Dong Su Jeon

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.

Bipolar resistive switching characteristics in tantalum nitride-based resistive random access memory devices

This paper reports the bipolar resistive switching characteristics of TaNx-based resistive random access memory (ReRAM). The conduction mechanism is explained by formation and rupture of conductive filaments caused by migration of nitrogen ions and vacancies; this mechanism is in good agreement with either Ohmic conduction or the Poole-Frenkel emission model. The devices exhibit that the reset voltage varies from −0.82 V to −0.62 V, whereas the set voltage ranges from 1.01 V to 1.30 V for 120 DC sweep cycles. In terms of reliability, the devices exhibit good retention (>105 s) and pulse-switching endurance (>106 cycles) properties. These results indicate that TaNx-based ReRAM devices have a potential for future nonvolatile memory devices.

Low power NiN-based resistive switching memory device using Ti doping

In this study, we investigated the properties of Ti-doped NiN-based resistive switching random access memories (ReRAMs) in comparison with both Al-doped and conventional NiN-based samples. The Ti dopants form metallic TiN particles in the nitride film, which induce local electric fields during the forming process causing filaments to form close to the TiN clusters. The TiN components in the filaments reduce the current level for the high resistive switching state (HRS) and low resistive switching state (LRS). In our testing, the Ti-doped sample had a current of 10 nA in the HRS and 23 μA in the LRS with a high on/off ratio (>103). This implies that the Ti doping effect enabled the sample to operate at low power. Furthermore, the Ti-doped samples also exhibited highly uniform operating parameters. In terms of reliability, the retention was measured to be >106 s at 85 °C, and the endurance was found to be at least 107 cycles. These results indicate that Ti-doped NiN-based ReRAM devices have significant adva...

Improved uniformity in the switching characteristics of ZnO-based memristors using Ti sub-oxide layers

In this paper, improved uniformity in the resistive switching (RS) characteristics of ZnO-based memristors using Ti sub-oxide layers (metallic TiO x , insulating TiO y ) is reported. Compared with Pt/Ti/ZnO/Pt cells, more reliable and reproducible RS operation was observed in Pt/TiO x (or TiO y )/ZnO/Pt cells, particularly with insulating TiO y , because Ti sub-oxide layers play the role of oxygen reservoirs that help rupture the conducting filament. By comparison, Pt/TiO y /ZnO/Pt cells exhibited the best performance, with a large on/off ratio (~105) at a read voltage of 0.4 V, and highly stable low- and high-resistive state operation for 100 direct-current sweep cycles.

Effects of oxygen doping concentration on resistive switching in NiN-based resistive switching memory

In this study, NiN-based resistive switching (RS) random access memory was doped with various concentrations of oxygen, and its uniform set/reset operation and current levels were examined. As compared with undoped RS layers, RS layers deposited with an oxygen flow rate of 5 sccm were more uniform and exhibited higher on/off ratios by forming oxy-nitride. In contrast, RS layers deposited with oxygen flow rates less than 5 sccm showed poor performance due to oxygen acting as a defect. The authors demonstrated that the oxygen doping process can improve the RS characteristics of NiN films and help clarify the RS phenomena associated with these films.

Ti-Doped GaOx Resistive Switching Memory with Self-Rectifying Behavior by Using NbOx/Pt Bilayers

Crossbar arrays (CBAs) with resistive random access memory (ReRAM) constitute an established architecture for high-density memory. However, sneak paths via unselected cells increase the total power consumption of these devices and limit the array size. To eliminate such sneak-path problems, we propose a Ti/GaOx/NbOx/Pt structure with a self-rectifying resistive-switching (RS) behavior. In this structure, to reduce the operating voltage, we used a Ti/GaOx stack to increase the number of trap sites in the RS GaOx layer through interfacial reactions between the Ti and GaOx layers. This increase enables easier carrier transport with reduced electric fields. We then adopted a NbOx/Pt stack to add rectifying behavior to the RS GaOx layer. This behavior is a result of the large Schottky barrier height between the NbOx and Pt layers. Finally, both the Ti/GaOx and NbOx/Pt stacks were combined to realize a self-rectifying ReRAM device, which exhibited excellent performance. Characteristics of the device include a low operating voltage range (-2.8 to 2.5 V), high on/off ratios (∼20), high selectivity (∼104), high operating speeds (200-500 ns), a very low forming voltage (∼3 V), stable operation, and excellent uniformity for high-density CBA-based ReRAM applications.

AlN/ITO hybrid electrodes with conducting filament for 365 nm ultraviolet light-emitting diodes

Hybrid transparent conductive electrodes (TCEs) consisting of AlN rods with conducting filaments (CFs) and ITO films was proposed to improve the current injection, spreading effect, and optical transmittance for 365 nm p-AlGaN based LEDs, and we demonstrated their electrical and optical properties. When comparing the performance of the LEDs with proposed hybrid TCE with reference LEDs having conventional ITO-TCEs, we observed the increased light-output powers of 6% and the reduced forward voltages of 8%, which may result from the improvement of ohmic contact behavior on the p-AlGaN layers by employing filament-embedded TCE, i.e., AlN/ITO hybrid electrodes.

Various metal-doped ITO as transparent conductive electrode for near-ultraviolet light emitting diodes

We fabricated under various metal doped indium tin oxide (ITO) transparent conductive electrodes (TCE) for use in near-ultraviolet (NUV) light emitting diodes (LEDs). The role of metal is to improve the transmittance especially in NUV region and current spreading of ITO. The ITO/metal (Ti, Ga, Ge, Al) TCEs (annealed at 550°C, 1 min) exhibit 90.5 ~ 94.7% transmittance at 385 nm on the quartz substrate and the sheet resistance is ranged from 23.2 to 73.5 Ω/□ on the NUV LED wafer.