Vlasta Sedlakova

Low-frequency noise of thick-film resistors as quality and reliability indicator

Abstract The non-linearity and the noise of thick-film resistors are parameters that can be used to make a prediction of resistor reliability. The noise spectroscopy measurements of thick-film resistors are proposed as a diagnostic tool for the prediction of possible types of failure. The correlation between noise spectral density data and the results of accelerated aging of thick-film resistors at high temperature were made for HS80 and 2000 resistor pastes.

Noise and transport characterisation of tantalum capacitors

Abstract A low frequency noise and charge carrier transport mechanisms were investigated on tantalum capacitors made by various producers. The model of Ta–Ta2O5–MnO2 MIS structure was used to give physical interpretation of I–V characteristics in normal and reverse modes. The noise in time and frequency domain was examined and noise sources were identified. We evaluated correlation between leakage current and noise spectral density and discussed corresponding quality and reliability indicators.

RTS in submicron MOSFETS and quantum dots

In the present paper, emphasis is laid on those RTS showing a capture process, which deviates from the standard Shockley-Read-Hall kinetics. A modified two-step approach is proposed. In this case the charge carrier quantum transitions represent a primary process X(t), which involves two or three quantum states. The measurable quantity is the current modulation, which has discrete states, too. The current modulation is then represented by a secondary process Y(t). The proposed model can explain some of the complex switching phenomena being measured in nanoscale devices. The quadratic dependence of the capture rate on the current and the noise spectral density dependence on the current and temperature are analysed. It is shown that the occupation time probability density for emission is given by a superposition of two exponential dependencies, whereas the capture time constant distribution is purely exponential.

Noise in Submicron Metal–Oxide–Semiconductor Field Effect Transistors: Lateral Electron Density Distribution and Active Trap Position

Experiments were carried out for the n-channel devices, processed in a 0.3 µm spacer less complementary metal–oxide–semiconductor technology. Random-telegraph-signal measurements were performed for the constant gate voltage. It is supposed that electron concentration in the channel decreases from the source to the drain contact. Lateral component of the electric field is inhomogeneous in the channel and it has a minimum value near the source and reaching the maximum value near the drain electrode. Drain current is given by two components – diffusion and drift ones. Diffusion current component is independent on the x-coordinate and it is equal to the drift current component for the low electric field. The model explaining the experimentally observed capture time constant dependence on the lateral electric field and the trap position is given. From the dependence of the capture time constant τc on the drain current could be calculated longitudinal coordinate of the trap position.

Noise in amperometric NO2 sensor

Nitrogen dioxide (NO2) is a highly toxic gas harmful to the environment, which can be threat to human health even at low concentrations. To overcome limitations of standard solid NO2 sensors based on inorganic materials, a new sensor with solid polymer electrolytes (SPE) was developed. Our study deals with investigation of fluctuation phenomena in the electrochemical NO2 sensor, which is based on three-electrode topology and solid polymer electrolyte. Experimental result shows that generation-recombination (G-R) noise seems to be main components of current fluctuations in this sensor. The concentration of detected matter affects noise spectral density of sensor. As the concentration increases, G-R noise rises and is supposed to be connected with chemical processes on active layer of sensor. The shift of G-R component is supposed to be caused by increased flux density between active layer and environment.

Comparison of effectiveness of gas sensing by low frequency fluctuations in resistance and microbalance quartz gas sensors

Selectivity and sensitivity of gas sensing can be improved by fluctuation enhanced sensing. This possibility was investigated in resistive Taguchi Gas Sensors (TGS). Research results confirm that such an approach can strongly increase gas detection sensitivity. We suppose that low frequency fluctuations can be utilized to improve gas detection in other types of gas sensors. Fluctuations in the Quartz Crystal Microbalance (QCM) gas sensor for gas detection improving have been investigated. The sensor used in an experiment utilizes an ordinary quartz oscillator with a surface covered by a chemical layer absorbing humidity. The paper presents results of 1/ƒ noise measurements in both types of sensors at different humidity. The prototype QCM sensor and resistive gas sensors of Figaro company were investigated. The results show advantages of this technique for future industrial applications.

Noise and Charge Storage in Nb2O5 Thin Films

A low frequency noise and DC leakage current measurements have been performed on the MIS structure NbO − Nb2O5 − MnO2. The mechanism of current flow and current noise sources were determined from these measurements. The insulating layer thickness is 50 to 150 nm, relative permittivity about 38. The charge is accumulated not only on NbO and MnO2 electrodes, but also in the Nb2O5 insulating layer. The charge carrier transport is determined by the Poole‐Frenkel mechanism and tunnelling in the normal mode (for NbO electrode positive). In this case g‐r noise is dominant for Poole‐Frenkel mechanism and 1/f noise is dominant for tunnelling.

Low Frequency Noise of Tantalum Capacitors

A low frequency noise and charge carriers transport mechanism analysis was performed on tantalum capacitors in order to characterise their quality and reliability. The model of Ta−Ta2O5−MnO2 MIS structure was used to give physical interpretation of VA characteristic both in normal and reverse modes. The self-healing process based on the high temperature MnO2−Mn2O3 transformation was studied and its kinetic determined on the basis of noise spectral density changes. The correlation between leakage current and noise spectral density was evaluated and noise reliability indicator was suggested. In normal mode the noise spectral density at rated voltage increases with second power of current and it varies within two decades for given leakage current value. In reverse mode there is only weak correlation and for given applied voltage, the leakage current for all ensemble varies only by one order, whereas the noise spectral density of the same samples spread in five orders.

Tantalum and Niobium oxide capacitors: Field crystallization, leakage current kinetics and reliability

The study of the charge carrier transport in Ta and NbO capacitors was performed to analyze the leakage current kinetics at high temperature and high electric field for MnO2 and Conducting Polymer (CP) cathode. Leakage current of Ta and NbO capacitors at the room temperature is driven by the Ohmic and Poole-Frenkel mechanism at the rated voltage. It was found that these capacitors are very stable for temperature below 100°C. High temperature and high voltage applications are considered to be limited by the field crystallization mechanisms and ions diffusion. The leakage current changes in high electric field and at the elevated temperature T = 400 K could be divided into three time intervals: (i) Leakage current is stable (in some samples is slightly decreasing or increasing) during a period of 1 to 10 days. (ii) Leakage current increases with the slope 5 to100 pA/s for time interval about 10 days. (iii) Leakage current is stable or slightly increases with the slope less than 1 pA/s. Activation energy decreases during the ageing period from 0.55 to 0.45 eV. Leakage current variations are partly reversible. Irreversible changes of leakage current appear on about 1% of samples after ageing. Further investigation in this field can lead to the enhancement of reliability and performance of these capacitors.

Noise analysis of infrared detectors

Pyroelectric infrared detectors convert the changes in incoming infrared light to electric signals. Pyroelectric materials are characterized by having spontaneous electric polarization, which is altered by temperature changes as infrared light illuminates the elements. Since our sensor series uses this effect they can be used at ambient temperature even in the presence of thermal noise. By choosing appropriate infrared receiving electrodes, they serve a wide range of applications. Sometimes pyroelectric infrared detectors generate a false alarm. They include thermal resistor and FET device which can be a source of random signals. This paper deals with the measurement of output and transfer characteristics and voltage low noise spectral density. By the help these characteristics we can evaluate detectors and reduce false alarms.