Controlling Cu Migration on Resistive Switching, Artificial Synapse, and Glucose/Saliva Detection by Using an Optimized AlO x Interfacial Layer in a-CO x -Based Conductive Bridge Random Access Memory.

The Cu migration is controlled by using an optimized AlO x interfacial layer, and effects on resistive switching performance, artificial synapse, and human saliva detection in an amorphous-oxygenated-carbon (a-CO x )-based CBRAM platform have been investigated for the first time. The 4 nm-thick AlO x layer in the Cu/AlO x /a-CO x /TiN x O y /TiN structure shows consecutive >2000 DC switching, tight distribution of SET/RESET voltages, a long program/erase (P/E) endurance of >109 cycles at a low operation current of 300 µA, and artificial synaptic characteristics under a small pulse width of 100 ns. After a P/E endurance of >108 cycles, the Cu migration is observed by both ex situ high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy mapping images. Furthermore, the optimized Cu/AlO x /a-CO x /TiN x O y /TiN CBRAM detects glucose with a low concentration of 1 pM, and real-time measurement of human saliva with a small sample volume of 1 µL is also detected repeatedly in vitro. This is owing to oxidation-reduction of Cu electrode, and the switching mechanism is explored. Therefore, this CBRAM device is beneficial for future artificial intelligence application.

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 O2- 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.

Understanding of multi-level resistive switching mechanism in GeOx through redox reaction in H2O2/sarcosine prostate cancer biomarker detection.

Formation-free multi-level resistive switching characteristics by using 10 nm-thick polycrystalline GeOx film in a simple W/GeOx/W structure and understanding of switching mechanism through redox reaction in H2O2/sarcosine sensing (or changing Ge°/Ge4+ oxidation states under external bias) have been reported for the first time. Oxidation states of Ge0/Ge4+ are confirmed by both XPS and H2O2 sensing of GeOx membrane in electrolyte-insulator-semiconductor structure. Highly repeatable 1000 dc cycles and stable program/erase (P/E) endurance of >106 cycles at a small pulse width of 100 ns are achieved at a low operation current of 0.1 µA. The thickness of GeOx layer is found to be increased to 12.5 nm with the reduction of polycrystalline grain size of <7 nm after P/E of 106 cycles, which is observed by high-resolution TEM. The switching mechanism is explored through redox reaction in GeOx membrane by sensing 1 nM H2O2, which is owing to the change of oxidation states from Ge0 to Ge4+ because of the enhanced O2- ions migration in memory device under external bias. In addition, sarcosine as a prostate cancer biomarker with low concentration of 50 pM to 10 µM is also detected.

Negative voltage modulated multi-level resistive switching by using a Cr/BaTiOx/TiN structure and quantum conductance through evidence of H2O2 sensing mechanism.

Negative voltage modulated multi-level resistive switching with quantum conductance during staircase-type RESET and its transport characteristics in Cr/BaTiOx/TiN structure have been investigated for the first time. The as-deposited amorphous BaTiOx film has been confirmed by high-resolution transmission electron microscopy. X-ray photo-electron spectroscopy shows different oxidation states of Ba in the switching material, which is responsible for tunable more than 10 resistance states by varying negative stop voltage owing to slow decay value of RESET slope (217.39 mV/decade). Quantum conductance phenomenon has been observed in staircase RESET cycle of the memory devices. By inspecting the oxidation states of Ba+ and Ba2+ through measuring H2O2 with a low concentration of 1 nM in electrolyte/BaTiOx/SiO2/p-Si structure, the switching mechanism of each HRS level as well as the multi-level phenomenon has been explained by gradual dissolution of oxygen vacancy filament. Along with negative stop voltage modulated multi-level, current compliance dependent multi-level has also been demonstrated and resistance ratio up to 2000 has been achieved even for a thin (<5 nm) switching material. By considering oxidation-reduction of the conducting filaments, the current-voltage switching curve has been simulated as well. Hence, multi-level resistive switching of Cr/BaTiOx/TiN structure implies the promising applications in high dense, multistate non-volatile memories in near future.