Cheng-Hsien Wu

Study of Ag thin films deposited on porous silicon

Abstract The experimental results of DC I - V measurements of Ag thin films on porous silicon are presented. The 200 A thick Ag thin films were deposited by RF magnetron sputtering. The substrate is p-type anodized porous silicon containing a random fractal surface structure with various size dimensions. For comparison, Ag thin films were also deposited on HNO 3 oxidized porous silicon. All porous silicon samples were analyzed by X-ray diffraction, SEM, PL, and FTIR spectroscopy, before and after oxidation. DC I - V measurements were performed on the Ag thin films. Nonlinear I - V behavior has been observed which can be explained by the random tunneling junction network model. The nonlinear I - V behavior strongly relates to the surface roughness which affects the tunneling effect at the interconnections of junction resistors. For a smooth surface of oxidized porous silicon, the deposited Ag thin films have a linear I - V relation in two current regions, but their resistances drop sharply in two discontinuous steps. Fractal-like I - V behavior, which needs more detailed investigation, was also observed.

Nitrogen Buffering Effect on Oxygen in Indium-Tin-Oxide-Capped Resistive Random Access Memory With NH 3 Treatment

In this letter, we demonstrate the differing influences of a nitrogen buffering effect in both the switching layer and the indium-tin-oxide (ITO) electrode layer of resistive random access memory (RRAM) which has undergone an NH3 treatment. The nitrogen buffering effect in the switching layer cannot counteract the electric field force, leading to similar I-V characteristics compared with the ITO/Hf:SiO2/TiN control structure RRAM. The nitrogen in the ITO electrode layer, however, works as an oxygen buffer and makes it easier for the redox reaction to occur, leading to improvements in performance, such as concentrated voltages and better endurance.

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.

Ultra-Low Switching Voltage Induced by Inserting SiO 2 Layer in Indium–Tin–Oxide-Based Resistance Random Access Memory

A lower switching voltage of indium-tin-oxide (ITO)-based resistance random access memory (RRAM) with an inserted SiO2 thin film was presented. The amplitude of switching voltage of device was below 0.2 V whether measured by direct current or alternating current sweep operation. Notably, the observed reset voltage increased with temperature. To clarify the switching mechanism, conduction current fitting and switching voltage statistics were applied to explore the regular voltage variation dependent on temperature. In addition, a reaction model was proposed to explain the oxygen concentration gradient induced between the inserted SiO2 and ITO electrode on the ITO-based RRAM device.

Effect of charge quantity on conduction mechanism of high-and low-resistance states during forming process in a one-transistor-one-resistor resistance random access memory

The forming process is a necessary and irreversible process to activate the resistance switching behavior in a resistance random access memory (RRAM) device. However, during the forming process, an overshoot current leads to device damage and causes inferior resistance switching characteristics; consequently, the process is considered to be a key factor in device degradation. In this paper, we find that a discontinuous conduction path can be formed by a pulse forming process such that the operation current can be reduced. We further investigate how the charge quantity during the forming process affects the carrier conduction mechanism of HRS, with all experiments and results demonstrated on one-transistor–one-resistor (1T1R) devices.

Obtaining Lower Forming Voltage and Self-Compliance Current by Using a Nitride Gas/Indium–Tin Oxide Insulator in Resistive Random Access Memory

This paper investigates the characteristics of applying indium-tin oxide (ITO) with and without nitride gas (N2) as the insulator in resistive random access memory (RRAM). After cosputtering an ITO target with N2 as the insulator and capping the same ITO material as the top electrode, the device exhibits rectifier and resistance switching characteristics before and after the forming process, respectively. The Schottky diodelike rectifier mechanism was also verified by various temperature measurements. Furthermore, robust resistance switching at a positive forming voltage, smaller than that required during negative bias forming, can be achieved. Both positive and negative forming processes are examined with current fitting results, which show different dominant mechanisms when using positive or negative biases. All these mechanisms have also been verified by temperature effect experiments, which confirmed the dominant conduction mechanisms. This, in combination with the fact that the positive forming voltage itself is smaller than the negative forming voltage, and decreases with device scale down, provides two highly beneficial results. This good performance achieved by using ITO with N2 suggests significant progress of RRAM and remarkable potential applications.

Modifying Indium-Tin-Oxide by Gas Cosputtering for Use as an Insulator in Resistive Random Access Memory

In this paper, indium-tin-oxide (ITO) was used to act as both insulator and top electrode in resistive random access memory (RRAM) on identical bottom substrates. This is achieved by cosputtering an ITO target with nitride (N2) or oxygen (O2) gas as the insulator; then capping by an ITO electrode, such that both the rectifier and RRAM characteristics can be achieved before and after a forming process, respectively. In contrast, using pure ITO as an insulator does not exhibit RRAM behavior. To verify the rectifier and RRAM characteristics, material analyses and electrical measurements at various temperatures were conducted. Reliability tests including retention and endurance were also applied to verify the resistance switching stability. Finally, the rectifier and RRAM conduction models were proposed to examine the resistance switching behaviors. By applying the ITO material as both electrode and insulator, the resistance switching characteristic with high reliability is thus obtained.

Complementary resistive switching behavior for conductive bridge random access memory

In this study, a structure of Pt/Cu18Si12O70/TiN has been investigated. By co-sputtering the Cu and SiO2 targets in the switching layer, we can measure the operation mechanism of complementary resistive switching (CRS). This differs from conventional conductive bridge random access memory (CBRAM) that tends to use Cu electrodes rather than Cu18Si12O70. By changing the voltage and compliance current, we can control device operating characteristics. Because Cu distributes differently in the device depending on this setting, the operating end can be located at either the top or bottom electrode. Device current–voltage (I–V) curves are used to demonstrate that the CRS in the CBRAM device is a double-electrode operation.

Recovery of failed resistive switching random access memory devices by a low-temperature supercritical treatment

The successful recovery of resistive switching random access memory (RRAM) devices that have undergone switching failure is achieved by introducing a low-temperature supercritical-fluid process that passivates the switching layer. These failed RRAM devices, which are incapable of switching between high- and low-resistance states, were treated with supercritical carbon dioxide with pure water at 120 ?C for 1 h. After the treatment, the devices became operational again and showed excellent current?voltage (I?V) characteristics and reliability as before. On the basis of the current conduction mechanism fitting results, we propose a model to explain the phenomenon.

Inert Pt electrode switching mechanism after controlled polarity-forming process in In2O3-based resistive random access memory

In this study, we demonstrate a forming technique that enables us to control whether the switching layer of a Pt/In2O3/TiN device is near the Pt electrode or the TiN electrode. This means that In2O3-based resistive random access memory (RRAM) can be switched at either the active or inert electrode. The resistive switching current–voltage (I–V) curves for both electrodes exhibit stable memory windows. Through material and electrical analyses, we found that the reason for switching at the inert electrode is the oxygen-vacancy-rich characteristic of In2O3. Finally, a physical model is proposed to explain this phenomenon.