Hee Dong Kim

Stable Bipolar Resistive Switching Characteristics and Resistive Switching Mechanisms Observed in Aluminum Nitride-based ReRAM Devices

The authors report upon the ultrafast bipolar switching characteristics observed in aluminum nitride (AlN)-based resistive random access memory devices ReRAMs. The set and reset states were measured to be as low as 2 μA and 5 nA, respectively, at Vread = 0.1 V. Regarding pulse operations, very fast switching characteristics were achieved at 3 V/10 ns for the set operation and -3 V/10 ns for the reset operation. In addition, the AlN-based ReRAMs showed an endurance value of over ~ 108 cycles and a retention time of over ten years at 85°C. These results show that this AlN-based ReRAM can be used as a promising high-speed nonvolatile memory device.

Transparent Resistive Switching Memory Using ITO/AlN/ITO Capacitors

This letter covers the fabrication of a transparent resistive random access memory (T-ReRAM) device using ITO/AlN/ITO capacitors and its observed resistive switching characteristics. This AIN-based T-ReRAM shows a transmittance above 80% (including the substrate) in the visible region and an excellent switching behavior under ±3 V/10 ns with a high-to-low resistance ratio greater than 102. In the reliability test, the device showed an endurance of >; 108 cycles and a retention time of >; 105 s at 85°C. We believe that the AIN-based T-ReRAM presented in this letter could be a milestone for future see-through electronic devices.

Transparent Multi-level Resistive Switching Phenomena Observed in ITO/RGO/ITO Memory Cells by the Sol-Gel Dip-Coating Method

A reduced graphene oxide (RGO)-based transparent electronic memory cell with multi-level resistive switching (RS) was successfully realized by a dip-coating method. Using ITO/RGO/ITO structures, the memory device exhibited a transmittance above 80% (including the substrate) in the visible region and multi-level RS behavior in the 00, 01, 10, and 11 states by varying the pulse height from 2 V to 7 V. In the reliability test, the device exhibited a good endurance of over 105 cycles and a long data retention of over 105 s at 85°C in each state. We believe that the RGO-based transparent memory presented in this work could be a milestone for future transparent electronic devices.

ITO/Ag/ITO multilayer-based transparent conductive electrodes for ultraviolet light-emitting diodes

ITO/Ag/ITO (IAI) multilayer-based transparent conductive electrodes for ultraviolet light-emitting diodes are fabricated by reactive sputtering, optimized by annealing, and characterized with respect to electrical and optical properties. Increasing the annealing temperature from 300°C to 500°C decreased the sheet resistance and increased the transmittance. This may result from an observed improvement in the crystallinity of the IAI multilayer and a reduction in the near-UV absorption coefficient of Ag. We observed the lowest sheet resistance (9.21 Ω/sq) and the highest optical transmittance (88%) at 380 nm for the IAI multilayer samples annealed in N₂ gas at 500°C.

Improved reliability of Au/Si3N4 /Ti resistive switching memory cells due to a hydrogen postannealing treatment

The effect of hydrogen-postannealing on the endurance and data retention characteristics of an Au/Si3N4/Ti resistance memory cell is investigated. Compared to the as-deposited sample, the set and reset currents of the Au/Si3N4/Ti sample annealed at 250 °C for 30 min in a N2–H2 ambient gas, are reduced from 10 mA to 1.5 mA and from 3 mA to 5 μA, respectively, whereas the current ratio increases from ∼0.5×101 to ∼103. In addition, its reliability features, including its endurance (>103 cycles) and retention time (>ten years), have been improved due to the reduction in the interface trap.

Effect of nanopyramid bottom electrodes on bipolar resistive switching phenomena in nickel nitride films-based crossbar arrays

The improved resistive switching (RS) performance characteristics of nickel nitride (NiN) films-based crossbar array (CBA) memory resistors-such as reduction in the operating voltages, reset current and current/voltage variations; no initial forming process; and set/reset speeds--are demonstrated using nanopyramid-patterned (NPP) platinum-bottom electrodes. Compared with a conventional CBA sample with flat-bottom electrodes, both the voltage and the current of the set and reset operations are respectively reduced when NPP samples are used. The drastic reduction in the variation of the operating voltage and current is of particular interest. We explain the RS process using the model of the redox-reaction-mediated formation and rupture of the conducting filaments in the NiN films, based on the capacitance-voltage and conductance-voltage characteristics under different resistance states.

Fabrication of wide-bandgap transparent electrodes by using conductive filaments: Performance breakthrough in vertical-type GaN LED

For realizing next-generation solid-state lighting devices, performance breakthroughs must be accomplished for nitride-based light-emitting diodes (LEDs). Highly transparent conductive electrodes (TCEs) may be key to achieving this goal, as they provide uniform current injection and distribution across a large device area, eventually increasing the light output power. However, the trade-off between electrical conductivity and optical transmittance of LEDs must be addressed. Herein, we introduce a novel strategy based on TCEs fabricated using wide-bandgap (WB) materials such as SiNx, incorporated beneath the n-type electrode of vertical-type LEDs, and show the feasibility of this strategy. We employ a novel electrical breakdown (EBD) technique to form conductive filaments (or current paths) between a TCE and n-GaN (GaN: gallium nitride). By employing the EBD process, we obtain both ohmic behavior for SiNx TCE/n-GaN and a current spreading effect across n-GaN. These results demonstrate the tremendous potential of WB-TCEs for use in high-performance optoelectronic devices.

Effect of Work Function Difference Between Top and Bottom Electrodes on the Resistive Switching Properties of SiN Films

In this letter, the effect of the work function difference between various top electrodes (TE-Ni, W, Ti, and Al) and the Pt bottom electrode, ΔΦ_M, on the resistive switching (RS) of SiN thin films was investigated. The cells with W and Ti TEs showed stable RS, but others failed to show RS. In particular, the Ti TE exhibited low operating currents (~2 μA) and good retention properties (<; ~104 s at 85 °C). On the basis of the analysis of conduction mechanisms, it is found that stable RS of SiN films might be strongly related to the activation energy of traps induced by ΔΦ_M. Thus, the RS properties of the SiN films can be improved by engineering ΔΦ_M without additional processes.

Realization of One-Diode-Type Resistive-Switching Memory with Cr-SrTiO3 Film

The authors report a silicon-based one-diode–type resistive-switching memory (RRAM) device with self-rectifying properties and high electrical properties. The RRAM cell consisted of Al/Cr–SrTiO3/Si and revealed intrinsic diode properties, so that unwanted sneaky currents could be removed from an RRAM crossbar array without extra switching devices. The insulator–metal transition property of the proposed device was explained using the space-charge–limited conduction mechanism. The memory device showed good characteristics including high ON/OFF ratio (~106), low reset current (~10-11 A), high speed at low voltage (200 ns, 2 V), and reasonable endurance (>104 cycles) and retention characteristics (>104 s).

Self-selection bipolar resistive switching phenomena observed in NbON/NbN bilayer for cross-bar array memory applications

In this letter, to integrate bipolar resistive switching cells into cross bar array (CBA) structure, we study one-selector (1S) and one-resistor (1R) behavior of a niobium oxynitride (NbON) and niobium nitride (NbN) bilayer for the applications of resistive random access memory (RRAM). In this structure, a NbN layer exhibits bipolar switching characteristics while a NbON layer acts as the selector. The NbN-based 1S1R devices within a single RRAM memory cell can be directly integrated into a CBA structure without the need of extra diodes; this can significantly reduce the fabrication complexity.