30-09-2009, 07:09 PM
Low-resistance printed conductors crucial for the development of ultra-low cost electronic systems such as radio frequency identification tags. Low resistance conductors are required to enable the fabrication of high-Q inductors, capacitors, tuned circuits, and interconnect. Furthermore, conductors of appropriate work function are also required to enable fabrication of printed Schottky diodes, necessary for rectification in RFID circuits. Last year, we demonstrated the formation of low-resistance conductive printed structures using gold nano particles. Here we demonstrate, for the first time, technologies for formation of printed conductors using silver and copper nano particles. These are particularly advantageous for several reasons. First, both silver and copper offer a 2X reduction in sheet resistance over gold, resulting in improved interconnect performance and inductor Q. Second, the material costs associated with both silver and copper are expected to be significantly cheaper than gold. Third, the work function of silver enables the fabrication of all-printed Schottky diodes with a silver rectifying contact to many common printable organic semiconductors. Solutions of organic-encapsulated silver and copper nano particles may be printed and subsequently annealed to form low-resistance conductor patterns. We describe novel processes for forming silver and copper nano particles, and discuss the optimization of the printing/annealing processes to demonstrate plastic-compatible low-resistance conductors. By optimizing both the size of the nano particle and the encapsulate sublimation kinetics, it is possible to produce particles that anneal at low-temperatures (<150C) to form continuous films having low resistivity and appropriate workfunction for formation of rectifying contacts. This represents a major component required for all-printed RFID.