Low-Voltage High-Frequency Vertical Organic Transistors

• Applicants: Professor Dr. Johann-Wolfgang Bartha; Professor Dr.-Ing. Frank Ellinger; Professor Dr. Karl Leo
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering ; Experimental Condensed Matter Physics
• Term: from 2014 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 240553371

• Final Report Year: 2018

Final Report Abstract

In this project, we successfully developed processes for the ALD of Al2O3, HfO2 and Ta2O5. The deposited layers were characterized in terms of their use in OFETs and combined into stacks. Extensive ALD-coated samples were provided for integration into OFETs. Electrical analysis of the ALD layers in MIS structures showed the best electrical results for HfO2 / Al2O3 in terms of k-value and leakage current densities. Pure Ta2O5, however, is unsuitable as a dielectric, but can be significantly improved with a 30 nm Al2O3 layer. By combining with Al2O3, the k-values, leakage current densities and threshold voltages can be modified by varying the individual layer thicknesses and layer sequences both for stacks with HfO2 and Ta2O5. Overall, the use of pure HfO2 or HfO2 in combination with a thin Al2O3 layer is recommended with regard to k-value and leakage current density. The use of SAM can potentially improve mobility in the channel. In the experiments carried out, SAM layers could be deposited from phenol. Further investigations would be necessary to reduce the uncertainties and to further optimize the process. Vertical organic field effect transistors (VOFETs) and organic permeable base transistors (OPBTs) are found to be promising candidates for low-voltage applications. Our stateof-the-art VOFETs can achieve ON/OFF current ratio of >105. OPBTs can reach intrinsic gain of 28 dB and cutoff frequency above 10 MHz below 5 V. A Colpitts oscillator was demonstrated based on the OPBTs, reaching 5.22 MHz which is the fastest reported organic oscillator so far.

Publications

• Günther A. A., Hossbach C., Sawatzki M., Kasemann D., Bartha J.W., and Leo K., “Controlling threshold voltage and leakage currents in vertical organic field-effect transistors by inversion mode operation” Appl. Phys. Lett. 107, 233302 (2015)
  Günther A. A., Hossbach C., Sawatzki M., Kasemann D., Bartha J.W., and Leo K.
  
• Comparison of MLD-processes with aromatic and linear organic precursor investigated by in situ QCM and in vacuo XPS, 16th AVS conference on Atomic Layer Deposition, Dublin, Ireland, 2016
  Fischer, D.; Knaut, M. ; Albert, M.; Bartha, J.W.
  
• Organic electronic devices with inorganic high-k gate oxides grown by Atomic Layer Deposition, 16th AVS conference on Atomic Layer Deposition, Dublin, Ireland, 2016
  Hossbach, C. ; Günther, A.; Lüssem, B.; Sawatzki, M.; Henke, T.; Knaut, M.; Kasemann, D.; Shadeedi, A.A.; Albert, M.; Leo, K.; Bartha, J.W.
  
• “A Fully-Printed Self- Biased Polymeric Audio Amplifier for Driving Fully-Printed Piezoelectric Loudspeakers”, IEEE Transactions on Circuits and Systems I: Regular Papers 63(6), 785–794, 2016
  B. Kheradmand-Boroujeni, G. C. Schmidt, D. Höft, M. Bellmann, K. Haase, K. Ishida, R. Shabanpour, T. Meister, C. Carta, P. Ghesquiere, A. C. Hübler, and F. Ellinger
  
• “Contact Doping for Vertical Organic Field-Effect Transistors”, Adv. Funct. Mater. 26: 768–775
  Günther, A. A., Sawatzki, M., Formánek, P., Kasemann, D. and Leo, K.
  
• “Small-signal characteristics of fullyprinted high-current flexible all-polymer three-layer-dielectric transistors”, Journal of Elsevier Organic Electronics 34, 267–275, 2016
  B. Kheradmand-Boroujeni, G. C. Schmidt, D. Höft, K. Haase, M. Bellmann, K. Ishida, R. Shabanpour, T. Meister, C. Carta, A. C. Hübler, and F. Ellinger
  
• Optimierung und Anwendung der Schwingquarzmesstechnik zur Untersuchung und Kontrolle der Atomlagenabscheidung, Dissertation TU Dresden, 2017
  Martin Knaut
  
• “Organic Power Electronics: Transistor Operation in the kA/cm2 Regime,” Journal of Nature Scientific Reports, vol. 7, Article number 44713, 2017
  M. P. Klinger, A. Fischer, F. Kaschura, J. Widmer, B. Kheradmand-Boroujeni, F. Ellinger, and K. Leo
  
• “A Pulse- Biasing Small-Signal Measurement Technique Enabling 40 MHz Operation of Organic Transistors,” Journal of Nature Scientific Reports, vol. 8, Article number 7643, 2018
  B. Kheradmand-Boroujeni, M. P. Klinger, A. Fischer, H. Kleemann, K. Leo, and F. Ellinger