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为了研究阻变存储器导电细丝的形成位置和分布规律, 使用X射线光电子能谱研究了Ti/HfO2/Pt阻变存储器件单元中Hf 4f的空间分布, 得到了阻变层的微结构信息. 通过I-V测试, 得到该器件单元具有典型的阻变特性; 通过针对Hf 4f的不同深度测试, 发现处于低阻态时, 随着深度的增加, Hf4+化学组分单调地减小; 而处于高阻态和未施加电压前, 该组分呈现波动分布; 通过Hf4+在高阻态和低阻态下组分含量以及电子能损失谱分析, 得到高阻态下Hf4+组分的平均含量要高于低阻态; 另外, 高阻态和低阻态下的O 1s谱随深度的演变也验证了Hf4+的变化规律. 根据实验结果, 提出了局域分布的氧空位聚簇可能是造成这一现象的原因. 空位簇间的链接和断裂决定了导电细丝的形成和消失. 由于导电细丝容易在氧空位缺陷聚簇的地方首先形成, 这一研究为导电细丝的发生位置提供了参考.The origin of the resistance switching behavior in HfO2 is explained in terms of filament formation/rupture under an applied voltage. In order to investigate the position and process of conductive filament in resistive switching memory, the resistive switching and chemical structure of Ti/HfO2/Pt memory device are studied. Through current-voltage measurement, typical resistive switching behavior is observed in Ti/HfO2/Pt device cells; through detecting Hf 4f with different depths by using X-ray photoelectron spectroscopy. It is observed that the Hf4+ decreases monotonically with depth increasing towards HfO2/Pt interface in low resistance state, while a fluctuation distribution of Hf4+ is shown in high resistance state and in the pristine Ti/HfO2/Pt device. The concentration of Hf4+ in high resistance state is higher than that in low resistance state, which is confirmed by measuring the electron energy loss spectrum. Additionally, the O 1s spectrum shows a similar result consistent with the Hf 4f one. The above result is explained by the existence of locally accumulated oxygen vacancies in the oxide bulk layer in high resistance state and pristine states. It is proposed that the oxygen vacancy clusters dominantly determine the resistivity by the connecting/rupture between the neighbor cluster sites in the bulk. The cluster defects are the preexisting structural distortion/injure by charge trapping defects due to the fixed charge which could confine the nucleation of oxygen vacancies and bigger distortion could be enhanced or recovered via the transportation of oxygen vacancies under the external voltage. Oxygen vacancies are driven away from the clusters under SET electrical stimulus, and then recover back to original cluster sites under RESET process.#br#The previous presumption of the ideal evenly-distributed state for oxygen vacancies in the bulk of resistance random access memories (RRAMs) device leads to an issue about where the filaments occur/form first since the oxygen vacancy defects show uniform distribution in the active oxide bulk layer. Since the conductive filament is easily formed in the cluster region of oxygen vacancies, this study could provide a deep understanding of the formation of conductive filament in RRAMs device.
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Keywords:
- hafnium oxide /
- oxygen vacancy /
- conductive filament /
- resistive switching memory
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[1] Sawa A 2008 Mater. Today 11 28
[2] Waser R, Dittmann R, Staikov G, Szot K 2009 Adv. Mater. 21 2632
[3] Liu D Q, Cheng H F, Zhu X, Wang N N, Zhang C Y 2014 Acta Phys. Sin. 63 187301 (in Chinese) [刘东青, 程海峰, 朱玄, 王楠楠, 张朝阳 2014 63 187301]
[4] Shang D S, Sun J R, Shen B G 2013 Chin. Phys. B 22 067202
[5] Zhang T, Bai Y, Jia C H, Zhang W F 2012 Chin. Phys. B 21 107304
[6] Zhang T, Yin J, Zhao G F, Zhang W F, Xia Y D, Liu Z G 2014 Chin. Phys. B 23 087304
[7] Jiang R, Wu Z, Du X, Han Z, Sun W 2015 Appl. Phys. Lett. 107 013502
[8] Dong Z K, Duan S K, Hu X F, Wang L D 2014 Acta Phys. Sin. 63 128502 (in Chinese) [董哲康, 段书凯, 胡小方, 王丽丹 2014 63 128502]
[9] Li Y T, Long S B, L H B, Liu Q, Wang Q, Wang Y, Zhang S, Lian W T, Liu S, Liu M 2011 Chin. Phys. B 20 017305
[10] Jiang R, Li Z 2008 Appl. Phys. Lett. 92 012919
[11] Chen R, Zhou L W, Wang J Y, Chen C J, Shao X L, Jiang H, Zhang K L, L L R, Zhao J S 2014 Acta Phys. Sin. 63 067202 (in Chinese) [陈然, 周立伟, 王建云, 陈长军, 邵兴隆, 蒋浩, 张楷亮, 吕联荣, 赵金石 2014 63 067202]
[12] Chen Y N, Xu Z, Zhao S L, Yin F F, Zhang C W, Jiao B Y, Dong Y H 2011 Chin. Phys. B 20 127303
[13] Jiang R, Xie E, Wang Z 2007 J. Mater. Sci. 42 7343
[14] Miao F, Strachan J P, Yang J J, Zhang M X, Goldfarb I, Torrezan A C, Eschbach P, Kelley R D, Medeiros-Ribeiro G, Williams R S 2011 Adv. Mater. 47 5633
[15] Kim S, Lee D, Park J, Jung S, Lee W, Shin J, Woo J, Choi G, Hwang C 2012 Nanotechnology 32 325702
[16] Jiang R, Xie E, Chen Z, Zhang Z 2006 Appl. Surf. Sci. 253 2421
[17] Liu Q, Sun J, Lv H B, Long S, Yin K B, Wan N, Li Y T, Sun L, Liu M 2012 Adv. Mater. 24 1844
[18] Lin Y S, Zeng F, Tang S G, Liu H Y, Chen C, Gao S, Wang Y G, Pan F 2013 J. Appl. Phys. 113 064510
[19] Jiang R, Xie E, Wang Z 2006 Appl. Phys. Lett. 89 142907
[20] Morant C, Galan L, Sanz J M 1990 Surf. Interface Anal. 112 304
[21] Muller D A, Nakagawa N, Ohtomo A, Grazul J L, Hwang H Y 2004 Nature 430 657
[22] Leisegang T, Stocker H, Levin A, Weibach T, Zschornak M, Gutmann E, Rickers K, Gemming S, Meyer D 2009 Phys. Rev. Lett. 102 087601
[23] Jiang W, Noman M, Lu Y M, Bain J A, Salvador P A, Skowronski M 2011 J. Appl. Phys. 110 034509
[24] Park C, Seo Y, Jung J, Kim D W 2008 J. Appl. Phys. 103 054106
[25] Chen Y S, Chen B, Gao B, Chen L P, Lian G L, Liu L F, Wang Y, Liu X Y, Kang J F 2011 Appl. Phys. Lett. 99 072113
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