F. Loffredo

Printing of polymer microlenses by a pyroelectrohydrodynamic dispensing approach.

The investigation of a method for fabricating microlenses by a nozzle-free inkjet printing approach is reported. The new method, based on a pyroelectrohydrodynamic mechanism, is also able to dispense viscous liquids and to draw liquid phase drops directly from the reservoir. Specifically, by dispensing optical grade polymer dissolved in different solvent mixtures, microlenses were printed with a pattern defined directly through this deposition method. The reliability of the microlenses and the tunability of their focal properties were demonstrated through profilometric and inteferometric analyses.

All-inkjet printed organic transistors: Dielectric surface passivation techniques for improved operational stability and lifetime

Abstract We report about the use of a printed pentafluorothiophenol layer on top of the dielectric surface as a passivation coating to improve the operational stability of all-ink-jet printed transistors. Transistors with bottom-gate structure were fabricated using cross-linked poly-4-vinylphenol (c-PVP) as dielectric layer and an ink formulation of an amorphous triarylamine polymer as semiconductor. The resulting TFTs had low turn-on voltage (Vth

All-inkjet-printed thin-film transistors: manufacturing process reliability by root cause analysis

We report on the detailed electrical investigation of all-inkjet-printed thin-film transistor (TFT) arrays focusing on TFT failures and their origins. The TFT arrays were manufactured on flexible polymer substrates in ambient condition without the need for cleanroom environment or inert atmosphere and at a maximum temperature of 150 °C. Alternative manufacturing processes for electronic devices such as inkjet printing suffer from lower accuracy compared to traditional microelectronic manufacturing methods. Furthermore, usually printing methods do not allow the manufacturing of electronic devices with high yield (high number of functional devices). In general, the manufacturing yield is much lower compared to the established conventional manufacturing methods based on lithography. Thus, the focus of this contribution is set on a comprehensive analysis of defective TFTs printed by inkjet technology. Based on root cause analysis, we present the defects by developing failure categories and discuss the reasons for the defects. This procedure identifies failure origins and allows the optimization of the manufacturing resulting finally to a yield improvement.

Graded-size microlens array by the pyro-electrohydrodynamic continuous printing method.

In the present work, the pyro-electrohydrodynamic technique was used for the realization of tunable-size microlens arrays. Poly(methyl methacrylate) dissolved in different solvent mixtures was used as the polymeric material for the realization of the microstructures. By controlling the experimental parameters and in particular, the volume of the drop reservoir, graded-size square arrays of tens of microlenses with focal length in the range 1.5-3 mm were produced. Moreover, the optical quality and geometrical features were investigated by profilometric and interferometric analysis.

Microlens array manufactured by inkjet printing: study of the effects of the solvent and the polymer concentration on the microstructure shape

Recently, the inkjet printing (IJP) technology was advised as a direct method for the fabrication of high-quality and high-precision microlenses overcoming the drawbacks of the traditional techniques which usually require multiple complex processing steps making the fabrication costly. IJP has the great advantage to be extremely versatile in definition of the patterns of microstructures to be realized employing polymers with suitable optical transmission and thermo-mechanical properties. In the present work, we reported the manufacturing of microlenses by inkjet printing Poly(methyl methacrylate) (PMMA) solutions prepared with different solvents (toluene, N-Methyl-2-pyrrolidone, chlorobenzene, ortho-dichlorobenzene) and solvent mixtures at different mixing ratios and investigated the effects of these parameters on the shape and the geometry of the microstructures. These structures were analyzed by means of interferometric Mach- Zehnder technique in confocal configuration and the wave aberrations were evaluated. The results showed the feasibility of manufacturing microlenses via IJP with diameters ranging from 40 to 90 μm and focal lengths of the order of magnitude of hundred micron.

Study of the interference effects in an optical cavity for organic light-emitting diode applications

The interference effects generated in a bottom-emitting electroluminescent device fabricated on a polymer underlayer introduced with the aim of improving the anode roughness have been studied. The analysis of the interference fringes at different detection angles and the spatial coherence demonstrates that this phenomenon is due to multiple internal reflections that propagate in the polymer layer. This effect can be eliminated by modifying the polymer thickness and the incidence angle of the electromagnetic radiation at the anode-polymer interface. Inkjet etching technology is adopted for microcavities-shaped polymer structuring to destroy the resonator effect of the optical cavity.

Plasma functionalization procedure for antibody immobilization for SU-8 based sensor.

In this paper, we report the study on a new protocol for the immobilization process of antigen/antibody assay on SU-8 layers by oxygen plasma treatment. Plasma treatments, at different plasma powers and for different duration times, are performed and their effects on immobilization efficiency are studied. The chemical properties and the surface morphology of SU-8 before and after the functionalization and immobilization of (IgG) are then verified by Raman spectroscopy and atomic force microscopy (AFM). An increase of the surface roughness of SU-8 layers is observed after the oxygen plasma treatment and an intensity variation of functional groups is also evidenced. To demonstrate the validity of the process the distribution of IgG immobilized on SU-8 surfaces is detected by fluorescence microscopy measurement after incubation with fluorescein isothiocyanate (FITC)-tagged anti-human IgG. An increase of the amount of the adsorbed protein of about 20% and a good repeatability on antigen/antibody distribution on the surface are detected for IgG on plasma treated substrates. Finally, label free measurements are performed by SU-8 optical ring resonators reaching detection limits of 0.86ngcm(-2). The proposed approach offers a smart protocol for IgG immobilization on SU-8 substrate that can be easily extended to different antigen/antibody assay and polymeric materials for the realization of high performance immunosensors.

Photosensing Properties of Pentacene OFETs Based on a Novel PMMA Copolymer Gate Dielectric

In the present work, bottom-gate top-contact organic field effect transistors (OFETs) were fabricated by evaporating a pentacene semiconductor film on top of a new insulating poly(methyl methacrylate) (PMMA) copolymer containing methacrylate units. The PMMA copolymer was synthesized in order to combine the well-known insulating properties of PMMA with the possibility to be efficiently photocured enabling photopatterning-based organic circuitry integration processes. The properties of the pentacene layer deposited on ITO/PMMA copolymer stack were studied through morphological and structural analyses. Device photoresponses and photoexcitated transients were investigated and compared to reference devices based on standard PMMA gate dielectric.

Nanocomposite polymer carbon-black coating for triggering pyro-electrohydrodynamic inkjet printing

The pyro-electrohydrodynamic (EHD) manipulation of liquids has been discovered and demonstrated recently as a high resolution printing technique avoiding the use of nozzles and external electrodes. The activation of the pyro-electric effect is usually achieved on ferroelectric crystals by an external heating source or by an infrared laser. Here, we show an original modality for triggering the pyro-EHD process through a light-absorbing polymer nanocomposite thin layer deposited on the ferroelectric substrate, thus overcoming some limitations of the previous configuration. Significant simplification and compactness of the set-up is achieved thanks to the nanocomposite coating, since a commercial low-cost white-light halogen lamp can be adopted to trigger the pyro-jetting process from a liquid reservoir. Remarkably, high resolution is achieved in dispensing very high viscous liquids. Practical demonstrations in polymer optical microlenses direct printing using polydimethylsiloxane and poly(methyl methacrylate) are finally reported to validate the approach in handling high-viscous polymers for practical applications.

Inkjet printed graphene-based chemi-resistors for gas detection in environmental conditions

In this work, we report on the inkjet printing as potential technology to manufacture chemi-resistors based on liquid phase exfoliated graphene. With respect to the conventional solution-processable methods, the main IJP capability is related to the deposition of small ink volumes that entails a more controlled drying process. This specific potentiality of the IJP technique were exploited in order to investigate the reproducibility of the device performances upon NO2 and NH3 exposure and operating in environmental conditions.