Transparent resistive random access memory (T-RRAM) based on Gd2O3 film

Transparent resistive random access memory (T-RRAM) based on Gd 2O 3 film and its resistiveswitching characteristicsKou-Chen Liu 1,*, Wen-Hsien Tzeng 2, Kow-Ming Chang 2, Yi-Chun Chan 1, Chun-Chih Kuo 1, and Chun-Wen Cheng 11Institute of Electro-Optical Engineering, Chang Gung University, Tao-Yuan, 33302, Taiwan, R.O.C 2Institute of Electronics, Department of Electronics Engineering, National Chiao Tung University, HsinChu, 30010, Taiwan,R.O.CAbstract- A transparent resistive random access memory (T-RRAM) based on ITO/Gd 2O 3/ITO capacitor structure is successful y fabricated on Gl ass substrate by pul se l aser deposition (PLD) at room temperature. Under bipo l ar operation, the ITO/Gd 2O 3/ITO device exhibits reliable and stab le resistive switching behaviors for more than 200 switching cyc es and ow operation vo tage of -2V/+2V. Furthermore, our device demonstrates nonpol ar resistive switching characteristic which exhibits high potential to be applied for the next generation nonvolatile memory.I. I NTRODUCTIONResistive random access memory (RRAM) attracts muchattention in recent years owning to advantag es of simple structure, hig h density, low power consumption, etc. Many transition metal oxide (TMO) were proposed to demonstrate the resistive switching (RS) behavior, such as NiO[1], TiO 2[2], and Cu 2O[3], however, the switching mechanism of RRAM is still on debate. TMO material exhibits excellent merits of simple composition and high functionality and compatibility to integ rate with CMOS technolog y, even TMO film integ rated with transparent conducting oxide (TCO) has reported several months ag o. It’s called T-RRAM which shows not only RS behavior but also highly transparency to UV light proposed by Park et al.[4] at the first time. Furthermore, by integrating with transparent electronic components, a total see-throu g hembedded electronic device could put into realization.However, since the switching mechanism of the RS behavior is still needed further investig ation, it’s essential to discuss on other TMO material to have a better understanding for the sake of stable RS of T-RRAM. In this study, we investig ated the resistive switching characteristics of T-RRAM based on ITO/Gd 2O 3/ITO capacitor structure. After forming process, both unipolar and bipolar RS behavior could be observed on our T-RRAM device. Bipolar RS properties show more reliable and stable switchin characteristics of RRAM behavior. Endurance, retention, *Contacting Author: Kou-Chen Liu is with Institute of Electro-Optical Engineering, Chang Gung University, Tao-Yuan, 33302, Taiwan, R.O.C (phone:+886-3-2118800; fax: +886-3-2118507; email:jacobliu@.tw ) fabrication process condition of Gd 2O 3 film and electrical conduction behavior of fresh, HRS and LRS are also discussed here.II. E XPERIMENTSGlass substrate was prepared and used in this experiments. Before the main structure deposition, the g lass surface is cleaned by DI water, and then followed acetone solution for 10 min. Then, ITO bottom electrode was deposited by dc sputterin system. 10 min pre-sputterin under workin pressure of 30 mTorr is experimented and then ITO film with thickness of 1000A was deposited in Ar gas of 15 sccm. Metal oxide Gd2O3 was deposited by pulse laser deposition (PLD) at 25ć under oxyg en partial pressure of 10 mTorr for 10 min. This room temperature (RT) fabrication process provides advantag es such as low thermal budg et and easy compatible with back-end fabrication process. Then top electrode ITO with the same process condition of bottom electrode was deposited by dc sputtering system with a shadow mask. Electrical characteristics was measured by HP 4156C under different measurement temperature from 25ć to 85ć. Current flow from top side electrode ITO to bottom side ITO was defined as positive sweep.III. R ESULTS AND DISCUSSION The typical unipolar and bipolar RS characteristics of our ITO/Gd 2O 3/ITO capacitor structure in dc sweep mode are shown in Fig. 1 and Fig. 2, respectively. Forming process was needed in the beginning for all our samples to activate our T-RRAM device with certain current compliance of 1 mA. Both unipolar and bipolar RS characteristics could be observed in our samples irrespectively of the operation polarity, i.e. nonpolar RS properties. Though unipolar RS behavior is more applicable for integ rated current desig n to have smaller cell size and hi her device density, however, the electricalcharacteristics of unipolar RS is less stable than bipolar RS in this samples. Only 15 times of switching cycles with unstable RS characteristic and larg e voltag e dispersion is observed shown in Fig. 1. Bipolar switching characteristics of our T-RRAM device switches to ON (OFF) state by neg ative (positive) bias is shown in Fig. 2. Excellent and reliable RS978-1-4244-3544-9/10/$25.00 ©2010 IEEEcharacteristic of more than 200 switching cycles are observed. Low operation voltage of only -2V/+2V is needed to operate our T-RRAM device. During a continuously automatic dc sweeping bias, our device could switch to ON or OFF state with low voltag e dispersion among the 200 switching cycles shown in Fig. 3. A larg e voltag e operation window of 1V is observed and there is no voltag e overlap in our T-RRAM device. Endurance of our device is shown in Fig. 4. Among the 200 switching cycles, there has a large high to low resistance ratio of about 5. The negative operated dc sweep on HRS curve was translated to positive side on both voltag e and current values, and then the electrical conduction behavior of HRS and LRS are fitted and shown in Fig. 5. The conduction mechanismin the LRS is dominated by Ohmic conduction with a slope of approximately 1. The conduction behavior in the HRS is Ohmic conduction at low voltag e (I͉V), and space-charg e limited current (SCLC) (I͉V2) at high voltage. A transparent T-RRAM based on ITO/Gd2O3/ITO structure was fabricated and investigated here. Excellent and reliable bipolar switching characteristics with low operation voltag e of -2V/+2V, no voltag e overlap, and more than 200 switching cycles are observed. Furthermore, our T-RRAM demonstrates nonpolar switching behavior which exhibits high potential to be applied for next generation nonvolatile memory.R EFERENCES[1] I.G. Baek, M.S. Lee, S. Seo, M.J. Lee, D.H. Seo, D.–S. Suh, J.C. Park,S.O. Park, H.S. Kim, I.K. Yoo, U.-In. Chung, J.T. Moon, “Hig hly Scalable Non-volatile Resistive Memory using Simple Binary Oxide Driven by Asymmetric Unipolar Voltag e Pulses,” IEDM Tech. Dig.(2004) pp.587[2] B.J. Choi, D.S. Jeong, S.K. Kim, C. Rohde, S. Choi, J.H. Oh, H.J. Kim,C.S. Hwang, K.Szot, R. Waser, B. Reicheng erg, S. Tiedke, “Resistiveswitchin mechanism of TiO2 thin films rown by atomic-layer deposition,” J. Appl. Phys. 98 (2005) 033715[3] A. Chen, S. Haddad, Y.-C. Wu, T.-N. Fang, Z. Lan, S. Avanzino, S.Pang rle, M. Buynoski, M. Rathor, W. Cai, N. Tripsas, C. Bill, M.VanBuskirk, and M. Tag uchi, “Non-Volatile Resistive Switching for Advanced Memory Applications,” IEDM Tech. Dig. (2005) pp.746[4] J.W. Seo, J.-W. Park, K.S. Lim, J.-H. Yang, and S.J. and Kang,“Transparent resistive random access memory and its characteristics for nonvolatile resistive switching,” Appl. Phys. Lett, 93, 223505 (2008)Fig. 1. The typical unipolar resistive switching characteristicsFig. 2. The typical bipolar resistive switching characteristics of Fig. 3. Operation voltag e distribution of the ITO/ Gd O/ITO Fig. 4. The resistance values of HRS and LRS versus the number Fig. 5. The conduction behavior of LRS is mainly dominated by。