Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7EECS 235, Spring 2009“Electrochemical Nanoimprinting with Solid State Super-ionic Stamps”Keng H. Hsu, Peter L. Schultz, Placid M. Ferreira, and Nicholas X. FangNano Lett., 2007, 7 (2), 446-451EECS 235, Spring 2009Category Optical Lithography and Nanoimprinting followed by deposition and lift-off (or etching)1Electrochemical Micromachining2Solid State Electrochemical NanoimprintingVirtues • Works with all metals• High resolution (w/NI)• Accord w/ IC fab (w/OP)• High aspect ratios• Single patterning step• High resolution • High aspect ratios • Single patterning step• Ambient environment• Performed without liquidsProblems & Potential Problems• Multistep process• Medium resolution (w/OP)• Stamp lifetime (w/NI)• Field diff limited resolution • Poor geometric fidelity• Requires calibration of electrode feed rate• Stamp lifetime not explored• Only developed for copper and silver so farComparison of parallel top-down methods used to create metallic nanostructures1. S. Zankovych, T. Hoffman, J. Seekamp, J.U. Brunch, C.M. Torres Nanotechnology 2001, 12, 91-952. A.L Trimmer, J.L. Hudson, M. Kock, R. Schuster Applied Physics Letters 2003, 82, 3327-3329Electrochemical MicromachiningEECS 235, Spring 2009Solid state super-ionic stamping processStamp: Ag2S solid electrolyte (super-ionic conductor)Patterned material (anode, Ag)Metallic electrode back of stamp (cathode)Potential between anode and cathode held constantStamping pressure held constantMobile Ag+ ions move through defect lattice and channels to recombine w/ e- at cathodePotential drop at interface causes oxidation of Ag and results in mobile Ag+ ionsStamp released when current approaches zeroEECS 235, Spring 2009Solid state super-ionic stamping: first generation results(A) FIB etched Ag2S stamp(B) Stamped 300nm Ag substrate at Vbias=0.8V(D) Close up of imprinted letters showing spurs on the surface(C) Perspective viewKeng H. Hsu, Peter L. Schultz, Placid M. Ferreira, and Nicholas X. Fang Nano Lett., 2007, 7 (2), 446-451Concentric CirclesPitch: 500 390 240 nmRectangles60 nm to 1.3 µmLettersLine width: 200 nmHeight: 300nmEECS 235, Spring 2009Solid state super-ionic stamping: first generation resultsKeng H. Hsu, Peter L. Schultz, Placid M. Ferreira, and Nicholas X. Fang Nano Lett., 2007, 7 (2), 446-451Line witdths(left to right)1600 to 60 nmPitchTop right set: 30 nmTop left set: 50 nmMiddle set: 200 nmBottom set: 350 nmHeight100 nm (60 nm lines only 30 nm)Stamped 300nm Ag substrate at Vbias=0.3VEECS 235, Spring 2009Anodic sweep analysis for Ag dissolutionIncreasing dissolution rate with increase in V (dissolution by breaking space charge layer at interfaceAnodic dissolution switches from charge transfer control to diffusion control)Anodic Sweep at 20 mVs-1Evolution of total current over etch time for stamping processFall off associated with depletion of Ag substrateEECS 235, Spring 2009ConclusionsVariation in etch time for subsequent runs using same stamp (80 nm substrates)Potential Drawbacks• Stamp lifetime has not been fully investigated yet• Patterning layers difficult (alignment and anodic contact)• Limited range of materials investigated (Ag, Cu)Demonstrated Possibilities• Inexpensive• High aspect ratios possible• High resolution (50 nm)• Patterning of acute angles possible (15º)• Conducted in ambient environment• Doesn’t require liquids• Single step
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