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铁电材料的极化翻转特性是铁电存储器实现“0, 1”信息读写的物理基础, 因此极化翻转的稳定性直接决定器件的服役可靠性. 在交变电场循环载荷下, HfO2基新型铁电薄膜存在唤醒(wake-up)、疲劳(fatigue)和极化翻转电流峰分裂(split-up)等极化翻转不稳定现象, 严重制约了其在铁电存储器件中的实际应用. 探明极化翻转行为复杂演变的微观机制, 从而提出优化稳定性的可行措施是目前工作的重难点, 但是基于传统测试手段的研究难以解决上述问题. 一阶回转曲线图谱法被誉为迟滞系统研究中的“指纹鉴定”, 已在磁性材料特征参数演变规律的解析中得到成功应用. 本文首先介绍一阶回转曲线图谱法的基本原理和实现方法, 接着以Si掺杂HfO2铁电薄膜为实验对象, 利用该方法获得了薄膜内电畴极化翻转特征临界场的分布密度随外场加载历史的演变, 为理解铁电材料的极化翻转行为提供了重要的微观物理机理信息.
From physical point of view, the “0, 1” read/write operation of ferroelectric memory is based on the polarization switching of ferroelectric memory. Therefore, the reliability of device relies directly on the stability of polarization switching behavior. The polarization behaviors of HfO2-based ferroelectric thin films subjected to bipolar cyclic electric field often exhibit wake-up, fatigue and split-up of transient switching current. These unstable switching properties seriously restrict the practical application of this new-type ferroelectric material in memory devices. It therefore becomes the critical task to explore the mechanism behind the complex evolution of polarization switching and find out possible approaches to optimizing the stability. However, it will be extremely difficult to accomplish the task by the traditional characterization methods. First-order reversal curve (FORC) diagram is regarded as “fingerprint identification” in the study of hysteresis systems, and has been used successfully to analyze the characteristic parameters of magnetic materials. The FORC diagram can intuitively determine the type, size and domain status of magnetic particles from distribution of both coercive field and interaction field. Moreover, it is also found that the FORC diagram is sensitive to measuring temperature. In this work, first, the Preisach model and implementation method of the FORC diagram are introduced. Then using Keithley 4200-SCS equipped with a remote pulse measurement unit, 60 FORCs are recorded for Si-doped HfO2 ferroelectric thin films experiencing different external field loading histories. By the mathematical treatment, switching density distributions determined by FORC measurements are obtained to explore the evolution of coercive field and bias field. The FORC diagram of pristine film contains three distribution regions with different bias fields, which merge into one distribution with an almost zero bias field after 104 wake-up cycles. Two oppositely biased regions can be observed after 2 × 109 sub-cycling treatments. Surprisingly, the bias fields nearly vanish again after 104 wake-up cycles. The main change of bias field instead of coercive field indicates that the migration of oxygen vacancies is likely to be the dominant mechanism behind the complex polarization switching behavior for HfO2-based ferroelectric thin films. -
Keywords:
- first-order reversal curve diagram /
- ferroelectric thin film /
- hafnium oxide /
- polarization switching
[1] 钟维烈 1996 铁电体物理学 (北京: 科学出版社) 第1页
Zhong W L 1996 Ferroelectric Physics (Beijing: Science Press) p1 (in Chinese)
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Zhang Q 2011 Ph. D. Dissertation (Changchun: Jilin University) (in Chinese)
[3] 孙静 2012 博士学位论文 (湘潭: 湘潭大学)
Sun J 2012 Ph. D. Dissertation (Xiangtan: Xiangtan University) (in Chinese)
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图 1 以铁电材料为例的Preisach模型示意图 (a) 电畴单元对外电场的极化翻转响应; (b) 材料对外电场的总极化响应
Fig. 1. Schematic diagrams of Preisach model for ferroelectric materials: (a) Polarization switching response of a domain element to applied electric field; (b) total polarization switching response of materials to applied electric field.
图 2 铁电材料的一阶回转曲线测试方法和一阶回转曲线测试图谱获得原理示意 (a) 施加的扫描电场, 回转场Er从正向饱和电场(Esat)逐渐过渡到负向饱和电场(–Esat); (b) P-E一阶回转曲线示意图; (c) 计算得到的实验Preisach密度的几何解释(灰色部分)
Fig. 2. Outline of first-order reversal curve (FORC) measurement method for ferroelectric materials and approach of getting FORC diagram: (a) Sweep of the reversal field (Er) from positive saturation electric field (Esat) to negative saturation electric field (–Esat); (b) schematic of the measured P-E first-order reversal curves; (c) geometric interpretation of calculated experimental Preisach density (the gray area).
图 3 FORC测试前期准备 (a) 测试电路示意图; (b) 两个电极直径450 μm的已击穿测试点的I-V曲线; (c) 直径200 μm测试点的小信号C-E特性曲线
Fig. 3. Preparation for FORC measurement: (a) Schematic of measurement circuit; (b) I-V curve of two broken-down test points with an electrode diameter of 450 μm; (c) small signal C-E characteristic curve of a test point with an electrode diameter of 200 μm
图 4 wake-up处理后Si掺杂HfO2铁电薄膜的FORC实测图 (a) 实际测得的I-E瞬态电流响应曲线; (b) 利用Matlab软件对瞬态电流I进行简单积分得到的P-E曲线; (c), (d)以E和Er为坐标的三维和二维分布密度图谱; (e), (f)以Ebias和Ec为坐标的三维和二维分布密度图谱
Fig. 4. FORC measurement of Si doped HfO2 ferroelectric thin films after wake-up treatment: (a) Measured I-E transient current response curves; (b) P-E curves obtained by simple integration of transient current I by using MATLAB software; (c) three- and (d) two-dimensional diagrams of distribution density with E and Er as coordinates; (e) three- and (f) two-dimensional diagrams of distribution density with Ebias and Ec as coordinates.
图 5 10 nm厚Si:HfO2铁电薄膜在循环电场载荷下的P-E电滞回线和I-E瞬态电流曲线的演变 (a), (b)初始未极化样品在3 MV/cm, 1 kHz电场循环加载下的wake-up效应; 对wake-up处理后的样品施加2 MV/cm, 50 kHz的循环电场, (c), (d)在2 MV/cm, 1 kHz电场下测试观察到的fatigue效应, (e), (f)在3.5 MV/cm, 1 kHz电场下测试观察到的split-up效应; 上方插图展示了具体的电场循环和测试顺序
Fig. 5. Evolution of P-E/I-E hysteresis loops of 10 nm thick Si:HfO2 ferroelectric thin films subjected to bipolar electric field cycling. (a), (b) Wake-up effect observed for pristine sample subjected to 3 MV/cm and 1 kHz bipolar field cycling. For woken-up sample subjected to 2 MV/cm and 50 kHz, (c), (d) fatigue effect monitored by 2 MV/cm and 1 kHz field, (e), (f) split-up effect monitored by 3.5 MV/cm and 1 kHz field. Details of cycling and measurement sequences are shown on top of the figures.
图 6 Si掺杂HfO2铁电薄膜的FORC翻转密度分布 (a) 初始未极化样品; (b) 经3 MV/cm, 1 kHz电场循环加载104次唤醒处理后的样品; (c) 经过2 × 109次2 MV/cm, 50 kHz低场亚循环后的样品; (d) 再次经4 × 104次3 MV/cm, 1 kHz唤醒处理后的样品. 第二行中的P-E电滞回线和I-E曲线示意图分别对应于各自翻转密度分布的极大值(如灰色箭头所示). 第三行相应地显示了各状态下实测得到的P-E电滞回线和I-E曲线
Fig. 6. FORC switching density distribution of Si:HfO2 ferroelectric thin films: (a) Pristine sample; (b) after 104 cycles of 3 MV/cm and 1 kHz wake-up treatment; (c) after 2 × 109 cycles of 2 MV/cm and 50 kHz sub-cycling; (d) after 4 × 104 cycles of 3 MV/cm and 1 kHz wake-up treatment again. The schematic P-E hysteresis loops and I-E curves in the second row correspond to the maxima (as shown by the gray arrow) of their respective switching density distributions. The third row shows the measured P-E hysteresis loop and I-E curve correspondingly.
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[1] 钟维烈 1996 铁电体物理学 (北京: 科学出版社) 第1页
Zhong W L 1996 Ferroelectric Physics (Beijing: Science Press) p1 (in Chinese)
[2] 张芹 2011 博士学位论文 (长春: 吉林大学)
Zhang Q 2011 Ph. D. Dissertation (Changchun: Jilin University) (in Chinese)
[3] 孙静 2012 博士学位论文 (湘潭: 湘潭大学)
Sun J 2012 Ph. D. Dissertation (Xiangtan: Xiangtan University) (in Chinese)
[4] Böscke T S, Müller J, Bräuhaus D, Schröder U, Böttger U 2011 Appl. Phys. Lett. 99 102903
Google Scholar
[5] Sang X, Grimley E D, Schenk T, Schroeder U, LeBeau J M 2015 Appl. Phys. Lett. 106 162905
Google Scholar
[6] Park M H, Lee Y H, Kim H J, Kim Y J, Moon T, Kim K D, Muller J, Kersch A, Schroeder U, Mikolajick T, Hwang C S 2015 Adv. Mater. 27 1811
Google Scholar
[7] Xu L, Nishimura T, Shibayama S, Yajima T, Migita S, Toriumi A 2016 Appl. Phys. Express 9 091501
Google Scholar
[8] Starschich S, Boettger U 2017 J. Mater. Chem. C 5 333
Google Scholar
[9] Huang F, Chen X, Liang X, Qin J, Zhang Y, Huang T, Wang Z, Peng B, Zhou P, Lu H, Zhang L, Deng L, Liu M, Liu Q, Tian H, Bi L 2017 Phys. Chem. Chem. Phys. 19 3486
Google Scholar
[10] Starschich S, Griesche D, Schneller T, Böttger U 2015 ECS J. Solid State Sci. Technol. 4 419
Google Scholar
[11] Zhou D Y, Xu J, Li Q, Guan Y, Cao F, Dong X, Müller J, Schenk T, Schröder U 2013 Appl. Phys. Lett. 103 192904
Google Scholar
[12] Zhou D Y, Guan Y, Vopson M M, Xu J, Liang H L, Cao F, Dong X L, Mueller J, Schenk T, Schroeder U 2015 Acta Mater. 99 240
Google Scholar
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Google Scholar
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Google Scholar
[15] Pike C, Fernandez A 1999 J. Appl. Phys. 85 6668
Google Scholar
[16] Roberts A P, Pike C R, Verosub K L 2000 J. Geophys. Res. B: Solid Earth 105 28461
Google Scholar
[17] Roberts A P, Liu Q, Rowan C J, Chang L, Carvallo C, Torrent J, Horng C S 2006 J. Geophys. Res. B: Solid Earth 111 B12S35
Google Scholar
[18] Pan Y, Petersen N, Winklhofer M, Davila A F, Liu Q, Frederichs T, Hanzlik M, Zhu R 2005 Earth Planet. Sci. Lett. 237 311
Google Scholar
[19] Carvallo C, Muxworthy A R, Dunlop D J 2006 Phys. Earth Planet. Inter. 154 308
Google Scholar
[20] Cima L, Laboure E, Muralt P 2002 Rev. Sci. Instrum. 73 3546
Google Scholar
[21] Stancu A, Ricinschi D, Mitoseriu L, Postolache P, Okuyama M 2003 Appl. Phys. Lett. 83 3767
Google Scholar
[22] Piazza D, Stoleriu L, Mitoseriu L, Stancu A, Galassi C 2006 J. Eur. Ceram. Soc. 26 2959
Google Scholar
[23] Stancu A, Mitoseriu L, Stoleriu L, Piazza D, Galassi C, Ricinschi D, Okuyama M 2006 Physica B 372 226
Google Scholar
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Google Scholar
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Google Scholar
[26] Ricinschi D, Mitoseriu L, Stancu A, Postolache P, Okuyama M 2010 Integr. Ferroelectr. 67 103
Google Scholar
[27] Mayergoyz I D 1991 Mathematical Models of Hysteresis (New York: Springer-Verlag) pp18−20
[28] Olsen T, Schröder U, Müller S, Krause A, Martin D, Singh A, Müller J, Geidel M, Mikolajick T 2012 Appl. Phys. Lett. 101 082905
Google Scholar
[29] Stefan Mueller, Johannes Müller, Schroeder U 2013 IEEE Trans. Device Mater. Reliab. 13 93
Google Scholar
[30] Schenk T, Schroeder U, Pesic M, Popovici M, Pershin Y V, Mikolajick T 2014 ACS Appl. Mater. Interfaces 6 19744
Google Scholar
[31] Yurchuk E, Müller J, Knebel S, Sundqvist J, Graham A P, Melde T, Schröder U, Mikolajick T 2013 Thin Solid Films 533 88
Google Scholar
[32] Hoffmann M, Schroeder U, Schenk T, Shimizu T, Funakubo H, Sakata O, Pohl D, Drescher M, Adelmann C, Materlik R, Kersch A, Mikolajick T 2015 J. Appl. Phys. 118 072006
Google Scholar
[33] Hyuk Park M, Joon Kim H, Jin Kim Y, Lee W, Moon T, Seong Hwang C 2013 Appl. Phys. Lett. 102 242905
Google Scholar
[34] Hoffmann M, Schenk T, Kulemanov I, Adelmann C, Popovici M, Schroeder U, Mikolajick T 2015 Ferroelectrics 480 16
Google Scholar
[35] Weinreich W, Reiche R, Lemberger M, Jegert G, Müller J, Wilde L, Teichert S, Heitmann J, Erben E, Oberbeck L, Schröder U, Bauer A J, Ryssel H 2009 Microelectron. Eng. 86 1826
Google Scholar
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Google Scholar
[37] Starschich S, Menzel S, Böttger U 2016 Appl. Phys. Lett. 108 032903
Google Scholar
[38] Fengler F P G, Pešić M, Starschich S, Schneller T, Künneth C, Böttger U, Mulaosmanovic H, Schenk T, Park M H, Nigon R, Muralt P, Mikolajick T, Schroeder U 2017 Adv. Electron. Mater. 3 1600505
Google Scholar
[39] Park M H, Kim H J, Kim Y J, Lee Y H, Moon T, Kim K D, Hyun S D, Hwang C S 2015 Appl. Phys. Lett. 107 192907
Google Scholar
[40] Grimley E D, Schenk T, Sang X, Pešić M, Schroeder U, Mikolajick T, LeBeau J M 2016 Adv. Electron. Mater. 2 1600173
Google Scholar
[41] Kim H J, Park M H, Kim Y J, Lee Y H, Moon T, Kim K D, Hyun S D, Hwang C S 2016 Nanoscale 8 1383
Google Scholar
[42] Park M H, Kim H J, Kim Y J, Lee Y H, Moon T, Kim K D, Hyun S D, Fengler F, Schroeder U, Hwang C S 2016 ACS Appl. Mater. Interfaces 8 15466
Google Scholar
[43] Lomenzo P D, Takmeel Q, Zhou C, Fancher C M, Lambers E, Rudawski N G, Jones J L, Moghaddam S, Nishida T 2015 J. Appl. Phys. 117 134105
Google Scholar
[44] Lomenzo P D, Richter C, Mikolajick T, Schroeder U 2020 ACS Appl. Electron. Mater. 2 1583
Google Scholar
[45] Lomenzo P D, Slesazeck S, Hoffmann M, Mikolajick T, Max B 2019 19th Non-Volatile Memory Technology Symposium (NVMTS) Durham, United States, October 28−30, 2019 p19467083
[46] Li S D, Zhou D Y, Shi Z X, Hoffmann M, Mikolajick T, Schroeder U 2021 ACS Appl. Electron. Mater. 3 2415
Google Scholar
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