Tian-Jian Chu

Physical and chemical mechanisms in oxide-based resistance random access memory

In this review, we provide an overview of our work in resistive switching mechanisms on oxide-based resistance random access memory (RRAM) devices. Based on the investigation of physical and chemical mechanisms, we focus on its materials, device structures, and treatment methods so as to provide an in-depth perspective of state-of-the-art oxide-based RRAM. The critical voltage and constant reaction energy properties were found, which can be used to prospectively modulate voltage and operation time to control RRAM device working performance and forecast material composition. The quantized switching phenomena in RRAM devices were demonstrated at ultra-cryogenic temperature (4K), which is attributed to the atomic-level reaction in metallic filament. In the aspect of chemical mechanisms, we use the Coulomb Faraday theorem to investigate the chemical reaction equations of RRAM for the first time. We can clearly observe that the first-order reaction series is the basis for chemical reaction during reset process in the study. Furthermore, the activation energy of chemical reactions can be extracted by changing temperature during the reset process, from which the oxygen ion reaction process can be found in the RRAM device. As for its materials, silicon oxide is compatible to semiconductor fabrication lines. It is especially promising for the silicon oxide-doped metal technology to be introduced into the industry. Based on that, double-ended graphene oxide-doped silicon oxide based via-structure RRAM with filament self-aligning formation, and self-current limiting operation ability is demonstrated. The outstanding device characteristics are attributed to the oxidation and reduction of graphene oxide flakes formed during the sputter process. Besides, we have also adopted a new concept of supercritical CO2 fluid treatment to efficiently reduce the operation current of RRAM devices for portable electronic applications.

Characteristics and Mechanisms of Silicon-Oxide-Based Resistance Random Access Memory

Traditionally, a large number of silicon oxide materials are extensively used as various dielectrics for semiconductor industries. In general, silicon oxide cannot be used as resistance random access memory (RRAM) due to its insulating electrical properties. In this letter, we have successfully produced resistive switching and forming-free behaviors by zinc doped into silicon oxide. The current-voltage fitting data show that current transport mechanism is governed by Poole-Frenkel behavior in high-resistance state and Ohms law in low-resistance state, consisting with filament theory. Additionally, good endurance and retention reliabilities are exhibited in the zinc-doped silicon oxide RRAM.

Charge Quantity Influence on Resistance Switching Characteristic During Forming Process

In this letter, we presented that the charge quantity is the critical factor for forming process. Forming is a pivotal process in resistance random access memory to activate the resistance switching behavior. However, overforming would lead to device damage. In general, the overshoot current has been considered as a degradation reason during the forming process. In this letter, the quantity of charge through the switching layer has been proven as the key element in the formation of the conduction path. Ultrafast pulse forming can form a discontinuous conduction path to reduce the operation power.

Characteristics of hafnium oxide resistance random access memory with different setting compliance current

In this Letter, the characteristics of set process of hafnium oxide based resistance random access memory are investigated by different set processes with increasing compliance current. Through current fitting, carrier conduction mechanism of low resistance state changes from hopping to surface scattering and finally to ohmic conduction with the increase of setting compliance current. Experimental data of current-voltage measurement under successive increasing temperature confirms the conduction mechanism transition. A model of filament growth is eventually proposed in a way by merging discrete metal precipitates and electrical field simulation by comsol Multiphysics further clarifies the properties of filament growth process.

Hopping effect of hydrogen-doped silicon oxide insert RRAM by supercritical CO 2 fluid treatment

In this letter, we introduced hydrogen ions into titanium metal doped into SiO2 thin film as the insulator of resistive random access memory (RRAM) by supercritical carbon dioxide (SCCO)2 fluid treatment. After treatment, low resistance state split in to two states, we find the insert RRAM, which means it has an operating polarity opposite from normal RRAM. The difference of the insert RRAM is owing to the resistive switching dominated by hydrogen ions, dissociated from OH bond, which was not by oxygen ions as usual. The current conduction mechanism of insert RRAM was hopping conduction due to the metal titanium reduction reaction through SCCO2.

Electrical conduction mechanism of Zn:SiOx resistance random access memory with supercritical CO2 fluid process

In this study, the electrical conduction mechanism of Zn:SiOx resistance random access memory (RRAM) treated with supercritical CO2 fluid (SCCO2) process was investigated by low temperature measurement. The current of low resistance state for current-voltage curves in SCCO2-treated and untreated Zn:SiOx RRAM were measured and compared under a low temperature range from 100 K to 298 K. The electrical conduction mechanisms of hopping conduction and metal-like behaviors in SCCO2-treated and untreated Zn:SiOx RRAM were discussed, respectively. Finally, the electrical conduction mechanism was analyzed and verified by the chemical composition and bonding intensity of XPS analyses.

Low Temperature Improvement Method on

To improve the resistive switching properties of the resistive random access memory (RRAM), the supercritical carbon dioxide (SCCO₂) fluid is used as a low temperature treatment. In this letter, the Zn:SiO<i>x</i> thin films are treated by SCCO₂ fluid mixed with pure water. After SCCO₂ fluid treatment, the resistive switching qualities of the Zn:SiO_x thin films are carried out by XPS, fourier transform infrared spectroscopy, and IV measurement. We believe that the SCCO₂-treated Zn:SiO_x thin film is a proresistive switching properties mising material for RRAM applications due to its compatibility with portable flat panel display.

{\rm Zn{:}SiO}_{x}

Incorporation of nitrogen as an oxygen-confining layer in the resistance switching reaction region is investigated to improve the reliability of resistance random access memory (RRAM). The switching mechanism can be attributed to the formation and rupture of conduction filaments. A compatible WSiON (around 5 nm) layer is introduced at the interface of tungsten silicon oxide (WSiOx) and TiN electrode to prevent the randomly diffusing oxygen ions surpassing the storage region of the WSiON layer. The double-layer WSiOx/WSiON memory structure would enhance the endurance over 100 times so as to better confirm the WSiOx RRAM application of nonvolatile memory.

Resistive Random Access Memory Devices

In this letter, dual ion effect induced reset process of lithium silicate resistance random access memory (RRAM) devices is studied and discussed. Unlike the traditional silicon oxide-based RRAM, lithium ions also participate in the resistive switching process except for the oxygen ions. Owing to the twofold chemical reaction, the high resistance states are randomly distributed in a wide range. Schottky emission can be obtained through conduction current fitting, and a reaction model is established to demonstrate the special behaviors of the two types of ions, which also clarifies the gradual change of current fitting results.

Endurance Improvement Technology With Nitrogen Implanted in the Interface of

In this letter, the special role of hydrogen ions in hafnium doped silicon oxide resistive random access memory (RRAM) is presented. In addition to the more typical oxygen ion-dominated resistive switching, hydrogen ions were also observed to trigger a resistance transformation phenomenon, producing a tri-resistive device. Unlike a normal RRAM device, a hydrogen plasma-treated device is operated with a reversed voltage polarity, and the direction of hydrogen ion migration results in the chemical bonds breaking and repairing. By changing the voltage polarity and stop voltage, this tri-resistive behavior can be achieved. This particular hydrogen-induced switching behavior suggests a different RRAM switching mechanism and is finally explained by our model.