Monitoring Oxygen Movement by Raman Spectroscopy of Resistive Random Access Memory with a Graphene-Inserted Electrode Supplementary Information He Tian, 1,2 Hong-Yu Chen, 3 Bin Gao, 3,4 Shimeng Yu, 3 Jiale Liang, 3 Yi Yang, 1 Dan Xie, 1 Jinfeng Kang, 4 Tian-Ling Ren, 1* Yuegang Zhang, 2,,* H.-S. Philip Wong 3* 1 Institute of Microelectronics, Tsinghua University, Beijing 100084, China and Tsinghua National Laboratory for Information Science and Technology (TNList), Tsinghua University, Beijing 100084, China 2 The Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA 3 Center for Integrated Systems and Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA 4 Institute of Microelectronics, Peking University, Beijing 100871, China These authors contributed equally to this work Current address: Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, China. E-mail: ygzhang2012@sinano.ac.cn *Corresponding Author E-mail: RenTL@tsinghua.edu.cn, yzhang5@lbl.gov, hspwong@stanford.edu This file includes: SUPPLEMENTARY FIG. S1-S6 SUPPLEMENTARY MTHODS SUPPLEMENTARY DISCUSSION SUPPLEMENTARY REFERENCES
SUPPLEMENTARY FIGURES AND CAPTIONS 100M LRS HRS Resistance (Ω) 10M 1M @100 O C 100k 0.0 20.0k 40.0k 60.0k 80.0k 100.0k Retention Time (s) Figure S1 Retention measurement of G-RRAM. The retention time up to 10 5 seconds (which is equal to ~27.8 hours) at 100 C is achieved.
40 10M RESET Current (µa) 35 30 25 20 Left Right 1M LRS Resistance (Ω) 15 0 10 20 30 40 50 SET Compliance (µa) 100k Figure S2 The RESET current (shown in the left y-axis) and LRS resistance (shown in the right y-axis) as a function of the SET current compliance of G-RRAM.
Resistance (Ω) 10 9 10 8 10 7 10 6 HRS @0.3V Stress LRS 10 5 10 100 1k Time (s) Figure S3 READ immunity test of G-RRAM. Good READ-disturb immunity is achieved under a constant voltage stress of 0.3 V.
a G-RRAM b C-RRAM TiN/Ti SLG TiN/Ti O 2- O 2- O 2- O 2- O 2- O 2- Figure S4 During the SET process, (a) the O 2- is trapped in the SLG for the G-RRAM; (b) the O 2- is trapped in the TiN/Ti for the C-RRAM. a G-RRAM b C-RRAM TiN/Ti SLG TiN/Ti O 2- O 2- O 2- O 2- O 2- O 2- Figure S5 During the RESET process, (a) the O 2- in SLG go back to the for the G-RRAM; (b) the O 2- in TiN/Ti go back to the for the C-RRAM.
2.5eV 5.6eV 4.5eV SLG 4.3eV Ti 4.7eV TiN 8.5eV Figure S6 Schematic view of the energy level alignment (with respect to the vacuum level) of the G-RRAM with / /SLG/Ti/TiN structure. The work function of the, SLG, S1 Ti, TiN and E c, E v of the are depicted.
SUPPLEMENTARY MTHODS Graphene growth and transfer process: The SLG is grown by chemical vapor deposition on copper foil (25 µm, Alfa inc.). The 3 3 cm 2 SLG is transferred on the center of a 4-inch wafer. The detail graphene growth and transfer method is described in the Ref. S2. Device fabrication Process: As shown in Figure 1b, nominally planar surface with the embedded platinum () bottom electrode S3 is first fabricated and followed by (5nm) deposition using atomic layer deposition (ALD). The ALD HfO 2 conditions are thermal standard at 200 degree Celsius with 40 cycles under the base pressure of the chamber 100-200 millitorr using tetrakis (dimethylamido) hafnium and water precursors. Then the as-grown SLG is transferred on the substrate (Figure 1c) and patterned by photolithography and oxygen plasma etching (Figure 1d). Finally, the top electrode (TiN/Ti) is deposited and patterned by lithography and dry etch (Figure 1e). Ti is contact to graphene as an adhesion layer and TiN is on top for probing. After the whole process is completed, the region covered by SLG is defined as G-RRAM and the region uncovered by SLG is defined as C-RRAM. Characterizations: The surface morphology is observed by Quanta FEG 450 SEM (FEI Inc.). The Raman spectroscopy is obtained using a laser with wavelength of 532 nm (HORIBA Inc.). The RRAM electrical characteristics are measured using the Agilent 4156C semiconductor analyzer (Agilent Inc.).
SUPPLEMENTARY DISCUSSION To understand the underlying mechanism of the Joule heating generate in G-RRAM and C-RRAM, we perform finite element simulation to study the temperature distribution of the filament in the. The Fourier s law can be written as: ( ) J = k[ x, T ( x)] dt x (S1) dx Where, x is the position, T(x) is the temperature at that position, k is the thermal conductivity of the. In our simulations, we only consider the steady-state case. Finite element modeling is used to perform a steady-state thermal analysis of the system to evaluate temperature profile. Comsol Multiphysics, S4 a finite element analysis program, is employed. The thermal conductivity of is 5 W/(m K). S5 The resistance of filament region is 10 times higher to the oxide region. In our simulation results, the highest temperature region in G-RRAM is located at the SLG/ interface due to the higher local electrical resistance. The local temperature rises during programming so that the inserted graphene material could be annealed.
SUPPLEMENTARY REFERENCES S1. Xu, K. et al. Direct measurement of Dirac point energy at the graphene/oxide interface. Nano Lett., 2012, 10.1021/nl303669w. S2. Li, X. et al. Large-area synthesis of high-quality and uniform graphene films on copper foils. Science, 2009, 324: 1312-1314. S3. Franklin, A. D. et al. Sub-10 nm carbon nanotube transistor. Nano Lett., 2012, 12: 758-762. S4. For more information, please see Comsol website at: http://www.comsol.com/ S5. Meyer, R. & Kohlstedt, H. 1-D simulation of a novel nonvolatile resistive random access memory device. IEEE Trans Ultrason Ferroelectr Freq Control 53, 2340-2348 (2006).