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1

Leakage Current Degradation Due to Ion Drift and Diffusion in Tantalum and Niobium Oxide Capacitors

Kuparowitz M., Sedlakova V., Grmela L.

Metrology and Measurement Systems

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2017

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Vol. 24, nr 2

255--264

EN

High temperature and high electric field applications in tantalum and niobium capacitors are limited by the mechanism of ion migration and field crystallization in a tantalum or niobium pentoxide insulating layer. The study of leakage current (DCL) variation in time as a result of increasing temperature and electric field might provide information about the physical mechanism of degradation. The experiments were performed on tantalum and niobium oxide capacitors at temperatures of about 125°C and applied voltages ranging up to rated voltages of 35 V and 16 V for tantalum and niobium oxide capacitors, respectively. Homogeneous distribution of oxygen vacancies acting as positive ions within the pentoxide layer was assumed before the experiments. DCL vs. time characteristics at a fixed temperature have several phases. At the beginning of ageing the DCL increases exponentially with time. In this period ions in the insulating layer are being moved in the electric field by drift only. Due to that the concentration of ions near the cathode increases producing a positively charged region near the cathode. The electric field near the cathode increases and the potential barrier between the cathode and insulating layer decreases which results in increasing DCL. However, redistribution of positive ions in the insulator layer leads to creation of a ion concentration gradient which results in a gradual increase of the ion diffusion current in the direction opposite to the ion drift current component. The equilibrium between the two for a given temperature and electric field results in saturation of the leakage current value. DCL vs. time characteristics are described by the exponential stretched law. We found that during the initial part of ageing an exponent n = 1 applies. That corresponds to the ion drift motion only. After long-time application of the electric field at a high temperature the DCL vs. time characteristics are described by the exponential stretched law with an exponent n = 0.5. Here, the equilibrium between the ion drift and diffusion is achieved. The process of leakage current degradation is therefore partially reversible. When the external electric field is lowered, or the samples are shortened, the leakage current for a given voltage decreases with time and the DCL vs. time characteristics are described by the exponential stretched law with an exponent n = 0.5, thus the ion redistribution by diffusion becomes dominant.

2

Voltage Dependence of Supercapacitor Capacitance

Szewczyk A., Sikula J., Sedlakova V., Majzner J., Sedlak P., Kuparowitz T.

Metrology and Measurement Systems

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2016

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Vol. 23, nr 3

403--411

EN

Electronic Double-Layer Capacitors (EDLC), called Supercapacitors (SC), are electronic devices that are capable to store a relatively high amount of energy in a small volume comparing to other types of capacitors. They are composed of an activated carbon layer and electrolyte solution. The charge is stored on electrodes, forming the Helmholtz layer, and in electrolyte. The capacitance of supercapacitor is voltage- dependent. We propose an experimental method, based on monitoring of charging and discharging a supercapacitor, which enables to evaluate the charge in an SC structure as well as the Capacitance-Voltage (C-V) dependence. The measurement setup, method and experimental results of charging/discharging commercially available supercapacitors in various voltage and current conditions are presented. The total charge stored in an SC structure is proportional to the square of voltage at SC electrodes while the charge on electrodes increases linearly with the voltage on SC electrodes. The Helmholtz capacitance increases linearly with the voltage bias while a sublinear increase of total capacitance was found. The voltage on SC increases after the discharge of electrodes due to diffusion of charges from the electrolyte to the electrodes. We have found that the recovery voltage value is linearly proportional to the initial bias voltage value.

3

Supercapacitor Degradation Assesment by Power Cycling and Calendar Life Tests

Sedlakova V., Sikula J., Majzner J., Sedlak P., Kuparowitz T., Buergler B., Vasina P.

Metrology and Measurement Systems

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2016

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Vol. 23, nr 3

345--358

EN

Degradation of Supercapacitors (SC) is quantified by accelerated ageing tests. Energy cycling tests and calendar life tests are used since they address the real operating modes. The periodic characterization is used to analyse evolution of the SC parameters as a whole, and its Helmholtz and diffusion capacitances. These parameters are determined before the ageing tests and during 3 × 105 cycles of both 75% and 100% energy cycling, respectively. Precise evaluation of the capacitance and Equivalent Series Resistance (ESR) is based on fitting the experimental data by an exponential function of voltage vs. time. The ESR increases linearly with the number (No) of cycles for both 75% and 100% energy cycling, whereas a super-linear increase of ESR vs. time of cycling is observed for the 100% energy cycling. A decrease of capacitance in time had been evaluated for 2000 hours of ageing of SC. A relative change of capacitance is ΔC/C0 = 16% for the 75% energy cycling test and ΔC/C0 = 20% for the 100% energy cycling test at temperature 25°C, while ΔC/C0 = 6% for the calendar test at temperature 22°C for a voltage bias V = 1.0 Vop. The energy cycling causes a greater decrease of capacitance in comparison with the calendar test; such results may be a consequence of increasing the temperature due to the Joule heat created in the SC structure. The charge/discharge current value is the same for both 75% and 100% energy cycling tests, so it is the Joule heat created on both the equivalent series resistance and time-dependent diffuse resistance that should be the source of degradation of the SC structure. The diffuse resistance reaches a value of up to 30Ω within each 75% energy cycle and up to about 43Ω within each 100% energy cycle.

4

Current Fluctuation Measurements of Amperometric Gas Sensors Constructed with Three Different Technology Procedures

Sedlak P., Kubersky P., Skarvada P., Hamacek A., Sedlakova V., Majzner J., Nespurek S., Sikula J.

Metrology and Measurement Systems

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2016

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Vol. 23, nr 4

531--543

EN

Electrochemical amperometric gas sensors represent a well-established and versatile type of devices with unique features: good sensitivity and stability, short response/recovery times, and low power consumption. These sensors operate at room temperature, and therefore have been applied in monitoring air pollutants and detection of toxic and hazardous gases in a number of areas. Some drawbacks of classical electrochemical sensors are overcome by the solid polymer electrolyte (SPE) based on ionic liquids. This work presents evaluation of an SPE-based amperometric sensor from the point of view of current fluctuations. The sensor is based on a novel three-electrode sensor platform with solid polymer electrolytes containing ionic liquid for detection of nitrogen dioxide − a highly toxic gas that is harmful to the environment and presenting a possible threat to human health even at low concentrations. The paper focuses on using noise measurement (electric current fluctuation measurement) for evaluation of electrochemical sensors which were constructed by different fabrication processes: (i) lift-off and drop-casting technology, (ii) screen printing technology on a ceramic substrate and (iii) screen printing on a flexible substrate.

5

Analysis of noise and non-linearity of I-V characteristics of positive temperature coefficient chip thermistors

Sita Z., Sedlakova V., Majzner J., Sedlak P., Sikula J., Grmela L.

Metrology and Measurement Systems

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2013

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Vol. 20, nr 4

635--644

EN

Noise spectroscopy and I-V characteristic non-linearity measurement were applied as diagnostic tools in order to characterize the volume and contact quality of positive temperature coefficient (PTC) chip sensors and to predict possible contact failure. Correctly made and stable contacts are crucial for proper sensing. I-V characteristics and time dependences of resistance were measured for studied sensors and, besides the samples with stable resistance value, spike type resistance fluctuation was observed for some samples. These spikes often disappear after about 24 hours of voltage application. Linear I-V characteristics were measured for the samples with stable resistance. The resistance fluctuation of burst noise type was observed for some samples showing the I-V characteristic dependent on the electric field orientation. We have found that the thermistors with high quality contacts had a linear I-V characteristic, the noise spectral density is of 1/f type and the third harmonic index is lower than 60 dB. The samples with poor quality contacts show non-linear I-V characteristics and excess noise is given by superposition of g-r and 1/fn type noises, and the third harmonic index is higher than 60 dB.

6

Non-linear electro-ultrasonic spectroscopy of high-voltage varistors

Cichosz J., Hasse L., Szewczyk A., Sedlak P., Sedlakova V., Sikula J.

Elektronika : konstrukcje, technologie, zastosowania

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2012

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Vol. 53, nr 9

85-87

EN

The electro-ultrasonic spectroscopy as a new nondestructive method for varistor quality evaluation have been proposed. It is focused on non-homogeneities and defects detection in tested structures. Specially prepared samples having different structure of grains were preliminary measured by means of an Atomic Force Microscope. The system for electro-ultrasonic spectroscopy of high-voltage varistors has been described. The experimental results confirmed a possibility of heterogeneous structures detection directly after production or during exploitation.

PL

W artykule zaproponowano nową metodę nieniszczącego badania jakości warystorów za pomocą spektroskopii elektro-ultradźwiękowej. Metoda ta umożliwia detekcję defektów i niejednorodności struktury badanych warystorów. Specjalnie przygotowane próbki struktur warystorowych posiadających różną strukturę ziaren zostały wstępnie przebadane przyz użyciu mikroskopu sił atomowych. Przedstawiono system do spektroskopii elektro-ultradźwiękowej oraz rezultaty badań wybranych egzemplarzy warystorów wysokonapięciowych. Potwierdziły one możliwość detekcji różnej struktury ziaren bezpośrednio w trakcie produkcji warystorów oraz stopnia ich degradacji podczas eksploatacji.

7

Diagnostic of ZnO varistors by means of nondestructive testing

Hasse L., Smulko J., Olesz M., Sedlakova V., Sikula J., Sedlak P.

Zeszyty Naukowe Wydziału Elektrotechniki i Automatyki Politechniki Gdańskiej

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2011

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Nr 30

51-56

EN

Standard industrial testing of high-voltage varistors for surge arresters demands application of high voltages and intensive currents. Nondestructive methods for varistor quality and endurance evaluation have been proposed and described. They rely on the application of resonant ultrasound spectroscopy, electroultrasonic spectroscopy, noise measurement and nonlinearity testing at voltages lower than continuous operating range. The achieved results show that these methods could be successively applied for varistor specimens at the production stage and in laboratory circumstances.

PL

Normatywne testy przemysłowe warystorów wysokonapięciowych stosowanych w ogranicznikach przepięć wymagają użycia wysokich napięć oraz prądów o odpowiednio dużych wartościach. Zaproponowano i opisano metody nieniszczące do oceny jakości i trwałości warystorów. Polegają one na zastosowaniu rezonansowej spektroskopii ultradźwiękowej, spektroskopii elektro-ultradźwiękowej, pomiarów szumów i testowaniu nieliniowości w zakresie napięć mniejszych od ciągłego napięcia pracy. Uzyskane wyniki wskazują, że metody nieniszczące mogą być z powodzeniem stosowane w odniesieniu do struktur warystorowych, zarówno w warunkach produkcyjnych jak i laboratoryjnych.

8

Ultrasonic spectroscopy of silicon single crystal

Sedlak P., Tofel P., Sedlakova V., Majzner J., Sikula J., Hasse L.

Metrology and Measurement Systems

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2011

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Vol. 18, nr 4

621-630

EN

Specimens of Si single crystals with different crystal orientation [100] and [110] were studied by Electro-Ultrasonic Spectroscopy (EUS) and Resonant Ultrasonic Spectroscopy (RUS). A silicon single crystal is an anisotropic crystal, so its properties are different in different directions in the material relative to the crystal orientation. EUS is based on interaction of two signals: an electric AC signal and an ultrasonic signal, which are working on different frequencies. The ultrasonic wave affects the charge carriers' transport in the structures and the intermodulation electrical signal which is created due to the interaction between the ultrasonic wave and charge carriers, is proportional to the density of structural defects. RUS enables to measure natural frequencies of free elastic vibrations of a simply shaped specimen by scanning a selected frequency range including the appropriate resonances of the measured specimens.

9

Noise spectroscopy and nonlinearity testing of passive electronic components

Šikula J., Sedlakova V.

Zeszyty Naukowe Wydziału ETI Politechniki Gdańskiej. Technologie Informacyjne

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2005

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T. 8

901-910

EN

Traditional methods to predict reliability for electronic passive elements during production process are more and more difficult to fulfillment due to requirements on the very long ageing period and enormous number of specimens. To characterize quality and durability they can be replaceable by noise spectroscopy (including for example, low-frequency noise and partial discharge measurement) or non-linearity testing. The methodology and the results of noise, partial discharge and non-linearity measurements for thick film resistors, M-I-M, tantalum and niobium capacitors have been presented in the paper.

PL

Tradycyjne metody badania niezawodności elektronicznych elementów pasywnych są coraz trudniejsze do wyegzekwowania przy wymaganych długich czasach starzenia elementów oraz masowej produkcji. Przy badaniach jakości (trwałości) mogą być one zastąpione przez spektroskopię szumową (w tym m.in. przez pomiary szumów i badania wyładowań niezupełnych) czy też testowanie nieliniowości. W pracy przedstawiono metodykę i wyniki ich zastosowania w odniesieniu do rezystorów grubowarstwowych, kondensatorów M-I-M, tantalowych oraz z tlenkiem niobu.