Short CommunicationResistive switching characteristics of Sm2O3 thin films for nonvolatile memory applications
Highlights
► We study a Sm2O3 thin film as a switching layer into resistive random access memory. ► The electrical characteristics of the RRAM show superior stabilities. ► The resistance switching is ascribed to the formation/rupture of conductive filament(s).
Introduction
Recently, resistance random access memories (RRAMs) have attracted extensive attention for replacement of conventional flash memory in next-generation nonvolatile memory applications due to their simple structure, low operating power, high response speed, and high scalability [1], [2], [3]. The metal–insulator-metal capacitance structure exhibit a reversible electric-field-induced resistance switching phenomenon between the high resistance state (HRS) and low resistance state (LRS), making it suitable to record information. Up to now, the resistance switching behavior has been reported in various materials, including perovskite oxides, transition metal oxides, organics, etc. [4], [5], [6], [7], [8], [9], [10], [11]. Among these materials, high dielectric constant (high-k) materials recently have been widely investigated due to its potential use for gate dielectrics in advanced metal–oxide–semiconductor (MOS) devices. Therefore, it is interesting to investigate the RRAMs device based on high-k materials, which are appropriate to integration with CMOS process in the future. Samarium oxide (Sm2O3) is one of important rare earth oxide materials. Because of its high thermal stability, large band gaps (4.33 eV), and a proper conduction band offset with Si, it has been investigated as high-k materials to substitute SiO2 in CMOS device [12], [13], [14], [16]. In addition, previous study has reported the high-k material used as a switching material for RRAM meets the criteria for the possibility of ultra-high endurance as those shown in Hf–O and Ta–O systems [15]. However, there is lack of work in discussing the resistive switching property of Sm2O3 thin films. Hence, in this work, the resistive switching characteristic of Pt/Sm2O3/TiN structure is studied. The device exhibited stable repeatable bipolar switching behavior, and the resistance switching mechanism was discussed using a space–charge limited current model.
Section snippets
Experiment
The proposed resistive nonvolatile memories were fabricated as follows. The Sm2O3 thin films were deposited on TiN/SiO2/Si substrates at room temperature (RT) by an RF magnetron sputtering system using a Sm2O3 target (4″ in diameter, 99.999%). The sputtering was performed with a RF power of 120 W and in pure argon ambient with a working pressure of 8 mTorr. Finally, the Pt with a thickness of 200 nm was deposited on the Sm2O3 films by DC magnetron sputtering to complete the Pt/Sm2O3/TiN sandwiched
Results and discussion
The crystal structure of the Sm2O3 films was examined by X-ray diffraction (XRD). From the XRD spectra shown in Fig. 1a, the Sm2O3 films exhibited an obvious peak at about 53°, corresponding to the (622) textured orientation [17]. In order to investigate the composition of the resistance switching layer, the X-ray photoelectron spectroscopy (XPS) analysis is performed, and the binding energies have been calibrated by taking the carbon C 1s peak (285.0 eV) as reference. The XPS spectrum of Sm 3d
Conclusion
In conclusion, this study investigated the bipolar resistance switching characteristics of the Sm2O3 RRAM with the Pt/Sm2O3/TiN structure. The Sm2O3 thin films deposited by RF magnetron sputtering at room temperature are polycrystalline structure. The proposed memory device exhibits excellent resistance switching with a HRS/LRS ratio of about 2 orders during 104 cycles endurance test and the sequential 85 °C retention test for 104 s. In addition, the dominant conduction mechanisms of LRS and HRS
Acknowledgments
This work was performed at National Science Council Core Facilities Laboratory for Nano-Science and Nano-Technology in Kaohsiung-Pingtung area and was supported by the National Science Council of the Republic of China under Contract Nos. NSC-99-2120-M-110-001 and NSC 97-2112-M-110-009-MY3.
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