EECS 235, Spring 2009 “Electrochemical Nanoimprinting with Solid State Super-ionic Stamps” Keng H. Hsu, Peter L. Schultz, Placid M. Ferreira, and Nicholas X. Fang Nano Lett., 2007, 7 (2),

EECS 235, Spring 2009 CategoryOptical Lithography and Nanoimprinting followed by deposition and lift-off (or etching) 1 Electrochemical Micromachining 2 Solid State Electrochemical Nanoimprinting Virtues 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 liquids Problems & 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 far Comparison of parallel top-down methods used to create metallic nanostructures 1.S. Zankovych, T. Hoffman, J. Seekamp, J.U. Brunch, C.M. Torres Nanotechnology 2001, 12, A.L Trimmer, J.L. Hudson, M. Kock, R. Schuster Applied Physics Letters 2003, 82, Electrochemical Micromachining

EECS 235, Spring 2009 Solid state super-ionic stamping process Stamp: Ag 2 S solid electrolyte (super-ionic conductor) Patterned material (anode, Ag) Metallic electrode back of stamp (cathode) Potential between anode and cathode held constant Stamping pressure held constant Mobile Ag+ ions move through defect lattice and channels to recombine w/ e - at cathode Potential drop at interface causes oxidation of Ag and results in mobile Ag+ ions Stamp released when current approaches zero

EECS 235, Spring 2009 Solid state super-ionic stamping: first generation results (A)FIB etched Ag 2 S stamp (B) Stamped 300nm Ag substrate at V bias =0.8V (D) Close up of imprinted letters showing spurs on the surface (C) Perspective view Keng H. Hsu, Peter L. Schultz, Placid M. Ferreira, and Nicholas X. Fang Nano Lett., 2007, 7 (2), Concentric Circles Pitch: nm Rectangles 60 nm to 1.3 µm Letters Line width: 200 nm Height: 300nm

EECS 235, Spring 2009 Solid state super-ionic stamping: first generation results Keng H. Hsu, Peter L. Schultz, Placid M. Ferreira, and Nicholas X. Fang Nano Lett., 2007, 7 (2), Line witdths(left to right) 1600 to 60 nm Pitch Top right set: 30 nm Top left set: 50 nm Middle set: 200 nm Bottom set: 350 nm Height 100 nm (60 nm lines only 30 nm) Stamped 300nm Ag substrate at V bias =0.3V

EECS 235, Spring 2009 Anodic sweep analysis for Ag dissolution Increasing dissolution rate with increase in V (dissolution by breaking space charge layer at interface Anodic dissolution switches from charge transfer control to diffusion control) Anodic Sweep at 20 mVs -1 Evolution of total current over etch time for stamping process Fall off associated with depletion of Ag substrate

EECS 235, Spring 2009 Conclusions Variation 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 patterning