Recent advances in organic-based materials for resistive memory applications

Overview of Resistive Random Access Memory (RRAM): Materials, Filament Mechanisms, Performance Optimization, and Prospects

Organic transistors are being developed for a variety of flexible electronics applications. They are usually fabricated on polymeric substrates, but considering the significant negative impact of plastic waste on the global environment and taking into account the many desirable properties of paper, there have also been efforts to use paper as a substrate for organic transistors. In this review we provide a brief overview of these efforts.

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Organic transistors on paper: a brief review

Since the emergence of memristors (or memristive devices), how to integrate them into arrays has been widely investigated. After years of research, memristor crossbar arrays have been proposed and realized with potential applications in nonvolatile memory, logic and neuromorphic computing systems. Despite the promising prospects of memristor crossbar arrays, one of the main obstacles for their development is the so-called sneak-path current causing cross-talk interference between adjacent memory cells and thus may result in misinterpretation which greatly influences the operation of memristor crossbar arrays. Solving the sneak-path current issue, the power consumption of the array will immensely decrease, and the reliability and stability will simultaneously increase. In order to suppress the sneak-path current, various solutions have been provided. So far, some reviews have considered some of these solutions and established a sophisticated classification, including 1D1M, 1T1M, 1S1M (D: diode, M: memristor, T: transistor, S: selector), self-selective and self-rectifying memristors. Recently, a mass of studies have been additionally reported. This review thus attempts to provide a survey on these new findings, by highlighting the latest research progress realized for relieving the sneak-path issue. Here, we first present the concept of the sneak-path current issue and solutions proposed to solve it. Consequently, we select some typical and promising devices, and present their structures and properties in detail. Then, the latest research activities focusing on single-device structures are introduced taking into account the mechanisms underlying these devices. Finally, we summarize the properties and perspectives of these solutions.

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Research progress on solutions to the sneak path issue in memristor crossbar arrays

Metal oxide resistive switching memories have been a crucial component for the requirements of the Internet of Things, which demands ultra-low power and high-density devices with new computing principles, exploiting low cost green products and technologies. Most of the reported resistive switching devices use conventional methods (physical and chemical vapor deposition), which are quite expensive due to their up-scale production. Solution-processing methods have been improved, being now a reliable technology that offers many advantages for resistive random-access memory (RRAM) such as high versatility, large area uniformity, transparency, low-cost and a simple fabrication of two-terminal structures. Solution-based metal oxide RRAM devices are emergent and promising non-volatile memories for future electronics. In this review, a brief history of non-volatile memories is highlighted as well as the present status of solution-based metal oxide resistive random-access memory (S-RRAM). Then, a focus on describing the solution synthesis parameters of S-RRAMs which induce a massive influence in the overall performance of these devices is discussed. Next, a precise analysis is performed on the metal oxide thin film and electrode interface and the recent advances on S-RRAM that will allow their large-area manufacturing. Finally, the figures of merit and the main challenges in S-RRAMs are discussed and future trends are proposed.

Recent Progress in Solution-Based Metal Oxide Resistive Switching Devices.

Paper-basedpentacene organic thin-film transistors (OTFTs) with spin-coated gelatin (G) stacked gate dielectric layers, the Au/pentacene/G/G matrix-embedded iron (FeG)/Al/paper structure, were fabricated. The proposed composite-stacked bio-dielectric layer can be implemented using solutions with the degradable biomaterials. These materials enable a large-area printing of use-and-throw devices. Control devices (Au/pentacene/G/Al and Au/pentacene/FeG/Al structure) were also fabricated for comparison. High-performance paper-based OTFT constructed from the stacked gate dielectric layer exhibited a carrier mobility of 8 cm2/Vs, an ON/OFF current ratio of approximately 103, a subthreshold swing of 0.6 V/decade, and a threshold voltage of −1.4 V. These results are compatible to those OTFTs fabricated on other substrates. Therefore, the emerging biomaterial-based transistors on paper substrates may help in developing low-cost, environment-friendly devices.

Biodegradable Materials for Organic Field-Effect Transistors on a Paper Substrate

The silver-embedded gelatin (AgG) thin film produced by the solution method of metal salts dissolved in gelatin is presented. Its simple fabrication method ensures the uniform distribution of Ag dots. Memory devices based on AgG exhibit good device performance, such as the ON/OFF ratio in excess of 105 and the coefficient of variation in less of 50%. To further investigate the position of filament formation and the role of each element, current sensing atomic force microscopy (CSAFM) analysis as well as elemental line profiles across the two different conditions in the LRS and HRS are analyzed. The conductive and nonconductive regions in the current map of the CSAFM image show that the conductive filaments occur in the AgG layer around Ag dots. The migration of oxygen ions and the redox reaction of carbon are demonstrated to be the driving mechanism for the resistive switching of AgG memory devices. The results show that dissolving metal salts in gelatin is an effective way to achieve high-performance organic-electronic applications.

Highly Uniform Resistive Switching Properties of Solution-Processed Silver-Embedded Gelatin Thin Film.

This study investigates the preparation and electrical properties of Al/cobalt-embedded gelatin (CoG)/ indium tin oxide (ITO) resistive switching memories. Co. elements can be uniformly distributed in gelatin without a conventional dispersion procedure, as confirmed through energy dispersive X-ray analyzer and X-ray photoelectron spectroscopy observations. With an appropriate Co. concentration, Co. ions can assist the formation of an interfacial AlOx layer and improve the memory properties. High ON/OFF ratio, good retention capability, and good endurance switching cycles are demonstrated with 1 M Co. concentration, in contrast to 0.5 M and 2 M memory devices. This result can be attributed to the suitable thickness of the interfacial AlOx layer, which acts as an oxygen reservoir and stores and releases oxygen during switching. The Co. element in a solution-processed gelatin matrix has high potential for bio-electronic applications.

https://www.mdpi.com/1996-1944/11/1/32/pdf

Nonvolatile Resistive Switching Memory Utilizing Cobalt Embedded in Gelatin.

High-resistance state (HRS) current has significant effect on the reliability and power consumption of resistive switching memories. Low HRS current is helpful for obtaining ultra-low power and for high ON/OFF ratio nonvolatile memory application. The reduced HRS current of a sol–gel magnesium titanate nickelate-based resistive random access memory by using nickel (II) acetylacetone as substitute for acetylacetone in magnesium titanate (MTO) was presented. Forming-free, high ON/OFF ratio of over $10^{6}$ , excellent current distribution and good retention at 85 °C were achieved. Moreover, the effect of nickel (Ni) on the surface roughness, operation voltage, switching cycles, HRS current, ON/OFF ratio, current distribution, and switching behavior was explored. These results indicate that the incorporation of Ni in sol-gel MTO is an effective way to achieve high-performance memory devices.

Bipolar Resistive Switching Behavior in Sol-Gel MgTiNiO x Memory Device

The use of a threshold-switching Ni/NbO2/Ni device with a memory-switching Pt/magnesium zirconate titanate/Al device on a flexible substrate was proposed to suppress undesired sneak currents. The proposed flexible one selector and one resistor (1S1R) memory device exhibits a low operation voltage, good ON/OFF ratio of $10^{5}$ , uniform current distribution, excellent flexibility, and stable ${I}$ – ${V}$ curve at 85 °C. The good selection and memory properties of the flexible 1S1R memory device are highly promising for high-density and low-power flexible electronic applications.

Cheng-Jung Lee

Papers

Biodegradable Materials for Organic Field-Effect Transistors on a Paper Substrate

Highly Uniform Resistive Switching Properties of Solution-Processed Silver-Embedded Gelatin Thin Film.

Nonvolatile Resistive Switching Memory Utilizing Cobalt Embedded in Gelatin.

Bipolar Resistive Switching Behavior in Sol-Gel MgTiNiO x Memory Device

Bipolar Resistive Switching Characteristics in Flexible Pt/MZT/Al Memory and Ni/NbO 2 /Ni Selector Structure