The emerging nonvolatile memory, three-dimensional vertical resistive random-access memory (VRRAM), inspired by the vertical NAND structure, has been proposed to replace NAND flash memory which has reached its integration limit. To improve the vertical ionic diffusion occurring in the conventional VRRAM structure, we propose a Pt/HfO2/TiO2/Ti self-aligned VRRAM with physically confined switching cells through sidewall thermal oxidation. We achieved stable bipolar switching, endurance (>104 cycles), and retention (>104 s) responses, and improved the interlayer leakage current issue through a distinctive self-aligned structure. Additionally, we elucidated the switching mechanism by analyzing current levels concerning ambient temperature. To utilize VRRAM for neuromorphic computing, the biological synaptic functions are emulated by applying pulse stimulation to the synaptic cell. The weight modulation of biological synapses is demonstrated based on potentiation, depression, spike-rate-dependent plasticity, and spike-timing-dependent plasticity. Additionally, we improve the pattern recognition rate by creating a linear conductance modulation with an incremental pulse train in pattern recognition simulations. The stable electrical characteristics and implementation of various synaptic functions demonstrate that self-aligned VRRAM is suitable for neuromorphic systems as a high-density synaptic device.
. [J]. Frontiers of Physics, 2024, 19(6): 63203.
Subaek Lee, Juri Kim, Sungjun Kim. Self-aligned TiOx-based 3D vertical memristor for a high-density synaptic array. Front. Phys. , 2024, 19(6): 63203.
Monzio Compagnoni C. , Goda A. , S. Spinelli A. , Feeley P. , L. Lacaita A. , Visconti A. . Reviewing the evolution of the NAND flash technology. Proc. IEEE, 2017, 105(9): 1609 https://doi.org/10.1109/JPROC.2017.2665781
Pavan P. , Bez R. , Olivo P. , Zanoni E. . Flash memory cells ‒ An overview. Proc. IEEE, 1997, 85(8): 1248 https://doi.org/10.1109/5.622505
4
Micheloni R. , Crippa L. , Zambelli C. , Olivo P. . Architectural and integration options for 3D NAND flash memories. Computers, 2017, 6(3): 27 https://doi.org/10.3390/computers6030027
5
H. Hsiao Y. , T. Lue H. , C. Chen W. , P. Chang K. , H. Shih Y. , Y. Tsui B. , Y. Hsieh K. , Y. Lu C. . Modeling the impact of random grain boundary traps on the electrical behavior of vertical gate 3D NAND flash memory devices. IEEE Trans. Electron Dev., 2014, 61(6): 2064 https://doi.org/10.1109/TED.2014.2318716
H. Lee G. , Hwang S. , Yu J. , Kim H. . Architecture and process integration overview of 3D nand flash technologies. Appl. Sci. (Basel), 2021, 11(15): 6703 https://doi.org/10.3390/app11156703
8
Goda A., 3-D NAND technology achievements and future scaling perspectives, IEEE Trans. Electron Dev. 67(4), 1373 (2020)
9
Y. Lu C. . Future prospects of NAND flash memory technology-the evolution from floating gate to charge trapping to 3D stacking. J. Nanosci. Nanotechnol., 2012, 12(10): 7604 https://doi.org/10.1166/jnn.2012.6650
10
S. Kim S. , K. Yong S. , Kim W. , Kang S. , W. Park H. , J. Yoon K. , S. Sheen D. , Lee S. , S. Hwang C. . Review of semiconductor flash memory devices for material and process issues. Adv. Mater., 2023, 35(43): 2370310 https://doi.org/10.1002/adma.202370310
11
S. Meena J. , M. Sze S. , Chand U. , Y. Tseng T. . Overview of emerging nonvolatile memory technologies. Nanoscale Res. Lett., 2014, 9(1): 526 https://doi.org/10.1186/1556-276X-9-526
12
K. Upadhyay N. , Jiang H. , Wang Z. , Asapu S. , Xia Q. , Joshua Yang J. . Emerging memory devices for neuromorphic computing. Adv. Mater. Technol., 2019, 4(4): 1800589 https://doi.org/10.1002/admt.201800589
13
Molas G. , Nowak E. . Advances in emerging memory technologies: From data storage to artificial intelligence. Appl. Sci. (Basel), 2021, 11(23): 11254 https://doi.org/10.3390/app112311254
14
K. Lee J. , Kim S. . Comparative analysis of low-frequency noise based resistive switching phenomenon for filamentary and interfacial RRAM devices. Chaos Solitons Fractals, 2023, 173: 113633 https://doi.org/10.1016/j.chaos.2023.113633
15
Endoh T. , Koike H. , Ikeda S. , Hanyu T. , Ohno H. . An overview of nonvolatile emerging memories-spintronics for working memories. IEEE J. Emerg. Sel. Top. Circuits Syst., 2016, 6(2): 109 https://doi.org/10.1109/JETCAS.2016.2547704
16
Zahoor F. , Z. Azni Zulkifli T. , A. Khanday F. . Resistive random access memory (RRAM): An overview of materials, switching mechanism, performance, multilevel cell (MLC) storage, modeling, and applications. Nanoscale Res. Lett., 2020, 15(1): 90 https://doi.org/10.1186/s11671-020-03299-9
17
Heo J. , Cho Y. , Ji H. , H. Kim M. , H. Lee J. , K. Lee J. , Kim S. . Noise-assisted transport mechanism analysis and synaptic characteristics in ZrOx/HfAlOx-based memristor for neuromorphic systems. APL Mater., 2023, 11(11): 111103 https://doi.org/10.1063/5.0175587
18
Shen Z. , Zhao C. , Qi Y. , Xu W. , Liu Y. , Z. Mitrovic I. , Yang L. , Zhao C. . Advances of RRAM devices: Resistive switching mechanisms, materials and bionic synaptic application. Nanomaterials (Basel), 2020, 10(8): 1437 https://doi.org/10.3390/nano10081437
19
Ju D. , Kim S. , Kim S. . Highly uniform resistive switching characteristics of Ti/TaOx/ITO memristor devices for neuromorphic system. J. Alloys Compd., 2023, 961: 170920 https://doi.org/10.1016/j.jallcom.2023.170920
20
T. Li Y. , B. Long S. , Liu Q. , B. Lü H. , Liu S. , Liu M. . An overview of resistive random access memory devices. Chin. Sci. Bull., 2011, 56(28−29): 3072 https://doi.org/10.1007/s11434-011-4671-0
21
B. Roldán J. , Miranda E. , Maldonado D. , N. Mikhaylov A. , V. Agudov N. , A. Dubkov A. , N. Koryazhkina M. , B. González M. , A. Villena M. , Poblador S. , Saludes-Tapia M. , Picos R. , Jiménez-Molinos F. , G. Stavrinides S. , Salvador E. , J. Alonso F. , Campabadal F. , Spagnolo B. , Lanza M. , O. Chua L. . Variability in resistive memories. Adv. Intell. Syst., 2023, 5(6): 2200338 https://doi.org/10.1002/aisy.202200338
22
Stasner P. , Kopperberg N. , Schnieders K. , Hennen T. , Wiefels S. , Menzel S. , Waser R. , J. Wouters D. . Reliability effects of lateral filament confinement by nano-scaling the oxide in memristive devices. Nanoscale Horiz., 2024, 9(5): 764 https://doi.org/10.1039/D3NH00520H
23
Fang Y. , Yu Z. , Wang Z. , Zhang T. , Yang Y. , Cai Y. , Huang R. . Improvement of HfOx-based RRAM device variation by inserting ALD TiN buffer layer. IEEE Electron Device Lett., 2018, 39(6): 819 https://doi.org/10.1109/LED.2018.2831698
24
C. Chen Y. , F. Chang Y. , Wu X. , Zhou F. , Guo M. , Y. Lin C. , C. Hsieh C. , Fowler B. , C. Chang T. , C. Lee J. . Dynamic conductance characteristics in HfOx-based resistive random access memory. RSC Adv., 2017, 7(21): 12984 https://doi.org/10.1039/C7RA00567A
25
K. Li H. , P. Chen T. , G. Hu S. , Liu P. , Liu Y. , S. Lee P. , P. Wang X. , Y. Li H. , Q. Lo G. . Study of multilevel high-resistance states in HfOx-based resistive switching random access memory by impedance spectroscopy. IEEE Trans. Electron Dev., 2015, 62(8): 2684 https://doi.org/10.1109/TED.2015.2445339
26
L. Urquiza M. , M. Islam M. , C. T. Van Duin A. , Cartoixà X. , Strachan A. . Atomistic insights on the full operation cycle of a HfO2-based resistive random access memory cell from molecular dynamics. ACS Nano, 2021, 15(8): 12945 https://doi.org/10.1021/acsnano.1c01466
27
De Stefano F. , Houssa M. , V. Afanas’Ev V. , A. Kittl J. , Jurczak M. , Stesmans A. . Nature of the filament formed in HfO2-based resistive random access memory. Thin Solid Films, 2013, 533: 15 https://doi.org/10.1016/j.tsf.2012.12.097
28
Hardtdegen A. , La Torre C. , Cuppers F. , Menzel S. , Waser R. , Hoffmann-Eifert S. . Improved switching stability and the effect of an internal series resistor in HfO2/TiOx bilayer ReRAM cells. IEEE Trans. Electron Dev., 2018, 65(8): 3229 https://doi.org/10.1109/TED.2018.2849872
29
Ban S. , Kim O. . Improvement of switching uniformity in HfOx-based resistive random access memory with a titanium film and effects of titanium on resistive switching behaviors. Jpn. J. Appl. Phys., 2014, 53(6S): 06JE15 https://doi.org/10.7567/JJAP.53.06JE15
30
J. Huang Y. , H. Shen T. , H. Lee L. , Y. Wen C. , C. Lee S. . Low-power resistive random access memory by confining the formation of conducting filaments. AIP Adv., 2016, 6(6): 065022 https://doi.org/10.1063/1.4954974
31
Y. Liu H. , L. Hsu Y. , X. Zheng Y. . Investigation of oxygen deficiency-rich/oxygen deficiency-poor stacked TiO2 based resistive random access memory by mist chemical vapor deposition. Ceram. Int., 2022, 48(19): 28881 https://doi.org/10.1016/j.ceramint.2022.04.038
32
Bousoulas P. , Giannopoulos I. , Asenov P. , Karageorgiou I. , Tsoukalas D. . Investigating the origins of high multilevel resistive switching in forming free Ti/TiO2−x-based memory devices through experiments and simulations. J. Appl. Phys., 2017, 121(9): 094501 https://doi.org/10.1063/1.4977063
33
Park J. , Jung S. , Lee J. , Lee W. , Kim S. , Shin J. , Hwang H. . Resistive switching characteristics of ultra-thin TiOx. Microelectron. Eng., 2011, 88(7): 1136 https://doi.org/10.1016/j.mee.2011.03.050
34
Yu Y. , Yang F. , Mao S. , Zhu S. , Jia Y. , Yuan L. , Salmen M. , Sun B. . Effect of anodic oxidation time on resistive switching memory behavior based on amorphous TiO2 thin films device. Chem. Phys. Lett., 2018, 706: 477 https://doi.org/10.1016/j.cplett.2018.06.063
35
Kim J. , H. Choi J. , Kim S. , Choi C. , Kim S. . Transition of short-term to long-term memory of Cu/TaOx/CNT conductive bridge random access memory for neuromorphic engineering. Carbon, 2023, 215: 118438 https://doi.org/10.1016/j.carbon.2023.118438
36
H. Kim C. , Lim S. , Y. Woo S. , M. Kang W. , T. Seo Y. , T. Lee S. , Lee S. , Kwon D. , Oh S. , Noh Y. , Kim H. , Kim J. , H. Bae J. , H. Lee J. . Emerging memory technologies for neuromorphic computing. Nanotechnology, 2019, 30(3): 032001 https://doi.org/10.1088/1361-6528/aae975
37
A. Makarov V. , A. Lobov S. , Shchanikov S. , Mikhaylov A. , B. Kazantsev V. . Toward reflective spiking neural networks exploiting memristive devices. Front. Comput. Neurosci., 2022, 16: 859874 https://doi.org/10.3389/fncom.2022.859874
38
N. Matsukatova A. , V. Prudnikov N. , A. Kulagin V. , Battistoni S. , A. Minnekhanov A. , D. Trofimov A. , A. Nesmelov A. , A. Zavyalov S. , N. Malakhova Y. , Parmeggiani M. , Ballesio A. , L. Marasso S. , N. Chvalun S. , A. Demin V. , V. Emelyanov A. , Erokhin V. . Combination of organic-based reservoir computing and spiking neuromorphic systems for a robust and efficient pattern classification. Adv. Intell. Syst., 2023, 5(6): 2200407 https://doi.org/10.1002/aisy.202200407
39
Park J. , H. Kim T. , Kwon O. , Ismail M. , Mahata C. , Kim Y. , Kim S. , Kim S. . Implementation of convolutional neural network and 8-bit reservoir computing in CMOS compatible VRRAM. Nano Energy, 2022, 104: 107886 https://doi.org/10.1016/j.nanoen.2022.107886
40
Yu S. , Y. Chen H. , Gao B. , Kang J. , S. P. Wong H. . HfOx-based vertical resistive switching random access memory suitable for bit-cost-effective three-dimensional cross-point architecture. ACS Nano, 2013, 7(3): 2320 https://doi.org/10.1021/nn305510u
41
Al-Haddad A. , Wang C. , Qi H. , Grote F. , Wen L. , Bernhard J. , Vellacheri R. , Tarish S. , Nabi G. , Kaiser U. , Lei Y. . Highly-ordered 3D vertical resistive switching memory arrays with ultralow power consumption and ultrahigh density. ACS Appl. Mater. Interfaces, 2016, 8(35): 23348 https://doi.org/10.1021/acsami.6b05424
42
Jiang Z. , Qin S. , Li H. , Fujii S. , Lee D. , Wong S. , S. P. Wong H. . Next-generation ultrahigh-density 3-D vertical resistive switching memory (VRSM)-Part II: Design guidelines for device, array, and architecture. IEEE Trans. Electron Dev., 2019, 66(12): 5147 https://doi.org/10.1109/TED.2019.2950595
43
Kim H. , Lee J. , W. Kim H. , Woo J. , H. Kim M. , H. Lee S. . Definition of a localized conducting path via suppressed charge injection in oxide memristors for stable practical hardware neural networks. ACS Appl. Mater. Interfaces, 2023, 15(44): 51444 https://doi.org/10.1021/acsami.3c13514
44
S. Kim S. , K. Yong S. , Kim J. , M. Choi J. , W. Park T. , Y. Kim H. , J. Kim H. , S. Hwang C. . Fabrication of a hole-type vertical resistive-switching random-access array and intercell interference induced by lateral charge spreading. Adv. Electron. Mater., 2023, 9(3): 2200998 https://doi.org/10.1002/aelm.202200998
45
A. Mojarad S. , P. Goss J. , S. K. Kwa K. , Zhou Z. , A. S. Al-Hamadany R. , J. R. Appleby D. , K. Ponon N. , Oneill A. . Leakage current asymmetry and resistive switching behavior of SrTiO3. Appl. Phys. Lett., 2012, 101(17): 173507 https://doi.org/10.1063/1.4764544
46
Ali S. , Bae J. , H. Lee C. , P. Kobayashi N. , Shin S. , Ali A. . Resistive switching device with highly asymmetric current-voltage characteristics: A solution to backward sneak current in passive crossbar arrays. Nanotechnology, 2018, 29(45): 455201 https://doi.org/10.1088/1361-6528/aadd6f
47
C. Chen Y.C. Lin C.T. Hu S.Y. Lin C.Fowler B.Lee J., A novel resistive switching identification method through relaxation characteristics for sneak-path-constrained selectorless RRAM application, Sci. Rep. 9(1), 12420 (2019)
48
Yu M. , Cai Y. , Wang Z. , Fang Y. , Liu Y. , Yu Z. , Pan Y. , Zhang Z. , Tan J. , Yang X. , Li M. , Huang R. . Novel vertical 3D structure of TaOx-based RRAM with self-localized switching region by sidewall electrode oxidation. Sci. Rep., 2016, 6(1): 21020 https://doi.org/10.1038/srep21020
49
A. Koroleva A.S. Kuzmichev D.G. Kozodaev M.V. Zabrosaev I.V. Korostylev E.M. Markeev A., CMOS-compatible self-aligned 3D memristive elements for reservoir computing systems, Appl. Phys. Lett. 122(2), 022905 (2023)
50
Lee K. , Park K. , J. Lee H. , S. Song M. , C. Lee K. , Namkung J. , H. Lee J. , Park J. , C. Chae S. . Enhanced ferroelectric switching speed of Si-doped HfO2 thin film tailored by oxygen deficiency. Sci. Rep., 2021, 11(1): 6290 https://doi.org/10.1038/s41598-021-85773-7
51
Xie W. , Li R. , Xu Q. . Enhanced photocatalytic activity of Se-doped TiO2 under visible light irradiation. Sci. Rep., 2018, 8(1): 8752 https://doi.org/10.1038/s41598-018-27135-4
52
A. Khera E. , Mahata C. , Imran M. , A. Niaz N. , Hussain F. , A. Khalil R. , Rasheed U. . Improved resistive switching characteristics of a multi-stacked HfO2/Al2O3/HfO2 RRAM structure for neuromorphic and synaptic applications: Experimental and computational study. RSC Adv., 2022, 12(19): 11649 https://doi.org/10.1039/D1RA08103A
53
Wang Q. , Niu G. , Roy S. , Wang Y. , Zhang Y. , Wu H. , Zhai S. , Bai W. , Shi P. , Song S. , Song Z. , H. Xie Y. , G. Ye Z. , Wenger C. , Meng X. , Ren W. . Interface-engineered reliable HfO2-based RRAM for synaptic simulation. J. Mater. Chem. C, 2019, 7(40): 12682 https://doi.org/10.1039/C9TC04880D
54
Y. Wang S. , W. Huang C. , Y. Lee D. , Y. Tseng T. , C. Chang T. . Multilevel resistive switching in Ti/CuxO/Pt memory devices. J. Appl. Phys., 2010, 108(11): 114110 https://doi.org/10.1063/1.3518514
55
Stoliar P. , Levy P. , J. Sanchez M. , G. Leyva A. , A. Albornoz C. , Gomez-Marlasca F. , Zanini A. , Toro Salazar C. , Ghenzi N. , J. Rozenberg M. . Nonvolatile multilevel resistive switching memory cell: A transition metal oxide-based circuit. IEEE Trans. Circuits Syst. II Express Briefs, 2014, 61(1): 21 https://doi.org/10.1109/TCSII.2013.2290921
56
H. Chen P. , Y. Lin C. , C. Chang T. , K. Eshraghian J. , T. Chao Y. , D. Lu W. , M. Sze S. . Investigating selectorless property within niobium devices for storage applications. ACS Appl. Mater. Interfaces, 2022, 14(1): 2343 https://doi.org/10.1021/acsami.1c20460
57
H. Chen K. , M. Tsai T. , M. Cheng C. , J. Huang S. , C. Chang K. , P. Liang S. , F. Young T. . Schottky emission distance and barrier height properties of bipolar switching Gd: SiOx RRAM devices under different oxygen concentration environments. Materials (Basel), 2017, 11(1): 43 https://doi.org/10.3390/ma11010043
58
Li Y. , Zhong Y. , Zhang J. , Xu L. , Wang Q. , Sun H. , Tong H. , Cheng X. , Miao X. . Activity-dependent synaptic plasticity of a chalcogenide electronic synapse for neuromorphic systems. Sci. Rep., 2014, 4(1): 4906 https://doi.org/10.1038/srep04906
59
Chen J. , Zhu C. , Cao G. , Liu H. , Bian R. , Wang J. , Li C. , Chen J. , Fu Q. , Liu Q. , Meng P. , Li W. , Liu F. , Liu Z. . Mimicking neuroplasticity via ion migration in van der Waals layered Copper indium thiophosphate. Adv. Mater., 2022, 34(25): 2104676 https://doi.org/10.1002/adma.202104676
60
Ismail M. , Abbas H. , Sokolov A. , Mahata C. , Choi C. , Kim S. . Emulating synaptic plasticity and resistive switching characteristics through amorphous Ta2O5 embedded layer for neuromorphic computing. Ceram. Int., 2021, 47(21): 30764 https://doi.org/10.1016/j.ceramint.2021.07.257
