High-Resolution Ink-Jet Printing of All-Polymer Transistor Circuits
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High-Resolution
Ink-Jet Printing of All-Polymer Transistor Circuits
H. Sirringhaus, T. Kawase, and R.H. Friend Introduction Impressive advances in vapor-phase deposition and photolithographic patterning techniques have been fueling the silicon microelectronics revolution over the last 40 years. However, for many interesting classes of materials, including biological materials or functional synthetic polymers, vacuum deposition and photolithography are not the techniques of choice for producing ordered structures and devices. Many of these materials selfassemble into well-ordered microstructures when deposited from solution,1 and patterning may be more readily achieved by solution-based selective deposition and direct-printing techniques. It is appealing to consider novel ways of manufacturing functional circuits and devices based on techniques that are similar to printing visual information onto paper. Microfabrication by solution self-assembly and direct printing is particularly attractive for thin-film transistor (TFT) circuits based entirely on organic polymers, in which semiconducting conjugated polymers are used for the active layers, conducting polymers are used for electrodes and interconnects, and conventional insulating polymers are used for the dielectric and isolation layers. These are of interest for applications such as active-matrix-display addressing2 or logic circuits in active identification tags and labels.3 Over the last 3–4 years, rapid advances in performance have been reported on the materials front since semiconducting conjugated polymers with improved structural regularity and chemical purity have become available. By making use of supramolecular self-organization mechanisms, it is possible to deposit ordered thin polymer films from solution
MRS BULLETIN/JULY 2001
in which charge-carrier mobilities of 102 –101 cm2/V s can be achieved.4–6 These values are approaching those of thin-film amorphous silicon (0.1–1 cm2/V s) and small-molecule organic field-effect transistors7–9 (0.1–5 cm2/V s). All-polymer TFT circuits consisting of a few hundred transistors were first fabricated by a group at Philips Research Laboratories, The Netherlands, who used a more conventional photolithographic approach for patterning with 1-m resolution.10 Circuits of similar complexity and impressive performance have also been demonstrated using small organic molecules deposited at the last stage of an otherwise conventional silicon process.11,12 Several nonconventional, direct-printing approaches have been proposed. Screen printing has been used to pattern source/ drain and gate electrodes of conducting inks with channel lengths of 100 m.13 Soft lithographic techniques based on poly(dimethylsiloxane) (PDMS) stamps have been used to selectively deposit selfassembled monolayers onto thin films of gold that can be used as etch masks for the etching of gold source/drain electrodes.14 Using PDMS stamps as phase-shift masks15 in a photolithographic process, gold source/ drain electrodes have been defined with channel
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