Electrical and Electronic Engineering - Theses
Permanent URI for this collection
Search Results
1 - 1 of 1
-
ItemSilicon nanowire and graphene nanoribbon biological sensors( 2014)One-dimensional (1D) nanoscale devices such as silicon nanowires or graphene nanoribbons have recently received massive research interest thanks to their extraordinary properties. While silicon nanowires (SiNWs) exhibit remarkable surface sensitivity due to their large surface-to-volume ratio, graphene nanoribbons (GNRs) with their unique structure and electrical characteristics promise to deliver rapid and highly sensitive sensors that are flexible and biocompatible. In this thesis, a reliable top-down fabrication technique using CMOS compatible processes is presented, from which state-of-the-art SiNW and GNR device structures are fabricated. The core of the technique is the electron beam lithography (EBL) technology which allows for the formation of nanometre scaled patterns. SiNWs and GNRs fabricated using this method are uniform, well-aligned and have excellent control over device dimensions. The technique can be applied to fabricate other nanoscale structures with a variety of materials. For the first time, a simulation study of a three-dimensional (3D) SiNW biological sensor model demonstrates that the SiNW exhibits an AC-transfer function that resembles that of a high pass filter. It is illustrated that as molecules with a higher net charge attach to the nanowire and displace more charge carriers within the nanowire channel, the filter's corner frequency decreases. This property of SiNW leads to a novel frequency-based detection mechanism that enables one to estimate the concentration of target analytes. To experimentally verify above simulation findings, a boron-doped SiNW with specially designed test pads is fabricated and experimentally characterized at frequencies up to 30 GHz. A transmission line model with a combination of passive circuit elements is proposed. Fitting is then performed based on the SiNW's de-embedded scattering parameters to extract its equivalent circuit components. The study makes significant contribution to the broadband response of SiNWs. It also serves as a guideline towards designing SiNW for biological sensing applications. GNRs are graphene that is cut into ultra-thin strips. Broadband measurement and characterization of GNR, a potential candidate for biological sensor devices, is also demonstrated. Accurate high frequency lumped circuit equivalent models are proposed from which equivalent circuit GNR sensing device components are extracted. It is determined that for narrow devices, inductance dominates. This finding provides important insights into the utilization of GNR as a flexible and biological compatible sensing device. Finally, SiNW devices are then constructed to produce highly sensitive sensors. Here, a functionalized SiNW sensor is demonstrated to provide label-free and sensitive detection of single-stranded deoxyribonucleic acid (DNA). Electrical measurements exhibit changes in device conductance upon specific binding of complementary target DNA. An application is demonstrated where SiNW-based sensors are produced using the technique and new theory described in this thesis. The work in this thesis serves as a development platform for a point-of-care genetic testing device that promises significant contribution to the field of personalized drug treatment and clinical analysis.