Downscaling of self-aligned, all-printed polymer thin-film transistors

Printing is an emerging approach for low-cost, large-area manufacturing of electronic circuits, but it suffers from poor resolution, large overlap capacitances, and film thickness limitations resulting in slow circuit speed and high operating voltages. Here we demonstrate a self-aligned printing approach that allows downscaling of printed organic thin-film transistors to channel lengths of 100 - 400 nm. The use of a cross-linkable polymer gate dielectric with 30 - 50 nm thickness ensures that basic scaling requirements are fulfilled and operating voltages are below 5 V. The device architecture minimizes contact resistance effects enabling clean scaling of transistor current with channel length. A self-aligned gate configuration minimizes the parasitic overlap capacitance to low values of down to 0.2-0.6 pF/mm and allows reaching transition frequencies of fT = 1.6 MHz. Our self-aligned process provides a path for improving the performance of printed organic transistor circuits by downscaling while remaining compatible with the requirements of large-area, flexible electronics manufacturing.

Reference: Yong-Young Noh, Ni Zhao, Mario Caironi and Henning Sirringhaus, Downscaling of self-aligned, all-printed polymer thin film transistors, Nature Nanotechnology 2 (12), 784-789 (2007)

Multicomponent semiconducting polymer systems with low crystallization-induced percolation threshold

Blends and other multicomponent systems are used in various polymer applications to meet multiple requirements that cannot be fulfilled by a single material. In polymer optoelectronic devices it is often desirable to combine the semiconducting properties of the conjugated species with the excellent mechanical properties of certain commodity polymers. Here we investigate bicomponent blends comprising semicrystalline regioregular poly(3-hexylthiophene) and selected semicrystalline commodity polymers, and show that, owing to a highly favourable, crystallization-induced phase segregation of the two components, during which the semiconductor is predominantly expelled to the surfaces of cast films, we can obtain vertically stratified structures in a one-step process. Incorporating these as active layers in polymer field-effect transistors, we find that the concentration of the semiconductor can be reduced to values as low as 3 wt% without any degradation in device performance. This is in stark contrast to blends containing an amorphous insulating polymer, for which significant reduction in electrical performance was reported. Crystalline-crystalline/semiconducting-insulating multicomponent systems offer expanded flexibility for realizing high-performance semiconducting architectures at drastically reduced materials cost with improved mechanical properties and environmental stability, without the need to design all performance requirements into the active semiconducting polymer itself.

Reference: Shalom Goffri, Christian Muller, Natalie Stingelin-Stutzmann, Dag W. Breiby, Christopher P. Radano, Jens W. Andreasen, Richard Thompson, Rene A. J. Janssen, Martin M. Nielson, Paul Smith and Henning Sirringhaus, "Multicomponent semiconducting polymer systems with low crystallization-induced percolation threshold", Advanced Materials 18(20), 2708 - 2712 (2006)

Ambipolar, Light-Emitting, Bottom Contact/Top Gate Polymer Field-Effect Transistor

Video: Light Emission from F8BT bottom contact/top gate transistor (mpeg (5.1 MB)

We fabricated bright, ambipolar, light-emitting polymer field-effect transistors in a bottom-contact/top-gate structure using poly(9,9-di-n-octylfluorene-alt- benzothiadiazole) (F8BT) as a green-emitting semiconductor, which show balanced hole and electron mobilities. The emission zone, observed as a bright line, is well defined and can be moved through the channel.
Reference: Jana Zaumseil, Carrie L. Donley, Ji-Seon Kim, Richard H. Friend and Henning Sirringhaus, "Efficient Top-Gate, Ambipolar, Light-Emitting Field-Effect Transistors Based on a Green-Light-Emitting Polyfluorene", Advanced Materials 18(20), 2708 - 2712 (2006)

Spatial Control of the Recombination Zone in an Ambipolar Organic Light-emitting Transistor

Light-emission at different gate voltages and constant current, channel length = 80 μm

VIDEOS

Light Emission at constant gate voltage (mpeg (5.9 MB), avi (2.2 MB))

Light Emission from the channel edge (mpeg (4.7 MB), avi (1.9 MB))

Light Emission at constant drain current (mpeg (5.4 MB), avi (1.9 MB))

We demonstrate that the position of the recombination and emission zone in an ambipolar organic light-emitting transitor can be controlled through the applied voltages in both constant gate voltage and constant current mode. We use the electroluminescent polymer OC1C10-PPV, suitable injecting electrodes (Ca/Au) and a trapfree dielectric (BCB) to fabricate organic field-effect transistors that support both hole and electron transport. At certain bias conditions opposite charge carriers are injected from source and drain electrode, respectively, and form accumulation layers. Where these meet charge recombination and light emission take place, visible as a narrow line. This is an unambiguous proof and visualisation of conjunct channels of holes and electrons in ambipolar transistors.

Schematic structure of a light-emitting transistor.

J. Zaumseil R. H. Friend and Henning Sirringhaus; "Spatial Control of the Recombination Zone in an Ambipolar Light-Emitting Organic Transistor", Nature Materials 5 , 69–74 (2006) Self-Aligned Inkjet Printing with Sub-Hundred-Nanometer Resolution We developed a new self-aligned additive printing technique (SAP) that uses standard inkjet-printing equipment, but is capable of achieving sub-100 nm resolution without any lithographic steps. Very small gaps between two printed electrodes can be defined uniformly and with high yield by controlling the receeding contact-line motion of liquid conductive ink droplets that are repelled and flow off the surface of a previously deposited electrode. Polymer transistors fabricated with this technique are two orders of magnitude faster than previous organic printed transistor circuits. We believe SAP to be a potentially scalable and practically manufacturable nanopatterning tool for liquid-based hierarchical self-assembly of functional nanostructures in a broad range of fields and applications. Reference: C. W. Sele, T. von Werne, R. H. Friend and Henning Sirringhaus; "Lithography-Free, Self-Aligned Inkjet Printing with Sub-Hundred-Nanometer Resolution ", Adv. Mater. 17, 997 (2005) General Observation of Electron Transport in Polymer Field-Effect Transistors We have shown that many well known conjugated polymers are capable of conducting electrons in field-effect transistors when appropriate injecting electrodes (e.g. Ca) and trap-free dielectrics (e.g. BCB) are used. These polymers include polyfluorenes (e.g. F8BT, see graph), PPVs and polythiophenes (P3HT). Electron mobilities are similar to hole mobilities in these materials. This opens the way to ambipolar devices which are crucial for low power CMOS applications in organic electronics. Schematic structure and performance characteristics of n-type polymer transistors with BCB as a trap-free dielectric. Reference: L.-L. Chua, J. Zaumseil, J.-F. Chang, E.C.W. Ou, P.K.H. Ho, H. Sirringhaus and R.H. Friend, "General Observation of n-Type Field-Effect Behaviour in Organic Semiconductors" Nature 434, 194 (2005)

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