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M. R. Latif 1 , I. Csarnovics 1,2 , T. Nichol 1 , S. Kökényesi 2 , A. Csik, 3 M. Mitkova 1 1. Department of Electrical and Computer Engineering Boise State University, Boise, ID - USA 2.Department of Experimental Physics, University of Debrecen, Debrecen - Hungary 3.Institute of Nuclear Research (ATOMKI), Debrecen - Hungary Photolithography Free Ge-Se Based Memristive Arrays Material Characterization and Devices Testing Acknowledgment: This work was supported by the IMI-NFG under NSF Grant # DMR 0844014, TAMOP 4.2.2./B-10/1-2010-0024 and TAMOP 4.2.2.A- 11/2/KONV-2012-0032 projects, which are co-financed by the European Union and European Social Fund. The financial support of the Czech I. Motivation II. Experimental Details III. EDS Mapping EDS mapping of the data provides evidence of compositional distribution of different elements in the array stack. IV. Film Characterization - AFM RMS value of surface roughness in 25µm 2 area of cells # 1, 10 and 20 in the array. The result shows that the SNMP method is suitable for via formation. Quality of the surface depends upon the films’ structure. Sample Cell No. RMS Surface Roughness in the ChG film after ion bombardment by AFM Ge 20 Se 80 1 21.7 10 4.52 20 2.31 Ge 30 Se 70 1 5.15 10 7.21 20 8.67 Ge 40 Se 60 1 1.97 10 1.78 20 1.89 VI. Electrical Testing The IV curves for cells # 20 in the arrays are presented in the following figures. It is obvious that ChG surface with higher roughness results in a poorer device performance. Devices threshold voltages (V th ) and the resistance plots are shown below: The array allows individual device addressing. Devices show six orders of magnitude difference between the low resistive state (LRS) and high resistive state (HRS). V th of Ge 30 Se 70 and Ge 40 Se 60 shows excellent repeatability. Increase in Ge concentration results in improvement of the devices’ performance which is attributed to the formation of Ge-Ge bonds. Devices performance depends on the film roughness which results in voids occurrence that obstructs bridge formation. The devices showed good endurance at over 10 3 cycles. 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 -10n 0 10n 20n 30n 40n 50n 60n C u rren t (A ) V o ltag e (V ) C ell20 100 C ycles 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 -10n 0 10n 20n 30n 40n 50n 60n C u rren t (A ) V o ltag e (V ) C ell20 100 C ycles 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 -10n 0 10n 20n 30n 40n 50n 60n C u rren t (A ) V o ltag e (V ) 100 C ycles C ell20 Ge 20 Se 80 Device Ge 30 Se 70 Device Ge 40 Se 60 Device 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Vth HRS LRS 100 C ycles/C ell Threshold Voltage (V) 10k 100k 1M 10M 100M 1G 10G 100G 1T R esistance ( ) C ell1 C ell8 C ell16 C ell20 0.2 0.4 0.6 0.8 1.0 1.2 Vth HRS LRS 100 C ycles/C ell Threshold Voltage (V) C ell1 C ell4 C ell8 C ell12 C ell16 C ell20 10k 100k 1M 10M 100M 1G 10G 100G 1T R esistance ( ) -0.2 0.0 0.2 0.4 0.6 0.8 1.0 C ell20 C ell16 C ell12 C ell8 C ell4 C ell1 Vth HRS LRS 100 C ycles/C ell Threshold Voltage (V) 1k 10k 100k 1M 10M 100M 1G 10G 100G R esistance ( ) Ge 20 Se 80 Device Ge 30 Se 70 Device Ge 40 Se 60 Device VII. Conclusion V. Raman Spectroscopy Analysis A memristive array with devices build by Ge-Se thin films and Ag bridging the two device electrodes is demonstrated. SNMP method for array formation shows excellent yield with stable ON/OFF ratio. The individual devices demonstrate reliable performance. Additional improvement in the cells can be achieved by formation of smoother layers within the vias and filling them homogeneously with thick Ag films. SNMS Setup Profilometer Image Profilometer Scan SNMS Measurement 0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0 2 0 0 2 2 0 2 4 0 2 6 0 T m e [ s ] G e 4 0 S e 6 0 W S # 6 s p u t e r n g 8 0 0 n m d e e p c r a e ( s p u t m e 2 7 5 s e c ) File:DT06379.SAD D ate:2/25/2013 1:59:37 P M Si[29] Ge Se W [186] D T 06379.S AD 0 20 40 60 80 100 120140 160 220 200 180 260 240 Tim e [s] Intensity [cps] 10 0 10 1 10 4 10 5 10 2 10 3 Success already achieved at the single cell level suggests that conductive bridge memristor is well positioned for ultra high performance memory, neuromorphic computing and logic applications. A high density conductive bridge memristor arrays on thin films metal/insulator/metal (MIM) stack is demonstrated in this work. ChG ChG Ag ChG ChG Ag 1µm 150nm 150nm 20nm -30nm 20nm -30nm 20nm -30nm Ag W electrode 100nm 1µm 150nm Si <100> SiO 2 100nm ChG V ias filled w ith A g ChG Ag ChG ES S e-S e ES O u tsid e V ia C o u n ts (a rb .) In sid e V ia CS ETH C o u n ts (a rb .) O u tsid e V ia In sid e V ia 150 200 250 300 350 400 W avenum b er (cm -1 ) C o u n ts (a rb .) In sid e V ia O u tsid e V ia Ge 24.8 ± 0.51 Se 75.2 ± 0.51 Ge 30.7 ± 0.15 Se 69.3 ± 0.15 Ge 38.8 ± 0.14 Se 61.2 ± 0.14 Ge 25.6 ± 0.061 Se 74.4 ± 0.061 Ge 31.2 ± 0.037 Se 68.8 ± 0.037 Ge 39.9 ± 0.19 Se 60.1 ± 0.19 Source com position : Ge 20 Se 80 Ge 30 Se 70 Ge 40 Se 60 Ge 30 Se 70 V irg in Ge 30 Se 70 V ia 0.0 0.5 14 21 ETH ES/C S C o u n ts (a rb .) Ge 40 Se 60 V irg in Ge 40 Se 60 V ia 0.32 0.40 ETH ES /C S C o u n ts (a r Ge 40 Se 60 Ge 30 Se 70 V irg in V ia A re a s (a rb .) A re a s (a rb .) A re a s (a rb .) CS ES S e-S e Ge 20 Se 80 Ge 30 Se 70 Ge 40 Se 60 Areas (Arb.) Areas (Arb.) Areas (Arb.) Virgin Via Counts (Arb.) Counts (Arb.) Counts (Arb.) Counts (Arb.) Counts (Arb.) Ge 40 Se 60 Ge 30 Se 70 Ge 20 Se 80
