Musarrat Hasan

Reproducible hysteresis and resistive switching in metal-CuxO-metal heterostructures

Materials showing reversible resistance switching between high-resistance state and low-resistance state at room temperature are attractive for today’s semiconductor technology. In this letter, the reproducible hysteresis and resistive switching characteristics of metal-CuxO-metal (M-CuxO-M) heterostructures driven by low voltages are demonstrated. The fabrication of the M-CuxO-M heterostructures is fully compatible with the standard complementary metal-oxide semiconductor process. The hysteresis and resistive switching behavior are discussed. The good retention characteristics are exhibited in the M-CuxO-M heterostructures by the accurate controlling of the preparation parameters.

An electrically modifiable synapse array of resistive switching memory

This paper describes the resistive switching of a cross-point cell array device, with a junction area of 100 nm x 100 nm, fabricated using ultraviolet nanoimprinting. A GdO(x) and Cu-doped MoO(x) stack with platinum top and bottom electrodes served as the resistive switching layer, which shows analog memory characteristics with a resistance ratio greater than 10. To demonstrate a neural network circuit, we operated the cell array device as an electrically modifiable synapse array circuit and carried out a weighted sum operation. This demonstration of cross-point arrays, based on resistive switching memory, opens the way for feasible ultra-high density synapse circuits for future large-scale neural network systems.

Uniform resistive switching with a thin reactive metal interface layer in metal-La0.7Ca0.3MnO3-metal heterostructures

A thin samarium (Sm) metal layer was introduced to improve the resistive hysteresis and switching uniformity. Sm reacts with the La0.7Ca0.3MnO3 and forms a thin interface oxide layer, which is responsible for the switching. The switching occurs without any forming process. Compared with conventional resistive memory device based on localized filament formation, Sm∕La0.7Ca0.3MnO3 devices show area-dependent resistance which indicates uniform resistive switching. Under a positive bias, electromigration of oxygen ions (O2−) forms thicker oxide (SmOx), which dissociates under a negative bias, causes high and low resistance states, respectively. Estimated data retention of more than 10yr was observed at 85°C.

Excellent uniformity and reproducible resistance switching characteristics of doped binary metal oxides for non-volatile resistance memory applications

We have investigated various doped metal oxides such as copper doped molybdenum oxide, copper doped Al₂O₃, copper doped ZrO₂, aluminium doped ZnO, and Cu_xO for novel resistance memory applications. Compared with non-stoichiometric oxides (Nb₂O_5-x, ZrO_x, SrTiO_x), doped metal oxides show higher device yield. Moreover, Cu:MoO_x have demonstrated excellent memory characteristics such as reliability under programming cycles, potential multi-bit operation, good data retention, highly scalable property, and fast switching speed. The switching mechanism of the copper doped molybdenum oxide can be explained by the generation and rupture of multi-filaments under the electrical stress

Improvement of reproducible hysteresis and resistive switching in metal-La0.7Ca0.3MnO3-metal heterostructures by oxygen annealing

Materials showing reversible resistance switching between high-resistance state and low-resistance state at room temperature are attractive for today’s semiconductor technology. In this letter, the improvement of reproducible hysteresis and resistive switching characteristics of metal-La0.7Ca0.3MnO3-metal (M-LCMO-M) heterostructures is demonstrated. The fabrication of the M-LCMO-M heterostructures is compatible with the standard complementary metal-oxide semiconductor process. The effect of oxygen annealing on the improvement of the hysteresis and resistive switching is discussed. The good retention characteristics are exhibited in the M-LCMO-M heterostructures by the accurate controlling of the preparation parameters.

Sub-15 nm n+/p-germanium shallow junction formed by PH3 plasma doping and excimer laser annealing

An n + /p germanium (Ge) ultrashallow junction formed by PH 3 plasma doping (PLAD) and KrF excimer laser annealing is demonstrated. In order to improve the n-type dopant activation without significant diffusion in the n + /p-Ge junction, we applied laser annealing on the PLAD samples. Compared with rapid thermal annealing (RTA), the laser annealing yielded shallower junction depth (∼15 nm) with low sheet resistance and comparable leakage current characteristics in the Ge n + /p junction. Therefore, PLAD with laser annealing can be considered as an alternative method for fabricating future Ge metal-oxide-semiconductor field-effect-transistors.

Electrical and reliability characteristics of copper-doped carbon (CuC) based resistive switching devices for nonvolatile memory applications

We have investigated copper-doped carbon (CuC) as a new solid-state electrolyte material for resistive switching devices. Compared with CuS electrolytes, CuC devices demonstrate good memory characteristics such as a high resistance ratio of over two orders, higher operation voltage, and high temperature retention characteristics. Using 1000 cell array devices, we have also confirmed uniform distributions of resistance and switching voltages. Both high and low resistance states showed negligible degradation of resistance for over 104 s at 85 °C, confirming good retention characteristics.

Nanoscale Resistive Switching of a Copper–Carbon-Mixed Layer for Nonvolatile Memory Applications

The nanoscale resistance switching property of copper-carbon-mixed (Cu-C) layer was investigated for nonvolatile memory applications. The Cu-C layer of the cross-point cell array showed typical filament switching with two orders of on/off ratio, exhibiting stable resistance switching and a narrow distribution of set and reset voltages in the nanoscale junction. In addition, we investigated the area dependence of operation current. Based on these results and current-voltage dependence on temperature, we discussed a potential switching mechanism of Cu-C layer.

Effect of oxygen migration and interface engineering on resistance switching behavior of reactive metal/polycrystalline Pr 0.7 Ca 0.3 MnO 3 device for nonvolatile memory applications

An in-depth study on the resistive switching mechanism of perovskite oxide based device was performed. Compared with filament type resistive switching device, excellent switching uniformity was obtained due to controlled redox reaction at metal/oxide interface. Electromigration of oxygen ion under the bipolar electric filed can explain the switching behavior. Formation of ultrathin AlOx at the interface can guarantee excellent retention characteristics at 125 °C. Compared with the large area (50 × 50 um2) memory cell, the nanoscale device (Φ=50 nm) showed better memory performance such as faster switching speed, better uniformity, endurance, and retention characteristics.

A Materials Approach to Resistive Switching Memory Oxides

Several oxides have recently been reported to have resistance-switching characteristics for nonvolatile memory (NVM) applications. Both binary and ternary oxides demonstrated great potential as resistive-switching memory elements. However, the switching mechanisms have not yet been clearly understood, and the uniformity and reproducibility of devices have not been sufficient for gigabit-NVM applications. The primary requirements for oxides in memory applications are scalability, fast switching speed, good memory retention, a reasonable resistive window, and constant working voltage. In this paper, we discuss several materials that are resistive-switching elements and also focus on their switching mechanisms. We evaluated non-stoichiometric polycrystalline oxides (Nb₂O 5 , and ZrO x ) and subsequently the resistive switching of CU x O and heavily Cu-doped MoO x film for their compatibility with modern transistor-process cycles. Single-crystalline Nb-doped SrTiO₃(NbSTO) was also investigated, and we found a Pt/single-crystal NbSTO Schottky junction had excellent memory characteristics. Epitaxial NbSTO film was grown on an Si substrate using conducting TiN as a buffer layer to introduce single-crystal NbSTO into the CMOS process and preserve its excellent electrical characteristics.