Vertical Organic Thin-Film Transistors with an Anodized Permeable Base for Very Low Leakage Current

High-Frequency Operation of Vertical Organic Field-Effect Transistors

The high-frequency and low-voltage operation of organic thin-film transistors (OTFTs) is a key requirement for the commercial success of flexible electronics. Significant progress has been achieved in this regard by several research groups highlighting the potential of OTFTs to operate at several tens or even above 100 MHz. However, technology maturity, including scalability, integrability, and device reliability, is another crucial point for the semiconductor industry to bring OTFT-based flexible electronics into mass production. These requirements are often not met by high-frequency OTFTs reported in the literature as unconventional processes, such as shadow-mask patterning or alignment with unrealistic tolerances for production, are used. Here, ultra-short channel vertical organic field-effect transistors (VOFETs) with a unity current gain cut-off frequency (f_T ) up to 43.2 MHz (or 4.4 MHz V^-1 ) operating below 10 V are shown. Using state-of-the-art manufacturing techniques such as photolithography with reliable fabrication procedures, the integration of such devices down to the size of only 12 × 6 µm2 is shown, which is important for the adaption of this technology in high-density circuits (e.g., display driving). The intrinsic channel transconductance is analyzed and demonstrates that the frequencies up to 430 MHz can be reached if the parasitic electrode overlap is minimized.

Efficient and low-voltage vertical organic permeable base light-emitting transistors

Organic light-emitting transistors, three-terminal devices combining a thin-film transistor with a light-emitting diode, have generated increasing interest in organic electronics. However, increasing their efficiency while keeping the operating voltage low still remains a key challenge. Here, we demonstrate organic permeable base light-emitting transistors; these three-terminal vertical optoelectronic devices operate at driving voltages below 5.0 V; emit in the red, green and blue ranges; and reach, respectively, peak external quantum efficiencies of 19.6%, 24.6% and 11.8%, current efficiencies of 20.6 cd A^-1, 90.1 cd A^-1 and 27.1 cd A^-1 and maximum luminance values of 9,833 cd m^-2, 12,513 cd m^-2 and 4,753 cd m^-2. Our simulations demonstrate that the nano-pore permeable base electrode located at the centre of the device, which forms a distinctive optical microcavity and regulates charge carrier injection and transport, is the key to the good performance obtained. Our work paves the way towards efficient and low-voltage organic light-emitting transistors, useful for power-efficient active matrix displays and solid-state lighting.

Vertical organic permeable dual-base transistors for logic circuits

The main advantage of organic transistors with dual gates/bases is that the threshold voltages can be set as a function of the applied second gate/base bias, which is crucial for the application in logic gates and integrated circuits. However, incorporating a dual gate/base structure into an ultra-short channel vertical architecture represents a substantial challenge. Here, we realize a device concept of vertical organic permeable dual-base transistors, where the dual base electrodes can be used to tune the threshold voltages and change the on-currents. The detailed operation mechanisms are investigated by calibrated TCAD simulations. Finally, power-efficient logic circuits, e.g. inverter, NAND/AND computation functions are demonstrated with one single device operating at supply voltages of <2.0 V. We believe that this work offers a compact and technologically simple hardware platform with excellent application potential for vertical-channel organic transistors in complex logic circuits.

The development of vertical organic transistors with controllable threshold voltage is highly desirable for integrated circuit-based displays and sensors. Here, the authors report vertical organic permeable dual-based transistors with independently tunable on-currents and threshold voltages.

High-Performance Ultra-Short Channel Field-Effect Transistor Using Solution-Processable Colloidal Nanocrystals

We demonstrate high-mobility solution-processed inorganic field-effect transistors (FETs) with ultra-short channel (USC) length using semiconductor CdSe nanocrystals (NCs). Capping of the NCs with hybrid inorganic-organic CdCl₃^--butylamine ligands enables coarsening of the NCs during annealing at a moderate temperature, resulting in the devices having good transport characteristics with electron mobilities in the saturation regime reaching 8 cm² V^-1 s^-1. Solution-based processing of the NCs and fabrication of thin films involve neither harsh conditions nor the use of hydrazine. Employing photolithographic methods, we fabricated FETs with a vertical overlap of source and drain electrodes to achieve a submicrometer channel length. To the best of our knowledge, this is the first report on an USC FET based on colloidal semiconductor NCs. Because of a short channel length, the FETs show a normalized transconductance of 4.2 m V^-1 s^-1 with a high on/off ratio of 10⁵.