Abstract

Electronics fabricated on ultra-large scales and in high volumes, will require novel approaches to pattern formation. Substituting photolithography with printing for patterning these devices is particularly interesting because of the potential to increase production speed and decrease cost by eliminating many process steps-without changing the overall fabrication schemes. Printing will also improve the capability to produce electronics on flexible and curved surfaces.

This dissertation introduces a letterpress printing technology to directly print etch masks for macroelectronics fabrication. In this process, a stamp with raised features transfers a polymer melt film onto the workpiece, where it serves as a mask for wet or dry etching. Using such printed polymer masks, the patterning of materials with feature sizes relevant to macroelectronics is demonstrated. The compatibility of this process with electronics fabrication is demonstrated, by producing amorphous silicon thin film transistors using letterpress printed etch masks. Replacing photolithography does not degrade the transistor performance.

Nonuniform etch mask profiles are created by viscous fingering during the printing process. These can be smoothed by heating, which allows capillary forces to drive polymer spreading. In doing this, however, the footprint of the microstructures can be distorted by spreading along the solid surface. Such spreading can limit the resolution of printed features.

Modeling and numerical simulation of the capillary spreading phenomenon shows the effect of feature size, geometry, and ink properties. This allows prediction of the effect of spreading on printing resolution and pattern fidelity. Simulation of various geometries—including infinite and finite lines, intersections, and other shapes relevant to macroelectronics fabrication—demonstrates the effect of patterns on spreading. From such simulations it is possible to predict the amount of distortion that will occur within a given time. A method for generating design rules from these simulations is presented, and examples are given. The model is extended to include effects of homogeneous solidification, which can be used to arrest the spreading and maintain pattern fidelity and resolution. The model's description is general and applies to a number of printing technologies that utilize Newtonian fluid inks, for which pattern distortion is driven by capillary spreading.