Poplab Research Update March 4th

self-aligned nanotube-phase change memory device

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Phase Change MemoryPhase-Change MemoryNon-volatileFast access timeLarge dynamic rangeHigh enduranceHigh packing densityRadiation resistant2

1st Level Cache2nd Level Cache

Main MemoryHard Disk DriveSRAMSRAMDRAMParameterDRAMSRAMNAND FlashPCMNon-volatileNoNoYesYesAccess time10 ns2 ns25 s50 nsEndurance >1015>10151051012Density1X1X4X2~4XVoltage1.5 V1.5 V10 V1.5 V

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Phase Change MaterialChalcogenide compound: Ge2Sb2Te5 (GST)Amorphous CrystallineLarge contrast in resistivityFast crystallization time ~ 1 ns3AmorphousCrystallineA. Kolobov et al., Nat. Mater. (2004).

M. Lankhorst et al., Nat. Mater. (2005).

www.webelements.com

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Self-Aligned PCM Nanowire4

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MotivationAllow us to build PCM nanowires with different sizesThis provides an excellent platform to study the scalability of the PCM devicesObserve any size dependent effect on key parameters such as drift coefficient, activation energy, threshold field, crystallization temperature.

Wong et al, Proc IEEE (2010)Phase-change memory is highly scalable with electrode size

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Experimental DesignAssumption:width of nano-trench depends on the input power, bias duration and background temperature

DOE: 4-factor 3*2*2*2 fractional factorial experimental design X1: input voltage bias (3 levels: 20V, 25V and 30V)X2: bias duration (2 levels: 5ms and 1s)X3: background temperature (2 levels: 293K and 373K)X4: sample (2 levels: S8_22_17 and S8_33_14)

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Experimental ProcedureForm nano-trench Use Keithley 4200 pulse mode to change the bias duration and voltage biasUse temperature controller to change the background temperatureUse the optical microscope to verify the formation of the trenchUse AFM to measure the width of the nanowires

optical image:S8_22_1725V1s293K

AFM image:S8_22_1725V1s293K

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Image Result

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Data ResultDevice Voltage (V)Duration (ms)Temperature (K)width 1 (nm)width 2 (nm)width 3 (nm)avg width (nm)22,17205293133.9114.2115.1121.133,14201000293126.9117.7127.5124.022,17255293129.5118129.8125.833,14251000293131.4133.2146.9137.233,14301000293159.1148147.2151.422,17305293266276.1244.3262.133,14305373340342.2338.2340.133,14205373218.6207.6218.2214.822,17201000373205.8218231.4218.433,14255373286.6254.4275.5272.222,17251000373350.9325.9336.4337.722,17301000373406396.3358.6387.0

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Normal Probability Plot

Normal Probability plot for the raw data has outliers ->One or more factors are likely statistically significant

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If a normal probability plot for the raw data has outliers, then one or more factors are likely statistically significant.Median 25%-ile 75%-ile Min Max likely statistically significant.

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DOE Scatter Plots

X 3 is the most important, X 1 the second important, X 4, X 2 weak

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Narrow Trench Formation12

30 V, pulse,On/off: 0.2/20 msNo. of Pulses: 1000@225 K Width = ~10 nmDepth = ~1 nm

35/15 V, pulse,On/off: 0.2/0.5 msNo. of Pulses: 1000@225 K Width = 22 nmDepth = 2.2 nm

40 V, pulse,On/off: 1sNo. of Pulses: 1@175 K Width = 48 nmDepth = 11.3 nm

40 V, pulse,On/off: 1sNo. of Pulses: 1@175 K Width = 45 nmDepth = 38.1 nm

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Thank You13

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