Finite-Element Modelling of Biotransistors

Current research efforts in biosensor design attempt to integrate biochemical assays with semiconductor substrates and microfluidic assemblies to realize fully integrated lab-on-chip devices. The DNA biotransistor (BioFET) is an example of such a device. The process of chemical modification of the FET and attachment of linker and probe molecules is a statistical process that can result in variations in the sensed signal between different BioFET cells in an array. In order to quantify these and other variations and assess their importance in the design, complete physical simulation of the device is necessary. Here, we perform a mean-field finite-element modelling of a short channel, two-dimensional BioFET device. We compare the results of this model with one-dimensional calculation results to show important differences, illustrating the importance of the molecular structure, placement and conformation of DNA in determining the output signal

Moving liquids with light: Photoelectrowetting on semiconductors

Liquid transport in microchip-based systems is important in many areas such as Laboratory-on-a-chip, Microfluidics and Optofluidics. Actuation of liquids in such systems is usually achieved using either mechanical displacement11 or via energy conversion e.g. electrowetting which modifies wetting. However, at the moment there is no clear way of actuating a liquid using light. Here, by linking semiconductor physics and wetting phenomenon a brand new effect "photoelectrowetting" is demonstrated for a droplet of conducting liquid resting on an insulator-semiconductor stack. Optical generation of carriers in the space-charge region of the underlying semiconductor alters the capacitance of the insulator-semiconductor stack; the result of this is a modification of the wetting contact angle of the droplet upon illumination. The effect is demonstrated using commercial silicon wafers, both n- and p-type having a doping range spanning four orders of magnitude (6\times1014-8\times1018 cm-3), coated with a commercial fluoropolymer insulating film (Teflon\textregistered). Impedance measurements confirm that the observations are semiconductor space-charge related effects. The impact of the work could lead to new silicon-based technologies in the above mentioned areas

Electron states in a silicon nanowire in the presence of surface potential and field

In this paper, the energy states of electrons in a silicon nanowire are analytically calculated in the presence of a surface potential and an electric field, as in a nanowire field-effect transistor. The calculations are done for both partial and complete volume inversion and accumulation biasing conditions. Computations are performed for the and orientations of the silicon nanowire. The results show the effects of the surface potential, the electric field and the transverse dimensions of the nanowire on the electron energies and wavefunctions. Depending on the combinations of the surface potential and electric field, the energy level can increase, decrease or remain constant as the thickness of the nanowire increases. It is also observed that higher surface potentials can significantly change the energy states due to the increase of volume inversion/accumulation.X111sciescopu