本論文將探討金屬元素摻雜於氧化亞銅應用於電阻式記憶體之研究。在一般情況下，摻雜金屬元素，會使得氧化亞銅產生更多缺陷。當金屬元素摻雜於氧化亞銅薄膜時，只要其缺陷的能階差很小，就會在其薄膜以及晶界處產生其它額外的缺陷，這種現象會使得在能隙內產生更多能階。因此，電子可以藉由較小的操作電壓跳躍於不同的缺陷，達到載子傳輸。
在此項研究中，三種在pH=9條件下電鍍的氧化亞銅作為電阻式記憶體之主動層。分別為無摻雜氧化亞銅、摻雜鈉以及摻雜銻之氧化亞銅。使用三電極沉積系統進行電化學沉積，而Ag/AgCl和Pt分別用作參考電極以及輔助電極，透明導電玻璃ITO基板則用作工作電極。將電鍍儀以定電壓-0.4伏並以水浴法將電解液溫度保持在60°C予以電鍍沉積。使用場發射掃描式電子顯微鏡、X光繞射光譜儀、能量色散光譜儀以及化學分析電子光譜儀(ESCA)分析薄膜材料特性。半導體參數分析儀用於電阻式記憶體電流電壓測量。其中，三者參數在Forming步驟上皆屬於Forming-free。在100次電壓循環操作下，無摻雜氧化亞銅、摻雜鈉之氧化亞銅和摻雜銻之氧化亞銅分別有0.3 ~ 3.2V, 0.2 ~ 2V和0.8 ~ 2.9V的Set電壓區間以及0.8~1.9V, 1.2~1.8V和1.6~2.2V的Reset電壓區間。其高低阻態比(HRS/LRS ratio)無摻雜氧化亞銅、摻雜鈉之氧化亞銅和摻雜銻之氧化亞銅分別有1.0，2.0以及1.6個數量級；記憶體保存力(Endurance)其阻態比值，無摻雜氧化亞銅、摻雜鈉之氧化亞銅和摻雜銻之氧化亞銅分別有1.3，2.0以及1.7個數量級。本實驗數據指出，摻雜鈉之氧化亞銅不但在Set/Reset電壓有最小的區間，且在其耐操度和資料保存力上也有最好的特性。本實驗中的兩個不同金屬摻雜氧化亞銅薄膜確實改善了電阻式記憶體的電性特性。
沉積氧化亞銅薄膜運用簡易且方便電鍍方式，此方式與CMOS製程過程相容。Forming-free、較低的Set/Reset操作電壓以及功耗較低等優勢，相信優化過後的摻雜鈉之氧化亞銅作為電阻式記憶體於未來記憶體的應用上會有很大的潛力。

This thesis studies the efforts of metal elements doping in cuprous oxide (Cu2O) for its application to resistive random access memory (RRAM). Doping, in general, can result in more defects in cuprous oxide. When metal is doped into a cuprous oxide thin film, additional defects in the film as well as at grains’ boundaries will be generated, which could generate many energy levels within the forbidden bandgap, as long as the energy level difference of the defects is small enough, the electrons can easily transport via hopping the different defect sites with the help of a small bias voltage.
In this study, three types of cuprous oxide electroplated at a condition of pH=9 were used as the RRAM active layer. Three types of precursor solutions were prepared for undoped Cu2O (Un-Cu2O), Na-doped Cu2O (Cu2O_Na) and Sb-doped Cu2O (Cu2O_Sb). Electrodeposition was carried out by using three-electrode electrodeposition system, whereas Ag/AgCl and Pt were used as a reference electrode and a counter electrode respectively. The ITO substrate was used as a working electrode. The deposition was potentiostatically controlled at a voltage of -0.4V, and the electrolyte temperature during the deposition process was maintained at 60°C using a water bath. The deposited film properties were analyzed using scanning electron microscope, X-ray diffractor, energy dispersive spectometer, and X-ray photoelectron spectroscopy. Semiconductor device parameter analyzer was used for RRAM’s current-voltage measurements.
All three RRAMs have the characteristic of forming free. The range of set voltages, evaluated 100 cycles, of the Un-Cu2O, Cu2O_Na and Cu2O¬_Sb RRAMs are 0.3~3.2V, 0.2~2V and 0.8~2.9V, respectively. The ranges of the reset voltages of the Un-Cu2O, Cu2O_Na and Cu2O¬_Sb RRAM are 0.8~1.9V, 1.2~1.8V and 1.6~2.2V, respectively. The high and low resistance ratio (HRS/LRS) of the Un-Cu2O, Cu2O_Na and Cu2O¬_Sb are about 1.0, 2.0 and 1.6 orders of magnitude, respectively. The high and low resistance ratio in retention of the Un-Cu2O, Cu2O_Na and Cu2O¬_Sb are about 1.1, 2.0 and 1.3 orders of magnitude, respectively. The data indicates that the Cu2O_Na RRAM exhibits not only the smallest set and reset voltages range, but also has better performance in endurance and retention. The two different metal doped Cu2O films do improve the electrical properties and performance of the RRAM devices.
Electroplating of Cu2O film is a simple process and compatible with CMOS manufacturing process. Forming free and lower set/rest voltages consume low power in RRAM operations. It is believed that an optimized Na doped Cu2O film has the potential to be used in the future for RRAM applications.

[1] Dekker, Rob, Frans Beenker, and Loek Thijssen. "Fault modeling and test algorithm development for static random access memories." International Test Conference 1988 Proceeding@ m_New Frontiers in Testing. IEEE, 1988.
[2]Kim, Yoongu, et al. "Flipping bits in memory without accessing them: An experimental study of DRAM disturbance errors." ACM SIGARCH Computer Architecture News 42.3 (2014): 361-372.
[3] Yuan, Jack H., et al. "Dense vertical programmable read only memory cell structure and processes for making them." U.S. Patent No. 5,343,063. 30 Aug. 1994.
[4] Bez, Roberto, et al. "Introduction to flash memory." Proceedings of the IEEE 91.4 (2003): 489-502.
[5] Engel, B. N., et al. "A 4-Mb toggle MRAM based on a novel bit and switching method." IEEE Transactions on Magnetics 41.1 (2005): 132-136.
[6] Moore, John, and Terry Gilton. "PCRAM cell manufacturing." U.S. Patent Application No. 10/017,053.
[7] Wong, H-S. Philip, et al. "Metal–oxide RRAM." Proceedings of the IEEE 100.6 (2012): 1951-1970.
[8] Cagli, Carlo, et al. "Evidence for threshold switching in the set process of NiO-based RRAM and physical modeling for set, reset, retention and disturb prediction." 2008 IEEE International Electron Devices Meeting. IEEE, 2008.
[9] Chien, W. C., et al. "Unipolar Switching Behaviors of RTO $hbox {WO} _ {X} $ RRAM." IEEE electron device letters 31.2 (2010): 126-128.
[10] Lee, H. Y., et al. "Low power and high speed bipolar switching with a thin reactive Ti buffer layer in robust HfO2 based RRAM." 2008 IEEE International Electron Devices Meeting. IEEE, 2008.
[11] Sawa, A., et al. "Hysteretic current–voltage characteristics and resistance switching at a rectifying Ti∕ Pr 0.7 Ca 0.3 Mn O 3 interface." Applied Physics Letters 85.18 (2004): 4073-4075.
[12] Larentis, Stefano, et al. "Resistive switching by voltage-driven ion migration in bipolar RRAM—Part II: Modeling." IEEE Transactions on Electron Devices 59.9 (2012): 2468-2475.
[13] Minami, Tadatsugu, Toshihiro Miyata, and Yuki Nishi. "Relationship between the electrical properties of the n-oxide and p-Cu2O layers and the photovoltaic properties of Cu2O-based heterojunction solar cells." Solar energy materials and solar cells 147 (2016): 85-93.
[14] Yang, Woo-Young, Wan-Gee Kim, and Shi-Woo Rhee. "Radio frequency sputter deposition of single phase cuprous oxide using Cu2O as a target material and its resistive switching properties." Thin Solid Films 517.2 (2008): 967-971.
[15] Sato, Naoya, et al. "Characterization of electrical properties and photosensitivity of SnS thin films prepared by the electrochemical deposition method." Solar energy materials and solar cells 85.2 (2005): 153-165.
[16] Rossnagel, S. M., and J. Hopwood. "Magnetron sputter deposition with high levels of metal ionization." Applied Physics Letters 63.24 (1993): 3285-3287.
[17] Zang, Zhigang. "Efficiency enhancement of ZnO/Cu2O solar cells with well oriented and micrometer grain sized Cu2O films." Applied Physics Letters 112.4 (2018): 042106.
[18] Jia, Ran, et al. "Sandwich-structured Cu2O photodetectors enhanced by localized surface plasmon resonances." Applied Surface Science 332 (2015): 340-345.
[19] Zhang, Huigang, et al. "One‐pot synthesis and hierarchical assembly of hollow Cu2O microspheres with nanocrystals‐composed porous multishell and their gas‐sensing properties." Advanced Functional Materials 17.15 (2007): 2766-2771.
[20] Elfadill, Nezar G., et al. "Electrochemical deposition of Na-doped p-type Cu2O film on n-type Si for photovoltaic application." Journal of Electroanalytical Chemistry 767 (2016): 7-12.
[21] Baek, Seung Ki, et al. "Low‐Temperature Processable High‐Performance Electrochemically Deposited p‐Type Cuprous Oxides Achieved by Incorporating a Small Amount of Antimony." Advanced Functional Materials 25.32 (2015): 5214-5221.
[22] Emtage, P. R., and W. Tantraporn. "Schottky emission through thin insulating films." Physical Review Letters 8.7 (1962): 267.
[23] Miyazaki, Terunobu, and N. Tezuka. "Giant magnetic tunneling effect in Fe/Al2O3/Fe junction." Journal of magnetism and magnetic materials 139.3 (1995): L231-L234.
[24] Rose, A. "Space-charge-limited currents in solids." Physical Review 97.6 (1955): 1538.
[25] Kolodzey, James, et al. "Electrical conduction and dielectric breakdown in aluminum oxide insulators on silicon." IEEE Transactions on Electron Devices 47.1 (2000): 121-128.
[26] Yan, P., et al. "Conducting mechanisms of forming-free TiW/Cu2O/Cu memristive devices." Applied Physics Letters 107.8 (2015): 083501.
[27] Zhang, Guoqiang, et al. "The role of field electron emission in polypropylene/aluminum nanodielectrics under high electric fields." ACS applied materials & interfaces 9.11 (2017): 10106-10119.
[28] Minami, Tadatsugu, Toshihiro Miyata, and Yuki Nishi. "Relationship between the electrical properties of the n-oxide and p-Cu2O layers and the photovoltaic properties of Cu2O-based heterojunction solar cells." Solar energy materials and solar cells 147 (2016): 85-93.
[29] Winning, M., G. Gottstein, and L. S. Shvindlerman. "Stress induced grain boundary motion." Acta materialia 49.2 (2001): 211-219.
[30] Ollila, H. J., et al. "SEM–EDS characterization of inorganic material in refuse-derived fuels." Fuel 85.17-18 (2006): 2586-2592.
[31] Theunissen, G. S. A. M., Aloysius JA Winnubst, and A. J. Burggraaf. "Surface and grain boundary analysis of doped zirconia ceramics studied by AES and XPS." Journal of materials science 27.18 (1992): 5057-5066.
[32] Lv, H. B., et al. "Improvement of endurance and switching stability of forming-free CuxO RRAM." 2008 Joint Non-Volatile Semiconductor Memory Workshop and International Conference on Memory Technology and Design. IEEE, 2008.
[33] Bersuker, G., et al. "Metal oxide RRAM switching mechanism based on conductive filament microscopic properties." 2010 International Electron Devices Meeting. IEEE, 2010.
[34] Vandelli, Luca, et al. "Comprehensive physical modeling of forming and switching operations in HfO2 RRAM devices." 2011 International Electron Devices Meeting. IEEE, 2011.