Impact of electrically formed interfacial layer and improved memory characteristics of IrOx/high-κx/W structures containing AlOx, GdOx, HfOx, and TaOx switching materials
© Prakash et al.; licensee Springer. 2013
Received: 9 July 2013
Accepted: 15 August 2013
Published: 6 September 2013
Improved switching characteristics were obtained from high-κ oxides AlOx, GdOx, HfOx, and TaOx in IrOx/high-κx/W structures because of a layer that formed at the IrOx/high-κx interface under external positive bias. The surface roughness and morphology of the bottom electrode in these devices were observed by atomic force microscopy. Device size was investigated using high-resolution transmission electron microscopy. More than 100 repeatable consecutive switching cycles were observed for positive-formatted memory devices compared with that of the negative-formatted devices (only five unstable cycles) because it contained an electrically formed interfacial layer that controlled ‘SET/RESET’ current overshoot. This phenomenon was independent of the switching material in the device. The electrically formed oxygen-rich interfacial layer at the IrOx/high-κx interface improved switching in both via-hole and cross-point structures. The switching mechanism was attributed to filamentary conduction and oxygen ion migration. Using the positive-formatted design approach, cross-point memory in an IrOx/AlOx/W structure was fabricated. This cross-point memory exhibited forming-free, uniform switching for >1,000 consecutive dc cycles with a small voltage/current operation of ±2 V/200 μA and high yield of >95% switchable with a large resistance ratio of >100. These properties make this cross-point memory particularly promising for high-density applications. Furthermore, this memory device also showed multilevel capability with a switching current as low as 10 μA and a RESET current of 137 μA, good pulse read endurance of each level (>105 cycles), and data retention of >104 s at a low current compliance of 50 μA at 85°C. Our improvement of the switching characteristics of this resistive memory device will aid in the design of memory stacks for practical applications.
KeywordsResistive switching W/TaOx Ti nanolayer Oxygen ion migration Nanofilament
Resistive random access memory (RRAM) with a simple metal-insulator-metal structure shows promising characteristics in terms of scalability, low power operation, and multilevel data storage capability and is suitable for next-generation memory applications[1–4]. RRAM devices with simple structure and easy fabrication process that are compatible with high-density 3D integration will be needed in the future. Various oxide switching materials such as HfOx[6–9], TaOx[3, 10–15], AlOx[16–19], GdOx, TiOx[21–23], NiOx[24, 25], ZrOx[26–29], ZnO[30–32], SiOx, and GeOx[34–36] have been used in nanoscale RRAM applications. However, their nonuniform switching and poorly understood switching mechanisms are currently the bottlenecks for the design of nanoscale resistive switching memory. Generally, inert metal electrodes and various interfacial methods are used to improve resistive switching memory characteristics. We previously reported polarity-dependent improved memory characteristics using IrOx nanodots (NDs) in an IrOx/AlOx/IrOx-NDs/AlOx/W structure. However, improved memory performance using different high-κ oxide switching materials such as AlOx, GdOx, HfOx, and TaOx in IrOx/high-κx/W structures has not been reported yet. Using different high-κ oxides in the same structure may reveal a unique way to design novel RRAM devices for practical applications. Electrical formation of an interfacial layer at the IrOx/high-κx interface is important to improve resistive switching memory characteristics. Using this approach, high-density memory could be achieved using an IrOx/AlOx/W cross-point structure, which we also report here.
In this study, we show that the electrically formed oxygen-rich interfacial layer at the IrOx/high-κx interface in an IrOx/high-κx/W structure plays an important role in improving the resistive switching memory characteristics of the structure. The positive-formatted(PF) devices exhibited more switching cycles compared to the negative-formatted (NF) ones and do not depend on the switching material. When the pristine resistive memory device is formed using positive polarity bias on the TE, it is termed as PF, while the negative voltage-formed device is termed as an NF device. PF devices with similar switching behavior are obtained using different high-κ oxide films of AlOx, GdOx, HfOx, and TaOx. The switching mechanism is the formation/oxidation of oxygen vacancies in a conducting filament by controlling the migration of oxygen ions through the electrically formed interfacial layer. This unique phenomenon helps to design high-density cross-point memory using an IrOx/AlOx/W structure. This cross-point memory was forming-free, exhibiting 1,000 consecutive ‘dc’ cycles at a current compliance (CC) of <200 μA and a small operation voltage of ±2 V, highly uniform switching (yield >95%) with multilevel capability (at least four different levels of low resistance state (LRS)). The device can be switched even using a very small current of 10 μA, which makes it useful for low power applications. The surface morphology and roughness of the structure were observed by atomic force microscopy (AFM). The device size and interfaces of layers were investigated by transmission electron microscopy (TEM). These observations show that the improved performance of this device structure can be attributed to the electrically formed O-rich interfacial layer at the top electrode/filament interface. The devices have also shown good read endurance of >105 cycles and data retention at 85°C under a low CC of 50 μA.
Results and discussion
Improved resistive switching characteristics independent of switching material are observed for IrOx/high-κx/W stacks with a via-hole structure fabricated by positive formation because they contain an electrically formed interfacial layer. High-κ oxides AlOx, GdOx, HfOx, and TaOx were used as switching materials, and similar switching behavior with improved switching uniformity was obtained because overshoot current was minimized in the via-hole structure. AFM images revealed that the BEs of cross-point devices had a higher surface roughness than that of the via-hole devices, which facilitated forming-free switching, improving the switching characteristics. Excellent resistive switching was obtained in Ir/AlOx/W cross-point structures using the same PF via-hole design. These devices showed forming-free resistive switching with excellent switching uniformity (>95% yield) over 1,000 dc cycles (approximately 1,000 ac cycles) under low operation voltage/current of ±2 V/200 μA. Multilevel LRSs were obtained by controlling the CCs from 10 to 200 μA with a pulse read endurance of >105 cycles for each level and data retention at room temperature and 85°C under a low CC of 50 μA. This study reveals a route to design nanoscale nonvolatile memory with improved characteristics.
This work was supported by the National Science Council (NSC), Taiwan, under contract number: NSC-101-2221-E-182-061. The authors thank Electronic and Optoelectronic Research Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan, for their partially experimental support.
- Waser R, Dittmann R, Staikov G, Szot K: Redox-based resistive switching memories-nanoionic mechanisms, prospects, and challenges. Adv Mater 2009, 21: 2632. 10.1002/adma.200900375View Article
- Sawa A: Resistive switching in transition metal oxides. Mater Today 2008, 11: 28.View Article
- Lee MJ, Lee CB, Lee D, Lee SR, Chang M, Hur JH, Kim YB, Kim CJ, Seo DH, Seo S, Chung UI, Yoo IK, Kim K: A fast, high-endurance and scalable non-volatile memory device made from asymmetric Ta2O(5-x)/TaO(2-x)bilayer structures. Nat Mater 2011, 10: 625. 10.1038/nmat3070View Article
- Liu Q, Sun J, Lv H, Long S, Yin K, Wan N, Li Y, Sun L, Liu M: Real-time observation on dynamic growth/dissolution of conductive filaments in oxide-electrolyte-based ReRAM. Adv Mater 1844, 2012: 24.
- Yu S, Chen HY, Gao B, Kang J, Wong HSP: HfOx-based vertical resistive switching random access memory suitable for bit-cost-effective three-dimensional cross-point architecture. ACS Nano 2013, 7: 2320. 10.1021/nn305510uView Article
- Lee HY, Chen PS, Liu WH, Wang SM, Gu PY, Hsu YY, Tsai CH, Chen WS, Chen F, Tsai MJ, Lien C: Robust high-resistance state and improved endurance of HfOxresistive memory by suppression of current overshoot. IEEE Electron Device Lett 2011, 32: 1585.View Article
- Yu S, Guan X, Wong HSP: Conduction mechanism of TiN/HfOx/Pt resistive switching memory: a trap-assisted-tunneling model. Appl Phys Lett 2011, 99: 063507. 10.1063/1.3624472View Article
- Chen YY, Goux L, Clima S, Govoreanu B, Degraeve R, Kar GS, Fantini A, Groeseneken G, Wouters DJ, Jurczak M: Endurance/retention trade-off on HfO2/ metal cap1T1R bipolar RRAM. IEEE Trans Electron Dev 2013, 60: 1114.View Article
- Lee J, Bourim EM, Lee W, Park J, Jo M, Jung S, Shin J, Hwang H: Effect of ZrOx/HfOxbilayer structure on switching uniformity and reliability in nonvolatile memory applications. Appl Phys Lett 2010, 97: 172105. 10.1063/1.3491803View Article
- Rahaman SZ, Maikap S, Tien TC, Lee HY, Chen WS, Chen F, Kao MJ, Tsai MJ: Excellent resistive memory characteristics and switching mechanism using a Ti nanolayer at the Cu/TaOxinterface. Nanoscale Res Lett 2012, 7: 345. 10.1186/1556-276X-7-345View Article
- Prakash A, Maikap S, Lai CS, Lee HY, Chen WS, Chen F, Kao MJ, Tsai MJ: Improvement uniformity of resistive switching parameters by selecting the electroformation polarity in IrOx/TaOx/WOx/W structure. Jpn J Appl Phys 2012, 51: 04DD06.View Article
- Chen C, Song C, Yang J, Zeng F, Pan F: Oxygen migration induced resistive switching effect and its thermal stability in W/TaO x /Pt structure. Appl Phys Lett 2012, 100: 253509. 10.1063/1.4730601View Article
- Prakash A, Maikap S, Chiu HC, Tien TCS, Lai CS: Enhanced resistive switching memory characteristics and mechanism using a Ti nanolayer at the W/TaOx interface. Nanoscale Res Lett 2013, 8: 288. 10.1186/1556-276X-8-288View Article
- Ninomiya T, Wei Z, Muraoka S, Yasuhara R, Katayama K, Takagi T: Conductive filament scaling of TaOx bipolar ReRAM for improving data retention under low operation current. IEEE Trans Electron Dev 2013, 60: 1384.View Article
- Yang JJ, Zhang MX, Strachan JP, Miao F, Pickett MD, Kelley RD, Medeiros-Ribeiro G, Williams RS: High switching endurance in TaOx memristive devices. Appl Phys Lett 2010, 97: 232102. 10.1063/1.3524521View Article
- Banerjee W, Maikap S, Lai CS, Chen YY, Tien TC, Lee HY, Chen WS, Chen FT, Kao MJ, Tsai MJ, Yang JR: Formation polarity dependent improved resistive switching memory characteristics using nanoscale (1.3 nm) core-shell IrOx nano-dots. Nanoscale Res Lett 2012, 7: 194. 10.1186/1556-276X-7-194View Article
- Banerjee W, Maikap S, Rahaman SZ, Prakash A, Tien TC, Li WC, Yang JR: Improved resistive switching memory characteristics using core-shell IrOx nano-dots in Al2O3/WOx bilayer structure. J Electrochem Soc 2012, 159: H177. 10.1149/2.067202jesView Article
- Wu Y, Yu S, Lee B, Wong P: Low-power TiN/Al2O3/Pt resistive switching device with sub-20 μA switching current and gradual resistance modulation. J Appl Phys 2011, 110: 094104. 10.1063/1.3657938View Article
- Fang RC, Sun QQ, Zhou P, Yang W, Wang PF, Zhang DW: High-performance bilayer flexible resistive random access memory based on low-temperature thermal atomic layer deposition. Nanoscale Res Lett 2013, 8: 92. 10.1186/1556-276X-8-92View Article
- Jana D, Maikap S, Tien TC, Lee HY, Chen WS, Chen FT, Kao MJ, Tsai MJ: Formation-polarity-dependent improved resistive switching memory performance using IrOx/GdOx/WOx/W structure. Jpn J Appl Phys 2012, 51: 04DD17.View Article
- Yang L, Kuegeler C, Szot K, Ruediger A, Waser R: The influence of copper top electrodes on the resistive switching effect in TiO2thin films studied by conductive atomic force microscopy. Appl Phys Lett 2009, 95: 013109. 10.1063/1.3167810View Article
- Yang JJ, Pickett MD, Li X, Ohlberg DAA, Stewart DR, Williams RS: Memristive switching mechanism for metal/oxide/metal nanodevices. Nat Nanotechnol 2008, 3: 429. 10.1038/nnano.2008.160View Article
- Park J, Biju KP, Jung S, Lee W, Lee J, Kim S, Park S, Shin J, Hwang H: Multibit operation of TiOx-based ReRAM by Schottky barrier height engineering. IEEE Electron Dev Lett 2011, 32: 476.View Article
- Lee SR, Char K, Kim DC, Jung R, Seo S, Li XS, Park GS, Yoo IK: Resistive memory switching in epitaxially grown NiO. Appl Phys Lett 2007, 91: 202115. 10.1063/1.2815658View Article
- Ielmini D, Nardi F, Cagli C: Physical models of size-dependent nanofilament formation and rupture in NiO resistive switching memories. Nanotechnology 2011, 22: 254022. 10.1088/0957-4484/22/25/254022View Article
- Guan W, Long S, Jia R, Liu M: Nonvolatile resistive switching memory utilizing gold nanocrystals embedded in zirconium oxide. Appl Phys Lett 2007, 91: 062111. 10.1063/1.2760156View Article
- Wang SY, Lee DY, Tseng TY, Lin CY: Effects of Ti top electrode thickness on the resistive switching behaviors of rf-sputtered ZrO2memory films. Appl Phys Lett 2009, 95: 112904. 10.1063/1.3231872View Article
- Li Y, Long S, Lv H, Liu Q, Wang Y, Zhang S, Lian W, Wang M, Zhang K, Xie H, Liu S, Liu M: Improvement of resistive switching characteristics in ZrO2film by embedding a thin TiO x layer. Nanotechnology 2011, 22: 254028. 10.1088/0957-4484/22/25/254028View Article
- Lin CC, Chang YP, Lin HB, Lin CH: Effect of non-lattice oxygen on ZrO2-based resistive switching memory. Nanoscale Res Lett 2012, 7: 187. 10.1186/1556-276X-7-187View Article
- Chiu FC, Li PW, Chang WY: Reliability characteristics and conduction mechanisms in resistive switching memory devices using ZnO thin films. Nanoscale Res Lett 2012, 7: 178. 10.1186/1556-276X-7-178View Article
- Peng CN, Wang CW, Chan TC, Chang WY, Wang YC, Tsai HW, Wu WW, Chen LJ, Chueh YL: Resistive switching of Au/ZnO/Au resistive memory: an in situ observation of conductive bridge formation. Nanoscale Res Lett 2012, 7: 559. 10.1186/1556-276X-7-559View Article
- Younis A, Chu D, Li S: Bi-stable resistive switching characteristics inTi-doped ZnO thin films. Nanoscale Res Lett 2013, 8: 154. 10.1186/1556-276X-8-154View Article
- Liu CY, Huang JJ, Lai CH, Lin CH: Influence of embedding Cu nano-particles into a Cu/SiO2/Pt structure on its resistive switching. Nanoscale Res Lett 2013, 8: 156. 10.1186/1556-276X-8-156View Article
- Rahaman SZ, Maikap S, Chen WS, Lee HY, Chen FT, Kao MJ, Tsai MJ: Repeatable unipolar/bipolar resistive memory characteristics and switching mechanism using a Cu nanofilament in a GeOx film. Appl Phys Lett 2012, 101: 073106. 10.1063/1.4745783View Article
- Cheng CH, Chin A, Yeh FS: Ultralow switching energy Ni/GeOx/HfON/TaN RRAM. IEEE Electron Dev Lett 2011, 32: 366.View Article
- Prakash A, Maikap S, Rahaman SZ, Majumdar S, Manna S, Ray SK: Resistive switching memory characteristics of Ge/GeO x nanowires and evidence of oxygen ion migration. Nanoscale Res Lett 2013, 8: 220. 10.1186/1556-276X-8-220View Article
- Banerjee W, Maikap S, Tien TC, Li WC, Yang JR: Impact of metal nano layer thickness on tunneling oxide and memory performance of core-shell iridium-oxide nanocrystals. J Appl Phys 2011, 110: 074309. 10.1063/1.3642961View Article
- Michaelson HB: The work function of the elements and its periodicity. J Appl Phys 1977, 48: 4729. 10.1063/1.323539View Article
- Prakash A, Maikap S, Lai CS, Tien TC, Chen WS, Lee HY, Chen FT, Kao MJ, Tsai MJ: Bipolar resistive switching memory using bilayer TaOx/WOx films. Solid-State Electron 2012, 77: 35.View Article
- Long S, Cagli C, Ielmini D, Liu M, Sune J: Analysis and modeling of resistive switching statistics. J Appl Phys 2012, 111: 074508. 10.1063/1.3699369View Article
- Long S, Cagli C, Ielmini D, Liu M, Suñé J: Reset statistics of NiO-based resistive switching memories. IEEE Electron Dev Lett 2011, 32: 1570.View Article
- Liu Q, Long S, Wang W, Tanachutiwat S, Li Y, Wang Q, Zhang M, Huo Z, Chen J, Liu M: Low-power and highly uniform switching in ZrO2-Based ReRAM with a Cu nanocrystal insertion layer. IEEE Electron Dev Lett 2010, 31: 1299.
- Liu Q, Long S, Lv H, Wang W, Niu J, Huo Z, Chen J, Liu M: Controllable growth of nanoscale conductive filaments in solid-electrolyte-based ReRAM by using a metal nanocrystal covered bottom electrode. ACS Nano 2010, 4: 6162. 10.1021/nn1017582View Article
- Lee HY, Chen YS, Chen PS, Gu PY, Hsu YY, Wang SM, Liu WH, Tsai CH, Sheu SS, Chiang PC, Lin WP, Lin CH, Chen WS, Chen FT, Lien CH, Tsai MJ: Evidence and solution of over-RESET problem for HfOx based resistive memory with sub-ns switching speed and high endurance. Tech Dig - Int Electron Dev Meet 2010, 19. 7.1 7.1
- Torrezan AC, Strachan JP, Medeiros-Ribeiro G, Williams RS: Sub-nanosecond switching of a tantalum oxide memristor. Nanotechnology 2011, 22: 485203. 10.1088/0957-4484/22/48/485203View Article
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.