Ing. Vojtěch Povolný

The selective detection of ammonia (NH3), nitrogen dioxide (NO2), carbon oxides (CO2 and CO), acetone ((CH3)2CO), and toluene (C6H5CH3) is investigated by means of a gas sensor array based on polyaniline nanocomposites. The array composed by seven different conductive sensors with composite sensing layers are measured and analyzed using machine learning. Statistical tools, such as principal component analysis and linear discriminant analysis, are used as dimensionality reduction methods. Five different classification methods, namely k-nearest neighbors algorithm, support vector machine, random forest, decision tree classifier, and Gaussian process classification (GPC) are compared to evaluate the accuracy of target gas determination. We found the Gaussian process classification model trained on features extracted from the data by principal component analysis to be a highly accurate method reach to 99% of the classification of six different gases.

Non-planar fluxgate sensors measuring the magnetic fields in the uT range are required for electric current, position, and torque transducers. We report the first sensor based on an inkjet-printed 17 mm diameter ring core. The sensor wide open-loop linear range of  1.5 mT allows to operate it without feedback. We describe the preparation of the very stable magnetic ink based on citrate-stabilized 13 nm diameter Mn-Zn ferrite nanoparticles that occur in superparamagnetic regime at room temperature. By printing 100 layers the total thickness of the inkjet-printed core was 2.2 µm. The achieved sensitivity was 10 mV/mT for 25 kHz excitation frequency

Refractory metals (titanium, molybdenum, and zirconium) with a gold overlayer were used to form ohmic contacts on {113}-oriented boron doped diamond epitaxial layers (boron concentration ranging from 1019 to 1021 cm−3). Morphology and thickness of deposited layers were determined by AFM and X-SEM; resistivity, carrier concentration and mobility were determined by Hall measurement. Specific contact resistance RCsp of evaporated Ti/Au, Zr/Au, and Mo/Au contacts was measured using c-TLM structures after different annealing stages at temperatures up to 850 °C. Results show that on layers with {113} orientation it is possible to achieve ohmic contacts of comparable quality as for layers with {100} orientation. For all three metal systems, the lowest values for specific contact resistance reached 1 × 10−6 Ω.cm2. Ti/Au contacts show a stable ohmic behavior over the whole range of annealing temperatures, while Mo/Ti contacts had to be annealed above 500 °C to reduce the Schottky barrier and achieve good ohmic contact on lower B doped layers. Zr/Au contacts exhibit the lowest adhesion and required annealing to at least 700 °C to achieve ideal electrical and mechanical properties. Mo/Au and Zr/Au contacts on highly boron doped layers (~1021 cm−3) show excellent contacts when annealed at 700 °C, and therefore can be considered as improved candidates for ohmic contacts for diamond-based high-temperature power electronics than the conventional Ti/Au (Ti/Pt/Au) contact system. In summary, this study confirms the suitability of {113} oriented boron doped diamond epitaxial layers for the fabrication of diamond power electronic devices with excellent ohmic contacts.

The paper solves the model of the miniature Power supply based on the piezoelectric cantilever. The aim of the future is to further hybrid integration and use of nanotechnology. Contents of the article belongs to the category of renewable energy sources with environment energy conversion into electrical energy. The work is focused on the use in small temperature differences.

The article reports for the first time about the successful fabrication of pseudo-vertical diodes on {113} oriented homoepitaxial boron-doped diamond using molybdenum as a metal for both the Schottky and ohmic contacts. Results confirm that the use of {113} oriented homoepitaxial boron-doped diamond for the fabrication of high-temperature power devices is advantageous, as it enables high-quality Schottky and ohmic contacts.

The low resistance of ohmic contacts on diamond layers is important for the fabrication of diamond power electronic devices with fast switching capabilities for future high voltage applications. The low barrier height between the metal and diamond, high level of boron doping and annealing at elevated temperatures are the most critical parameters to reach the lowest contact resistivity. In this work, we report on titanium/gold ohmic contacts prepared on the heavily boron-doped (113) epitaxial diamond layers. The contact resistance has been characterized by the Circular Transmission Line Model (cTLM) structures. We used the analytical model of field enhanced emission, tunneling and the image force influence including Fermi level position dependence on the boron concentration for theoretical Ti/Au contact analysis and the Silvaco TCAD 2D simulation to estimate the measurement error associated with the nonzero metal resistance. We show that the resulting simulation values are consistent with the experimental results.

Epitaxial growth of diamond is critically important for the fabrication of diamond-based electronic devices. The emerging study of the epitaxial diamond growth on the (113) vicinal surfaces evidences highly needed high growth rates and low structural defects concentrations with both p- and n-type doping. In this work, we compare the morphology and dopant concentration incorporation of heavily boron-doped (113) epitaxial diamond layers with conventionally studied (100) and (111) epitaxial layers. Epitaxial layers were grown using resonance cavity Microwave Plasma Enhanced Chemical Vapor Deposition (MWPECVD) system. The surface morphology of epitaxial layers was studied by optical microscopy and atomic force microscopy, whereas the boron incorporation homogeneity was determined by Raman spectroscopy mapping. Heavily boron-doped (113) epitaxial diamond layers can be grown at a high growth rate with a smooth surface, without pyramidal hillocks or non-epitaxial crystallite defects, and with homogeneous boron concentration. These results confirm that epitaxial diamond growth on (113) vicinal surfaces is a promising solution for the development and fabrication of diamond-based electronic devices. (9) (PDF) Effect of the substrate crystalline orientation on the surface morphology and boron incorporation into epitaxial diamond layers. Available from: https://www.researchgate.net/publication/349892789_Effect_of_the_substrate_crystalline_orientation_on_the_surface_morphology_and_boron_incorporation_into_epitaxial_diamond_layers [accessed Aug 25 2021].

Passive components like resistor, capacitor and inductor are basic stones of electrical circuits. Development of these components has come a long way which means that today we can reach very precise values. Inkjet printing is an alternative method how to fabricate electrical components. Inkjet printing has become more popular in recent few years thanks to fast process of fabricating from layout preparation to final product and with effective usage of material it is more efficient and ecological method of fabrication of samples.

Although significant efforts have been dedicated to optimize the quality of epitaxial diamond layers, reported properties of diamond based electronic devices do not yet approach expected theoretical values. Recent works indicate that boron-doped and phosphorous-doped diamond can be grown on atomically stepped (113) surfaces (A. Tallaire et al., 2016; M.-A. Pinault-Thaury et al., 2019), however the electrical properties of these layers have not been studied in detail. In this work, we report on structural and electrical properties of boron-doped epitaxial diamond layers grown on (113) substrates. Properties of the diamond layers have been investigated by means of scanning electron microscopy, atomic force microscopy, Hall effect, secondary ion mass spectrometry and Raman spectroscopy. Our results show that boron-doped diamond layers can be grown on (113) substrates at high deposition rates with atomically flat surfaces, excellent electrical properties and high boron incorporation efficiency.

This paper presents fabrication of printed interdigital capacitors on a flexible and lightweight polyester (PET) substrate. Capacitors were fabricated using inkjet printing technology and conventional low temperature (100-150°C) curing method. The surface of printed capacitors were covered with dielectric material, which lend capacitor a specific value of permittivity, but also serves as protective coating. Cross-linked poly-4- vinylphenol (cPVP) and SU-8 were applied as dielectric materials and experimental results are compared.