Browsing by Author "Hakonen, Pertti J., Prof., Aalto University, Department of Applied Physics, Finland"

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    Engineering Ultra-Sensitive Nanoelectronics for Microwave Applications
    (Aalto University, 2013) Lechner, Lorenz G.; O.V. Lounasmaa laboratory; O.V. Lounasmaa -laboratorio; NANO Group; Perustieteiden korkeakoulu; School of Science; Hakonen, Pertti J., Prof., Aalto University, Department of Applied Physics, Finland
    This thesis describes experimental work on nanoscale electronic devices, mainly made from carbon nanotubes and operating at microwave frequencies. The continued miniaturization of electronic devices requires advances in the materials and fabrication techniques as well as advances in the fundamental understanding of the physical processes. Nanoelectronics currently focusses on a number of different materials. However, no other material class has received more attention in recent years than those based on low-dimensional carbon, i.e. carbon nanotubes and graphene. Electronic transport in these one- and two-dimensional structures exhibits quantum phenomena. The characteristic length scales for electronic transport are fixed by the choice of active material and operating conditions. Nanoengineering allows to control the performance of a device by tuning its geometry with respect to these electronic length scales. While there are standard micro- and nanofabrication processes for semiconductor devices, certain tweaks are necessary to adapt them to the fabrication of carbon nanotube devices. Advanced nanofabrication using focused ion beam was employed to overcome conventional processing limitations. These hybrid patterning techniques were expanded to the fabrication of other non-carbon nanodevices as well. In order to exploit quantum behavior in fabricated carbon nanotube devices, they have to be operated within the low temperature and low bias limit. This was achieved by isolating them from perturbations of the outside world through cooling and shielding in cryogenic setups. The nanodevices under test were connected to macroscopic measurement equipment at room temperature using carefully designed measurement circuitry. We performed microwave measurements on resonant tunneling transistors made of single-walled carbon nanotube quantum dots in the Fabry–Pérot regime demonstrating a charge sensitivity of 5·10 exp-6 e/Hz exp1/2, comparable to the best values reported for carbon nanotube rf-SETs and for nanowire rf-electrometers. Microwave reflection measurements of the Josephson inductance of a S-MWNT-S system in a dissipative environment were used to determine its critical current from the frequency shift of the reflection magnitude at zero phase bias. Microwave measurements were employed to detect mechanical motion close to the quantum limit in a nanoelectromechanical system. We used focused ion beam cutting to produce uniform slits down to 10 nm, separating patterned resonators from their gate electrodes. The mechanical properties of the resonator were excellent and we obtained a low number of about 20 phonons at the equilibrium bath temperature.