Scalable cross-point resistive switching memory and mechanism through an understanding of H2O2/glucose sensing using an IrOx/Al2O3/W structure

Nano- and Microscale Optical and Electrical Biointerfaces and Their Relevance to Energy Research

Different research fields in energy sciences, such as photovoltaics for solar energy conversion, supercapacitors for energy storage, electrocatalysis for clean energy conversion technologies, and materials-bacterial hybrid for CO₂ fixation have been under intense investigations over the past decade. In recent years, new platforms for biointerface designs have emerged from the energy conversion and storage principles. This paper reviews recent advances in nano- and microscale materials/devices for optical and electrical biointerfaces. First, a connection is drawn between biointerfaces and energy science, and how these two distinct research fields can be connected is summarized. Then, a brief overview of current available tools for biointerface studies is presented. Third, three representative biointerfaces are reviewed, including neural, cardiac, and bacterial biointerfaces, to show how to apply these tools and principles to biointerface design and research. Finally, two possible future research directions for nano- and microscale biointerfaces are proposed.

Sarcosine Prostate Cancer Biomarker Detection by Controlling Oxygen in NiOx Membrane on Vertical Silicon Nanowires in Electrolyte-Insulator-Nanowire Structure

Sarcosine prostate cancer biomarker with the low concentration of 1 pM has been detected by controlling oxygen from 1 to 15 sccm in a NiO_x membrane on chemically etched vertical Si nanowires (SiNWs) in an electrolyte-insulator-nanowire (EIN) structure. The vertical Si nanowires with approximately 17 μm length and polycrystalline NiO_x membrane are observed by both field-emission scanning electron microscope (FE-SEM) and high-resolution transmission electron microscope (HRTEM) images, respectively. The optimized NiO_x membrane with oxygen content of 4 sccm on planar SiO_x/Si substrate shows good pH sensitivity of approximately 50 mV/pH, low hysteresis of 3.4 mV, and low drift rate of 2.4 mV/h as compared to other oxygen content membranes of 1, 10, and 15 sccm. Further, uric acid with the concentration of 0.1 μM is detected directly by using the optimized NiO_x membrane. In addition, repeatable H₂O₂ sensing with the low concentration of 10 pM as well as prostate cancer biomarker is detected, which is owing to the reduction-oxidation phenomena of the NiO_x membranes. The sensing mechanism is owing to the Ni²⁺/Ni³⁺ oxidation states of the NiO_x membrane, which is confirmed by X-ray photoelectron spectroscopy. The optimized NiO_x membrane on vertical Si nanowire in the EIN structure shows a good drift rate of 3.84 mV/h and sarcosine detection with improvement of approximately 1000 times as compared to the planar Si in an electrolyte-insulator-semiconductor (EIS) structure. This sensor paves a way to detect early-stage diagnosis of prostate cancer rapidly in the near future.

Controlling Resistive Switching by Using an Optimized MoS2 Interfacial Layer and the Role of Top Electrodes on Ascorbic Acid Sensing in TaO x-Based RRAM

Controlled resistive switching by using an optimized 2 nm thick MoS₂ interfacial layer and the role of top electrodes (TEs) on ascorbic acid (AA) sensing in a TaO _x-based resistive random access memory (RRAM) platform have been investigated for the first time. Both the high-resolution transmission electron microscopy (HRTEM) image and depth profile from energy dispersive X-ray spectroscopy confirm the presence of each layer in IrO _x/Al₂O₃/TaO _x/MoS₂/TiN structure. The pristine device including the IrO _x TE with the 2 nm thick interfacial layer shows the highest uniform rectifying direct current endurance >1000 cycles and a large rectifying ratio >3.2 × 10⁴, and a high nonlinearity factor >700 is obtained, greater than that of Pt and Ru TEs. After formation, this IrO _x device produces bipolar resistive switching characteristics and a long program/erase (P/E) endurance >10⁷ cycles at a low operation current of <50 μA with small pulse width of 100 ns. The stressed device shows a reduced Al₂O₃/TaO _x interface from the HRTEM image, which is owing to O^2- ions' migration toward TiN electrode. By adjusting the RESET voltage and current level, consecutive >100 complementary resistive switching as well as long P/E endurance of >10⁶ cycles are obtained. Schottky barrier height modulation at a low field is observed owing to reduction-oxidation of the TE, which is evidenced through reversible AA detection. At a higher field, Fowler-Nordheim tunneling and hopping conduction are observed. Ascorbic acid detection with a low concentration of 1 pM by using a porous IrO _x/Al₂O₃/TaO _x/MoS₂/TiN RRAM device directly is an additional novelty of this work, which will be useful in future for early diagnosis of scurvy.

Neuronal dynamics in HfOx/AlOy-based homeothermic synaptic memristors with low-power and homogeneous resistive switching

We studied the pseudo-homeothermic synaptic behaviors by integrating complimentary metal-oxide-semiconductor-compatible materials (hafnium oxide, aluminum oxide, and silicon substrate). A wide range of temperatures, from 25 °C up to 145 °C, in neuronal dynamics was achieved owing to the homeothermic properties and the possibility of spike-induced synaptic behaviors was demonstrated, both presenting critical milestones for the use of emerging memristor-type neuromorphic computing systems in the near future. Biological synaptic behaviors, such as long-term potentiation, long-term depression, and spike-timing-dependent plasticity, are developed systematically, and comprehensive neural network analysis is used for temperature changes and to conform spike-induced neuronal dynamics, providing a new research regime of neurocomputing for potentially harsh environments to overcome the self-heating issue in neuromorphic chips.

Interface State-Induced Negative Differential Resistance Observed in Hybrid Perovskite Resistive Switching Memory

Hybrid organic-inorganic perovskite, well-known as light-absorbing materials in solar cells, have recently attracted considerable interest for applications in resistive switching (RS) memory. A better understanding of the role of interface state in hybrid perovskite materials on RS behavior is essential for the development of practical devices. Here, we study the influence of interface state on the RS behavior of an Au/CH₃NH₃PbI₃/FTO memory device using a simple air exposure method. We observe a transition of RS hysteresis behavior with exposure time. Initially no hysteresis is apparent, but air exposure induces bipolar RS and a negative differential resistance (NDR) phenomenon. The reductions of I/Pb atomic ratio and work function on the film surface are examined using XPS spectra and Kelvin probe technique, verifying the produce of donor-type interface states (e.g., iodine vacancies) during CH₃NH₃PbI₃ film degradation. Studies on complex impedance spectroscopy confirm the responsibility of interface states in NDR behavior. Eventually, the trapping/detrapping of electrons in bulk defects and at interface states accounts for the bipolar RS behavior accompanied with the NDR effect.

Exploring oxygen-affinity-controlled TaN electrodes for thermally advanced TaOx bipolar resistive switching

Recent advances in oxide-based resistive switching devices have made these devices very promising candidates for future nonvolatile memory applications. However, several key issues remain that affect resistive switching. One is the need for generic alternative electrodes with thermally robust resistive switching characteristics in as-grown and high-temperature annealed states. Here, we studied the electrical characteristics of Ta2O5-x oxide-based bipolar resistive frames for various TaNx bottoms. Control of the nitrogen content of the TaNx electrode is a key factor that governs variations in its oxygen affinity and structural phase. We analyzed the composition and chemical bonding states of as-grown and annealed Ta2O5-x and TaNx layers and characterized the TaNx electrode-dependent switching behavior in terms of the electrode's oxygen affinity. Our experimental findings can aid the development of advanced resistive switching devices with thermal stability up to 400 °C.