity technologies and the latter term is used for fast,
lower capacity and volatile technologies. Along these lines, the main task
in the long run is the development of a technology which unifies memory
and storage technology into a ‘storage class memory’ with the advantages
of both. This would allow, for example, the design of computers where the
operating systems and other data do not need to be read out from the hard
disk drive to the main memory when it is switched on.
Today three technologies dominate the market – each of them highly spe-
cialized in its field of application, dynamic random access memory (DRAM),
flash memory, and magnetic hard disk drives. Emerging technologies such
as ferroelectric RAM (FeRAM), magnetoresistive RAM, phase-change RAM,
and resistive memory have or are about to enter the market. Over the past
decades a wide variety of organic and hybrid materials concepts have also
been utilized as hysteretic elements in memory cells, including conjugated
polymers, small molecules, organic/hybrid materials, chalcogenides, thin-
film perovskites, electromechanical switches, ferroelectric organic poly-
mers, etc. Depending on the individual functional principle, these materials
are integrated into memory elements utilizing a transistor, diode, capac-
itor or resistor device structure rendering an individual memory cell. Yet,
according to the International Technology Roadmap for Semiconductors,
in an overall comparison and benchmarking of the specific type of hyster-
etic materials used in memory cells, it is not only important to judge the
material’s electrical characteristics (with respect to scalability, read-out time,
write time, switching power, retention time and other parameters) but also
if the material is compatible with fabrication technology and if the device
element fulfils the design constraints for high density integration. Amongst
viii Foreword: Introduction to Organic Memory Technologies
the here-presented candidates, which cover ferroelectric and floating gate
organic transistor memory and different resistive memory technologies,
the latter one is doubtless the most promising candidate not only to replace
the existing technology with an organic counterpart but also to act as storage
class memory.
The contributions to this book address and summarize the ongoing
development in organic memory technology based on resistive switching
and transistor-based memory from the material development, processing
as well as from the device operation point of view. The classes of materials
presented range from conjugated polymers, to donor–acceptor structures
to hybrid material composite concepts to name just a few of them. For all
material concepts one finds a comprehensive discussion of the observed
electrical switching in the device, reflecting on the fact that despite consid-
erable research effort in this field, the true nature of resistive switching is
still uncertain.
Chapter 1 gives a basic and historic overview on existing and emerging
memory device concepts based on organic, polymeric and hybrid materi-
als. Existing transistor-based, capacitor-based and resistor-based device
concepts are discussed together with the observed operation principles.
Chapter 2 focuses on the recent development of resistive memory technol-
ogies based on organic and polymeric materials. The chapter covers basic
materials design principles to be applied, followed by a comprehensive dis-
cussion on the switching mechanism in organic resistor memory elements,
followed by a number of application-related examples of organic memory
devices. Chapter 3 reports on the use of donor–acceptor structures in resis-
tive memory devices. The chapter highlights the importance of structure to
property relationships in understanding the switching mechanism and also
discusses multilevel resistive memory devices. Chapter 4 focuses on describ-
ing the use of polyimide and functionalized polyimides for resistive memory
devices. Different applications of such devices are reviewed together with an
in detail discussion on the switching mechanism. Chapter 5 reports on the
use of non-conjugated polymers with electroactive chromophore pendants
in resistive memory devices. The design of molecules is discussed together
with their performance in devices and the observation of switching. Chapter
6 focuses on the use of polymer composites for resistive switching devices.
In addition to switching observations in hybrid polymer–nanoparticle sys-
tems and multilayer structures, polymer–ionic liquid composites are also
discussed. Chapter 7 discusses the design and development of different con-
jugated polymers for resistive switching elements, including a discussion of
the different observed switching mechanisms. Chapter 8 describes the use of
a variety of homo- and copolymers bearing donor–acceptor moieties for their
use in resistive memory devices. Chapter 9 reviews the use of ferroelectrics,
polymer electrets, polymer–molecular hybrids and self-assembled monolay-
ers in non-volatile transistor based memory devices. Chapter 10 discusses
the physics and fabrication of floating gate charge storage devices based
on organic transistors and possible implications for their use in emerging
Foreword: Introduction to Organic Memory Technologies ix
flexible digital memory electronics. Chapter 11 discusses the use of ferro-
electric materials in capacitor-, transistor- or diode-based storage devices
elucidating the interplay of polymer orientation, interfacial engineering and
device configuration, and memory performance.
References
1. M. Hilbert and P. López, Science, 2011, 332, 60.
2. G. E. Moore, Electronics, 1965, 114.
Preface
Organic memory devices have received extensive research interest recently
due to their advantages of structural flexibility, processability, light weight
and their simple manufacturing processes compared to those employed
in inorganic silicon technology. Such devices could have potential applica-
tions in flexible electronic components and wearable products. Three types
of organic memory devices have been reported in the literature, including
resistor-, capacitor- and transistor-type devices. There are several review arti-
cles in the field of organic memory but most of them report on a limited
subject, such as resistive memory. There is no comprehensive book on tun-
ing different types of memory characteristics through molecular design and
morphology manipulation. Thus, I accepted the invitation from the Royal
Society of Chemistry to edit this book to provide information on the recent
developments of organic electrical memory materials, device fabrication,
and switching mechanisms. In order to meet this objective, I have invited
the world-leading researchers in this field to write the book chapters, includ-
ing Prof. En-Tang Kang, Prof. Mitsuru Ueda, Prof. Jian Mei Lu, Prof. Guey-
Sheng Liou, Prof. Moonhor Ree, Prof. Jae-Suk Lee, and Prof. Yu-Tai Tao. In
this book, different types of charge storage materials, such as organic small
molecules, functional polyimides, nonconjugated polymers with pendent
chromophores, conjugated polymers, and polymer nanocomposites, are
summarized and correlated with their electrical memory characteristics. In
addition, various device configurations, including resistor and transistor-
type memory, are also discussed in detail along with the defined charge
storage mechanisms. The effects of the charge transfer strength, charge trap-
ping/de-trapping ability, surface polarity, interfacial energy barrier, and mor-
phology of the memory active layer on the electrical switching behaviours
are also comprehensively discussed in this book. I would like to express
my sincere appreciation to the chapter authors for spending their precious
RSC Polymer Chemistry Series No. 18
Electrical Memory Materials and Devices
Edited by Wen-Chang Chen
© The Royal Society of Chemistry 2016
Published by the Royal Society of Chemistry, www.rsc.org
xi