Po-Hsun Chen

Bulk Oxygen–Ion Storage in Indium–Tin–Oxide Electrode for Improved Performance of HfO 2 -Based Resistive Random Access Memory

Indium-tin-oxide (ITO) is investigated as the top electrode material in HfO2-based resistive random access memory cells. Experimental results show that in contrast to a metal (Pt) electrode, an ITO electrode provides for self-limiting current flow during the forming and SET processes, so that no compliance limit is necessary. This provides for low-power consumption, high endurance (>107 cycles), and short SET/RESET transition times (~50 ns). We propose that this is because ITO is an oxygen-vacancy-rich material, providing bulk storage for oxygen ions rather than surface storage as a metal electrode.

Resistive Switching Mechanism of Oxygen-Rich Indium Tin Oxide Resistance Random Access Memory

This letter investigates the double-ended resistive switching characteristics of indium tin oxide (ITO) resistance random access memory (RRAM). Resistive switching can be achieved around both the active TiN electrode and the inert Pt electrode. In addition, complementary resistance switching (CRS) characteristics can be observed without current compliance during dc voltage sweep operations. Electrical measurement data fitting results indicate that the oxygen-rich ITO near top and bottom electrodes works as a double-ended resistive switching layer. Based on the analysis of the current conduction mechanism, we propose a physical model to interpret the CRS behaviors in ITO RRAM devices.

Improving Performance by Doping Gadolinium Into the Indium-Tin–Oxide Electrode in HfO 2 -Based Resistive Random Access Memory

This letter investigates the characteristics of doping gadolinium (Gd) in an indium-tin-oxide (ITO) electrode in HfO2-based resistive random access memory (RRAM). Identical bottom electrodes and insulators were made but then capped by either pure ITO or a Gd:ITO top electrode. Doping Gd in the ITO electrode produces lower operation currents in both high-resistance state (HRS) and low-resistance state (LRS) as well as enlarging the memory window. This excellent performance suggests a remarkable potential to improve RRAM applications. Schottky emission mechanism dominates both HRS and LRS according to current fitting results, and is confirmed by temperature effect experiments. The resistive switching behavior of the Gd:ITO device is explained by our model and is also confirmed by material analysis and electrical measurements. Furthermore, reliability tests verify the Gd:ITO devices capability to perform data storage as a nonvolatile memory.

Resistance Switching Characteristics Induced by O2 Plasma Treatment of an Indium Tin Oxide Film for Use as an Insulator in Resistive Random Access Memory

In this study, an O2 inductively coupled plasma (ICP) treatment was developed in order to modify the characteristics of indium tin oxide (ITO) film for use as an insulator in resistive random access memory (RRAM). After the O2 plasma treatment, the previously conductive ITO film is oxidized and becomes less conductive. In addition, after capping the same ITO material for use as a top electrode, we found that the ITO/ITO(O2 plasma)/TiN device exhibits very stable and robust resistive switching characteristics. On the contrary, the nontreated ITO film for use as an insulator in the ITO/ITO/TiN device cannot perform resistance switching behaviors. The material analysis initially investigated the ITO film characteristics with and without O2 plasma treatment. The surface was less rough after O2 plasma treatment. However, the molar concentration of each element and measured sheet resistance results for the O2-plasma-treated ITO film were dramatically modified. Next, electrical measurements were carried out to examine the resistance switching stability under continuous DC and AC operation in this ITO/ITO(O2 plasma)/TiN device. Reliability tests, including endurance and retention, also proved its capability for use in data storage applications. In addition to these electrical measurements, current fitting method experiments at different temperatures were performed to examine and confirm the resistance switching mechanisms. This easily fabricated device, using a simple material combination, achieves excellent performance by using ITO with an O2 plasma treatment and can further the abilities of RRAM for use in remarkable potential applications.

Effects of erbium doping of indium tin oxide electrode in resistive random access memory

Identical insulators and bottom electrodes were fabricated and capped by an indium tin oxide (ITO) film, either undoped or doped with erbium (Er), as a top electrode. This distinctive top electrode dramatically altered the resistive random access memory (RRAM) characteristics, for example, lowering the operation current and enlarging the memory window. In addition, the RESET voltage increased, whereas the SET voltage remained almost the same. A conduction model of Er-doped ITO is proposed through current–voltage (I–V) measurement and current fitting to explain the resistance switching mechanism of Er-doped ITO RRAM and is confirmed by material analysis and reliability tests.

Controlling the Degree of Forming Soft-Breakdown and Producing Superior Endurance Performance by Inserting BN-Based Layers in Resistive Random Access Memory

In this letter, we propose a resistive switching memory with outstanding comprehensive performance by inserting buffer layers of silicon dioxide doped with boron nitride (BN: SiO2 into HfO resistance random access memory (RRAM). X-ray photoelectron spectroscopy (XPS) spectra confirms that hexagonal boron nitride (h-BN) exists in the BN:SiO2 layer. The Pt/BN:SiO2/HfO/BN:SiO2 /TiN structure was observed to have superior switching endurance >1012 cycles) and higher stability. This can be attributed to the oxygen ions generated during the forming process being localized by h-BN flakes which are formed during the sputter process. A physical model is proposed to explain the resistive switching behavior of HfO RRAM with the inserted BN-based layers.

Ultralow Power Resistance Random Access Memory Device and Oxygen Accumulation Mechanism in an Indium–Tin-Oxide Electrode

This paper proposes low power consumption resistance random access memory (RRAM) devices with indium-tin-oxide (ITO) electrodes. The development of the Internet of Things (IoT) is a trend in future technology, but the bottleneck in IoT development is high power consumption; therefore, targeting low-power-consumption memory is crucial for the IoT. ITO-capped RRAM devices have been shown to exhibit outstanding performance and low power consumption, and here, we propose an oxygen accumulation mechanism by analyzing device characteristics. We find that the conduction current mechanism will be affected by oxygen absorbance in the ITO electrode. During the forming and set processes, oxygen ions will be propelled into the ITO electrode due to its oxygen vacancy-rich property; therefore, we find Schottky emission both at high-resistance state and low-resistance state and that the device exhibits an automatic current compliance property. Varied stop-voltage measurements were carried out to verify the device mechanism. Because of its capability for oxygen storage, the thick ITO layer was confirmed to affect the characteristic due to a difference in oxygen gradient. A new structure and novel material are proposed, based on the devices with ITO electrodes to improve performance and reduce power consumption.

Engineering interface-type resistance switching based on forming current compliance in ITO/Ga2O3:ITO/TiN resistance random access memory: Conduction mechanisms, temperature effects, and electrode influence

In this paper, an ITO/Ga2O3:ITO/TiN structured resistance random access memory is introduced. Either interface or filament conduction mechanism can be induced depending on the forming compliance current, which has not been investigated before. Material analyses and electrical I–V measurements on this ITO/Ga2O3:ITO/TiN have also been carried out. The interface conduction mechanism was confirmed by a size-effect experiment, where resistance varied inversely to via size. In addition, the current fitting results show that Schottky emission dominates the on- and off-state currents. All physical mechanisms of device resistive switching behaviors are explained by our models and also confirmed by I–V characteristics.

Reducing operation voltages by introducing a low-k switching layer in indium–tin-oxide-based resistance random access memory

In this letter, we inserted a low dielectric constant (low-k) or high dielectric constant (high-k) material as a switching layer in indium–tin-oxide-based resistive random-access memory. After measuring the two samples, we found that the low-k material device has very low operating voltages (−80 and 110 mV for SET and RESET operations, respectively). Current fitting results were then used with the COMSOL software package to simulate electric field distribution in the layers. After combining the electrical measurement results with simulations, a conduction model was proposed to explain resistance switching behaviors in the two structures.

Influence of Ammonia on Amorphous Carbon Resistive Random Access Memory

This letter investigates the influence of ammonia on amorphous carbon resistance random access memory by sputtering the carbon target with argon and ammonia mixed gas. The device fabricated with ammonia (C (NH3)-RRAM) showed remarkable improvement in memory window and high resistance state as compared to the device deposited without ammonia. Material analysis confirmed the absorption signal of amine. Current fitting indicated the conduction mechanism changes from hopping conduction to Schottky conduction with the addition of ammonia. Finally, we propose a model to explain the influence of ammonia on the resistive switching behaviors of the amorphous carbon RRAM.