! " #$% &' &% ( ( &' &% ) * " " +( , - ". " / ' - !" !" # $ % # $ % & '% & '% &% &% "" () () ELEKTROTECHNICA & ELEKTRONICA E+E Vol. 49. No 3-4/2014 Monthly scientific and technical journal Published by: The Union of Electronics, Electrical Engineering and Telecommunications /CEEC/, BULGARIA Editor-in-chief: C O N T E N T S Prof. Ivan Yatchev, Bulgaria ELECTRONICS Deputy Editor-in-chief: Assoc. Prof. Seferin Mirtchev, Bulgaria Mariya P. Aleksandrova, Irena P. Nestorova Editorial Board: Fabrication of flexible hybrid low molecular Akad. Prof. Chavdar Rumenin, Bulgaria weight compound/polymer light emitting device Prof. Christian Magele, Austria by screen printing 2 Prof. Georgi Mladenov, Bulgaria Radoslav B. Borisov, Kaloyan I. Zlatkov, Prof. Georgi Stoyanov, Bulgaria Plamen I. Dankov Prof. Ewen Ritchie, Denmark Near-field measurements using low cost equipment Prof. Hannes Toepfer, Germany for RF device characterization 7 Dr. Hartmut Brauer, Germany Prof. Marin Hristov, Bulgaria Vladimir V. Dimitrov, Peter T. Goranov Prof. Maurizio Repetto, Italy Modelling of step-up DC converter 13 Prof. Radi Romansky, Bulgaria Prof. Rumena Stancheva, Bulgaria Svilen H. Stoyanov Prof. Takeshi Tanaka, Japan A linear converter of strain-gauge bridge bidirectional Prof. Ventsi Valchev, Bulgaria disbalance into frequency deviation 21 Dr. Vladimir Shelyagin, Ukraine Acad. Prof. Yuriy I. Yakymenko, Ukraine ELECTRICAL ENGINEERING Assoc. Prof. Zahari Zarkov, Bulgaria Nikolay Matanov Advisory Board: Optimization of the structure and the distribution Prof. Dimitar Rachev, Bulgaria of the reactive power compensation in the industrial Prof. Emil Vladkov, Bulgaria electrical supply systems 27 Prof. Emil Sokolov, Bulgaria Prof. Ervin Ferdinandov, Bulgaria TELECOMMUNICATIONS SCIENCE Prof. Ivan Dotsinski, Bulgaria Assoc. Prof. Ivan Vassilev, Bulgaria Ivaylo I. Atanasov, Evelina N. Pencheva Assoc. Prof. Ivan Shishkov, Bulgaria A functional model extension of OMA Prof. Jecho Kostov, Bulgaria device management 34 Prof. Lyudmil Dakovski, Bulgaria Prof. Mintcho Mintchev, Bulgaria ELECTROTECHNOLOGIES Prof. Nickolay Velchev, Bulgaria Elena Koleva, Nikolinka Christova, Georgi Mladenov, Assoc. Prof. Petar Popov, Bulgaria Dmitrii Trushnikov, Vladimir Belenkiy Prof. Sava Papazov, Bulgaria Prof. Stefan Tabakov, Bulgaria Neural network based approach for quality improvement of electron beam welding 42 Technical editor: Zahari Zarkov Corresponding address: E-LEARNING 108 “Rakovski” str. Hiroyuki Izumo, Keisuke Konishi, Rei Wada, Sofia 1000 Takashi Imagawa, Susumu Kise, Shenji Hatada, BULGARIA Takeshi Tanaka, Shigeo Hirano Tel. +359 2 987 97 67 Corporate education for manufacturing (Semiconductors) - e-mail: [email protected] http://epluse.fnts.bg creation of a training system and technical textbook 49 ISSN 0861-4717 ELECTRONICS Fabrication of flexible hybrid low molecular weight compound/polymer light emitting device by screen printing Mariya P. Aleksandrova, Irena P. Nestorova It is demonstrated successful fabrication of simple bicomponent single layer OLED produced by screen printing. The device exhibits high mechanical stability after 400 cycles of bending. Turn on voltage of 5 V and maximum brightness of 92 cd/m2 is achieved at current flow 2.9 mA. Luminous efficiency is higher than the reported for similarly produced devices, reaching 3.94 lm/W and the power consumption is average 50 mW - very suitable for portable devices with battery power supply. Another advantage of the thick film technology is the higher thermal stability when operates at maximum possible voltage of 30 V for several tenth of hours. It is due to the more efficient heat dissipation from 2 ȝm thick organic coating in comparison with the thin ones (hundreds nanometers). ɂɡɝɨɬɜɹɧɟ ɧɚ ɝɴɜɤɚɜɚ ɯɢɛɪɢɞɧɚ ɧɢɫɤɨɦɨɥɟɤɭɥɧɚ/ɩɨɥɢɦɟɪɧɚ ɫɜɟɬɨɢɡɥɴɱɜɚɳɚ ɫɬɪɭɤɬɭ- ɪɚ ɱɪɟɡ ɫɢɬɨɩɟɱɚɬ (Ɇɚɪɢɹ Ⱥɥɟɤɫɚɧɞɪɨɜɚ, ɂɪɟɧɚ ɇɟɫɬɨɪɨɜɚ). ɉɨɤɚɡɚɧɨ ɟ ɭɫɩɟɲɧɨɬɨ ɩɨɥɭɱɚ- ɜɚɧɟ ɧɚ ɩɪɨɫɬ ɟɞɧɨɫɥɨɟɧ ɞɜɭɤɨɦɩɨɧɟɧɬɟɧ OLED (ɨɪɝɚɧɢɱɟɧ ɞɢɫɩɥɟɟɧ ɟɥɟɦɟɧɬ) ɱɪɟɡ ɫɢɬɨɩɟ- ɱɚɬ. ɋɬɪɭɤɬɭɪɚɬɚ ɩɪɨɹɜɹɜɚ ɜɢɫɨɤɚ ɦɟɯɚɧɢɱɧɚ ɭɫɬɨɣɱɢɜɨɫɬ ɫɥɟɞ 400 ɰɢɤɴɥɚ ɧɚ ɨɝɴɜɚɧɟ. ɇɚɩ- ɪɟɠɟɧɢɟɬɨ ɧɚ ɡɚɩɚɥɜɚɧɟ ɧɚ ɥɭɦɢɧɟɫɰɟɧɰɢɹɬɚ ɟ 5 V, ɚ ɦɚɤɫɢɦɚɥɧɚɬɚ ɹɪɤɨɫɬ ɟ 92 cd/m2 ɢ ɟ ɞɨɫ- ɬɢɝɧɚɬɚ ɩɪɢ ɬɨɤ ɨɬ 2.9 mA. Ʌɭɦɢɧɟɫɰɟɧɬɧɚɬɚ ɟɮɟɤɬɢɜɧɨɫɬ ɟ ɩɨɞɨɛɪɟɧɚ ɫɩɪɹɦɨ ɞɨɤɥɚɞɜɚɧɢ ɜ ɥɢɬɟɪɚɬɭɪɚɬɚ ɫɬɨɣɧɨɫɬɢ ɡɚ ɩɨɞɨɛɟɧ ɬɢɩ ɭɫɬɪɨɣɫɬɜɚ ɢ ɟ 3.94 lm/W, ɚ ɤɨɧɫɭɦɢɪɚɧɚɬɚ ɦɨɳ- ɧɨɫɬ ɟ ɫɪɟɞɧɨ 50 mW, ɤɨɟɬɨ ɩɪɚɜɢ ɫɬɪɭɤɬɭɪɚɬɚ ɩɨɞɯɨɞɹɳɚ ɡɚ ɩɪɢɥɨɠɟɧɢɟ ɜ ɦɨɛɢɥɧɢ ɭɫɬɪɨɣ- ɫɬɜɚ Ⱦɪɭɝɨ ɩɪɟɞɢɦɫɬɜɨ, ɩɪɨɢɡɬɢɱɚɳɨ ɨɬ ɩɪɢɥɚɝɚɧɟɬɨ ɧɚ ɞɟɛɟɥɨɫɥɨɣɧɚ ɬɟɯɧɨɥɨɝɢɹ ɟ ɩɨ-ɞɨɛ- ɪɚɬɚ ɬɟɪɦɢɱɧɚ ɭɫɬɨɣɱɢɜɨɫɬ ɩɪɢ ɪɚɛɨɬɚ ɫ ɦɚɤɫɢɦɚɥɧɨ ɧɚɩɪɟɠɟɧɢɟ ɨɬ 30 V ɜ ɩɪɨɞɴɥɠɟɧɢɟ ɧɚ ɧɹɤɨɥɤɨ ɱɚɫɚ. Ɍɨɜɚ ɫɟ ɞɴɥɠɢ ɧɚ ɩɨ-ɟɮɟɤɬɢɜɧɨɬɨ ɬɨɩɥɢɧɧɨ ɪɚɡɫɟɣɜɚɧɟ ɨɬ ɞɟɛɟɥɢɹ 2 ȝm ɨɪɝɚɧɢ- ɱɟɧ ɫɥɨɣ ɜ ɫɪɚɜɧɟɧɢɟ ɫɴɫ ɫɥɭɱɚɹ ɧɚ ɬɴɧɴɤ ɧɚɧɨɫɥɨɣ. Introduction reported 100 nm screen printed film with four Despite of the significant improvement of the component blend from polystyrene doped with NPB, multilayer organic light emitting devices (OLEDs) [1], Alq3 and rubrene. In [8] has been processed [2], single layer OLED should not be neglected, polystyrene, rubrene, Į-NPD and DPVBi for white because of their simpler structure and easier OLED produced by screen printed film. It is used fabrication process [3]. Low molecular weight substance Ir(ppy)3 to enhance device brightness to 2 compound (LMWC) OLEDs have been more 470-750 cd/m , but the activation voltage hasn’t still developed in comparison with the high molecular been reduced and varied between 28-33 V. Earlier, weight compound (polymer) OLEDs. Both classes of Pardo et. al. have demonstrated screen printing of materials are implemented in the electroluminescent even less than 100 nm film as a new approach to “sandwich” type devices (the active layer is situated fabricate OLEDs [9]. As can be seen, in the researches between two electrodes) as a thin 50-150 nm films. In reported until now, screen printed films are thin. order to increase the efficiency of the single layer However, if the screen printed film is thick (which is OLED different approaches have been used as actually the idea of this method), then the volume of electrode’s surface treatment for roughness decrease the functional organic material would be higher and [4], replacing of the transparent electrode material [5] generated heat during operation would be better or doping with different nanoparticles, blended to the spread in the surrounding environment, instead to main emissive material [6]. Recently, some papers accumulate inside the structure and causes melting of regarding application of screen printing technique for the flexible substrate. organic electroluminescent layers [7], [8]. In [7] are In our paper we present results from fabrication 2 “ȿ+ȿ”, 3-4/2014 and testing of single layer hybrid flexible OLED, voltages 20-30V, providing high brightness of the obtained by screen printing. The samples produced are generated emission with no substrate damages, caused characterized by high stability after hundreds of by the heat. The reason is higher volume of organic bending cycles, because of the binder presence as well material, dissipating much better the heat to the as by high thermal stability due to the thick organic ambient through the upper metal electrode without film, dissipated effective the heat generated during thermal breakdown in comparison to thin films. The operation. There are no data about investigation of host polymer PVK, which also play a role of hole hybrid between LMWC and hole conductive host transporting material, added to the main material polymer, playing a role of binder in the same time. By provides viscosity increase and enhances the adhesion our knowledge there are no reports in the literature of the electroluminescent layer to the flexible about application of screen printing method for substrate. Although it is not shown on the figures, flexible OLED fabrication, as well as about using of when the concentration of the binder increases, the such bi-component organic mixture for glass or current flow and the luminance decrease, which could flexible based device, independently on the deposition be due to the quenching of the excited states from method. dominated host particles. The surface morphology of the screen printed hybrid LMWC/polymer coating Materials and methods was found to be strongly affected by the conditions Polyethylentherephtalate (PET) foil with sizes such as stencil resolution, strength and angle of the 30x30 mm served as a flexible substrate. Indium tin squeegee moving across the screen stencil, forcing oxide (ITO) electrode with thickness 180 nm, sheet paste into the mesh openings and planarity of the resistance 22 ohms/square and transparency for the covered surface. Microscopic view of the produced visible light 83%, was achieved by RF reactive thick film’s surface is shown on Fig. 1 at sputtering followed by UV treatment [10]. Tris (8- magnification 100. As can be seen in this case, after hydroxyquinolinato) aluminium soluble derivative supplying of the screen printed organic (Alq3-D) was used as yellow-green electrolumi- crystal/polymeric coating on flexible PET/ITO nescent material. It is mixed with binding host substrate there are no pinholes formed in the film in polymer polyvinylcarbazole (PVK) having enhanced comparison with the way they occur in polystyrene hole transporting properties. The weight ratio of 100 nm film screen printed on glass/ITO [7]. LMWC and the polymer