A Step Closer to Printing-Press Electronics

One goal for the future of electronics is the ability to print large, flexible circuits using machines similar to printing presses. While great strides have been made in developing bendable and lightweight organic materials to use in this type of circuitry, methods to deposit those materials over large areas have not been as successful. Recently, a research group developed a circuit-printing technique that addresses some of the problems that have plagued other attempts.

One such problem, perhaps the biggest, is the inability of the other methods to produce high-resolution features – those down to the micron, or millionth-of-a-meter, scale.

Another issue is the rather low conductivity of the polymer materials used as electrodes in the circuits, which suggests a need for inorganic (metallic) electric contacts. An additional problem is the slight mixing of ink that occurs when ink is layered, which occurs during most types of printing. In conventional graphic-arts printing the end product isn't affected, but, in the case of “electronic inks,” mixing would compromise the electrical characteristics of the circuit.

The research group, which includes scientists from the DuPont’s Material Science and Engineering division and Organic ID, a subsidiary of Weyerhaeuser that manufactures printable RFID (radiofrequency identification) tags on plastic, fabricated a printing plate used to print the source-drain level of an array of thin-film transistors. Each transistor has a two-micron channel length (the separation between the source and drain lines, which determines transistor performance). This is the smallest channel length so far achieved by circuit-printing processes that have the potential to scale to printing presses. The plate is made of a specific polymer material – one resistant to chemical solvents used with electronic materials – on a flexible backing of Mylar, a type of plastic sheeting.

“We envision that a new generation of high-resolution printing plates in combination with nano-based inks will provide the platform for manufacturing electronic devices very similarly to what you see in commercial printing houses today,” corresponding author Graciela Blanchet of DuPont told PhysOrg.com.

The researchers inked the plate with a solution of silver nanoparticles, which, after the solvent evaporated, left it coated with a dry film of silver (thereby avoiding any mixing issues). The group next pressed the plate onto a Mylar substrate, transferring the nanoparticles from the raised portions of the plate onto the Mylar without degrading the pattern's high-resolution features. At this point, the printed silver pattern can be sintered (a process in which heat is used to increase the conductivity of the film).

The pattern consists of an array of “interdigitated” source and drain lines – that is, two interlaced stacks of lines, source lines on the left and drain lines on the right – that are all about five microns in width and separated by two microns (the transistor channel's length). Each interdigitated array (with the number of line pairs varying from 17 to 120) acts as a transistor: The lines the left are connected, defining the source of the transistor, and the lines on the right are also connected, defining the drain.

The researchers compared their array of dry-printed thin-film silver transistors to an array of gold transistors they produced using “photolithography,” a traditional fabrication method. Their electrical characteristics were nearly identical.

This research is described in the June 7 online edition of Applied Physics Letters.

Citation: Hee Hyun Lee, J. J. Brondjik, N. G. Tassi, S. Mohapatra, M. Grigas, P. Jenkins, K. J. Dimmler, and Graciela B. Blanchet, “Direct printing of organic transistors with 2 μm channel resolution.” Appl. Phys. Lett. 90, 233509 (2007)

Copyright 2007 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

Related stories:

Nano-Sun: From Traditional Printing to High Resolution Nano-Printing
IBM researchers in collaboration with scientists from the ETH Zurich have demonstrated a new, efficient and precise technique to “print” at the nanoscale.
IBM Develops Computational Scaling Solution for Next Generation '22nm' Semiconductors
In response to ever increasing demands for smaller, more powerful and energy-efficient devices for cloud computing and high-performance servers, IBM today announced the semiconductor industry's first computationally based process for production of next generation 22nm semiconductors. Known as Computational Scaling (CS) -- a process that enables the production of complex, powerful and energy-efficient semiconductors at 22nms and beyond -- this new initiative will feature support from several of IBM's key partners initially including Mentor Graphics and Toppan Printing.
'Nanonet' circuits closer to making flexible electronics reality
Researchers have overcome a major obstacle in producing transistors from networks of carbon nanotubes, a technology that could make it possible to print circuits on plastic sheets for applications including flexible displays and an electronic skin to cover an entire aircraft to monitor crack formation.
Wiping out the coffee-ring effect advances inkjet printing of electronic circuits
Researchers in California report a key advance in efforts to use inkjet printing technology in the manufacture of a new generation of low cost, high-performance electronic circuits for flexible video displays and other products. Their study, which describes development of a new method for producing straighter, uniform circuits using inkjet-printing, is scheduled for the March 4 issue of ACS’ Langmuir.
Fine print: New technique allows fast printing of microscopic electronics
A new technique for printing extraordinarily thin lines quickly over wide areas could lead to larger, less expensive and more versatile electronic displays as well new medical devices, sensors and other technologies.
Improved e-jet printing provides higher resolution and more versatility
By combining electrically induced fluid flow with nanoscale nozzles, researchers at the University of Illinois have established new benchmarks for precision control and resolution in jet-printing processes.
Chemists direct silicon oxide into a selected hierarchical structure
Chemistry often seems to operate at random. However, scientists from the Max Planck Institute of Coal Research and the International Max Planck Research School "SurMat" have been able to change that: they grew silica particles from a solution onto a surface in such a way that a pattern of tiny little cones was regularly formed.
Printable Electronics Market To Surpass $7 Billion In Revenue in 2010…
According to a new report from NanoMarkets, an industry analyst firm, the market for printable electronics will generate estimated revenues of over $7 billion ($ US) in 2010 driven by demand for printable displays, RFID, photovoltaics, computer memory and other printable products. Information about the report, “Printable Electronics: Roadmaps, Markets and Opportunities” and a white paper can be accessed from the firm’s web site at http://www.nanomarkets.net .

News discussion:

Physics news