Firman Mangasa Simanjuntak

Bio: Firman Mangasa Simanjuntak is an academic researcher from University of Southampton. The author has contributed to research in topics: Resistive random-access memory & Memristor. The author has an hindex of 17, co-authored 40 publications receiving 717 citations. Previous affiliations of Firman Mangasa Simanjuntak include Tohoku University & National Dong Hwa University.

Status and Prospects of ZnO-Based Resistive Switching Memory Devices

Abstract: In the advancement of the semiconductor device technology, ZnO could be a prospective alternative than the other metal oxides for its versatility and huge applications in different aspects. In this review, a thorough overview on ZnO for the application of resistive switching memory (RRAM) devices has been conducted. Various efforts that have been made to investigate and modulate the switching characteristics of ZnO-based switching memory devices are discussed. The use of ZnO layer in different structure, the different types of filament formation, and the different types of switching including complementary switching are reported. By considering the huge interest of transparent devices, this review gives the concrete overview of the present status and prospects of transparent RRAM devices based on ZnO. ZnO-based RRAM can be used for flexible memory devices, which is also covered here. Another challenge in ZnO-based RRAM is that the realization of ultra-thin and low power devices. Nevertheless, ZnO not only offers decent memory properties but also has a unique potential to be used as multifunctional nonvolatile memory devices. The impact of electrode materials, metal doping, stack structures, transparency, and flexibility on resistive switching properties and switching parameters of ZnO-based resistive switching memory devices are briefly compared. This review also covers the different nanostructured-based emerging resistive switching memory devices for low power scalable devices. It may give a valuable insight on developing ZnO-based RRAM and also should encourage researchers to overcome the challenges.

Improving linearity by introducing Al in HfO2 as a memristor synapse device

Abstract: Artificial synapse having good linearity is crucial to achieve an efficient learning process in neuromorphic computing. It is found that the synaptic linearity can be enhanced by engineering the doping region across the switching layer. The nonlinearity of potentiation and depression of the pure device is 36% and 91%, respectively; meanwhile, the nonlinearity after doping can be suppressed to be 22% (potentiation) and 60% (depression). Henceforth, the learning accuracy of the doped device is 91% with only 13 iterations; meanwhile, the pure device is 78%. A detailed conduction mechanism to understand this phenomenon is proposed.

Impacts of Co doping on ZnO transparent switching memory device characteristics

Abstract: The resistive switching characteristics of indium tin oxide (ITO)/Zn1−xCoxO/ITO transparent resistive memory devices were investigated. An appropriate amount of cobalt dopant in ZnO resistive layer demonstrated sufficient memory window and switching stability. In contrast, pure ZnO devices demonstrated a poor memory window, and using an excessive dopant concentration led to switching instability. To achieve suitable memory performance, relying only on controlling defect concentrations is insufficient; the grain growth orientation of the resistive layer must also be considered. Stable endurance with an ON/OFF ratio of more than one order of magnitude during 5000 cycles confirmed that the Co-doped ZnO device is a suitable candidate for resistive random access memory application. Additionally, fully transparent devices with a high transmittance of up to 90% at wavelength of 550 nm have been fabricated.

Enhancing the memory window of AZO/ZnO/ITO transparent resistive switching devices by modulating the oxygen vacancy concentration of the top electrode

Abstract: The effect of a defect concentration-modified top electrode on the bipolar resistance switching of transparent Al-doped ZnO/ZnO/ITO [AZO(TE)/ZnO/ITO(BE)] devices was investigated. Different oxygen vacancy concentrations in the top electrode, Al-doped ZnO, can be simply controlled by modulating the sputtering working pressure condition from 1.2 to 12 mTorr. The oxygen vacancy concentration between AZO and ZnO may trigger oxygen diffusion at the interface and affect the switching characteristic. High oxygen release from a ZnO resistive layer caused by excessive oxygen vacancy concentration at the top electrode is responsible for reducing the memory window as a result of reduced oxygen available to rupture the filament. Top electrode based on lower oxygen vacancy concentration has a higher memory window and an asymmetric resistive switching characteristic. However, all set of devices have excellent endurance of more than 104 cycles. This study showed that an Al-doped ZnO top electrode helps not only to achieve a transparent device but also to enhance memory properties by providing a suitable oxygen vacancy concentration.

Enhanced switching uniformity in AZO/ZnO1−x/ITO transparent resistive memory devices by bipolar double forming

Abstract: The influence of single and double forming on the switching stability of AZO/ZnO1−x/ITO transparent resistive memory devices was investigated. Devices that underwent single forming exhibited severe switching instability, where as those that underwent double forming exhibited excellent switching uniformity. The quantity of conducting filaments can be limited by applying the two-step forming process. Consequently, the set/reset process can be controlled, enhancing switching stability. Satisfactory endurance with an acceptable ON/OFF ratio of 102 and satisfactory retention behavior of 104 s at room temperature confirmed the reliability of optimized devices. Furthermore, highly transparent devices (transparency of approximately 85% in visible range) have been fabricated.

Oxide Nanoelectronics On Demand

Abstract: Electronic confinement at nanoscale dimensions remains a central means of science and technology. We demonstrate nanoscale lateral confinement of a quasi–two-dimensional electron gas at a lanthanum aluminate–strontium titanate interface. Control of this confinement using an atomic force microscope lithography technique enabled us to create tunnel junctions and field-effect transistors with characteristic dimensions as small as 2 nanometers. These electronic devices can be modified or erased without the need for complex lithographic procedures. Our on-demand nanoelectronics fabrication platform has the potential for widespread technological application.

Resistive Random Access Memory (RRAM): an Overview of Materials, Switching Mechanism, Performance, Multilevel Cell (mlc) Storage, Modeling, and Applications

Abstract: In this manuscript, recent progress in the area of resistive random access memory (RRAM) technology which is considered one of the most standout emerging memory technologies owing to its high speed, low cost, enhanced storage density, potential applications in various fields, and excellent scalability is comprehensively reviewed. First, a brief overview of the field of emerging memory technologies is provided. The material properties, resistance switching mechanism, and electrical characteristics of RRAM are discussed. Also, various issues such as endurance, retention, uniformity, and the effect of operating temperature and random telegraph noise (RTN) are elaborated. A discussion on multilevel cell (MLC) storage capability of RRAM, which is attractive for achieving increased storage density and low cost is presented. Different operation schemes to achieve reliable MLC operation along with their physical mechanisms have been provided. In addition, an elaborate description of switching methodologies and current voltage relationships for various popular RRAM models is covered in this work. The prospective applications of RRAM to various fields such as security, neuromorphic computing, and non-volatile logic systems are addressed briefly. The present review article concludes with the discussion on the challenges and future prospects of the RRAM.

A comprehensive review on emerging artificial neuromorphic devices

Abstract: The rapid development of information technology has led to urgent requirements for high efficiency and ultralow power consumption. In the past few decades, neuromorphic computing has drawn extensive attention due to its promising capability in processing massive data with extremely low power consumption. Here, we offer a comprehensive review on emerging artificial neuromorphic devices and their applications. In light of the inner physical processes, we classify the devices into nine major categories and discuss their respective strengths and weaknesses. We will show that anion/cation migration-based memristive devices, phase change, and spintronic synapses have been quite mature and possess excellent stability as a memory device, yet they still suffer from challenges in weight updating linearity and symmetry. Meanwhile, the recently developed electrolyte-gated synaptic transistors have demonstrated outstanding energy efficiency, linearity, and symmetry, but their stability and scalability still need to be optimized. Other emerging synaptic structures, such as ferroelectric, metal–insulator transition based, photonic, and purely electronic devices also have limitations in some aspects, therefore leading to the need for further developing high-performance synaptic devices. Additional efforts are also demanded to enhance the functionality of artificial neurons while maintaining a relatively low cost in area and power, and it will be of significance to explore the intrinsic neuronal stochasticity in computing and optimize their driving capability, etc. Finally, by looking into the correlations between the operation mechanisms, material systems, device structures, and performance, we provide clues to future material selections, device designs, and integrations for artificial synapses and neurons.

CORRIGENDUM: Drosophila Kdm4 demethylases in histone H3 lysine 9 demethylation and ecdysteroid signalling

Abstract: CORRIGENDUM: Drosophila Kdm4 demethylases in histone H3 lysine 9 demethylation and ecdysteroid signalling