Self-aligned OTFT Technology

Organic transistors with short chanellengths

 

The switching speed of organic thin film transistors (OTFTs) is essentially determined by two factors:

  • the channel length, i.e. the distance between the channel electrodes (source and drain)
  • the parasitic gate capacitance, which is mainly determined by the area of overlap between channel electrodes and gate electrode 

The smaller channel length and overlap are, the faster an OTFT can get. In order to minimise both parameters in one process we have developed a self-aligned process for OTFTs, where a nanoimprinting process (NanoImprint Lithography, NIL) is combined with a back-substrate exposure step. In a first step a high-definition gate electrode is fabricated by means of NIL, which serves as an intrinsic photomask in a further step for the photolithographic definition of the channel electrodes, where UV-exposure is carried out through the transparent substrate. With that short channel OTFTs with minimised electrode overlap are realized. This process has been successfully employed for the fabrication of OTFT-based flexible active-matrix addressing backplanes for Liquid-Crystal-Displays (LCDs) in a large European project (POLARIC).

In a modification of this process the gate electrode is defined by contact photolithography instead of NIL. Here, channel lengths are not entirely that short, yet we can pattern active areas of up to 6” on a single flexible substrate. In this way, analog circuits of some 10s of OTFTs and a footprint of a fraction of a cm² were realised, as e.g. a 10kHz clocked comparator.

Digital and analog circuits on polymer foil

References

Organic Thin Film Transistors with Minimized Gate Overlaps by Self-Aligned Nanoimprinting
U. Palfinger et al., Adv. Mat. 22, 5115 (2010)

Self-aligned flexible organic thin-film transistors with gates patterned by nano-imprint lithography; H. Gold et al. Org. Electron. 22, 140 (2015)

High-Speed Plastic Integrated Circuits: Process, Integration, Design, and Test
Miguel Torres-Miranda et al., IEEE J. Emerg. Sel. Top. Circuits Syst.7, 133 (2017)

Self-Aligned Megahertz Organic Transistors Solution-Processed on Plastic
Stuart G. Higgins et al., Adv. Electron. Mater. 1, 1500024 (2015)

Switching from weakly to strongly limited injection in self-aligned, nano-patterned organic transistors.
Karin Zojer et al., Sci. Rep. 6, 31387 (2016)

Channel length variation in self-aligned, nanoimprint lithography structured OTFTs,
T. Rothländer et al., Org. Electron. 15, 3274 (2014)

Design and modeling of self-aligned nano-imprinted sub-micrometer pentacene-based organic thin-film transistors
F. Zanella et al., Org. Electron. 14,  2756 (2013)

High-performing submicron organic thin-film transistors fabricated by residue-free embossing
C. Auner et al., Org. Electron. 11, 552 (2010)

Residue-free room temperature UV-nanoimprinting of submicron organic thin film transistors
 C. Auner et al., Org. Electr. 10, 1466 (2009)

Submicron pentacene-based organic thin film transistors on flexible substrates
U. Haas et al., Appl. Phys. Lett. 91, 043511 (2007)

Orders-of-Magnitude Reduction of the Contact Resistance in Short-Channel Hot Embossed Organic Thin Film Transistors by Oxidative Treatment of Au-Electrodes
B. Stadlober et al., Adv. Funct. Mat. 17, 2687 (2007)