A. Jakubowski

Diamond-like carbon coatings for biomedical applications

Abstract The results of experimental studies on amorphous diamond carbon layers obtained by a new method of r.f. dense plasma chemical vapour deposition onto orthopaedic pins and screws are presented. Research on this subject which has been carried out over many years allows us to draw optimistic conclusions concerning the biomedical applications of diamond-like carbon (DLC). In particular, preliminary medical research on a new DLC-steel substrate system developed in 1992, which has just been concluded, is extremely promising.

Optoelectronic capillary sensors in microfluidic and point-of-care instrumentation.

This paper presents a review, based on the published literature and on the authors’ own research, of the current state of the art of fiber-optic capillary sensors and related instrumentation as well as their applications, with special emphasis on point-of-care chemical and biochemical sensors, systematizing the various types of sensors from the point of view of the principles of their construction and operation. Unlike classical fiber-optic sensors which rely on changes in light propagation inside the fiber as affected by outside conditions, optical capillary sensors rely on changes of light transmission in capillaries filled with the analyzed liquid, which opens the possibility of interesting new applications, while raising specific issues relating to the construction, materials and instrumentation of those sensors.

Modeling of SOI-MOS capacitors C-V behavior: partially- and fully-depleted cases

A model is presented for the C-V characteristics of partially-depleted (PD) and fully-depleted (FD) SOI-MOS capacitors. The proposed model is flexible, allowing introduction of all types of nonidealities typical to MOS type structures. New formulae for the low- and high-frequency capacitances of these structures are derived. Due to the various charges stored in these structures, unusual and more complex C-V curves are obtained. C-V curves where interface-state densities have been individually introduced (one at a time) at all three SiO/sub 2/-Si interfaces of the SOI-MOS-C are also demonstrated. The model has been validated by fitting the predicted HF C-V curves for SOI-MOS-C and its inherent structure, the SIS capacitor, to the experimental data. The extracted electrophysical parameters of the studied structures, for both PD and FD cases, are very close, if not the same as the values determined during their fabrication.

Modeling of SiGe-base heterojunction bipolar transistor with gaussian doping distribution

Abstract The results of numerical modeling of the base transit time and collector current of SiGe-base heterojunction bipolar transistors with a Gaussian base doping profile and two Ge profiles (linearly graded and box) are presented for the first time. The importance of including the dependence of minority carrier mobility on the drift field and the dependence of the effective density of states on the Ge concentration along the base is demonstrated through the analysis of base transit time and collector current. A function describing the decrease of the density of states product in strained SiGe layers with increasing Ge concentration is proposed.

Electrical behaviour and breakdown in plasma deposited cubic BN layers

Abstract The paper presents results of an investigation of the electrical properties of cubic boron nitride (c-BN) layers deposited onto silicon substrates by the reactive pulse plasma method. Current-voltage characteristics of the layers in metal/insulator/semiconductor (MIS) structures were investigated in a wide voltage range for films of various thicknesses, obtained under different technological conditions. On the basis of I-V measurements, the breakdown properties of BN layers were also evaluated. In spite of many similarities of c-BN films to diamond-like carbon films, we have found a slightly different character of electrical properties. In most cases we observed switching phenomena and voltage-controlled negative resistance. The dielectric strength of investigated layers shows a wide range of critical electric fields in the range 0.5–6.0 MV cm −1 . An attempt to explain the observed effects on the basis of existing models, valid for similar materials, is also made.

The properties of diamond-like carbon layers deposited onto SiO2 aerogel

Abstract Possible production of an SiO 2 aerogel coated with diamond-like carbon (DLC) by the r.f. decomposition of methane is presented. The r.f. decomposition of methane seems to be the most convenient method for the production of superhard carbon coating on silica aerogels. Aerogels are new materials obtained by removing solvent from gels under supercritical conditions. They are usually transparent, highly porous with very low density. Other unique properties such as a low heat transfer coefficient, low sound velocity, refractive index close to that of air, high purity, and easy doping by different inorganic and organic substances make their applications very promising in electronics, ceramics, catalysts and other fields. However, silica aerogels are problematic because they are brittle. The silica gel was obtained by hydrolysis and condensation of tetraethoxysilan. A two-step method was used. One set of gel samples was heated in the autoclave filled with alcohol and decompressed isothermally after reaching the critical point of the solvent. Another set was subjected to supercritical extraction of alcohol by carbon dioxide followed by isothermal decompression at a temperature higher than the critical temperature of CO 2 (304.2 K). In the processes described transparent aerogels of density 104–115 kg m -3 were obtained. In the paper the influence of DLC coating on the mechanical strength of the DLC-SiO 2 aerogel system is presented. The DLC layer was deposited onto two surfaces of an aerogel plate by r.f. plasma chemical vapour deposition. The DLC films are very hard and resistant to acids and bases. DLC, which is semitransparent for mass transfer, is a good material for sensors. Together with the aerogel substrate the DLC film creates a structure which is very promising for electronics.

PECVD formation of ultrathin silicon nitride layers for CMOS technology

The aim of this study was to check experimentally the feasibility of processing ultrathin Si 3 N 4 layers by low-temperature deposition of quality allowing in the future their application as the gate dielectric. The layers were grown in PECVD planar electrodes, RF plasma system. The optimisation of the technology was performed in order to obtain good reproducibility and control of the deposition process for ultrathin layers (thickness < 6 nm). The properties of the layers were studied by optical and electrical methods. The spectroscopic ellipsometry was used to determine the thickness and optical properties (e.g. refractive index) and check for any nonuniformity within the deposited layers. The test structures containing MOS capacitors and MOSFETs of different sizes with PECVD Si 3 N 4 layers as the gate dielectric were manufactured in order to perform electrical characterisation. Apart from the classical approach (C- V, I- V characteristics) the charge pumping technique has been also used to characterise the nitride-silicon interface. The obtained results have proved successful in the process optimisation effort and reasonably good (comparing to that in recent publications) properties of the formed system.

Breakdown properties of thin oxides in irradiated MOS capacitors

Abstract The influence of ionizing radiation on breakdown characteristics of MOS structures with thin gate oxides is investigated. It is found that, as the result of irradiation, a significant reduction in the number of medium-voltage defect-related breakdown events takes place. This improvement effect suggests that there is an interaction between defects responsible for early breakdowns and defects generated by radiation, which results in the hardening of oxide weak spots. The observed shortening of the time-to-breakdown for irradiated structures is explained in terms of radiation-induced positive charge and electron trap generation which, during subsequent TDDB stress, leads to enhancement of the internal oxide field. As the result of irradiation, a significant reduction of the field acceleration factor of oxide breakdown (determined for high, near critical electric fields) is also observed.

Short capillary tubing as fiber optic sensor of viscosity of liquids

Optical capillaries are used in capillary gas and liquid chromatography, capillary electrophoresis, absorbance spectroscopy, Raman spectroscopy etc. These micro-fluidic methods find applications in biotechnologies, medical diagnostic, drug discovery and environmental sciences. In the presented work we discuss some aspects of light guidance in capillary tubing made from silica glass or Teflon AF. The wide range of capillary constructions allows them to be used advantageously in specific applications. We have analyzed both theoretically and experimentally partially liquid filled optical capillaries as fiber optic sensor elements in laser light transmission and reflection conditions at 670, 1310 and 1550 nm. We have shown that the light transmission properties and signal in the reflectometric mode of work depend on capillary construction, their length and position of inserted liquid drop. The results obtained by us show that capillary tubing can be used as sensing elements in optical fiber sensors of surface tension and viscosity of small liquid samples with volume below 10-8 cm3.

Electrical properties of diamond-like CSi heterojunctions manufactured under ultraclean conditions

Abstract Breakdown tests of diamond-like carbon-silicon (DLC-Si) heterojunctions were performed. The DLC films were obtained by the r.f. chemical vapour deposition method under typical conditions and in the microelectronic standard technological laboratory. The differences between the breakdown diagrams of metal-insulator-semiconductor structures produced in the two ways were shown.