市面電子產品所使用的非揮發性記憶體(Non-Volatile Memory,NVM)，屬於電荷儲存式(Charge trap)的快閃記憶體~(Flash)，生活中的電子裝置日趨輕薄短小，製程尺寸隨之微縮，此種記憶體因物理限制，記憶體將會產生判讀錯誤，而無法如期運作。電阻式記憶體(Resistive~Random-access Memory,RRAM)為研發中的新型
NVM，其結構由上、下電極中間夾儲存材料組成，擁有結構簡單以及低寫入電壓等特性，有望突破目前面臨的困境。有研究指出於絕緣層中摻雜金屬奈米粒子，可增進元件性能與穩定性，而DNA本身擁有雙股螺旋結構，對金屬離子有特殊親和力，可作為良好合成金屬奈米粒子之模板。
本篇論文主要分為兩部分，第一部分著重於DNA奈米複合物特性分析，以光還原法於DNA薄膜中合成金屬奈米粒子，並以穿透式電子顯微鏡(TEM)、小角度X光散射(SAXS)等量測，深入了解奈米粒子於DNA薄膜中生成之狀態。第二部分之主題為對元件進行特性分析，元件製程上，使用表面改質DNA(Deoxyribonucleic Acid)作為儲存層材料，並使用銀與ITO(Indium Tin Oxide)作為電極製成元件，組成三明治結構，其展現雙極電阻轉換，並擁有可複寫式記憶體(Rewritable memory)特性。為了分析元件之雙極行為和導通機制，以溫度控制量測及電極材料改變，推測電阻轉換之成因可能為儲存層中，金屬導通路徑之形成與斷裂所致，進一步調整元件限制電流與絕緣層薄膜厚度，以驗證電阻轉換之機制。

In the electronics market, most non-volatile memories (NVMs) are charge-trap flash. As electronic devices are getting thinner and smaller, NVMs will no longer meet the demand due to the physical limit of devices. Resistive random-access memory (RRAM), the structure of which is an insulator between the top and bottom electrode, emerges as an attractive alternative for storage applications. RRAM is a promising candidate to overcome the challenge because it has a simple structure and low switching voltage. Some studies have suggested that the inclusion of metal nanoparticles in the insulating layer can improve the performance and stability of the devices. In this regard, deoxyribonucleic acid (DNA) has a double helix structure, which has been shown to exhibit a special affinity for the metal ions and can be used as a template for the synthesis of metal nanoparticles.

In this thesis, we present our investigations on DNA-based nanocomposite materials and memory devices. The first part of the study is emphasized on the characterization of the DNA nanocomposite, which consists of metal nanoparticles in a DNA matrix synthesized by a photoreduction method. The synthesis process of nanoparticles within the DNA matrix under light irradiation is characterized by several methods, including transmission electron microscope (TEM) and small-angle X-ray scattering (SAXS), in order to fully characterize the properties of the nanocomposites. The second part of the study is focused on the electrical characterization of DNA-based memory devices. The surfactant modified DNA biopolymer sandwiched by two electrodes exhibits a bipolar resistive switching behavior and a rewritable memory feature. In order to further analyze the bipolar behavior and the conduction mechanism of the device, several measurements, including temperature-dependent and electrode-dependent characterizations, are carried out. The results suggest that the mechanism of the resistive switching may be due to the formation and rupture of the metal conduction path in the insulating layer. The effects of the compliance current and the thickness of the insulating film are also presented to explain the mechanism of resistive switching behavior.

[1]“Alpha-step profilometer,” https://goo.gl/Kiapui.
[2]“JEOL JSE 7000F Field Emission SEM,” https://goo.gl/po9D3z.
[3]“Transmission electron microscope,” https://goo.gl/tTVCTA.
[4] E. W. Lim and R. Ismail, “Conduction mechanism of valence change resistive switching memory: a survey,” Electronics 4, 586–613 (2015).
[5] M. F. Chang, P. F. Chiu, and S. S. Sheu, “Circuit design challenges in embedded memory and resistive RAM (RRAM) for mobile SoC and 3D-IC,” in “Proceedings of the 16th Asia and South Pacific Design Automation Conference,” (IEEE Press, 2011), pp. 197–203.
[6] C. H. Cheng, C. Y. Tsai, A. Chin, and F. Yeh, “High performance ultra-low energy RRAM with good retention and endurance,” in “Electron Devices Meeting (IEDM), 2010 IEEE International,” (2010), pp. 19–4.
[7] C. Ho, C. L. Hsu, C. C. Chen, J. T. Liu, C. S. Wu, C. C. Huang, C. Hu, and F. L. Yang, “9nm half-pitch functional resistive memory cell with < 1μA programming current using thermally oxidized sub-stoichiometric WOx film,” in “Electron Devices Meeting (IEDM),” (2010), pp. 19–1.
[8] M. J. Lee, C. B. Lee, D. Lee, S. R. Lee, M. Chang, J. H. Hur, Y. B. Kim, C. J. Kim, D. H. Seo, S. Seo et al., “A fast, high-endurance and scalable non-volatile memory device made from asymmetric Ta2O5-x/TaO2-x bilayer structures,” Nature materials 10, 625–630 (2011).
[9] A. C. Torrezan, J. P. Strachan, G. M. Ribeiro, and R. S. Williams, “Sub-nanosecond switching of a tantalum oxide memristor,” Nanotechnology 22, 485203 (2011).
[10] F. Argall, “Switching phenomena in titanium oxide thin films,” Solid-State Electronics 11, 535–541 (1968).
[11] W. Hiatt and T. Hickmott, “Bistable switching in niobium oxide diodes,” Applied Physics Letters 6, 106–108 (1965).
[12] J. Gibbons and W. Beadle, “Switching properties of thin NiO films,” Solid-State Electronics 7, 785–790 (1964).
[13] F. Pan, S. Gao, C. Chen, C. Song, and F. Zeng, “Recent progress in resistive random access memories, switching mechanisms, and performance, ” Materials Science and Engineering: R: Report 83, 1-59 (2014).
[14] C. Pearson, L. Bowen, M. W. Lee, A. L. Fisher, K. E. Linton, M. R. Bryce, and M. C. Petty, “Focused ion beam and field-emission microscopy of metallic filaments in memory devices based on thin films of an ambipolar organic compound consisting of oxadiazole, carbazole, and fluorene units,” Applied Physics Letters 102, 99_1 (2013).
[15] J. Sun, Q. Liu, H. Xie, X. Wu, F. Xu, T. Xu, S. Long, H. Lv, Y. Li, L. Sun et al., “In situ observation of nickel as an oxidizable electrode material for the solid-electrolyte-based resistive random access memory,” Applied Physics Letters 102, 053502 (2013).
[16] K. C. Kwon, M. J. Song, K. H. Kwon, H. V. Jeoung, D. W. Kim, G. S. Lee, J. P. Hong, and J. G. Park, “Nanoscale CuO solid-electrolyte-based conductive-bridging-random-access-memory cell operating multi-level-cell and 1selector1resistor,” Journal of Materials Chemistry C 3, 9540–9550 (2015).
[17] T. Tsuruoka, K. Terabe, T. Hasegawa, and M. Aono, “Forming and switching mechanisms of a cation-migration-based oxide resistive memory,” Nanotechnology 21, 425205 (2010).
[18] I. Valov, “Redox-based resistive switching memories (ReRAMs): electrochemical systems at the atomic scale,” ChemElectroChem 1, 26–36 (2014).
[19] B. K. You, W. I. Park, J. M. Kim, K. I. Park, H. K. Seo, J. Y. Lee, Y. S. Jung, and K. J. Lee, “Reliable control of filament formation in resistive memories by self-assembled nanoinsulators derived from a block copolymer,” ACS nano 8, 9492–9502 (2014).
[20] C. Chen, S. Gao, F. Zeng, G. Tang, S. Li, C. Song, H. Fu, and F. Pan, “Migration of interfacial oxygen ions modulated resistive switching in oxide-based memory devices,” Journal of Applied Physics 114, 014502 (2013).
[21] S. Y. Wang, C. W. Huang, D. Y. Lee, T. Y. Tseng, and T. C. Chang, “Multilevel resistive switching in Ti/CuxO/Pt memory devices,” Journal of Applied Physics 108, 114110 (2010).
[22] Y. E. Syu, T. C. Chang, T. M. Tsai, Y. C. Hung, K. C. Chang, M. J. Tsai, M. J. Kao, and S. M. Sze, “Redox reaction switching mechanism in RRAM device with Pt/CoSiOx/TiN structure,” IEEE Electron Device Letters 32, 545–547 (2011).
[23] Z. Yan and J. M. Liu, “Coexistence of high performance resistance and capacitance memory based on multilayered metal-oxide structures,” Scientific reports 3, 2482 (2013).
[24] Y. Yang, F. Pan, F. Zeng, and M. Liu, “Switching mechanism transition induced by annealing treatment in nonvolatile Cu/ZnO/Cu/ZnO/Pt resistive memory: from carrier trapping/detrapping to electrochemical metallization,” Journal of Applied Physics 106, 123705 (2009).
[25] L. Bozano, B. Kean, V. Deline, J. Salem, and J. Scott, “Mechanism for bistability in organic memory elements,” Applied Physics Letters 84, 607–609 (2004).
[26] L. D. Bozano, B. W. Kean, M. Beinhoff, K. R. Carter, P. M. Rice, and J. C. Scott, “Organic materials and thin-film structures for cross-point memory cells based on trapping in metallic nanoparticles,” Advanced Functional Materials 15, 1933–1939 (2005). [27] H. T. Lin, Z. Pei, and Y. J. Chan, “Carrier transport mechanism in a nanoparticle-incorporated organic bistable memory device,” IEEE electron device letters 28, 569-571 (2007)
[28] J. Y. Chen, C. L. Hsin, C. W. Huang, C. H. Chiu, Y. T. Huang, S. J. Lin, W. W. Wu, and L. J. Chen, “Dynamic evolution of conducting nanofilament in resistive
switching memories,” Nano letters 13, 3671–3677 (2013).
[29] K. M. Kim, D. S. Jeong, and C. S. Hwang, “Nanofilamentary resistive switching in binary oxide system; a review on the present statusand outlook,” Nanotechnology 22, 254002 (2011).
[30] F. C. Chiu, “A review on conduction mechanisms in dielectric films,” Advances in Materials Science and Engineering 2014 (2014).
[31] P. Murgatroyd, “Theory of space-charge-limited current enhanced by Frenkel effect,” Journal of Physics D: Applied Physics 3, 151 (1970).
[32] I. Valov and M. N. Kozicki, “Cation-based resistance change memory,” Journal of Physics D: Applied Physics 46, 074005 (2013).
[33] I. Valov, R. Waser, J. R. Jameson, and M. N. Kozicki, “Electrochemical metallization memories–fundamentals, applications, prospects,” Nanotechnology 22, 254003 (2011).
[34] N. F. Mott and E. A. Davis, Electronic processes in non-crystalline materials (OUP Oxford, 2012).
[35] M. P. Houng, Y. H. Wang, and W. J. Chang, “Current transport mechanism in trapped oxides: a generalized trap-assisted tunneling model,” Journal of applied physics 86, 1488–1491 (1999).
[36] J. C. Scott and L. D. Bozano, “Nonvolatile memory elements based on organic materials,” Advanced Materials 19, 1452–1463 (2007).
[37] Q. D. Ling, D. J. Liaw, C. Zhu, D. S. H. Chan, E. T. Kang, and K. G. Neoh, “Polymer electronic memories: materials, devices and mechanisms,” Progress in
Polymer Science 33, 917–978 (2008).
[38] D. Prime and S. Paul, “Overview of organic memory devices,” (2009).
[39] B. Cho, S. Song, Y. Ji, T. W. Kim, and T. Lee, “Organic resistive memory devices: performance enhancement, integration, and advanced architectures,” Advanced Functional Materials 21, 2806–2829 (2011).
[40] W. P. Lin, S. J. Liu, T. Gong, Q. Zhao, and W. Huang, “Polymer-based resistive memory materials and devices,” Advanced Materials 26, 570–606 (2014).
[41] T. Hickmott, “Low-frequency negative resistance in thin anodic oxide films,” Journal of Applied Physics 33, 2669–2682 (1962).
[42] T. Hickmott, “Electron emission, electroluminescence, and voltage-controlled negative resistance in Al–Al2O3–Au diodes,” Journal of Applied Physics 36, 1885–1896 (1965).
[43] J. Simmons and R. Verderber, “New conduction and reversible memory phenomena in thin insulating films,” in “Proceedings of the Royal Society of London A: Mathematical, Physical and Engineering Sciences,” , vol. 301 (The Royal Society, 1967), pp. 77–102.
[44] C. Hogarth and M. Zor, “Some observations of voltage-induced conductance changes in thin films of evaporated polyethylene,” Thin Solid Films 27, L5–L7 (1975).
[45] C. A. Hogarth and T. Iqbal, “The electroforming of thin films of polypropylene,” International Journal of Electronics 47, 349–353 (1979).
[46] G. Dearnaley, D. Morgan, and A. Stoneham, “A model for filament growth and
switching in amorphous oxide films,” Journal of Non-Crystalline Solids 4, 593–612 (1970).
[47] R. Sutherland, “A theory for negative resistance and memory effects in thin insulating films and its application to Au-ZnS-Au devices,” Journal of Physics D: Applied Physics 4, 468 (1971).
[48] R. Thurstans and D. Oxley, “The electroformed metal-insulator-metal structure: a comprehensive model,” Journal of Physics D: Applied Physics 35, 802 (2002).
[49] J. Niziol, M. Sniechowski, E. Hebda, M. Jancia, and J. Pielichowski, “Properties of DNA complexes with new cationic surfactants,” Journal of Characterization and Development of Novel Materials 3, 107 (2011).
[50] C. Y. Hung, “Conduction mechanism of optically controlled multiple switching operations in DNA biopolymer devices,” Master’s thesis, National Tsing Hua University (2016).
[51] A. Mezei, R. Pons, and M. C. Morán, “The nanostructure of surfactant–DNA complexes with different arrangements,” Colloids and Surfaces B: Biointerfaces 111, 663–671 (2013).
[52] Y. Li, S. Long, Q. Liu, H. Lü, S. Liu, and M. Liu, “An overview of resistive random access memory devices,” Chinese Science Bulletin 56, 3072–3078 (2011).
[53] “Mie theory calculator,” https://nanocomposix.com/pages/tools.
[54] V. Amendola, O. M. Bakr, and F. Stellacci, “A study of the surface plasmon resonance of silver nanoparticles by the discrete dipole approximation method: effect of shape, size, structure, and assembly,” Plasmonics 5, 85–97 (2010).
[55] Y. Zhang, H. Wu, Y. Bai, A. Chen, Z. Yu, J. Zhang, and H. Qian, “Study of conduction and switching mechanisms in Al/AlOx/WOx/W resistive switching memory for multilevel applications,” Applied Physics Letters 102, 233502 (2013).
[56] M. Lagrange, D. Langley, G. Giusti, C. Jiménez, Y. Bréchet, and D. Bellet, “Optimization of silver nanowire-based transparent electrodes: effects of density, size and thermal annealing,” Nanoscale 7, 17410–17423 (2015).
[57] H. Sun, Q. Liu, C. Li, S. Long, H. Lv, C. Bi, Z. Huo, L. Li, and M. Liu, “Direct observation of conversion between threshold switching and memory switching induced by conductive filament morphology,” Advanced Functional Materials 24, 5679–5686 (2014).
[58] G. Wang, C. Li, Y. Chen, Y. Xia, D. Wu, and Q. Xu, “Reversible voltage dependent transition of abnormal and normal bipolar resistive switching,” Scientific Reports 6, 36953 (2016).
[59] R. Kaur, J. Kaur, and S. Tripathi, “Effect of Ag doping and insulator buffer layer on the memory mechanism of polymer nanocomposites,” Solid-State Electronics 109, 82–89 (2015).
[60] J. Chen and D. Ma, “Performance improvement by charge trapping of doping fluorescent dyes in organic memory devices,” Journal of applied physics 100, 034512
(2006).
[61] J. Chen, L. Xu, J. Lin, Y. Geng, L. Wang, and D. Ma, “Negative differential resistance effect in organic devices based on an anthracene derivative,” Applied physics letters 89, 083514 (2006).
[62] B. Jiao, Z. Wu, Q. He, Y. Tian, G. Mao, and X. Hou, “Dependence of the organic nonvolatile memory performance on the location of ultra-thin Ag film,” Journal of Physics D: Applied Physics 43, 035101 (2010).