Arved C. Hübler

Polymer-based organic field-effect transistor using offset printed source/drain structures

Organic field-effect transistors were fabricated using offset printed source/drain structures. Interdigitated electrode structures were printed with a poly(3,4–ethylenedioxythiophene) (PEDOT) formulation. A polymeric semiconductor polytriarylamine and different insulator layers were deposited by spin coating. A field-effect mobility of 3×10−3cm2V−1s−1 and on/off ratio of about 103 was achieved, making it possible to produce digital logic elements.

Complementary Ring Oscillator Exclusively Prepared by Means of Gravure and Flexographic Printing

A complementary ring oscillator has been prepared using exclusively fast and continuous rotary printing methods, namely, gravure and flexographic printing, so that all layers were additively deposited and no additional patterning nor interconnecting step whatsoever was involved. This became possible due to the availability of a printable air-stable n-type organic semiconductor, i.e., a small molecule perylene derivative. Using the same dielectric for both types of transistors, the characteristics of the n-type transistors are reasonably similar to the ones of the p-type transistors, which are based on the previously used organic semiconductor 6,13-bis(triisopropylsilylethynyl) pentacene. The printed circuits are robust against variations of individual transistor parameters and significantly outperform comparable unipolar circuits in terms of all relevant properties. The superior performance can be attributed to complementary circuitry, the advantage of which is thereby demonstrated for the case of printed circuits.

Printed MWCNT-PDMS-Composite Pressure Sensor System for Plantar Pressure Monitoring in Ulcer Prevention

In this paper, a low cost and flexible plantar pressure monitoring system is presented that is suited for everyday use to prevent pressure ulcers. To define the technical specifications of the sensor system, a gait analysis study was carried out. Analysis of measured data based on a multivariate approach and neural network classification shows that it is possible to dissociate between healthy and unhealthy rollover patterns. To implement a pressure sensor element, a multiwalled carbon nanotube (MWCNT)-polydimethylsiloxane (PDMS)-composite was selected. A sensor matrix made of the composite was fully printed to enable pressure distribution measurements. As a final application, a printed insole was fabricated with six single MWCNT-PDMS pressure sensors that were situated on characteristic points of the insole to detect the unhealthy rollover patterns. Its functionality to measure plantar pressures was proven on a human foot inside a running shoe during walking.

Carbon Nanotube Areas — Printed on Textile and Paper Substrates

Mass printing processes are the key technology to produce mass products to the point of one-disposable. Carbon nanotube (CNT) based structures were prepared by flexographic printing using multi-walled carbon nanotube (MWCNT) dispersions in water. The carbon nanotubes were applied to a textile substrate made of polyester and polyamide microfilaments and to both-side coated paper to produce electrically conductive layers that can be used, for example, as heating elements. Carbon nanotube layers with sheet resistivity ranging from 0.12 to 3.00 kΩ/sq were obtained. The ratio of radiation power PS (determined according to the Stefan-Boltzmann law) of the printed layers to the electrical power spent, represents the efficiency of the system. The samples on textile substrate with a surface temperature of 169°C have an efficiency of 25%, the paper samples with a surface temperature of 93 °C have an efficiency of about 15 %.

Analog Characteristics of Fully Printed Flexible Organic Transistors Fabricated With Low-Cost Mass-Printing Techniques

Fully printed organic field effect transistors (OFETs) are fabricated on a flexible, 100-μm-thick, polyethylene terephthalate substrate using high-throughput printing techniques: 1) Cyflex; 2) gravure; 3) screen; and 4) flexographic printing without using a cleanroom, and below 130°C. The dependence of the transconductance g_m, transit-frequency f_T, and intrinsic-gain on the bias drain current I_D are measured. The OFETs show intrinsic gain for I_D >10 nA mm (per millimeter width), and reach f_T=64 kHz at I_D = 16 μA/mm, whereas the g_m loss with frequency is 10% up to f_T. Unlike silicon MOSFETs, the dependence of the OFET g_m on the f_T in the subthreshold region is found to be weaker than I_D^1.0. In addition, the overlap capacitance of the staggered-geometry OFET shows strong frequency dependence, and this is shown to be related to the overlap semiconductor. For the first time, it is found that the impact of process variations and bias stress on the OFET analog characteristics can be significantly attenuated by biasing the device at a fixed I_D. This approach is tested on an array of five amplifiers, reaching the gain-bandwidth product of 32 kHz, within ±3.7% variations.

Naphtalenediimide-based donor–acceptor copolymer prepared by chain-growth catalyst-transfer polycondensation: evaluation of electron-transporting properties and application in printed polymer transistors

The semiconducting properties of a bithiophene-naphthalene diimide copolymer (PNDIT2) prepared by Ni-catalyzed chain-growth polycondensation (P1) and commercially available N2200 synthesized by Pd-catalyzed step-growth polycondensation were compared. Both polymers show similar electron mobility of ∼0.2 cm2 V−1 s−1, as measured in top-gate OFETs with Au source/drain electrodes. It is noteworthy that the new synthesis has several technological advantages compared to traditional Stille polycondensation, as it proceeds rapidly at room temperature and does not involve toxic tin-based monomers. Furthermore, a step forward to fully printed polymeric devices was achieved. To this end, transistors with PEDOT:PSS source/drain electrodes were fabricated on plastic foils by means of mass printing technologies in a roll-to-roll printing press. Surface treatment of the printed electrodes with PEIE, which reduces the work function of PEDOT:PSS, was essential to lower the threshold voltage and achieve high electron mobility. Fully polymeric P1 and N2200-based OFETs achieved average linear and saturation FET mobilities of >0.08 cm2 V−1 s−1. Hence, the performance of n-type, plastic OFET devices prepared in ambient laboratory conditions approaches those achieved by more sophisticated and expensive technologies, utilizing gold electrodes and time/energy consuming thermal annealing and lithographic steps.

Modified poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) source/drain electrodes for fully printed organic field-effect transistors consisting of a semiconductor blend

The influence of post-press treatment on the modification of printed source/drain electrodes made of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) with ethylene glycol is presented. Beside changes of the geometry and the conductivity of these mass printed structures, the work function of PEDOT:PSS can be tuned, leading to an improved performance of organic field effect transistors (OFETs). OFETs were built up with a new small molecule/polymer blend consisting of 6,13-bis[(cyclopropyldiisopropylsilyl)ethynyl] pentacene and poly(triarylamine), providing a field effect mobility of 0.2u2009cm2/Vs for fully printed devices in air. Ring oscillators based on these OFETs demonstrate a frequency of more than 1 kHz.

Analysis of dopamine on printed polymer thin film consisting of multi-walled carbon nanotubes

A novel film consisting of multi-walled carbon nanotubes (MWCNTs) was produced by means of a flexographic printing process on polycarbonate substrate. The electrochemical response of this MWCNT-PC film towards oxidation of dopamine to dopamine-o-quinone was investigated in phosphate buffer solution (pH 7) by means of cyclic voltammetry and electrochemical impedance spectroscopy. The findings demonstrate that the MWCNT-PC film possesses good performance for the electrochemical oxidation of dopamine. Namely, the fabricated MWCNT-PC film having a detection limit and sensitivity of 4.06xa0μM and 0.823xa0Axa0M−1xa0cm−2, respectively, seems to have greater detection ability towards dopamine/dopamine-o-quinone compared to other novel electrodes reported in the literature. The results of the present work are very promising and demonstrate that the MWCNT-PC film could be suitable for the electrochemical analysis of molecules with biological interest.Graphical abstract

Labeling the World: Tagging Mass Products with Printing Processes

There are many motivations for labeling items to link the real and the virtual world, including supply chain management; fabrication control process efficiency improvement; complete product traceability; product liability; quality guarantees; and recycling products correctly. The article discusses some of the automatic identification (auto-id) technologies that includes printed ID codes, 1D/2D bar codes, RFID, magnetic stripe and smart card(chip) to label various products. Labeling technologies for industrial applications must meet several demands, requiring highly efficient mass production processes for tagging technologies and readers.

Solution processable interface materials for nanoparticulate organic photovoltaic devices

Nanoparticulate zinc oxide can be prepared at low temperatures from solution processable zinc acetylacetonate. The use of this material as a cathode interfacial layer in nanoparticulate organic photovoltaic devices results in comparable performances to those based on reactive calcium layers. Importantly, the enhanced degradation stability and full solution processability make zinc oxide a more desirable material for the fabrication of large area printed devices.