Lithography‐Free, Self‐Aligned Inkjet Printing with Sub‐Hundred‐Nanometer Resolution

Abstract

Surface forces exerted on small liquid droplets on heterogeneous surfaces can be exploited for bottom±up hierarchical assembly of functional nanostructures. We demonstrate here a self-aligned additive printing technique that uses standard inkjet-printing equipment, but is capable of achieving sub-100 nm resolution without any lithographic step. Very small gaps between two printed electrodes are defined uniformly and with high yield by controlling the receding contact-line motion of liquid conductive-ink droplets that are repelled by and flow off the surface of a previously deposited electrode. We illustrate the potential of this technique by fabricating inkjet-printed polymer transistor circuits with sub-100 nm channel lengths that are more than two orders of magnitude faster than previous printed organic-transistor circuits.The application of graphic-arts printing techniques to liquid-based, additive patterning of functional materials promises to provide a new paradigm for manufacturing of large-area, low-cost electronic circuits on flexible substrates. [1,2] However, current resolution achievable with straight inkjet, offset, or gravure printing is limited to 20±50 lm. [3,4] The question of whether printing will be capable of submicrometer-feature definition is a crucial one. It will decide whether printingbased manufacturing will be able to embark on a roadmap of feature-size reductions and corresponding performance enhancements analogous to those of silicon integrated circuits, or whether the challenges of accurately positioning liquid droplets and controlling their flow on the substrate will prevent the use of printing in applications where high switching speeds require submicrometer features. It will also decide whether additive printing will become an important tool for bottom±up nanotechnology, e.g., interfacing with functional nanostructures self-assembled in the liquid phase from smaller building blocks. In principle, printing fulfils many of the material-compatibility requirements for liquid-based self-assembly, but for many systems a key requirement is a patterning resolution of less than 100 nm in order to match the length scale over which supramolecular structure formation can be controlled with high precision. [5,6] Here we demonstrate a novel bottom±up, self-aligned inkjet printing technique that is capable of defining sub-100 nm critical features with two simple additive printing steps using standard inkjet-printing equipment without the need for any lithography or precise relative alignment. The method comprises the steps of a) inkjet printing a first conductive pattern onto the substrate; b) selectively modifying the surface of the first conductive pattern to be of low surface energy without modifying the surface of the substrate; and c) inkjet printing a second conductive pattern that partially overlaps the first conductive pattern, but does not require precise relative alignment. The droplets of the second pattern are repelled by and flow off the low-energy surface of the first pattern and dr...

Organic transistors manufactured using inkjet technology with subfemtoliter accuracy

“…Although other nonlithographic patterning techniques have been used to manufacture organic TFTs with micrometer and submicrometer dimensions (12)(13)(14)(15)37), these methods usually require prepatterning processes based on original patterning forms such as photolithography masks, or they work only with low-mobility semiconductors. In our study, ultrafine patterning with single-micrometer resolution is demonstrated on high-mobility p-channel and n-channel organic semiconductors simply by digital fabrication without any prepatterning processes or original patterning forms.…”

“…We have manufactured p-channel and n-channel organic TFTs with source/drain contacts prepared by subfemtoliter inkjet printing of Ag nanoparticles deposited directly on the surface of the organic semiconductor layers, without the need for any photolithographic prepatterning (12, 13) or any surface pretreatment (14,15). This allows us to prepare top-contact TFTs with a channel length of 1 m. In contrast to bottomcontact TFTs (in which the contacts are defined before the deposition of the organic semiconductor and hence the channel length can be very small through the use of photolithography or electron-beam lithography), top-contact TFTs benefit from significantly lower contact resistance (16) but require a contact patterning technique that does not harm the organic semiconductor (17).…”

Characterization of Silver Inkjet Overlap-printing through Cohesion and Adhesion

“…Inkjet printing is applicable to various materials, including solution-based materials such as organometallics, organo-semiconductors, and polymers. It helps realize digitally driven direct productivity because it can transfer computer-aided designs directly onto device patterns and reduce material waste using a "drop-ondemand" material deposition [1][2][3][4].…”

Recent progress in direct patterning technologies based on nano-imprint lithography

“…However, these patterning methods have some drawbacks, such as complex process, waste of materials, long process time and substrate damage, induced by the etch process. To overcome these problems, many studies on direct nano-patterning techniques of functional materials have been conducted, such as dip-pen lithography [21][22][23], gravure offset printing [24][25][26], ink-jet lithography [27][28][29], and so on. These patterning techniques can directly fabricate nano-patterns composed of functional materials.…”