Phase-change photolithography: Rapid diffraction limited patterning of organic electronic materials

Z.I. Bedolla-Valdez, Z. Su, G. Gonal, T.L. Murrey, C.C. Cendra-Guinassi, A. Salleo, C. Grigoropoulos, A.J. Moulé
University of California Davis,
United States

Keywords: organic electronic, optical patterning, doping, lithography


The ability to pattern materials scalably and at low-cost using photolithography has been the key manufacturing advance that enabled the IT revolution and has driven Moore’s Law. Photolithographic methods are routinely used to fabricate heterostructures of inorganic electronic materials with lateral features of 10 µm because inadequate options to pattern and layer organic materials are available.1-2 The promise of organic electronics stems from the potential to combine the versatility of chemical synthesis to make designer materials with added functionality like flexibility, biocompatibility, and light weight and also from the reduced cost provided by low-temperature solution processing. A significant obstacle for the industrial development of organic electronic devices is the lack of a patterning technology having the disruptive power that photolithography exerted in traditional microelectronics. Here we present a complete set of patterning and sequential solution processing steps that enable rapid, non-destructive, optical patterning of both materials and/or dopants that can be universally applied to organic electronic materials to achieve sub-µm lateral features. This talk will review the progress made by our research team in organic semiconductor process development. The key innovations of our optical patterning process are the realizations that (1) organic semiconductors can be induced to change phases (solid  solution or solid  vapor) at low temperatures and (2) that large local temperature changes can be induced in the organic semiconductor by exciting optical absorbance using a focused laser. Combining these two ideas, we developed a sample environment that enables optical excitation of a solvent soaked organic semiconductor film to produce high resolution polymer patterning. Optical excitation is used to induce local heating of the semiconductor film by 20-200ºC.7 The local temperature increase makes dissolution spontaneous, dissolving the heating portion of the film into the solvent layer. Fig. 1a shows a schematic of the sample cell with a laser window and solvent layer. Fig. 1b shows AFM images of 1D and 2D patterns written into the semiconducting polymer film with resolution of ~300 nm. Fig. 2 shows an application of this technology. Here, P3HT/F4TCNQ nanowires with an “L” and “T” form were written using the method and sample cell shown in Fig. 1. Cross sections of the wires show directly written wire widths of