Table 4 Differences between top–down and bottom–up approach synthesis of SiNWs
From: Recent Advances in Silicon Nanowire Biosensors: Synthesis Methods, Properties, and Applications
Top–down approach | Bottom–up approach | |
---|---|---|
Device preparation | SiNW and device development were done by etching a silicon-on-insulator (SOI) wafer. | SiNWs are produced from molecular precursors by using a metal nano-cluster mediated VLS mechanism. |
Fabrication techniques are developed from technology like optical lithography, reactive ion etching, e-beam lithography, and anisotropic wet etching | For a transmission electron microscope (TEM) image, check Fig. 5b. | |
For a scanning electron microscope (SEM) image, check Fig. 5c. | ||
Merits | Docile to mass production | Easiness in the choice of material for nanowire development |
Alignment and directional control of the growth of nanowire crystal is possible [33]. | ||
Dependability and reproducibility of the synthesizing process | Various doping levels and high availability of dopants can be introduced during the synthesis. | |
No integration problems | There is high possibility of synthesizing SiNWs of diameter less than 10 nm. | |
SiNWs with several cross sections like triangular [34] and trapezoidal can be fabricated as its essential for selective functionalization of SiNWs [35]. | Appropriate for fabricating multilayer SiNW device structures | |
SiNWs with double-gate structures that are reinforced on a co-planar geometry can be produced (improved sensitivity) [36, 37]. | Flexible to incorporation with flexible and transparent device substrates [38] | |
Demerits | Demands a lot of time for processing | Leads to distribution of lengths and measurements of the synthesized SiNWs |
Costly | Device development involves precise arrangement and positioning of SiNWs resulting to integration problems. | |
Restricted choice of materials for SiNW fabrication | Extremely hard to realize accurate control of number of SiNWs bridging the source and drain electrodes resulting to disparities in batch-to-batch fabrication of SiNW devices | |
Incompatibility of surface chemistry with the tough processing of nanofabrication | Alignment problems related with long SiNWs | |
Measurements of SiNWs restricted by the resolution of the fabrication process | Mass production of SiNW devices almost impossible |