Aug 7, 2012
ZnO nanowires molded at low temperature by atomic layer deposition
For nearly a decade, ZnO nanowires have been an exciting topic for the scientific community thanks to the material’s potential applications in optics and electronics, and fabrication techniques and growth mechanisms have been well studied. However, production methods often involve high-temperature processes and can position nanowires in random locations, which makes microelectronics integration difficult. Scientists from the University of Freiburg (Nanotechnology, IMTEK – Department of Microsystems Engineering) and Fraunhofer Institute Freiburg (IAF), Germany, have been working on ways to improve the situation. The team proposes a combined technique involving microsystems engineering and atomic layer deposition to reduce the growth temperature and precisely control the position of ZnO nanowires.
Freiburg engineers Kittitat Subannajui, Firat Güder and Margit Zacharias have reported their latest results in the journal Nanotechnology. The method begins by using phase shift lithography to produce nanopolymer dots at desired positions on the wafer. The substrate containing the nanopolymer dots is etched to give nano pinholes, which act as a nanowire mold for atomic layer deposition (ALD). It transforms the former silicon nanowires by ALD into ZnO nanowires resulting in an ordered array of polycrystalline ZnO nanowires vertically arranged on the silicon wafer.
Current nanowire technology uses chemical vapour deposition (CVD) methods, which have an operational temperature above 700 °C. The operational temperature of ALD is in the range 110–150 °C, which is better suited for integration with micro-system technology.
The new method is said to be very flexible because it is not limited to the fabrication of ZnO nanowires. Operators can produce nanowires from any material that can be deposited by ALD into the nanopores.
More information can be found in the journal Nanotechnology.
About the author
The study was conducted by the Nanotechnology (NT) laboratory at IMTEK (Technical Faculty, Department of Microsystems Engineering) at the Albert Ludwigs University Freiburg, Germany. Part of the characterization was performed at the Fraunhofer Institute Freiburg (IAF – Institute for Applied Solid State Physics), Germany. Kittitat Subannajui was a former postdoc of the NT group at IMTEK. His work was related to the advanced fabrication of ZnO nanowires. Firat Güder is working as a postdoc at IMTEK. He has a strong interest in ALD processing. Julia Danhof was a former PhD at IAF and her work concentrated on micro photo luminescence (Micro PL). Andreas Menzel is a PhD student at NT/IMTEK, and his work is related to the functionalization and biological application of ZnO nanostructures. Dr Yang Yang is a group leader at NT/IMTEK. He is interested in nanomaterial fabrication and characterization. Lutz Kirste is a researcher at IAF working in XRD, and Chunyu Wang a former researcher working on nanosensors. PD Dr Volker Cimalla is a group leader at IAF specializing in electrical characterization. Prof. Ulrich Schwarz is group leader of the micro PL characterization team, IAF Freiburg. Prof. Margit Zacharias is leader of the Nanotechnology laboratory at IMTEK Freiburg, Germany.