Inkjet-printed vertically emitting solid-state organic lasers

In this paper, we show that Inkjet Printing can be successfully applied to external-cavity vertically-emitting thin-film organic lasers, and can be used to generate a diffraction-limited output beam with an output energy as high as 33.6 uJ with a slope efficiency S of 34%. Laser emission shows to be continuously tunable from 570 to 670 nm using an intracavity polymer-based Fabry-Perot etalon. High-optical quality films with several um thicknesses are realized thanks to ink-jet printing. We introduce a new optical material where EMD6415 commercial ink constitutes the optical host matrix and exhibits a refractive index of 1.5 and an absorption coefficient of 0.66 cm-1 at 550-680 nm. Standard laser dyes like Pyromethene 597 and Rhodamine 640 are incorporated in solution to the EMD6415 ink. Such large size " printed pixels " of 50 mm 2 present uniform and flat surfaces, with roughness measured as low as 1.5 nm in different locations of a 50um x 50um AFM scan. Finally, as the gain capsules fabricated by Inkjet printing are simple and do not incorporate any tuning or cavity element, they are simple to make, have a negligible fabrication cost and can be used as fully disposable items. This works opens the way towards the fabrication of really low-cost tunable visible lasers with an affordable technology that has the potential to be widely disseminated

In vivo recordings of brain activity using organic transistors.

In vivo electrophysiological recordings of neuronal circuits are necessary for diagnostic purposes and for brain-machine interfaces. Organic electronic devices constitute a promising candidate because of their mechanical flexibility and biocompatibility. Here we demonstrate the engineering of an organic electrochemical transistor embedded in an ultrathin organic film designed to record electrophysiological signals on the surface of the brain. The device, tested in vivo on epileptiform discharges, displayed superior signal-to-noise ratio due to local amplification compared with surface electrodes. The organic transistor was able to record on the surface low-amplitude brain activities, which were poorly resolved with surface electrodes. This study introduces a new class of biocompatible, highly flexible devices for recording brain activity with superior signal-to-noise ratio that hold great promise for medical applications

High transconductance organic electrochemical transistors.

The development of transistors with high gain is essential for applications ranging from switching elements and drivers to transducers for chemical and biological sensing. Organic transistors have become well-established based on their distinct advantages, including ease of fabrication, synthetic freedom for chemical functionalization, and the ability to take on unique form factors. These devices, however, are largely viewed as belonging to the low-end of the performance spectrum. Here we present organic electrochemical transistors with a transconductance in the mS range, outperforming transistors from both traditional and emerging semiconductors. The transconductance of these devices remains fairly constant from DC up to a frequency of the order of 1 kHz, a value determined by the process of ion transport between the electrolyte and the channel. These devices, which continue to work even after being crumpled, are predicted to be highly relevant as transducers in biosensing applications

Flexible Electronics Sensors for Tactile Multi-Touching

Flexible electronics sensors for tactile applications in multi-touch sensing and large scale manufacturing were designed and fabricated. The sensors are based on polyimide substrates, with thixotropy materials used to print organic resistances and a bump on the top polyimide layer. The gap between the bottom electrode layer and the resistance layer provides a buffer distance to reduce erroneous contact during large bending. Experimental results show that the top membrane with a bump protrusion and a resistance layer had a large deflection and a quick sensitive response. The bump and resistance layer provided a concentrated von Mises stress force and inertial force on the top membrane center. When the top membrane had no bump, it had a transient response delay time and took longer to reach steady-state. For printing thick structures of flexible electronics sensors, diffusion effects and dimensional shrinkages can be improved by using a paste material with a high viscosity. Linear algorithm matrixes with Gaussian elimination and control system scanning were used for multi-touch detection. Flexible electronics sensors were printed with a resistance thickness of about 32 μm and a bump thickness of about 0.2 mm. Feasibility studies show that printing technology is appropriate for large scale manufacturing, producing sensors at a low cost

Elaboration d'une expérience d'autodoublage de fréquence en solution de matériaux organiques multifonctionnels

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Inkjet-printed low-voltage organic thin-film transistors: Towards low-cost flexible electronics

International audienceIn this paper, we demonstrate how to enhance performances of Organic Thin-Film Transistors (OTFTs) made on flexible substrates by low-cost inkjet printing technique. Especially, we focus our attention on contact resistance to the channel in order to explain the differences in OTFT performances. For this, we first evaluate, on oxidized silicon wafer, the performances of several inkjetted couples of Organic Semiconductor(OSC)/Source and Drain (SD) electrodes compared to devices with evaporated metal SD. By this way, we show that inkjet printing is a suitable low-cost technique to dispense polymers and inorganic nanoparticules for the direct-writing of OTFTs. We obtain lower contact resistances when conducting polymer (PedotlPss) contacts the OTFT channel than evaporated metal (Au, Pt). Then, our strategy consists of printing the optimized OSC/SD electrodes couples on a multilayered cheap flexible substrate, coating with an ultrathin gate oxide (4nm), which allows low-operating for the printed OTFTs ([V] <3V). All these results pave the way towards flexible electronics applications. Copyright © 2007 Materials Research Society

Fake fingers in fingerprint recognition.

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Inkjet-printed polymer thin-film transistors: Enhancing performances by contact resistances engineering

International audienceIn this paper, we demonstrate how to enhance polymer thin-film transistors (PTFTs) performances made by low-cost inkjet printing technique. Indeed, in PTFTs, contact resistances between semiconducting conjugated polymers (SCPs) and Source and Drain (S&D) contacts may dominate the transport properties of such electronic devices. Here, we report measurements of these parasitic resistances for several couples of (i) SCPs, as active material, and (ii) electrodes, as S&D contacts, in bottom-contact inkjetted PTFTs. The differences in PTFT performances are discussed upon these contact resistance. For this, we evaluate the performances of several inkjetted couples of SCP/S&D compared to devices with evaporated metal-based S&D. By this way, we show that inkjet printing is a suitable low-cost technique to dispense polymers and inorganic nanoparticles for direct-writing of PTFTs. A significant reduction in the contact resistance RC was achieved when inkjetted Pedot: Pss-based S&D electrodes are used instead of evaporated metal-based S&D electrodes. The improved efficiency of charge carrier injection is assumed to be due to the formation of a p-doped interfacial layer at the interface between the SCP and the S&D electrodes. All these results pave the way towards flexible electronics applications by using inkjetted polymers both for electrodes and semiconducting active layer on flexible plastic substrate

Recent Progress in Flexible and Wearable All Organic Photoplethysmography Sensors for SpO2 Monitoring

Abstract Flexible and wearable biosensors are the next‐generation healthcare devices that can efficiently monitor human health conditions in day‐to‐day life. Moreover, the rapid growth and technological advancements in wearable optoelectronics have promoted the development of flexible organic photoplethysmography (PPG) biosensor systems that can be implanted directly onto the human body without any additional interface for efficient bio‐signal monitoring. As an example, the pulse oximeter utilizes PPG signals to monitor the oxygen saturation (SpO2) in the blood volume using two distinct wavelengths with organic light emitting diode (OLED) as light source and an organic photodiode (OPD) as light sensor. Utilizing the flexible and soft properties of organic semiconductors, pulse oximeter can be both flexible and conformal when fabricated on thin polymeric substrates. It can also provide highly efficient human‐machine interface systems that can allow for long‐time biological integration and flawless measurement of signal data. In this work, a clear and systematic overview of the latest progress and updates in flexible and wearable all‐organic pulse oximetry sensors for SpO2 monitoring, including design and geometry, processing techniques and materials, encapsulation and various factors affecting the device performance, and limitations are provided. Finally, some of the research challenges and future opportunities in the field are mentioned