Impact of O2 plasma treatment on novel amorphous oxide InWZnO on conductive bridge random access memory

https://doi.org/10.1016/j.surfcoat.2021.127539Get rights and content

Highlights

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    Effect of oxygen plasma treatment on novel tungsten-doped InWZnO film were investigated.

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    The plasma-treated InWZnO film is used as resistive switching layer.

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    This is attributed to the formation of oxygen-rich layer on the InWZnO surface.

Abstract

The impact of O2 plasma treatment on novel amorphous oxide InWZnO (IWZO) as conductive bridge random access memory (CBRAM) was investigated. A high-quality film on the surface of IWZO can be obtained by using remote O2 plasma treatment. The uniformity of O2 plasma sample is better than control sample, and also the set and reset voltage are more uniform and smaller to suitable for memory operation. Moreover, the O2 plasma sample shows excellent memory performance, such as high switching endurance cycles (up to 3 × 103), long retention time for 104 s at 85 °C. These results show that the surface modification with O2 plasma on IWZO CBRAM device is a critical technique for next generation memory applications.

Introduction

Amorphous transparent oxide material semiconductors have received a lot of attention in the application of flexible and transparent electronic devices, such as electronic skin, AMOLEDs, e-paper, biosensor, etc. Due to the characteristics with high visible light transmittance, excellent deposition uniformity, low process temperature and low cost. From many choices of oxide materials, IZO-based oxide semiconductors (such as InZnO, InGaZnO, Ta-InZnO,Hf-InZnO, etc.) have been considered as materials that is suitable for device application [[1], [2], [3], [4], [5]]. In addition, indium gallium zinc oxide (IGZO) is the most popular and attracting attention in the flat panel display industry. Nevertheless, IGZO is also used as a resistive switching layer in memory devices [[6], [7], [8]]. However, gallium (Ga) is a rare source on the earth, so that it is urgent to find a material to replace Ga to alleviate the exhaustion of resources. Fortunately, tungsten (W) is a good carrier suppressor material due to its high bonding ability with oxygen, which can be inhibited the excess oxygen vacancies generating and increase the stability in the oxide film. From the reasons mentioned above, InWZnO (IWZO) material is very suitable to be applied to thin film transistor [[9], [10], [11], [12]], and it also has high compatibility to integrate with memory, which is easy to realize the system on panel. If we require to further integrate the next generation of commercial flat-panel display industry, it is needs to pay more attention on the performance of amorphous transparent oxide film memory devices.

Recently, non-volatile memory has played an indispensable in electronic device. Resistive random access memory (RRAM) is received the most attention, which is consisted of a top electrode, a resistive switching layer and a bottom electrode. It can be divided into two types of operation mechanisms, one is valence change memory (VCM or OxRAM) based on anion/oxygen ion motion, and the other is electrochemical metallization memory (ECM or conductive-bridge RAM; CBRAM) based on cation motion [[13], [14], [15]]. OxRAM cell uses the oxygen vacancy in the solid electrolyte as a path to form conductive filaments [14,16]. CBRAM cell uses a solid electrolyte and an active electrode that provide metal ions to the solid electrolyte to use the metal ions as conductive filaments.

In addition, there are many methods that can be used to improve the performance of memory devices. For example, considering the oxygen doping, thermal annealing in an oxygen environment and supercritical fluid oxidation technology are all effective methods [17,18]. Plasma treatment is a widely accepted surface modification technology, which can react to thin films due to its physical effects and chemical reactions. It shows the advantages of low cost, high efficiency, large area uniformity, and low temperature process [[19], [20], [21]].

In this study, remote O2 plasma is used to be modified the surface of IWZO film in CBRAM device. The properties of materials and the behavior of resistance switching will be systematically discussed. By using AFM measurement, the surface roughness of IWZO film was still relatively flat after O2 plasma treatment. With XPS analysis, it can be found that O2 plasma surface modification can reduce the defects and increase oxygen lattice on the surface of IWZO film, which is attributed to the oxygen ion doping effect that make oxygen-rich layer on the surface. However, the electrical analysis of IWZO CBRAM devices can be investigated, such as endurance cycles, retention time, uniformity of the resistance distribution, set voltage and reset voltage. Based on the electrical analysis, it can be seen that the CBRAM device after O2 plasma treatment has better electric characterization. Therefore, this research indicates that oxygen plasma treated on IWZO film can effectively enhance the reliability of memory and provide a potential application in integrating TFT to achieve the demand of flat-panel display field.

Section snippets

Experimental

A 100-nm-SiO2 layer on the p-type Si wafer used as the substrate for device fabrication. First, a 3 nm-thick Ti adhesion layer and 100 nm-thick Pt bottom electrode were deposited on the SiO2 layer in sequence by DC magnetron sputtering. Subsequently, a 10 nm-thick a-IWZO film deposited on Pt/Ti/SiO2/Si substrate by RF magnetron sputtering at room temperature. The tungsten doped IZO (In-Zn-O) target was used for a-IWZO deposition. The total pressure of the sputtering chamber was controlled to be

Results and discussion

As shown in Fig. 1(b), TEM analysis exhibits that the stack structure of the CBRAM is completed by using all sputtering processes at room temperature, where the sequence of CBRAM device is Cu, TiW, IWZO and Pt. The Cu electrode is used to a top electrode, and the IWZO layer is a switching layer to change the resistance state of device, and the Pt electrode is used to ground. Among these layers, introducing an ultrathin TiW between Cu and IWZO is used as a barrier layer to prevent the Cu with

Conclusions

In conclusion, a novel amorphous oxide material IWZO with remote O2 plasma modification was applied in CBRAM device and was investigated in this study. According to the XPS analysis, the IWZO film with O2 plasma treatment has less defect and more oxygen lattice, which means that the high-quality film is formed on the surface of IWZO film. Moreover, the IWZO CBRAM device exhibits lower Vset and Vreset, the good endurance cycles (~ 3 × 103), better uniformity of resistance state, and stable

CRediT authorship contribution statement

Chih-Chieh Hsu: Data curation, Formal analysis, Investigation, Methodology, Validation, Visualization, Writing – review & editing. Po-Tsun Liu: Investigation, Project administration, Resources, Supervision, Validation, Writing – review & editing. Kai-Jhih Gan: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Writing – original draft. Dun-Bao Ruan: Conceptualization, Formal analysis, Investigation, Methodology. Yu-Chuan Chiu: Formal analysis, Investigation. Simon M.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

This work was supported by the Ministry of Science and Technology, Taiwan, under Contract MOST 109-2221-E-009-160-MY3, MOST110-2218-E-A49-013-MBK, MOST 109-2622-E-009 -009 -CC1 & MOST110-2218-E-A49-012-MBK.

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