TLM of Analysis for the Calculation of Contact Resistance in P3HT OFETs
Transfer Line Method was first suggested by the Luan and Neudeck for the calculation of contact resistance in amorphous silicon thin-film transistors in year 1992 . Transfer line method is the standard approach for the calculation of contact resistance in the field-effect transistors by fitting the total ON resistance of a device as the function of channel lengths. The article deals with detail contact resistance calculation by TLM in an OFET.
The total resistance (R) in an OFET can be divided into two parts. The channel resistance (Rch) is directly related with the sheet resistance (Rsh) and the total contact resistance, which are in series in an OFET. Mathematically,
Where, L is the channel length and W is the channel width.
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Fabrication of solid-state nanopores (d < 10 nm)
One of the possible field of interest for a bio-medical engineer or a biologist would be the label-free detection of a molecule directly at the site (sample source) with the lab-on-chip technology. This technology demands cheaper and portable bio-sensors. Current measurement through nanopore is one of the approaches towards label free detection of moleule which opens a broader perspective towards development of cheaper bio-sensors. Resistive pulse sensing technique (RPS) is applied to detect ingoing molecules through a nanopore sensor.
A nanopore conventionally used to be the biological nature, which includes a micele or α-Haemolysin pore. However, the diametre of a pore is not small enough to detect a single DNA sequence, despite the fact that they are quite noise-resistant. After rapid development of different micro and nanofabrication techniques, stable and size-controlled solid-state nanopores are possible. Solid state nanopores are fabricated on the crystalline materials like silicon dioxide, silicon nitride and gold (Au) substrates. These substrates are stable compared to biological nanopores.
Scopes of solid state nanopores are broader in range, like: DNA sequencing , detection of proteins or polypeptides or nucleic acids or antibody-virus binding[2,3], nanoparticles , synthetic polymers , antibody-antigen [6,7] interaction and ions . In RPS technique, the incoming molecule displaces the conductive liquid flowing through the nanopore, which gives decrement in current or increment in resistance as the electrical signal. In this article, two major solid-state nanopore fabrication techniques would be discussed. The two techniques are: Focused electron beam method (introduced at Kavli Institute of Nanoscience, Delft University of Technology) and Ion Sculpting Method (introduced at Harvard University). Nanopores with the size in the orders of nanometres (d = 1 - 10 nm) can be fabricated on the substrates with these methods.
Microelectronics: Fabrication of micro/nano structures on silicon surface
In microelectronics, fabrication of metal structures (micro/nano) are state-of-art research due to their broad range of applications. On of the major application of microfabrication is the production of thin-film transistors (TFTs). In one of the production process of TFT is by depositing metal structures on the silicon wafer (i.e. above the insulator layer). Channel region between these metal structures is the region where semiconductor is deposited to produce a working field-effect TFT. Major interest for scientists all over the world is the production of large area printable, low-cost and low-temperature processable TFTs.
For the production of low-cost TFTs, the fabrication technique too demands cheaper and the faster processes. Photolithograpy is such a cheaper and faster process, that yields TFTs with channel length down to 1um. However, the process is unreliable in nanometre scale. For futher, below 1um e-beam lithography is applied. E-beam lithograpy is very reliable, yields the TFT with channel in the orders of nanometers. But, the process is relatively expensive and slow. For sub-100 nm shadow based deposition is also beneficial. However, this is rather cubersome process and needs highly-skilled manpower. Apart from transistors, these structures could be also applied as the sensors and the thin micro/nano fluidic-channel in the field of lab-on-chip technology, plamonics for surface enhancement in thin film solar cells, surface analysis esp. in Surface Enhanced Raman Scattering Measurement e.t.c.