Manzar Siddik

Resistive switching characteristics and mechanism of thermally grown WOx thin films

Resistive switching characteristics of thermally oxidized tungsten thin films and their switching mechanism were investigated, modifying thickness of the active layer (WOx) by varying oxidation conditions. Two types of switching were observed in Pt/WOx/W memory devices. Thinner film (t ≤ 15 nm) exhibits clockwise switching (CWS) with filamentary characteristics, whereas thicker film (t ≥ 25 nm) exhibits counter-clockwise switching (CCWS) with more homogeneous conduction. Both switching modes are highly reliable and show good cycling endurance. The conduction phenomena in two different switching modes were examined. In the case of CWS, the conduction mechanism changes from Schottky emission to ohmic conduction due to the local bypass of Schottky barrier formed at Pt/WOx interface by oxygen vacancies. Contrary to CWS, CCWS showed a completely different conduction mechanism. The high resistance state is dominated by the Schottky emission at low electric field and by Poole–Frenkel emission at high electric fi...

Low temperature solution-processed graphene oxide/Pr0.7Ca0.3MnO3 based resistive-memory device

We propose a graphene oxide (GO)/Pr0.7Ca0.3MnO3 (PCMO) based resistance random access memory (RRAM) device. Both active layers were prepared by a sol-gel spin-coating method at low temperature (<300 °C).The fabricated Pt/GO/PCMO/Pt RRAM device shows good switching performance with an on/off ratio of about 100 and a retention property of more than 104 at 85 °C and reliable endurance characteristics. Moreover, the observed bipolar switching phenomena could be explained by the movement of oxygen ions across the GO–PCMO interface. These results suggest that the GO/PCMO device is a good candidate for use in resistive memory applications.

Asymmetric bipolar resistive switching in solution-processed Pt/TiO2/W devices

The resistive switching characteristics of Pt/TiO2/W devices in a submicrometre via-hole structure are investigated. TiO2 film is grown by the sol–gel spin coating technique. The device exhibits reversible and reproducible bistable resistive switching with a rectifying effect. The Schottky contact at the Pt/TiO2 interface limits electron injection under reverse bias resulting in a rectification ratio of >60 at 2 V in the low-resistance state. The switching mechanism in our device can be interpreted as an anion migration-induced redox reaction at the tungsten bottom electrode (W). The rectifying effect can significantly reduce the sneak path current in a crossbar array and provide a feasible way to achieve high memory density.

Quantized conductive filament formed by limited Cu source in sub-5nm era

For the first time, we have investigated the resistive switching characteristics in extreme size (sub-5nm) device. Less than 5nm effective electrode radius is confirmed by conductive-AFM and FIB-TEM analysis. The conductive filament source (Cu ions) is limited by applying novel fabrication technology. Due to the limited Cu source, we observe the quantized formation of conductive path, which results in the distinguishable conductance states and shows the feasibility of multi-bit operation. By controlling the motion of Cu ions precisely, ideal selection behavior for xpoint memory application was achieved.

Noise-Analysis-Based Model of Filamentary Switching ReRAM With

In this letter, we propose a model based on noise analysis for the filamentary switching mechanism in resistance random access memory having ZrOx/HfOx bilayer stacks. From the noise analysis results, we concluded that the current flowing during high-resistance state can be described as a trap-assisted current that flows through traps. It has been hypothesized that these traps are the cause of the instability of device parameters. To validate this, the noise analysis results of large-area devices were compared with those of small-area devices. As a consequence, we improved the uniformity of device parameters.

\hbox{ZrO}_{x}/\hbox{HfO}_{x}

The nitrogen-doped Ge2Sb2Te5 (GST) programmable metallization cell is investigated to address the low switching voltage and need for a high resistance ratio, which are critical issues for the filed-programmable gate array (FPGA) configuration. Nitrogen doping of GST yields Ge–N covalent bonds, as confirmed by x-ray photoelectron spectroscopy and Raman spectroscopy; this increases the resistivity of GST. Consequently, an excellent resistance ratio (∼107) with appropriate operating voltage and stable retention properties more than for 104 s at 85 °C are achieved. The results indicate that the film is a suitable alternative candidate for the logic switch in static-random-access-memory-based FPGA technology.

Stacks

For the high-density memory application of resistive random access memory (ReRAM), we study the complementary resistive switch (CRS) behavior of a HfOx-based ReRAM with a TiOx-based ReRAM. To control the operation voltages of the CRS device, we used ReRAMs having asymmetric set and reset voltages. Consequently, we achieved a wider voltage window for the read process, high switch speed, high reliability, and more than ten times readout margin from the heterodevice CRS.

Excellent resistive switching in nitrogen-doped Ge2Sb2Te5 devices for field-programmable gate array configurations

We report the effect of the interfacial oxide layer on switching uniformity in Ge2Sb2Te5 (GST)-based resistive switching memory devices. An interfacial oxide layer acting as an internal resistor was fabricated by the simple thermal oxidation process at low temperature and confirmed by x-ray photoelectron spectroscopy analysis. TiN/oxidized GST/GST/Pt devices showed extremely uniform resistance states owing to intentionally controlled current flow induced by the interfacial oxide layer, despite the filaments being randomly formed. Furthermore, the devices showed good memory performance, e.g., a large on/off resistance ratio (over four orders of magnitude) and reliable data retention (up to 104 s at 85 °C).

Operation Voltage Control in Complementary Resistive Switches Using Heterodevice

We proposed for the first time thermally-assisted resistive switching random access memory (ReRAM) device to overcome the voltage-time dilemma [1] using Ti/Pr<inf>0.7</inf>Ca<inf>0.3</inf>MnO<inf>3</inf> (Ti/PCMO) with Ge<inf>2</inf>Sb<inf>2</inf>Te<inf>5</inf> (GST) thermoelectric heater as well as thermal barrier (Fig. 1). “Thermoelectric heating effect” from GST/Ti junction [2] and “thermal barrier effect” from the heat confinement by GST and PCMO thermal insulators [3,4] successfully improved switching speed while “large effective Schottky barrier (SB) height (Ф<inf>eff</inf>)” provided excellent robustness to high-temperature retention and read/set/reset disturbance characteristics (Fig. 2).

Effect of interfacial oxide layer on the switching uniformity of Ge2Sb2Te5-based resistive change memory devices

We have investigated the effect of a Ge2Sb2Te5 (GST) thermal barrier on the reset operations in TiN/Cu/SiC/Pt devices. When the GST film was introduced as a thermal barrier, the device showed a lower reset voltage and a lower reset current than a device without the GST layer. In particular, the reset speed of the device with the GST layer was significantly faster at room temperature compared to the device without the GST layer. We attribute the improved resistive switching to the GST thermal barrier, which induces thermally assisted electrochemical reduction of the Cu filament.