An Approach towards the Printing of Polymer Circuits
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An Approach towards the Printing of Polymer Circuits Alexander Knobloch, Adolf Bernds and Wolfgang Clemens Siemens Corporate Technology, Paul-Gossen-Str. 100, D-91052 Erlangen, Germany ABSTRACT The combination of soluble polymers with printing and coating techniques enabled the fabrication of polymer field-effect transistors (PFETs) on flexible films. The devices were built in a top gate configuration, with four functional layers deposited. The electrodes were patterned by gravure offset printing, where source-drain were made from conducting polyanilin and carbon black filled conducting ink was used as gate material. The doctor blading technique was utilized for coating low viscosity solutions, where Poly(3-alkyllthiophene) served as active semiconductor material. Thus completely printed PFETs have been demonstrated. Further steps for printing integrated polymer circuits included the fabrication of inverters combined from two printed. Screen-printing could be used as an alternative to coating and has the potential to enable vertical electrical interconnects between top and bottom layer of circuits. To test the suitability insulating layers were screen-printed homogenously onto lithographically patterned electrodes made from gold. The PFETs´ yield was sufficient enough to let a 7-stage ring oscillator work with a clock frequency of 4 Hz. INTRODUCTION The performance of functional polymers has reached a level of being suitable for microelectronics applications, like electronic barcodes [1-3]. Especially soluble polymers benefit from high flexibility and easy processability, Nevertheless, this can be used only to full advantage, if new processing techniques are developed and investigated. Several groups already reported the printing of single layers for organic transistors [4]. For example source-drain electrodes were patterned by micro-contact printing, which is a highly precise type of flexographic printing [5,6]. Further patterned source-drain electrodes were applying using ink jet printing [7]. Screen-printing was used for deposited insulating material in a transistor [8], as well electrodes made from silver filled ink or doped poly(3,4-ethylenedioxythiophene) paste were printed [9,10]. However, so far no complete concept for printing of integrated polymer circuits was shown. Our work in printing of single polymer field effect transistors (PFETs) [11,12] is now extended to logical circuits. At first, the smallest logical elements – inverters – have been built and characterised. Our next steps for future integration of the inverters are presented. EXPERIMENTAL DETAILS PFETs were fabricated in a top gate configuration on flexible poly(ethyleneterephtalate) (PET) films [11]. First, dissolved polyanilin (PANI) was doctor bladed in thin layers onto the PET films. After drying patterns of conventional printing ink were transferred by gravure offset printing onto the conducting polymer. Then the unprotected PANI was etched and the ink removed afterwards. Thus it was possible to fabricate interdigital source-drain
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