Herbert Gold

Fabrication of n‐ and p‐Type Organic Thin Film Transistors with Minimized Gate Overlaps by Self‐Aligned Nanoimprinting

[∗] U. Palfi nger , C. Auner , H. Gold , A. Haase , J. Kraxner , G. Jakopic , J. R. Krenn , B. Stadlober Institute of Nanostructured Materials and Photonics Joanneum Research GmbH Franz-Pichlerstrasse 30, A-8160 Weiz (Austria) Fax: 0043-316-876-2710 Telephone: 0043-316-876-2721 E-mail: barbara.stadlober@joanneum.at T. Haber , M. Sezen , W. Grogger Institute for Electron Microscopy Graz University of Technology Steyrergasse 17, A-8010 Graz (Austria) G. Domann Fraunhofer-Institut für Silicatforschung ISC Neunerplatz 2, D-97082 Würzburg (Germany)

Submicron pentacene-based organic thin film transistors on flexible substrates

The authors demonstrate the fabrication of organic thin film transistors (OTFTs) based on pentacene with submicron channels on flexible substrates. Nanoimprint lithography is used for the patterning of the source and drain electrodes and processed directly on the spin-on gate dielectric, the structured gate electrode, and the flexible substrate. The use of sub-100-nm thin organic gate dielectrics enables full drain current saturation for devices with channel lengths down to 500nm. The submicron OTFTs exhibit negative threshold voltages with an absolute value well below 5V and have subthreshold swings around 0.5V/decade. This demonstrates the possibility to fabricate fully structured and miniaturized OTFTs operating at low voltages and paves the way for a low-cost fabrication of downscaled high performance organic electronic circuits.

Cellulose as biodegradable high-k dielectric layer in organic complementary inverters

We report on the natural source based and biodegradable material cellulose on Al2O3 as ultrathin hybrid high-k dielectric layer for applications in green electronics. Dielectric films of 16 nm cellulose (e ≈ 8.4) and 8 nm Al2O3 (e ≈ 9) exhibit low leakage currents up to electric fields of 1.5 MV/cm. Pentacene and C60 based organic thin film transistors show a well-balanced performance with operation voltages around 2 V. They are implemented in complementary inverters with excellent switching behavior, a small-signal gain up to 60 and with exceptionally high and balanced noise margin values of 82% at ultralow operation voltage (VDD = 2.5 V).

Nanoimprint Lithography-Structured Organic Electrochemical Transistors and Logic Circuits

We report on the fabrication of organic electrochemical transistors structured by nanoimprint lithography. The devices were scaled down as a result of our previous findings for inkjet printed transistors, where a reduced source-drain width and a shorter distance to the gate resulted in higher ON-to-OFF current ratios. We could show that these findings also prove true for transistors with feature sizes below 10 μm. Furthermore, we fabricated inverters and NAND gates with switching times below 1 s. These logic gates mark an important step for organic electrochemical transistors toward their usability in more complex logic circuits.

High-Speed Plastic Integrated Circuits: Process Integration, Design, and Test

In this paper we propose the design and measurement of functional analog and digital circuits with a response time below 1 ms, based on organic thin film transistors (OTFTs) fabricated by means of contact photolithography and self-alignment procedures. An adapted amorphous Silicon TFT compact model is used both in analytic equations and in DC Spice simulations for the design of simple organic circuits. Digital circuits such as inverters and logic gates are demonstrated with DC gains of almost 19 dB. Two analog circuits are also shown: first a differential amplifier with an open loop DC gain of 10 dB and a gain-bandwidth of 3 kHz, and second, a source coupled latch comparator tested with an input frequency of 1 kHz and a clock frequency of 10 kHz. These simple circuits comprised of only a few OTFTs are fabricated directly on flexible plastic sheets and therefore are ideal front-end interfaces for the control and fast read-out of flexible sensors.

Switching from weakly to strongly limited injection in self-aligned, nano-patterned organic transistors.

Organic thin-film transistors for high frequency applications require large transconductances in combination with minimal parasitic capacitances. Techniques aiming at eliminating parasitic capacitances are prone to produce a mismatch between electrodes, in particular gaps between the gate and the interlayer electrodes. While such mismatches are typically undesirable, we demonstrate that, in fact, device structures with a small single-sided interlayer electrode gap directly probe the detrimental contact resistance arising from the presence of an injection barrier. By employing a self-alignment nanoimprint lithography technique, asymmetric coplanar organic transistors with an intentional gap of varying size (< 0.2 μm) between gate and one interlayer electrode are fabricated. An electrode overlap exceeding 1 μm with the other interlayer has been kept. Gaps, be them source or drain-sided, do not preclude transistor operation. The operation of the device with a source-gate gap reveals a current reduction up to two orders of magnitude compared to a source-sided overlap. Drift-diffusion based simulations reveal that this marked reduction is a consequence of a weakened gate-induced field at the contact which strongly inhibits injection.

Process design kit and circuits at a 2 µm technology node for flexible wearable electronics applications(Conference Presentation)

In this work we present our most advanced technology node of organic thin film transistors (OTFTs) manufactured with a channel length as short as 2 μm by contact photolithography and a self-alignment process directly on a plastic substrate. Our process design kit (PDK) is described with P-type transistors, capacitors and 3 metal layers for connections of complex circuits. The OTFTs are composed of a double dielectric layer with a photopatternable ultra thin polymer (PNDPE) and alumina, with a thickness on the order of 100 nm. The organic semiconductor is either Pentacene or DNTT, which have a stable average mobility up to 0.1 cm2/Vs. Finally, a polymer (e.g.: Parylene-C) is used as a passivation layer. We describe also our design rules for the placement of standard circuit cells. A “plastic wafer” is fabricated containing 49 dies. Each die of 1 cm2 has between 25 to 50 devices, proving larger scale integration in such a small space, unique in organic technologies. Finally, we present the design (by simulations using a Spice model for OTFTs) and the test of analog and digital basic circuits: amplifiers with DC gains of about 20 dB, comparators, inverters and logic gates working in the frequency range of 1-10 kHz. These standard circuit cells could be used for signal conditioning and integrated as active matrices for flexible sensors from 3rd party institutions, thus opening our fab to new ideas and sophisticated pre-industrial low cost applications for the emerging fields of biomedical devices and wearable electronics for virtual/augmented reality.