비정질 IGZO를 이용한 Pt/IGZO/TaOx/W 구조를 가진 저항 변화 메모리의 특성 연구

Abstract

Resistive memory is a promising candidate for the next generation nonvolatile memories due to its fast set/reset operation, low power consumption, high storage density, and good scaling capability. It is generally believed that the crossbar architecture, with the smallest ideal cell area of 4F2, will yield the most economical solid-state memory. One of the bottlenecks of the crossbar array architecture for practical applications is crosstalk interference, which can lead to read-out errors. One solution is to introduce a rectifying diode(1D) to each cell. However, integrating a rectifying diode increases the complexity of the fabrication process and, thus, the cost. In terms of memory performance, the increase of read/write voltage and the degradation of the memory stability are considered as key concerns for future one-diode-one-ReRAM(1D-1R) structure. Furthermore, the current density of the diode is an important factor affecting its scaling limitation due to the dependence of current transport of many resistive switching materials on area. Recently, the quest of self-rectifying resistive memory has been actively pursued. The self-rectifying resistive memory has the obvious rectification in LRS, so the crosstalk phenomenon can be alleviated without serially connecting a diode. Owing to the self-rectifying effect, memory cell can significantly improve misreading in matrix crossbar memory without extra rectifying diodes. many researchers have been studied about self-rectifying effect and their research topics are mainly focused on self-rectifying effect that is due to a Schottky contact at the electrode/TMO interface. This phenomenon indicates that the electrode plays an important role in the rectifying effect. Therefore, the low or high barriers will form at the interface between various electrode metals and TMO due to the different metal workfunction, which are responsible for the different I-V characteristics. The barrier at the electrode/TMO interface blocks electrons flowing from top electrode to bottom electrode, which makes the negative current much smaller than the positive value. However, such kind of self-rectifying effect is difficult to select adequate electrode. On the other hand, self-rectifying effect in resistive switching memory with Pt/IGZO/TaOx/W structure in this research, is not due to a Schottky contact at the electrode/TMO interface. The rectifying effect is not directly affected by electrodes(Pt, Mo, Ni). Consequently, it has no difficulty in selecting any electrodes. Based on the result of TEM and AES analysis, asymmetric electrical behavior is attributed to the naturally self-formed Ta2O5 between IGZO and TaOx layer. When electrons flow from Pt top electrode to W bottom electrode, corresponding to the negative voltages, the electrons will encounter energy barrier. It is the barrier between IGZO and the interfacial TaOx. This barrier will block the current flow. On the other hand, when electrons flow from W bottom electrode to Pt top electrode, corresponding to the positive voltage, the electrons can’t flow easily. As a result, the current of negative voltage is much larger than the positive value. It is the naturally self-formed interfacial Ta2O5 layer that leads to the asymmetrical rectifying effect of the Pt/IGZO/TaOx/W. In conclusion, resistive memory device with Pt/IGZO/TaOx/W structure using IGZO was fabricated and investigated. We observe stable and repeatable resistive switching with a rectifying effect. It shows a remarkable self-rectifying effect at the LRS. This asymmetric electrical behavior is attributed to the naturally self-formed Ta2O5 between IGZO and TaOx, which introduces an energy barrier when electrons flow from top electrode and bottom electrode towards the bottom electrode and top electrode. The self-rectifying characteristic at LRS is an attractive property for resistive memory, which shows a potential use to minimize the cross-talk effect and alleviate the misreading in passive crossbar structure arrays.