B. I. Fomin

SOI nanowires as sensors for charge detection

The properties of silicon-on-insulator nanowires (SOI NWs) fabricated by means of electron lithography and gas etching of SOI in XeF2 or SF6:CFCl3 have been investigated. The method used to fabricate the nanowires was found to require no additional anneal to be given to the final structure for defect removal after nanostructuring. The sensitivity of SOI NWs to negative protein BSA molecules in the pH 7.4 buffer solution was shown to be as high as 1 femtomoles. The gate characteristics of SOI NWs were used to determine the charge density of particles adsorbed on the NW surface. A charge density of 4.6 × 1011 cm−2 was estimated for a 1 femtomole protein concentration. The combined use of open-channel structures with top gates was employed for determining the charge state of structure surfaces after different chemical treatments. Chemical treatments giving rise to a density of the negative charges on the surface of NWs ranging in the interval (7–23) × 1011 cm−2 were examined. Treatments in methanol (after removal of the native oxide) were found to provide stabilization of the SOI surface over a 3-h interval after the treatments.

SOI nanowire for the high-sensitive detection of HBsAg and α-fetoprotein

Silicon-on-isolator-nanowires (SOI-NWs) were used for the label-free, real-time biospecific detection of the hepatitis B marker HBsAg and cancer marker α-fetoprotein (AFP). Specific protein-protein recognition was carried out using individual NWs that were functionalized with antibodies. To solve the problem of non-specific binding of target protein molecules to the sensor element the use of a reference NW with immobilized antibodies against non-target proteins was proposed. Using individual SOI-NW surface functionalization allowed the fabrication of a NW array, containing working NWs and reference NWs within one chip. It was shown that this approach allows us to reach a detection limit up to 10(-14) and 10(-15) M for HBsAg and AFP, respectively. Our investigations also allowed us to reveal the influence of the charged state of the target protein molecules and antibodies in solutions with various pH values on the target protein detection limit. A high sensitivity NW-detector is of interest for the creation of diagnosticums for hepatitis B and for the early stages of cancer diseases.

Application of uncooled microbolometer detector arrays for recording radiation of the terahertz spectral range

The mechanism of occurrence of sensitivity of microbolometer detector arrays based on vanadium oxide to terahertz radiation are analyzed. Experimental data are given showing the possibility of increasing the sensitivity of microbolometer detectors in the terahertz range by using an additional thin metal absorbing layer applied on the microbolometer membrane. A polarization dependence of the sensitivity of microbolometers in the terahertz and far infrared spectral ranges is found. It is shown that the sensitivity of microbolometers in the terahertz range is due to the absorption of radiation in the narrow metal runs placed on the support legs of the microbolometers and playing the role of an ohmic contact between the heat-sensitive layer and the processing curcuit.

A SOI-nanowire biosensor for the multiple detection of D-NFATc1 protein in the serum

The detection of cancer protein marker D-NFATc1 in the serum with a reusable nanowire (NW) chip based on silicon-on-insulator (SOI) structures was demonstrated. The NW surface was modified with aptamers against D-NFATc1 to attain the biospecific detection of the target protein. Two fabricated NW chip types – with narrow NWs (w = 90 nm) and wide NWs (w = 3 μm) – were compared with respect to their reuse, i.e. the realizability of the repeated detection–regeneration cycles upon D-NFATc1 detection in the serum. The analysis of the serum has shown that the signal obtained with wide NWs was much more stable than that obtained with narrow NWs. This makes the SOI-NW biosensor with wide NWs much more suitable for protein analysis in biological fluids. The signal stability exhibited by the wide NWs allowed for performing repeated detection–regeneration cycles of this chip for multiple detection of D-NFATc1 protein in the serum with 10−14 M sensitivity. Although the narrow NW chip allows for attaining higher sensitivity (with the concentration detection limit DL = 10−15 M), it exhibits much less signal stability upon analysis of multicomponent biological fluids (serum).

Silicon nanowire transistors for electron biosensors

A method of nanostructuring of silicon-on-insulator (SOI) layers on the basis of gas etching in XeF2 or SF6:CFCl3 is developed for the purpose of obtaining SOI nanowire structures. SOI nanowire transistors (SOI NWTs) with free channels, used as sensors in electron detectors, are fabricated and tested. The results of experiments show that the method used to fabricate nanowires requires no high-temperature operations for elimination of defects after nanostructuring of SOI layers. The sensitivity of SOI NWTs to test molecules of bovine serum albumin is 10−15 mole/liter, which is one of the best results for nanowire biosensors.

SOI-nanowire biosensor for detection of D-NFATc1 protein

The nanowire (NW) detection is one of the fast-acting and high-sensitive methods, which can recognize potentially relevant protein molecules. A NW-biosensor based on the silicon-on-insulator (SOI)-structures has been used for biospecific label-free real time detection of the NFATc1 (D-NFATc1) oncomarker. For this purpose, SOI-nanowires (NWs) were modified with aptamers against NFATc1 used as molecular probes. It was shown that using this biosensor it is possible to reach sensitivity of 10−15 M. This sensitivity was comparable to that of the NW-biosensor with immobilized antibodies used as macromolecular probes. The results demonstrate that approaches used in this study are promising for development of sensor elements for high-sensitive diagnostics of diseases.

SOI nanowire transistor for detection of D-NFATc1 molecules

Nanowire (NW) detection is one of the fast and highly sensitive methods. An NW biosensor based on silicon-on-insulator (SOI) structures are used in the reported study for real-time label-free biospecific detection of the NFATc1 (D-NFATc1) cancer marker. For this purpose, the SOI NWs are functionalized with NFATc1 aptamers used as macromolecular probes. It is demonstrated that such a biosensor can ensure a detection limits up to 10−15 M, which is comparable with the sensitivity ensured by an NW biosensor with immobilized antibodies used as macromolecular probes. The results of this study demonstrate that such approaches to the development of sensor elements for highly sensitive diagnostics of diseases are really promising.

Ultra-thin SOI Layer Nanostructuring and Nanowire Transistor Formation for FemtoMole Electronic Biosensors

In this work nanostructuring of SOI layers with tenth nanometer thickness was made at last stage of electronic biochip producing using fluorine gas-plasma content etching. Electrical characterization verities that used fabrication approach produces high-quality devices operating up to temperatures close to liquid helium. The sensitivity of SOI NWs to negative ions Cl- in aqua solution (pH 6) was shown to be as high as 10 femtoMoles. The sensitivity of SOI NWs to negative protein BSA molecules in pH 7.4 buffer solution was shown to be as high as 1 femtoMoles.

Charge accumulation in the buried oxide of SOI structures with the bonded Si/SiO2 interface under γ-irradiation: effect of preliminary ion implantation

In this study, we examined the effect of preliminary boron or phosphorous implantation on charge accumulation in the buried oxide of SOI-MOSFETs irradiated with ?-rays in the total dose range (D) of 105?5???107?rad. The buried oxide was obtained by high-temperature thermal oxidation of Si, and it was not subjected to any implantation during the fabrication process of SOI structures. It was found that implantation with boron or phosphorous ions, used in fabrication technologies of SOI-MOSFETs, increases the concentration of precursor traps in the buried oxide of SOI structures. Unlike in the case of boron implantation, phosphorous implantation leads to an increased density of states at the Si/buried SiO2?interface during subsequent ?-irradiation. In the ?-irradiated SOI-MOSFETs, the accumulated charge density and the density of surface states in the Si/buried oxide layer systems both vary in proportion to kiln?D. The coefficients ki for as-fabricated and ion-implanted Si/buried SiO2?systems were evaluated. From the data obtained, it was concluded that a low density of precursor hole traps was a factor limiting the positive charge accumulation in the buried oxide of as-fabricated (non-implanted) SOI structures with the bonded Si/buried SiO2?interface.

Density dependence of electron mobility in the accumulation mode for fully depleted SOI films

The electron mobility µeff in the accumulation mode is investigated for undepleted and fully depleted double-gate n+–n–n+ silicon-on-insulator (SOI) metal–oxide–semiconductor field-effect transistors (MOSFET). To determine the range of possible values of the mobility and the dominant scattering mechanisms in thin-film structures, it is proposed that the field dependence of the mobility µeff be replaced with the dependence on the density Ne of induced charge carriers. It is shown that the dependences µeff(Ne) can be approximated by the power functions µeff(Ne) ∝ Ne-n, where the exponent n is determined by the chargecarrier scattering mechanism as in the mobility field dependence. The values of the exponent n in the dependences µeff(Ne) are determined when the SOI-film mode near one of its surfaces varies from inversion to accumulation. The obtained results are explained from the viewpoint of the electron-density redistribution over the SOI-film thickness and changes in the scattering mechanisms.