The device characteristics and performance of nanowire devices are thought to be determined primarily by the nanowire material properties. However, there is also considerable scope for the device structure or geometry to affect their characteristics and performance. Two different types of nanowire d...
The device characteristics and performance of nanowire devices are thought to be determined primarily by the nanowire material properties. However, there is also considerable scope for the device structure or geometry to affect their characteristics and performance. Two different types of nanowire devices are investigated from the viewpoint of their geometric effects. One is the nanowire field-effect transistor (NWFET) with bottom (back) gate, and the other is the amperometric enzyme biosensor using a nanowire electrode.
Firstly, the impact of the device structures of NWFETs on their electrical properties is explored by using 2- and 3-dimensional device simulations. Source/drain and gate electrode geometries for single-NWFETs and spaces between nanowires for arrayed-NWFETs are employed as variables. Fringing fields from source/drain electrodes (SDEs) and gate capacitance directly altered by them influence device characteristics not only by varying the channel barrier directly but also by causing a parasitic capacitance between electrodes. The geometry-induced distortions of threshold voltage, subthreshold swing, and transconductance should be carefully considered for understanding the device properties precisely. Specially, the proper consideration of the fringing fields from SDEs is essential to avoid an erroneous analysis of measured data. Applying the general constant Cox value without considering SDEs might induce critical mistakes. The geometry of a NWFET, which is usually overlooked, is one of the decisive parameters to determine its properties.
Secondly, the diffusion reaction processes for amperometric enzyme biosensors, which follow the Michaelis–Menten kinetics coupled with diffusion, have been simulated to explore the geometric effects of nanowire array electrodes (NWAEs) and nanowire array stack electrodes (NWASEs) from the viewpoint of enhanced mass transport and increased reaction surface area in two limiting cases. For practical analysis considering sensor fabrication, most samples are assumed to have the same unit square (1 × 1 cm2) footprint. In the reaction-controlled case, the surface area increment improves the sensitivity regardless of electrode geometry. However, in the diffusion-controlled case, well-controlled NWAE or NWASE geometries as well as the increased surface area improve the sensitivity when the peak current at an early stage of the reaction is measured. Peak current engineering by adjusting the geometric parameters of NWAEs and NWASEs will result in a highly sensitive amperometric enzyme biosensor in the diffusion-controlled case. In contrast to previous micro- and nanoelectrode array studies, we investigated NWASEs representing entangled nanowire network electrodes, and report significant improvements in both limiting cases.
The characteristics of devices or nanowire materials are generally extracted by fitting the measured experimental output, such as drain currents in FETs and amperometric currents in biosensors, to the analytic equations; however, the analytic solutions are usually established under the assumption of simple and general device structures, or without any structural consideration. From this study on the geometric effect of nanowire devices, it is obvious that the device structure affects the device characteristics and performance significantly. Through only optimizing the geometry, the device performance can be improved considerably. Therefore, the careful consideration of the geometries in nano-devices is essential for determining their characteristics and for maximizing their performance.
The device characteristics and performance of nanowire devices are thought to be determined primarily by the nanowire material properties. However, there is also considerable scope for the device structure or geometry to affect their characteristics and performance. Two different types of nanowire devices are investigated from the viewpoint of their geometric effects. One is the nanowire field-effect transistor (NWFET) with bottom (back) gate, and the other is the amperometric enzyme biosensor using a nanowire electrode.
Firstly, the impact of the device structures of NWFETs on their electrical properties is explored by using 2- and 3-dimensional device simulations. Source/drain and gate electrode geometries for single-NWFETs and spaces between nanowires for arrayed-NWFETs are employed as variables. Fringing fields from source/drain electrodes (SDEs) and gate capacitance directly altered by them influence device characteristics not only by varying the channel barrier directly but also by causing a parasitic capacitance between electrodes. The geometry-induced distortions of threshold voltage, subthreshold swing, and transconductance should be carefully considered for understanding the device properties precisely. Specially, the proper consideration of the fringing fields from SDEs is essential to avoid an erroneous analysis of measured data. Applying the general constant Cox value without considering SDEs might induce critical mistakes. The geometry of a NWFET, which is usually overlooked, is one of the decisive parameters to determine its properties.
Secondly, the diffusion reaction processes for amperometric enzyme biosensors, which follow the Michaelis–Menten kinetics coupled with diffusion, have been simulated to explore the geometric effects of nanowire array electrodes (NWAEs) and nanowire array stack electrodes (NWASEs) from the viewpoint of enhanced mass transport and increased reaction surface area in two limiting cases. For practical analysis considering sensor fabrication, most samples are assumed to have the same unit square (1 × 1 cm2) footprint. In the reaction-controlled case, the surface area increment improves the sensitivity regardless of electrode geometry. However, in the diffusion-controlled case, well-controlled NWAE or NWASE geometries as well as the increased surface area improve the sensitivity when the peak current at an early stage of the reaction is measured. Peak current engineering by adjusting the geometric parameters of NWAEs and NWASEs will result in a highly sensitive amperometric enzyme biosensor in the diffusion-controlled case. In contrast to previous micro- and nanoelectrode array studies, we investigated NWASEs representing entangled nanowire network electrodes, and report significant improvements in both limiting cases.
The characteristics of devices or nanowire materials are generally extracted by fitting the measured experimental output, such as drain currents in FETs and amperometric currents in biosensors, to the analytic equations; however, the analytic solutions are usually established under the assumption of simple and general device structures, or without any structural consideration. From this study on the geometric effect of nanowire devices, it is obvious that the device structure affects the device characteristics and performance significantly. Through only optimizing the geometry, the device performance can be improved considerably. Therefore, the careful consideration of the geometries in nano-devices is essential for determining their characteristics and for maximizing their performance.
주제어
#Geometry
#Nanowire
#Field-effect transistor
#Electrode
#Fringing field
#Amperometric enzyme biosensor
#Nanowire array electrode
#Nanowire array stack electrode
#Mass transport
#Surface area
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