Quantum-mechanical device concepts including ultra-thin functional ALD-films for terahertz applications

• Applicants: Professor Dr. Johann-Wolfgang Bartha; Professor Dr.-Ing. Christian Wenger
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: from 2013 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 226970965

• Final Report Year: 2019

Final Report Abstract

The project was dealing with the study and understanding of the deposition of ultra-thin dielectric layers and their electronic interaction with a bidimensional (2D) material, namely Graphene (G). This study was motivated by the thriving interest of 2D materials in electronics and the theoretical prediction that the use of graphene along with high-quality, ultra-thin dielectric layers could enable a new generation of ballistic hot electron transistors (HET). This type of HET is known as Graphene-base Transistor (GBT), where the 2D material takes the place of the base electrode, in a usual bipolar transistor, for the control of the vertical current. High-quality, ultra-thin dielectrics layers are critical for the operation of GBT. For this purpose, the Atomic Layer Deposition (ALD) of dielectrics on G was investigated. The challenge in the deposition of ultra-thin, pinhole-free layers on G is the lack of dangling bond on the sp2-carbon network. Furthermore, this project introduced an innovative approach by implementing nano-sized electrodes (<50 nm), which have been reported to induce a localized electric field enhancement. The objectives and efforts of this project were divided in two work packages: (1) the nucleation of ultrathin ALD dielectric layers on graphene and (2) the preparation of GBT structures and their electrical characterization. To this end, bright- and dark-field optical microscopy was applied for a fast and simple characterization of the G layers quality. Also, the ALD of Al2O3 on G with conductive and non-conductive substrates was investigated. Along with this, it was found that the use of a NF3 pretreatment to graphene and/or the variation of the deposition parameters of Al2O3 by ALD showed a beneficial impact to improve the coverage and reduce pinholes in the dielectric surface. Through a combination of optical lithography, wet/reactive ion etching, and chemical mechanical polishing conical Si tips of different pitch and diameters were produced. The tip of the Si-nt is further treated to obtain metallic contacts (CoSi2). The whole active area of these well-ordered and periodic Si-nt represent the simultaneous operation of up to 2 million Metal-Insulator-Metal (MIM) or Metal-Insulator-Graphene (MIG) devices, respectively. The transport mechanism of Al2O3 on Si-nt and large-area electrodes was systematically studied. Al2O3 layers deposited by ALD on Si-nt in MIM configuration showed a breakdown voltage > 12 MV/cm and a leakage current of ~1x10^-5 A/cm2 over a temperature range of -25 to 125°C. The transport mechanism showed by these samples fitted to a Fowler-Nordheim Tunneling. Furthermore, these samples were studied in a MIG configuration. The use of a Chemical Vapor Deposition (CVD) single graphene layer produced MIG devices with similar characteristics and transport mechanism as the MIM devices. The efforts and advances on the deposition of ultra-thin dielectrics on nano-sized electrodes and/or graphene, contribute to the understanding and improvement in the performance of future devices such as the 2D HET.

Publications

• Atomic Layer Depositions on Graphene: An investigation by joint in-situ real-time Spectroscopic Ellipsometry and direct surface analysis, 1. Turkish-German Workshop for Graphene Based Electronic Devices, 2014, Fırat Üniversitesi, Elazığ, Turkey
  M. Junige, Ch. Wenger, V. Darakchieva, T. Oddoy, G. Lupina, M. Albert, J. W. Bartha
  
• Graphene Based Electron Field Emitter, Proc. 18th Workshop on Dielectrics in Microelectronics (WODIM 2014), abstr. book, 37 (2014)
  Ch. Wenger, J. Kitzmann, A. Wolff, M. Fraschke, Ch. Walczyk, G. Lupina, W. Mehr, M. Junige, M. Albert, J.W. Bartha
  
• Atomic layer deposition of Al2O3 on NF3-pre-treated graphene, Proceedings Nanotechnology VII; 951915 (2015)
  M. Junige, T. Oddoy, R. Yakimova, V. Darakchieva, Ch. Wenger, G. Lupina, J. Kitzmann, M. Albert, J.W. Bartha
  
• Graphene based electron field emitter, J. Vac. Sci. Technol. B 33, 01A109 (2015)
  Ch. Wenger, J. Kitzmann, A. Wolff, M. Fraschke, C. Walczyk, G. Lupina, W. Mehr, M. Junige; M. Albert, J. W. Bartha
  
• In-Situ Real-Time Spectroscopic Ellipsometry for the Investigation of Atomic Layer Depositions on Graphene, 9th Workshop Ellipsometry (WSE 2015), Enschede, The Netherlands
  M. Junige, T. Oddoy, M. Geidel, V. Darakchieva, R. Yakimova, Ch. Wenger, G. Lupina, M. Albert, M. Schubert, J.W. Bartha
  
• In-vacuo study of functionalization approaches for the ALD of high-k dielectrics on graphene, AVS 15th International Conference on Atomic Layer Deposition, 2015, Portland, Oregon, USA
  M. Junige, T. Oddoy, R. Yakimova, V. Darakchieva, Ch. Wenger, G. Lupina, M. Albert, J. W. Bartha
  
• In-Vacuo X-Ray Photoelectron Spectroscopy for the Investigation of Pristine as Well as Pretreated Graphene, E-MRS Spring Meeting 2015, Lille, France
  M. Geidel, M. Junige, B. Adolphi, Ch. Wenger, G. Lupina, R. Yakimova, V. Darakchieva, M. Albert, J.W. Bartha
  
• Dielectric-Graphene and Silicon-Graphene integration for Graphene-Based Devices, Graphene 2016, Genova, Italy
  G. Lupina , C. Strobel, M. Junige , J. Kitzmann ,M. Lukosius , M. Albert , J.W. Bartha , Ch. Wenger
  
• Graphene Monolayers for Electronic Applications Evaluated by Optical Light Microscopy with Polarization. Graphene 2017, Barcelona, Spain
  M. Albert, M. Junige, Ch. Wenger, M. Lukosius, C.A. Chavarin, J.W. Bartha
  
• In-Situ Real-Time and In-Vacuo Study of the Temperature Impact on the Al2O3 ALD Nucleation upon Pristine Monolayer Graphene, 17th International Conference on Atomic Layer Deposition (ICALD 2017), Denver, USA
  M. Junige, J. Kitzmann, C.A. Chavarin, M. Geidel, J. Reif, M. Albert, G. Lupina, Ch. Wenger, J.W. Bartha
  
• Perfluorodecyltrichlorosilane-based seed-layer for improved chemical vapor deposition of ultrathin hafnium dioxide films on graphene, Scientific Reports 6:29223 (2017)
  J. Kitzmann, A. Göritz, M. Fraschke, M. Lukosius, Ch. Wenger, A. Wolff, G. Lupina
  
• Towards Graphene-Based Heterojunction Devices for Microelectronic Applications, Graphene 2017, Barcelona, Spain
  Ch. Wenger, C.A. Chavarin, C. Strobel, M. Junige, J. Kitzmann, M. Lukosius, G. Lupina, M. Albert, J.W. Bartha
  
• 49th IEEE Semiconductor Interface Specialist Conference (SISC), 2018, San Diego, USA
  C.A. Chavarin, M. Junige, M. Lukosius, J. Kitzmann, M. Albert, J.W. Bartha, Ch. Wenger
  
• Electrical characterization of 3 nm-thin Al2O3 films grown by atomic layer deposition for graphene base transistors, WODIM 2018 - 20th Workshop on Dielectrics in Microelectronics, 2018, Berlin, Germany
  M. Albert, M. Junige, J.W. Bartha, Ch. Wenger