Min Ju Yun

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.

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.

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.

Effect of embedded metal nanocrystals on the resistive switching characteristics in NiN-based resistive random access memory cells

The metal nanocrystals (NCs) embedded-NiN-based resistive random access memory cells are demonstrated using several metal NCs (i.e., Pt, Ni, and Ti) with different physical parameters in order to investigate the metal NCs dependence on resistive switching (RS) characteristics. First, depending on the electronegativity of metal, the size of metal NCs is determined and this affects the operating current of memory cells. If metal NCs with high electronegativity are incorporated, the size of the NCs is reduced; hence, the operating current is reduced owing to the reduced density of the electric field around the metal NCs. Second, the potential wells are formed by the difference of work function between the metal NCs and active layer, and the barrier height of the potential wells affects the level of operating voltage as well as the conduction mechanism of metal NCs embedded memory cells. Therefore, by understanding these correlations between the active layer and embedded metal NCs, we can optimize the RS properties of metal NCs embedded memory cells as well as predict their conduction mechanisms.

Improved resistive-switching characteristics observed in Pt embedded nickel-nitride films prepared by radio-frequency magnetron sputtering

In this paper, the authors report the forming-free bipolar-switching operation at low set/reset voltages (VSET/VRESET) using a Pt embedded-NiN based resistive random access memory (ReRAM) cell. Compared to conventional NiN based ReRAM cells, the variations in VSET and VRESET were reduced from 1 to 0.4 V and from 0.4 to 0.2 V, respectively, using the Pt embedded ReRAM cells. These results show that the embedded Pt particles might assist in the uniform formation of the conducting filaments in the NiN films, without an initial forming process. In addition, in the endurance and retention tests, Pt embedded ReRAM cells showed more stable repetitive dc cycling characteristics with a larger resistance ratio of approximately 1 × 101 and a longer data retention of over 105 s.

Improved reliability of Ti/ZrN/Pt resistive switching memory cells using hydrogen postannealing

The authors investigated the effects of hydrogen postannealing on data retention and set/reset current variation in a Ti/ZrN/Pt resistive switching memory cell. Annealing the Ti/ZrN/Pt sample in a N2 + H2 ambient gas versus a N2 ambient gas reduced the set currents from 10.4 to 4.1 mA and the reset currents from 1.2 to 0.2 μA, whereas the current ratio increased from ∼9 × 103 to ∼2 × 104. In addition, current variations in the set and reset states decrease at temperatures of 25 and 85 °C (>10yr) due to reduction of the interface trap by hydrogen passivation effects.