Seok Man Hong

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.

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.

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 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.