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Formation of Chemical Patterns on Planar Stamps for Microcontact Printing

IP.com Disclosure Number: IPCOM000013187D
Original Publication Date: 2000-Feb-01
Included in the Prior Art Database: 2003-Jun-17
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Abstract

Disclosed is a strategy to form patterns of chemicals on the surface of an elastomer that can be used as a stamp for microcontact printing. This strategy relies on the direct transfer of ink from a patterned inker pad onto a planar stamp wherever the stamp contacts the inker pad. Thus, the planar stamp can microcontact-print a pattern of chemicals onto a substrate provided that the diffusion of these chemicals on the stamp during the time that elapses between inking and printing is small compared to the dimensions of the patterns to be printed. Microcontact printing (mCP) is a lithographic technique for which a micropatterned, elastomeric stamp is first inked, dried, and then placed over a substrate to localize a chemical reaction between molecules from the ink and the substrate [1]. The printed pattern can lend the substrate various types of properties: protection against etching or corrosion, nucleation of metallization or of crystal growth, selective wetting or adhesion of molecules from a gaseous or liquid phase, for example. All demonstrations and applications of mCP so far used patterned stamps formed by polymerization of an elastomer on a mold. After the stamp is released, it retains the pattern of its mold even after multiple inking and printing steps, although mechanical deformations and swelling can compromise the accuracy of the printed pattern. Figure 1 illustrates a plausible strategy for using planar stamps for microcontact printing. The pattern is provided by the inker pad, and the ink is transferred directly from the inker pad to the stamp in the regions of contact, suggesting the term “contact inking” to describe this operation [2]. The stamp becomes a simple receptacle for the ink but still provides conformal contact to both inker pad and substrate by its elastomeric nature. The use of a flat stamp can offer some advantages compared to conventional mCP. First, fabrication of the stamp is easy: curing of its liquid prepolymer components occurs on a flat surface (no mold) from which the stamp can be peeled off without damaging. Second, contact inking a planar stamp separates the pattern-carry function from the conformal-contact function. Third, the surface of a flat stamp is not prone to mechanical deformations and distortions during printing. This results in a higher degree of freedom in the design of patterns as the stiff inker pad is the only element that has a physical pattern [3]. Contact inking planar stamps for mCP is mainly limited by the diffusion of the chemical pattern on the stamp. Highly diffusive inks like linear alkanethiols, for example, are not patternable with accuracy from an inker pad onto flat PDMS stamps. In contrast, polar Pd(II) compounds, used as a catalytic precursor for the electroless deposition of Cu, can be patterned onto flat, hydrophilized PDMS stamps, Figure 2. The Cu patterns formed on the substrate reveal how the time of contact inking the stamp and the concentration of Pd in ethanol affected the evolution of the pattern of catalyst on the stamp before printing it. In this example, direct inking was possible because the Pd complex has a small diffusion on the flat stamp and because the yield of transfer from the inker pad to the stamp and from the stamp to the substrate is very high. Optimization of the concentration of the Pd compound in the ink and of the duration of the transfer of the ink from the inker pad to the stamp leads to Cu patterns of good contrast and accuracy.

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Formation of Chemical Patterns on Planar Stamps for Microcontact Printing

   Disclosed is a strategy to form patterns of chemicals on the surface of an elastomer that can be used as a stamp for microcontact printing. This strategy relies on the direct transfer of ink from a patterned inker pad onto a planar stamp wherever the stamp contacts the inker pad. Thus, the planar stamp can microcontact-print a pattern of chemicals onto a substrate provided that the diffusion of these chemicals on the stamp during the time that elapses between inking and printing is small compared to the dimensions of the patterns to be printed.

     Microcontact printing (mCP) is a lithographic technique for which a micropatterned, elastomeric stamp is first inked, dried, and then placed over a substrate to localize a chemical reaction between molecules from the ink and the substrate [1]. The printed pattern can lend the substrate various types of properties: protection against etching or corrosion, nucleation of metallization or of crystal growth, selective wetting or adhesion of molecules from a gaseous or liquid phase, for example. All demonstrations and applications of mCP so far used patterned stamps formed by polymerization of an elastomer on a mold. After the stamp is released, it retains the pattern of its mold even after multiple inking and printing steps, although mechanical deformations and swelling can compromise the accuracy of the printed pattern.

     Figure 1 illustrates a plausible strategy for using planar stamps for microcontact printing. The pattern is provided by the inker pad, and the ink is transferred directly from the inker pad to the stamp in the regions of contact, suggesting the term "contact inking" to describe this operation [2]. The stamp becomes a simple receptacle for the ink but still provides conformal contact to both inker pad and substrate by its elastomeric nature. The use of a flat stamp can offer some advantages compared to conventional mCP. First, fabrication of the stamp is easy: curing of its liquid prepolymer components occurs on a flat surface (no mold) from which the stamp can be peeled off without damaging. Second, contact inking a planar stamp separates the pattern-carry function from the conformal-contact function. Third, the surface of a flat stamp is not prone to mechanical deformations and distortions during p...