Novel ferroelectric tunnel junctions for nonvolatile memories

transport to the sub-ground cave. Finegrained magnetite or greigite, produced by ironor sulfate-reducing bacteria under anoxic conditions in the soil, can be very sensitive to oxidation when exposed to air and can, thus, potentially change the magnetic property of the particles and make the ARM/SIRM value less reliable as a reflection of the soil hydrological condition. Another unresolved question lies in the lag time between a heavy rainfall event and the draining of the magnetic particles from the soil to the stalagmite deposit. Nevertheless, Xie et al. made a successful attempt in using geobiological approaches to address major archaeological questions. Uncertainties of the organic and inorganic proxies raised in this study can actually promote further geobiological research in other fields. For example, the study of fossil DNA from the hopanoid-producing bacteria in the peat bog may lead to better understanding of ancient microbial community structures responsive to the paleoclimatic conditions, while the examination of the sources and mechanisms of the formation of magnetic particles in the soil may strengthen the application of the ARM/SIRM in stalagmite research. Chuanlun Zhang


Shining Zhu
Nonvolatile memories, which retain data without an external power supply, have become increasingly important as consumer electronic products, such as smart phones and tablet personal computers become popular.Today, FLASH memories, where information is stored as charges on the floating gate, are ubiquitous.However, the continuous scaling down of memory devices requires technology where information is no longer stored as electrical charges to avoid statistic fluctuations in devices smaller than 10 nm in size.Memories based on phase-change, resistive-change and magnetic characteristics have been suggested.Most recently, resistive memories based on ferroelectric tunnel junctions (FTJs), composed of two metal electrodes separated by an ultrathin ferroelectric barrier, have been proposed as promising candidates for nonvolatile memory applications [1].FTJ memories are expected to show inherent advantages of both resistive and ferroelectric memories, such as simple architecture, low power consumption and radiation resistance.However, conventional FTJ devices, in which only the tunneling barrier height is controlled by the polarization direction in the barrier, have suffered from low ON/OFF ratios for years.Now, a team of researchers from Nanjing University, China, has noticed that a modulation on the barrier width in FTJs, in parallel with the modulation on the barrier height, can be exploited to greatly enhance the ON/OFF ratio [2].They have achieved an ON/OFF ratio of over 10 000 in a novel tunneling heterostructure by replacing one of the metal electrodes in a conventional metal/ferroelectric/metal FTJ with a heavily doped semiconductor.In this metal/ferroelectric/semiconductor FTJ, owing to the ferroelectric field effect, the surface of the semiconductor electrode can be switched between accumulation Downloaded from https://academic.oup.com/nsr/article-abstract/1/2/167/1397190 by guest on 18 December 2018

RESEARCH HIGHLIGHTS
and depletion in response to polarization reversal in the barrier.The tunneling electrons should experience an extra barrier as long as the semiconductor surface is toggled to depletion, leading to a colossal tunneling electroresistance (Fig. 1).Wen and colleagues epitaxially deposited a 3-nm-thick ultrathin BaTiO 3 film with an atomically smooth surface on a Nb-doped SrTiO 3 oxide semiconductor and then deposited Pt electrodes on top to form Pt/BaTiO 3 /Nb:SrTiO 3 tunnel junctions.These prototype devices show a tunneling electroresistance two orders greater than the best value ever reported in FTJs.The colossal ON/OFF ratio, low operation voltage (3 V for write and 100 mV for read), reliable switching reproducibility and long data retention suggest great potential for nondestructive readout nonvolatile memories.
Moreover, the team observed that the tunneling resistance could be modulated continuously by applying voltage pulses with increasing amplitude due to the continuous tuning on the domain structure in the barrier.This novel FTJ can actually function as a memristor, the adaptive circuit element theoretically predicted 40 years ago but discovered only very recently.The use of memristors may pave the way to future neuromorphic computational architectures.
The work by Wen and colleagues not only proposes a promising memory structure with potential to overcome semiconductor devices based on charge storage, but provides tremendous opportunities for innovation in nanoelectronics also.

Shining Zhu National Laboratory of Solid State Microstructures
and Department of Physics, Nanjing University, China E-mail: zhusn@nju.edu.cn

A new software paradigm for Internet computing
Gang Huang 1, * , Xiaoxing Ma 2 and Wei-Tek Tsai 3   The Internet, once a network of networks, has become not only the platform of choice for delivering services to increasingly mobile users, but also the connective tissue between people, information and things.Almost all new and popular computing and application paradigms were born in the Internet, or at least motivated by it, including Web 2.0, Social Networking, Mobile Internet, Cloud Computing, Internet of things, and big data.Software has played a central part in the evolution of the Internet.The open, dynamic, evolving environment of Internet computing continues to demand new software technologies in order to realize its rapid paradigm shifts.These new software technologies need to meet an increasing number of requirements; they need to be autonomous, situational, evolvable, cooperative, emergent, trustworthy and so on.
To support Internet computing from a software engineering perspective, Chinese researchers have proposed 'Internetware' [1-3], a software paradigm that enables developers to construct new applications or evolve legacy systems to include new characteristics.After 10 years of research and practice involving hundreds of researchers, professionals and students from China, the USA, Japan and Europe, the fundamental challenges to Internetware have been thoroughly investigated, with the following conclusions: r The Internetware software model defines the concept and content of software entities and their collaborations, as well as the environments hosting the entities.An entity provides business interfaces, allowing collaboration with other entities in terms of functional requirements.It further provides management interfaces for collaborating with the environment in terms of nonfunctional requirements.Both types of collaborations can be governed globally by software architectures.r The Internetware operating platform provides a set of mechanisms to develop, deploy and operate applications compliant with the Internetware software model.For example, Runtime Software Architecture for global ondemand collaboration and adaptation is implemented by a set of hooks that monitor and control the Internetware entities.These hooks can be automatically generated from the entity's management interfaces and the software architecture meta-models.r The Internetware engineering approach provides the principles, guidelines, patterns, tools and best practices for developing and evolving Internetware applications.Its core principle is 'software architecture for the whole life cycle'.In other words, the software architecture serves as a blueprint and governs each phase of software development.In particular, to better govern the development, software entities distributed over the Internet will be discovered, certificated and organized for a specific domain in a knowledge-based, model-driven manner.

Figure 1 .
Figure 1.Schematic drawings of the metal/ferroelectric/semiconductor structures and corresponding potential energy profiles for the ON and the OFF states, taking an n-type semiconductor for example.