Enhanced resistive switching phenomena using low-positive-voltage format and self-compliance IrO x /GdO x /W cross-point memories
© Jana et al.; licensee Springer. 2014
Received: 20 November 2013
Accepted: 25 December 2013
Published: 8 January 2014
Enhanced resistive switching phenomena of IrO x /GdO x /W cross-point memory devices have been observed as compared to the via-hole devices. The as-deposited Gd2O3 films with a thickness of approximately 15 nm show polycrystalline that is observed using high-resolution transmission electron microscope. Via-hole memory device shows bipolar resistive switching phenomena with a large formation voltage of -6.4 V and high operation current of >1 mA, while the cross-point memory device shows also bipolar resistive switching with low-voltage format of +2 V and self-compliance operation current of <300 μA. Switching mechanism is based on the formation and rupture of conducting filament at the IrO x /GdO x interface, owing to oxygen ion migration. The oxygen-rich GdO x layer formation at the IrO x /GdO x interface will also help control the resistive switching characteristics. This cross-point memory device has also Repeatable 100 DC switching cycles, narrow distribution of LRS/HRS, excellent pulse endurance of >10,000 in every cycle, and good data retention of >104 s. This memory device has great potential for future nanoscale high-density non-volatile memory applications.
KeywordsRRAM GdO x Self-compliance Resistive switching
There is an increasing demand for next-generation high-density non-volatile memory devices because flash memories are approaching their scaling limits. Among many candidates to replace the flash memory devices, resistive random access memory (RRAM) is one of the promising candidates, owing to its simple metal-insulator-metal structure, fast switching speed, low-power operation, excellent scalability potential, and high density in crossbar structure [1–4]. Many switching materials such as TaO x [5–7], AlO x [8, 9], HfO x [10–15], TiO x [16, 17], NiO x [18–21], WO x [22, 23], ZnO x [24, 25], ZrO x [26–31], SrTiO3 [32, 33], SiO x [34, 35], and Pr0.7Ca0.3MnO3 [36, 37] have been studied by several groups. However, the rare-earth oxide such as Gd2O3 could be a promising resistive switching material because of its high resistivity, high dielectric permittivity (κ = 16), moderate energy gap (Eg = approximately 5.3 eV), and higher thermodynamic stability . Recently, many researchers have reported the resistive switching properties by using Gd2O3 materials [38–40]. Cao et al.  have reported unipolar resistive switching phenomena using Pt/Gd2O3/Pt structure with a high RESET current of 35 mA. Liu et al.  have also reported unipolar resistive switching phenomena with a high RESET current of 10 mA in Ti/Gd2O3/Pt structure. Yoon et al.  have reported resistive switching characteristics using MoO x /GdO x bilayer structure with a RESET current of 300 μA. It is found that non-uniform switching and high overshoot current are the main drawbacks for practical application of non-volatile RRAM using Gd2O3 material. Even though many structures using the Gd2O3 materials have been reported, however, the cross-point memory devices using IrO x /GdO x /W structure have not yet been reported. It is reported  that the cross-point structure has a great potential for high-density memory application in the near future.
In this study, we discussed resistive switching phenomena of IrO x /GdO x /W cross-point memory structure. For comparison, the IrO x /GdO x /W via-hole structure has been also investigated. The IrO x /GdO x /W via-hole memory devices exhibit negative switching polarity, whereas the IrO x /GdO x /W cross-point memory devices show positive switching polarity. Switching non-uniformity and high operation voltage/current of the via-hole devices are observed. To improve the switching uniformity and control the current overshoot, we have designed the IrO x /GdO x /W cross-point memory devices. In the cross-point structure, IrO x /GdO x /W memory device shows stable and uniform positive switching due to the formation of oxygen-rich interfacial layer at the IrO x /GdO x interface. The cross-point memory device has self-compliance bipolar resistive switching phenomena of consecutive 100 cycles with narrow distribution of high resistance state (HRS), low resistance state (LRS), good device-to-device uniformity, excellent P/E cycles of >10,000, and good data retention with resistance ratio of 100 after 104 s under a low operation voltage of ±3.5 V.
Results and discussion
Enhanced resistive switching characteristics using the IrO x /GdO x /W cross-point memory structure have been obtained. The HRTEM image shows a polycrystalline structure of the GdO x films. The switching mechanism is based on the formation and rupture of the conducting filament by oxygen ion migration, and the oxygen-rich GdO x layer formation at the IrO x /GdO x interface acts as a series resistance to control the current overshoot effect and improves the switching uniformity as compared to the via-hole devices. The cross-point memory device shows self-compliance bipolar resistive switching phenomena of consecutive 100 cycles with narrow distribution of LRS and HRS, excellent P/E cycles of >10,000, and good data retention of >104 s with resistance ratio >102 under low operation voltage of ±3 V. This memory device paves a way for future nanoscale high-density non-volatile memory applications.
DJ is a Ph.D. student since September 2010, and AP has received his Ph.D. degree on July 2013 under the instruction of Professor SM. SM has been an Associate Professor in the Department of Electronic Engineering, Chang Gung University since August 2009. YYC is a Ph.D. student in the Department of Materials Science and Engineering, National Taiwan University, under the instruction of Professor JRY. HCC has been a Professor in the Department of Electronic Engineering, Chang Gung University since August 2010.
This work was supported by the National Science Council (NSC) of Taiwan, under the contract no. NSC-102-2221-E-182-057-MY2.
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