current-voltage and gate characteristics
scanning tunneling microscopy
S.V. Amitonov, D.E. Presnov, V.A. Krupenin
Development of microelectronics technology in the last decade allowed to cross 100 nm barrier and produce original nanoscale devices. One of such devices is a field effect transistor in which the semiconductor channel is made in the form of a nanowire – a structure with transversial dimensions less than 100 nm and length about few microns. The conductivity of the nanowires depends on the electric field in which it is located. Even small changes in the local field near the body of the nanowire can dramatically change its conductivity. Examples of such local perturbations are surface charges or nanoscale charged particles approaching the surface of the nanowires. Ability to register with such a device small charged particles led to intensive development of biosensors based on the NWFET to determine the extremely low concentrations of specific biomolecules and particles (proteins, DNA, viruses) up to the registration of individual acts of their connection to a specially prepared surface of the nanowire. Undoubted achievement of researchers is a demonstrated charge sensitivity of the NWFET, which approaches to the sensitivity of single-electron transistors. This allows to create on its basis ultrasensitive charge sensor with nanometer spatial resolution for a wide range of scanning probe and local devices of the new generation, which can be used in various fields of science, engineering and medicine.
The sensitivity of the NWFET to the external field is maximum in the subthreshold regime, when it begins to form a conducting channel. Furthermore Debye screening length must be equal to the transverse dimensions of the nanowire or exceed them. As a rule, there is no gate in the construction of local scanning-probe NWFET, and the last condition can be satisfied only to the preliminary selection of the degree of doping of silicon. This paper proposes a non-uniform doping of the depth of the top layer of SOI wafers (dopant concentration varied from 1020 cm-3 to 1017 cm-3 on 110 nm) to form an integrated structure of the NW and source-drain electrodes. The upper part of the inhomogeneously doped layer with metallic conductivity is used to form the source, drain, leads and pads structure, the nanowire is formed in the lower part of the semiconductor layer.
The presented method of manufacture nanostructures FET with a channel-nanowires is simple and allows to control and change during fabrication the main parameter of the device – the conductivity of the channel of the transistor, as well as provide an ohmic contact to the supply nanowire electrodes. Channel transistors, nanowires can be the basis for the creation of highly sensitive field/charge sensor with nanometer spatial resolution for scanning and for the local probe systems of the new generation. The high spatial resolution of the sensor-based nanowires can be achieved by changing its geometry, bend the wire at a sharp angle, and isolate it from the substrate (suspension). Cantilever with nanowires at the end can serve as a highly sensitive active probe, the spatial resolution of which will be determined by the diameter of the nanowires. Binding to the surface of the nanowires of specific molecular complexes will allow to create on its basis a local biosensor with high selective sensitivity.
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