Laser printing of organic thin film transistors – ILTO

In the frame of the project e-PLAST (ANR Blanc 2006), CINaM (Centre Interdisciplinaire de Nanoscience de Marseille) and LP3 laboratories have succeeded to print for the first time an Organic Thin Film Transistor (OTFT) by means of a laser process. This process called LIFT (Laser-Induced Forward Transfer) allows the transfer, from a donor substrate, of pixels with micrometer sizes (three to several hundreds of microns) of organic and inorganic materials in liquid or solid phase with a submicronic resolution. N-type and p-type OTFTs have been successfully printed, but their performances remained one to two orders of magnitude lower than the performances of similar OTFTS made by vacuum evaporation using masks to achieve the spatial resolution. Among the reasons of these reduced performances, quality of interfaces involved in the charges injection and transport (respectively source-drain electrodes/semiconductor and semiconductor/ dielectric) is crucial. Then, it appeared of prime importance to optimize the preparation of donor substrates, including the realization of multilayer films where critical interfaces are formed under vacuum, and their transfer in a single laser shot. Then, two laboratories have joined CINaM and LP3 to form the ILTO consortium (Laser Printing of Organic Thin Films Transistors). LPCML (Laboratoire de Physico-Chimie des Matériaux Luminescents) laboratory and ISM (Institut des Sciences Moléculaires) will bring to this project their fields of expertise respectively for organic and inorganic thin film deposition by PLD (Pulsed Laser Deposition) and physico-chemical  thin film characterizations. ILTO consists in four scientific tasks, each of them is led by one of the partner. The LPCML goals will be the realization, by means of PLD technique, of donor substrates with monolayer or multilayer thin films of organic and/or inorganic materials, and the characterization of their structural and morphological properties. These substrates are then used in a second task, coordinated by LP3, dedicated to the optimization of laser transfer of organic and inorganic materials in order to achieve the impression of OTFTs by LIFT.  The study of physico-chemical and structural characterizations of the deposited material is centered in a third task coordinated by ISM. For this task, characterizations tools based on near field and electronic microscopy (AFM, KPFM, SEM, TEM, XRD) will be implemented by the CINaM. Raman/AFM and Raman/SHG/UV-Vis coupled microscopy techniques as well as ellipsometry microscopy will be used to obtain morphological, chemical and optical informations about the layers by ISM.  A time-resolved fluorescence technique associated with an appropriate choice of 'probes' molecules, will be implemented by the CINaM  to study the photodegradation of the organic layers induced by the process. A fourth task coordinated by the CINaM is more devoted to the electrical characterizations of the printed OTFTs. Current-voltage characteristics of OTFTs will be measured and analysed. Specific techniques will be implemented to measure the contact resistance between source-drain electrodes and the semiconductor. Some treatments of the dielectric layer or source/drain electrodes will be considered in order to optimize the material behaviour during the LIFT process. Of course theses task are carried out in close collaboration by the different partners. This work should lead to the understanding of mechanisms inducing modifications of organic materials printed by LIFT. Optimizing the preparation of thin films by PLD and their transfer by LIFT should then allow OTFTs printing with performances high enough to address the numerous applications of organic microelectronics.