Tomasz Piasecki

Properties of conductive microstructures containing nano sized silver particles

The properties of the structures made by ink-jet printing with the use of the ink containing nano silver sized particles are presented. After structures printing on substrate, to obtain good electrical conductivity, sintering process is necessary. It is shown, that thermal process influences strongly the resistance, and after the process the resistivity of printed structures can be only a little bit higher than the value of the bulk material. Also different electrical test proved similarity between printed and bulk silver. It was stated that the adding some polymer materials for mechanical parameters improving of printed materials up to 1.5% of total mass of the ink do not influence significantly electrical parameters of the printed layers.

Application of quartz tuning forks for detection of endotoxins and Gram-negative bacterial cells by monitoring of Limulus Amebocyte Lysate coagulation.

Endotoxins, pyrogens of bacterial origin, are a significant threat in many areas of life. Currently, the test most commonly used for endotoxin level determination is LAL (Limulus Amebocyte Lysate) assay. This paper presents application of commercially available low-frequency piezoelectric tuning forks (QTFs) for endotoxin detection. Measurement of the decrease in the QTF oscillation amplitude provides information about the viscosity changes, occurring in the tested sample upon addition of LAL. That method was used to determine the concentrations of endotoxins and bacterial cells (E. coli O157:H19). The relevance of the obtained results was confirmed using a commercially available colorimetric LAL assay. The constructed system can detect bacterial endotoxins in the range of 0.001-5EU/ml and bacterial cells in the range of 10(2)-10(7)CFU/ml. The presented technique requires very simple sample preparation and the sensor response is obtained using compact, portable readout electronics. The single test cost is low compared to commercial endotoxin assays and other novel systems based on micromechanical sensors.

Geometrical, electrical and stability properties of thick‐film and LTCC microcapacitors

Purpose – Capacitors are frequently used in electronic circuits. Thick‐film technology allows fabrication of such components in the case of small‐ and medium‐capacitance values. They can also be manufactured in LTCC structures. The paper seeks to investigate the electrical properties of thick‐film and LTCC capacitors for as‐fired and long‐term thermally aged test structures in a wide frequency and temperature range.Design/methodology/approach – Sandwich and interdigitated planar capacitors were fabricated on alumina or LTCC substrates using standard screen printing and laser shaping. Various dielectric inks and electrodes materials were used. The crystalline phases in thick‐film dielectric films were identified.Findings – Planar and sandwich LTCC and thick‐film capacitors were designed and fabricated. Different technology variations were tested. X‐ray analysis indicated that both used commercial compositions, compatible with LTCC substrates are based on barium and titatium compounds. The difference in the...

Wide frequency range ac electrical characterization of thick-film microvaristors

ZnO-based thick-film microvaristors were investigated using impedance spectroscopy. Properties of planar and sandwich structures on alumina and LTCC substrates with different electrode material are compared. Experimental characteristics are approximated with electrical equivalent circuit. Fabrication technology influence on proposed model parameters is presented. Temperature dependent behavior is shown. Schottky barrier height was calculated as 0.46 eV and three electrop trap levels with activation energy of 0.17 eV, 0.25 eV and 0.38 eV were found.

Electrical properties of dielectric foil for embedded PCB capacitors

One of the methods of achieving high packaging density of passive elements on the PCB is using the capacitors embedded in multilayer PCB. Test structures consisting of embedded capacitors were fabricated using the FaradFlex® capacitive internal layers. Impedance spectroscopy and equivalent circuit modelling was used to determine their electrical properties such as the capacitance, parasitic resistance and inductance. The use of several stages of accelerated ageing allowed us to test the durability of the structures. The results showed good quality stability of the embedded elements. The spatial distribution of the capacitance of the test structures on the surface of the PCB form was tested. The influence of the process parameters during lamination on the values of embedded capacitors was revealed.

Modulation of excitation signal as a method for measurement of the mechanical properties of miniature piezoelectric resonant devices in a viscous and conductive environment

A novel approach to electric measurement of mechanical properties of piezoelectric resonators is presented. Modulation of the actuation signal and application of dedicated, in-house built readout electronics makes it possible to precisely analyse resonance response of low-frequency piezoelectric devices in conductive and viscous environment. The method presented is inexpensive and allows us to measure highly damped piezoelectric resonator properties without being influenced by the parasitic elements present in the resonator structure or due to the properties of the environment.

Nanopowder grain size effect on the ac electric properties of Eu doped BaTiO3 nanoceramic

The impedance spectra of BaTiO3 nanoceramics doped with Eu were measured. The samples originated from nanopowder which differed in grain size. The impedance spectra showed strong dependence on the measurement temperature. An electric equivalent circuit was elaborated and fitted to the measured spectra. Its analysis allowed to identify both conduction mechanisms and dielectric properties. The conductance analysis pointed to the diffusion as the main conductivity process which was independent on the grain size. The analysis of the dielectric properties suggested a coexistence of two phases: amorphous and crystalline. Contribution of the amorphous phase to the total electric permittivity was greater than the crystalline phase contribution at measurement frequencies below 1 MHz. Dielectric properties of the crystalline phase could be determined by the high frequency measurements or equivalent circuit modelling. The ferroelectric-paraelectric transition was observed in the crystalline phase. Contribution of the crystalline phase to the total permittivity increased with the grain size.

Fast impedance measurements at very low frequencies using curve fitting algorithms

The method for reducing the time of impedance measurements at very low frequencies was proposed and implemented. The reduction was achieved by using impedance estimation algorithms that do not require the acquisition of the momentary voltage and current values for at least one whole period of the excitation signal. The algorithms were based on direct least squares ellipse and sine fitting to recorded waveforms. The performance of the algorithms was evaluated based on the sampling time, signal-to-noise (S/N) ratio and sampling frequency using a series of Monte Carlo experiments. An improved algorithm for the detection of the ellipse direction was implemented and compared to a voting algorithm. The sine fitting algorithm provided significantly better results. It was less sensitive to the sampling start point and measured impedance argument and did not exhibit any systematic error of impedance estimation. It allowed a significant reduction of the measurement time. A 1% standard deviation of impedance estimation was achieved using a sine fitting algorithm with a measurement time reduced to 11% of the excitation signal period.

Electrical characterization of aluminium oxide―aluminium thin film composites by impedance spectroscopy

Abstract The impedance spectroscopy method has been used for diagnostics of the thin film sandwich structures containing two aluminium electrodes with the composite deposited between them. The aluminium oxide–aluminium composite was deposited in the high effective reactive pulsed magnetron sputtering process. The aim of the investigation was to obtain the metal–oxide composite layer in single magnetron sputtering process. The main purpose of presented research was to characterize the impedance of presented structure in the wide range of frequency. The electrical equivalent circuit of measured structures was described and led to the identification of the dielectric relaxation processes.

Application and modeling of functionally graded materials for optoelectronic devices

The paper reports on functionally graded materials (FGM), their classification and properties, the application of FGM for optoelectronic devices (epitaxially buffer layers, waveguides, photodetectors, solar cells) and modelling of FGM (generation function and band-gap structure)