טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentShlafman Michael
SubjectSuspended Carbon Nano-Tubes Based Nano Electro-Mechanical
Systems
DepartmentDepartment of Electrical Engineering
Supervisor Dr. Yuval Yaish
Full Thesis textFull thesis text - English Version


Abstract

The extraordinary carbon nanotubes (CNTs) triggered many individuals to pursue science and engineering based on them. Owing to their remarkable physical properties, whether mechanical, electrical, or, optical, researches have realized CNT based electronic devices, sensors, nano-electro-mechanical-systems (NEMS) and have been using CNTs for fundamental scientific research in general.

We address a couple of challenges for the realization of the aforementioned devices in this work. First is the hysteresis phenomenon in the transfer characteristics of CNT field effect transistors (FETs), which is a major obstacle for successful realization of such devices with reproducible response. Being the core element of envisioned integrated circuits or perhaps even more preferably sensors, CNTFETs cannot tolerate unstable response over time if they are to be seriously considered as future technology. Second is the perhaps even greater difficulty in positioning or growing the CNTs at specific locations and orientations. Furthermore we explore a revealed research opportunity of CNT resonances, which overcomes the difficulties of conventionally applied methods.

Undertaking the first problem, we prepare four kinds of CNTFETs and explore their hysteretic behavior. Their structure variations enable to pinpoint the physical mechanisms responsible for hysteresis. Two of them are comprised of CNT channel
(on-surface and suspended) with a thin insulating layer underneath and a single bulk global gate which modulates the CNT conductance. The third and fourth types consist of suspended CNT over a now metallic local gate underneath, where the fourth type contains a local gate which was patterned self-aligned with the source and drain electrodes. Interestingly, the fourth type of devices exhibit no hysteresis at all at ambient conditions.

Tackling the second problem, we present a simple, rapid, non-invasive, and scalable technique that enables optical imaging of CNTs. The CNT scaffold serves as a seed for nucleation and growth of small size, optically visible, nano-crystals. The successful and robust optical imaging allows not only locating CNTs but also, as in the case of suspended ones, to study their dynamic mechanical motion in a direct fashion.

Additionally, in this frame of work, we demonstrate non-linear duffing oscillations of very long and decorated CNTs and a transition phenomenon from hardening to softening of the resonator. Unlike the conventional methods, which are indirect, and thus lack important information about the resonance mode and the CNT device geometric parameters, we present a superior technique, which registers them directly. In addition, we show quantitative adherence of measurements to a theoretical model and numerical simulations developed in our research group. Although we currently deal with resonators in the kHz range, the physical mechanisms might be relevant for any scale including the MHz and THz range. Additionally, the setup and devices can be further perfected in order to enable the demonstration of CNT based resonators with previously unseen behavior.

We believe those newly introduced techniques alone, or, combined introduce essential flexibilities for the realization and measurement of novel and better devices both for science and engineering.