Low-resistance printed conductors are 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 interconnects. Furthermore, conductors of appropriate workfunction 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 nanoparticles. Here we demonstrate, for the first time, technologies for formation of printed conductors using silver and copper nanoparticles. 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 workfunction 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 nanoparticles may be printed and subsequently annealed to form low-resistance conductor patterns. We describe novel processes for forming silver and copper nanoparticles, and discuss the optimization of the printing/annealing processes to demonstrate plastic-compatible low-resistance conductors. By optimizing both the size of the nanoparticle and the encapsulant sublimation kinetics, it is possible to produce particles that anneal at low-temperatures (<150 °C) to form continuous films having low resistivity and appropriate workfunction for formation of rectifying contacts. This represents a major component required for allprinted RFID. INDRODUCTIONIn recent years, there has been tremendous interest in flexible electronics. Besides the obvious applications of flexible electronics in flat panel displays [1], flexible circuits are also promising for use in such applications as radio frequency identification (RFID) tags [2], low cost sensors [3], and other disposable electronic devices. In particular, devices based on organic semiconductors are considered to be very promising for these applications since they may potentially be fabricated entirely using printing technologies [4], eliminating the need for such major cost points as lithography, vacuum processing including physical vapor deposition, plasma etching, and chemical vapor deposition, while simultaneously allowing the use of reel-to-reel processing, resulting in reduced substrate handling and clean room costs as well. Furthermore, since printing is inherently additive in nature, material and disposal costs are also expected to be reduced, resulting in an extremely low net system cost.

We investigated the use of electron-beam lithography on pentacene and poly(3-hexylthiophene) field-effect transistors to achieve device isolation and enable the realization of nanoscale organic circuits. We determined the doses and exposure linewidths needed to suppress carrier transport, enabling direct patterning at the nanoscale. The precision limits were also studied through an analysis of proximity scattering effects. With an optimized pattern and exposure, we reduced off-currents by almost four orders of magnitude and gate leakage by three orders of magnitude on backgated devices. Our electron-beam isolation methods also increased the on/off ratio and drastically improved the subthreshold swing, thus attesting to the viability of this technique for patterning of organic circuits at the nanoscale.